We compute the non-Gaussian contribution to the covariance of the matter power spectrum at one-loop order in Standard Perturbation Theory (SPT), and using the framework of the effective field theory (EFT) of large scale structure (LSS). The complete one-loop contributions are evaluated for the first time, including the leading EFT corrections that involve seven independent operators, of which four appear in the power spectrum and bispectrum. In the basis where the three new operators are maximally uncorrelated, we find that two of them are suppressed at the few percent level relative to other contributions, and may thus be neglected. We extract the single remaining coefficient from N-body simulations, and obtain robust predictions for the non-Gaussian part of the covariance $C(k_i, k_j)$ up to $k_i + k_j \sim$ 0.3 h/Mpc. The one-parameter prediction from EFT improves over SPT, with the analytic reach in wavenumber more than doubled.
Dark energy affects the Hubble expansion rate (namely, the expansion history) $H(z)$ by an integral over $w(z)$. However, the usual observables are the luminosity distances or the angular diameter distances, which measure the distance-redshift relation. Actually, dark energy affects the distances (and the growth factor) by a further integration over functions of $H(z)$. Thus, the direct measurements of the Hubble parameter $H(z)$ at different redshifts are of great importance for constraining the properties of dark energy. In this paper, we show how the typical dark energy models, for example, the $\Lambda$CDM, $w$CDM, CPL, and holographic dark energy (HDE) models, can be constrained by the current direct measurements of $H(z)$ (30 data in total, covering the redshift range of $z\in [0.07,2.30]$). In fact, the future redshift-drift observations (also referred to as the Sandage-Loeb test) can also directly measure $H(z)$ at higher redshifts, covering the range of $z\in [2,5]$. We thus discuss what role the redshift-drift observations can play in constraining dark energy with the Hubble parameter measurements. We show that the constraints on dark energy can be improved greatly with the $H(z)$ data from only a 10-year observation of redshift drift.
Current acceleration of the cosmic expansion leads to coincidence as well as fine-tuning issues in the framework of general relativity. Dynamical scalar fields have been introduced in response of these problems, some of them invoking screening mechanisms for passing local tests of gravity. Recent lab experiments based on atom interferometry in a vacuum chamber have been proposed for testing modified gravity models. So far only analytical computations have been used to provide forecasts. We derive numerical solutions for chameleon models that take into account the effect of the vacuum chamber wall and its environment. With this realistic profile of the chameleon field in the chamber, we refine the forecasts that were derived analytically. We finally highlight specific effects due to the vacuum chamber that are potentially interesting for future experiments.
We provide the latest constraints on the power spectra of both scalar and tensor perturbations from the CMB data (including \textit{Planck}~2015, BICEP2 \& \textit{Keck Array} experiments) and the new BAO scales from SDSS-III BOSS observation. We find that the inflation model with a concave potential is preferred and both the inflation model with a monomial potential and the natural inflation model are marginally disfavored at around $95\%$ confidence level. But both the Brane inflation model and the Starobinsky inflation model fit the data quite well.
We measure the inhomogeneity of the large-scale structure and cosmic acceleration by measuring for the first time the angular distribution on the sky of the cosmological parameters that affect the luminosity distance, estimated from supernova data. We used the combination of SDSS-II and SNLS type Ia supernova samples. We divide the supernovae into equal-surface area pixels and estimate the cosmological parameters that minimize the chi-squared of the fit to the distance modulus in each pixel, hence producing maps of the cosmological parameters {Omega_{M}, Omega_{Lambda}, H_{0}}. We measure fluctuations about the average values of order 5-95% for the matter energy density Omega_{M}, of order 1-25% for the dark energy density Omega_{Lambda} and of order up to 5% for the Hubble parameter H_{0}. In poorly sampled pixels, these fluctuations are mostly due to an inhomogeneous coverage of the sky by the SN surveys; in contrast, in well sampled pixels, the measurements are robust enough to suggest a real fluctuation. We also measure the anisotropy of the parameters by computing the power spectrum of the corresponding parameters' maps up to ell=3. The power spectra of the energy densities have a local maximum at the quadrupole ell=2; in contrast, the power spectrum of H_{0} increases with the multipole, meaning that the maximum anisotropy can be at scales smaller than the minimum scale probed by the pixels. For an analytical toy model of an inhomogeneous ensemble of homogeneous pixels, we derive the backreaction term in the deceleration parameter due to the fluctuations of H_{0} across the sky and measure it to be of order 10^{-3} the corresponding average over the pixels in the absence of backreaction. In this model, backreaction is not a viable dynamical mechanism to emulate cosmic acceleration.
Since general relativity is a consistent low energy effective field theory, it is possible to compute quantum corrections to classical forces. Here we compute a quantum correction to the gravitational potential between a pair of polarizable objects. We study two distant bodies and compute a quantum force from their induced quadrupole moments due to two graviton exchange. The effect is in close analogy to the Casimir-Polder and London-van der Waals forces between a pair of atoms from their induced dipole moments due to two photon exchange. The new effect is computed from the shift in vacuum energy of metric fluctuations due to the polarizability of the objects. We compute the potential energy at arbitrary distances compared to the wavelengths in the system, including the far and near regimes. In the far distance, or retarded, regime, the potential energy takes on a particularly simple form: $V(r)=-3987\,\hbar\,c\,G^2\alpha_{1S}\,\alpha_{2S}/(4\,\pi\,r^{11})$, where $\alpha_{1S},\,\alpha_{2S}$ are the static gravitational quadrupole polarizabilities of each object. We provide estimates of this effect.
The potential $V(\phi)=\lambda \phi^{n}$ is responsible for the inflation of the universe and scalar field $\phi$ oscillates quickly around some point where $V(\phi)$ has a minimum. The end of this stage had an important role on the further evolution stages of the universe. The created particles were responsible for reheating the universe at the end of this stage. The behaviour of the inflation and reheating stages are often known as power law expansion $S(\eta) \varpropto \eta^{1+\beta}$, $S(\eta) \varpropto \eta^{1+\beta_{s}}$ respectively. The reheating temperature ($T_{rh}$) and $\beta_{s}$ give us valuable information about reheating stage. Recently people have studied the behaviour of $T_{rh}$ based on slow-roll inflation and initial condition of quantum normalization. It is shown that there is some discrepancy on $T_{rh}$ due to the quantum normalization \cite{acq}. Therefore the author has believed in \cite{acq} that the quantum normalization may not be a good initial condition. But it seems that we can remove this discrepancy by determining the appropriate parameter $\beta_{s}$ and therefore there is no need to say about the quality of quantum normalization. Then from given $\beta_{s}$, we can calculate $T_{rh}$, tensor to scalar ratio $r$ and parameters $\beta, n$ based on the Planck and WMAP-9 data. The observed results of $r, \beta_{s}, \beta$ and $n$ have consistency with their constrains. Also the results of $T_{rh}$ are in agreement with its general range and special range based on the DECIGO and BBO detectors.
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We show that a tiny correction to the inflaton potential can make critical changes in the inflationary observables for some types of inflation models.
We derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the Hubble Frontier Fields programme. Based on a subset of 11 multiply lensed systems with spectroscopic redshift we produce a lens model that is accurate enough to unveil new multiply lensed systems, totalling over a 100 arclets, and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using only the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of our mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images we provide detailed model comparisons to illustrate the precision of our model and hence the reliability of our de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example of jet-induced star formation, at redshift z=3.1.
We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.
We investigate the statistical power of higher-order statistics and cross-correlation statistics to constrain the primordial non-Gaussianity from the imaging surveys. In particular, we consider the local-type primordial non- Gaussianity and discuss how well one can tightly constrain the higher-order non-Gaussian parameters ($g_{\rm NL}$ and $\tau_{\rm NL}$) as well as the leading order parameter $f_{\rm NL}$ from the halo/galaxy clustering and weak gravitational lensing measurements. Making use of a strong scale-dependent behavior in the galaxy/halo clustering, Fisher matrix analysis reveals that the bispectra can break the degeneracy between non-Gaussian parameters ($f_{\rm NL}$, $g_{\rm NL}$ and $\tau_{\rm NL}$) and this will give simultaneous constraints on those three parameters. The combination of cross-correlation statistics further improves the constraints by factor of 2. As a result, upcoming imaging surveys like the Large Synoptic Survey Telescope have the potential to improve the constraints on the primordial non-Gaussianity much tighter than those obtained from the CMB measurement by Planck, giving us an opportunity to test the single-sourced consistency relation, $\tau_{\rm NL} \ge (36/25) f_{\rm NL}^2$.
We consider a non-standard cosmological model in which the universe contains as much matter as antimatter on large scales and presents a local baryon asymmetry. A key ingredient in our approach is that the baryon density distribution follows Gaussian fluctuations around a null value $\eta = 0$. Spatial domains featuring a positive (resp. negative) baryonic density value constitute regions dominated by matter (resp. antimatter). At the domains' annihilation interface, the typical density is going smoothly to zero, rather than following an abrupt step as assumed in previous symetric matter-antimatter models. As a consequence, the Cosmic Diffuse Gamma Background produced by annihilation is drastically reduced, allowing to easily pass COMPTEL's measurements limits. Similarly the Compton $y$ distorsion and CMB 'ribbons' are lowered by an appreciable factor. Therefore this model essentially escape previous constrainst on symetric matter-antimatter models. However, we produce an estimation of the CMB temperature fluctuations that would result from this model and confront it to data acquired from the Planck satellite. We construct a angular power spectrum in $\delta T / T_{CMB}$ assuming is can be approximated as an average of $C_\ell$ over a Gaussian distribution of $\Omega_B$ using Lewis & Challinor's CAMB software. The resulting $C_\ell$ are qualitatively satisfying. We quantify the goodness of fit using a simple $\chi^2$ test. We consider two distinct scenarios in which the fluctuations on $\Omega_B$ are compensated by fluctuations on $\Omega_{CDM}$ to assure a spatially flat $\Omega_\kappa = 0$ universe or not. In both cases, out best fit have $\Delta \chi^2 \gtrsim 2400$ (with respect to a fiducial $\Lambda$CDM model), empirically excluding our model by several tens of standard deviations.
Including the metric fluctuations of a realistic cosmological geometry we reconsider an earlier suggestion that measuring the relative time-of-flight of ultra-relativistic particles can provide interesting constraints on fundamental cosmological and/or particle parameters. Using convenient properties of the geodetic light-cone gauge we first compute, to leading order in the Lorentz factor and for a generic (inhomogeneous, anisotropic) space-time, the relative arrival times of two ultra-relativistic particles as a function of their masses and energies as well as of the details of the large-scale geometry. Remarkably, the result can be written as an integral over the unperturbed line-of-sight of a simple function of the local, inhomogeneous redshift. We then evaluate the irreducible scatter of the expected data-points due to first-order metric perturbations, and discuss, for an ideal source of ultra-relativistic particles, the resulting attainable precision on the determination of different physical parameters.
We consider an effective viscous pressure as the result of a backreaction of inhomogeneities within Buchert's formalism. The use of an effective metric with a time-dependent curvature radius allows us to calculate the luminosity distance of the backreaction model. This quantity is different from its counterpart for a "conventional" spatially flat bulk viscous fluid universe. Both expressions are tested against the SNIa data of the Union2.1 sample with only marginally different results.
In this paper, we investigate the Noether symmetries of a generalized scalar-tensor, Brans-Dicke type cosmological model, in which we consider explicit scalar field dependent couplings to the Ricci scalar, and to the scalar field kinetic energy, respectively. We also include the scalar field self-interaction potential into the gravitational action. From the condition of the vanishing of the Lie derivative of the gravitational cosmological Lagrangian with respect to a given vector field we obtain three cosmological solutions describing the time evolution of a spatially flat Friedman-Robertson-Walker Universe filled with a scalar field. The cosmological properties of the solutions are investigated in detail, and it is shown that they can describe a large variety of cosmological evolutions, including models that experience a smooth transition from a decelerating to an accelerating phase.
Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.
The nonlinear state of a high-beta collisionless plasma is investigated when an imposed linear shear amplifies or diminishes a uniform magnetic field, driving pressure anisotropies and hence firehose/mirror instabilities. The evolution of the resulting microscale turbulence is considered when the shear is switched off or reversed after one shear time (mimicking local behaviour of a macroscopic flow), so a new macroscale configuration is superimposed on the microscale state left behind by the previous one. There is a threshold value of plasma beta: when $\beta\ll\Omega/S$ (ion cyclotron frequency/shear rate), the emergence of firehose/mirror fluctuations driven unstable by shear and their disappearance when the shear is removed/reversed are quasi-instantaneous compared to the shear time, viz., the decay time of these fluctuations is $\sim\beta/\Omega \ll 1/S$ (this result follows from the free decay of the fluctuations being constrained by the same marginal-stability thresholds as their growth). In contrast, when $\beta\gtrsim\Omega/S$ ("ultra-high" beta), the old microscale state can only be removed on the shear timescale. In this regime, driven firehose fluctuations grow secularly to order-unity amplitudes, compensating for the decay of the mean field and so pinning pressure anisotropy at marginal stability with no appreciable scattering of particles---which is unlike what happens at moderate $\beta$. When the shear reverses, the shearing away of this firehose turbulence compensates for the increase in the mean field and thus prevents growth of the pressure anisotropy, stopping the system from going mirror-unstable. Therefore, at ultra-high beta, the system stays close to the firehose threshold, the mirror instability is largely suppressed, while the mean magnetic energy barely changes at all. Implications for plasma dynamo and thus the origin of cosmic magnetism are discussed.
In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local $f(R)$ gravity, (2) non local ghost free theory of gravity, and (3) non-minimally coupled gravity with SM sector and dilaton field. Next we apply conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory ($\Lambda_{UV}$) as well as the dark matter mass ($M$). We consider two cases- (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM particles. Finally, we propose some different UV complete models from a particle physics point of view, which can give rise to the same effective theory that we have deduced from extended theories of gravity.
Cosmological hysteresis, has interesting and vivid implications in the scenario of a cyclic bouncy universe. This, purely thermodynamical in nature, is caused by the asymmetry in the equation of state parameter during expansion and contraction phase of the universe, due to the presence of a single scalar field. When applied to variants of modified gravity models this phenomenon leads to the increase in amplitude of the consecutive cycles of the universe, provided we have physical mechanisms to make the universe bounce and turnaround. This also shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of $\oint pdV$ and on model parameters.
Links to: arXiv, form interface, find, astro-ph, recent, 1512, contact, help (Access key information)
We show that a tiny correction to the inflaton potential can make critical changes in the inflationary observables for some types of inflation models.
We derive a free-form mass distribution for the massive cluster AS1063 (z=0.348) using the completed optical imaging from the Hubble Frontier Fields programme. Based on a subset of 11 multiply lensed systems with spectroscopic redshift we produce a lens model that is accurate enough to unveil new multiply lensed systems, totalling over a 100 arclets, and to estimate their redshifts geometrically. Consistency is found between this precise model and that obtained using only the subset of lensed sources with spectroscopically measured redshifts. No significant offset is found between the centroid of our mass distribution and that of the X-ray emission map, suggesting a relatively relaxed state for this cluster, although a relatively large elongation of the mass distribution is apparent relative to the X-ray map. For the well resolved lensed images we provide detailed model comparisons to illustrate the precision of our model and hence the reliability of our de-lensed sources. A clear linear structure is associated with one such source extending 23 kpc in length, that could be an example of jet-induced star formation, at redshift z=3.1.
We update the constraint on the dark matter annihilation cross section by using the recent measurements of the CMB anisotropy by the Planck satellite. We fully calculate the cascade of dark matter annihilation products and their effects on ionization, heating and excitation of the hydrogen, hence do not rely on any assumption on the energy fractions that cause these effects.
We investigate the statistical power of higher-order statistics and cross-correlation statistics to constrain the primordial non-Gaussianity from the imaging surveys. In particular, we consider the local-type primordial non- Gaussianity and discuss how well one can tightly constrain the higher-order non-Gaussian parameters ($g_{\rm NL}$ and $\tau_{\rm NL}$) as well as the leading order parameter $f_{\rm NL}$ from the halo/galaxy clustering and weak gravitational lensing measurements. Making use of a strong scale-dependent behavior in the galaxy/halo clustering, Fisher matrix analysis reveals that the bispectra can break the degeneracy between non-Gaussian parameters ($f_{\rm NL}$, $g_{\rm NL}$ and $\tau_{\rm NL}$) and this will give simultaneous constraints on those three parameters. The combination of cross-correlation statistics further improves the constraints by factor of 2. As a result, upcoming imaging surveys like the Large Synoptic Survey Telescope have the potential to improve the constraints on the primordial non-Gaussianity much tighter than those obtained from the CMB measurement by Planck, giving us an opportunity to test the single-sourced consistency relation, $\tau_{\rm NL} \ge (36/25) f_{\rm NL}^2$.
We consider a non-standard cosmological model in which the universe contains as much matter as antimatter on large scales and presents a local baryon asymmetry. A key ingredient in our approach is that the baryon density distribution follows Gaussian fluctuations around a null value $\eta = 0$. Spatial domains featuring a positive (resp. negative) baryonic density value constitute regions dominated by matter (resp. antimatter). At the domains' annihilation interface, the typical density is going smoothly to zero, rather than following an abrupt step as assumed in previous symetric matter-antimatter models. As a consequence, the Cosmic Diffuse Gamma Background produced by annihilation is drastically reduced, allowing to easily pass COMPTEL's measurements limits. Similarly the Compton $y$ distorsion and CMB 'ribbons' are lowered by an appreciable factor. Therefore this model essentially escape previous constrainst on symetric matter-antimatter models. However, we produce an estimation of the CMB temperature fluctuations that would result from this model and confront it to data acquired from the Planck satellite. We construct a angular power spectrum in $\delta T / T_{CMB}$ assuming is can be approximated as an average of $C_\ell$ over a Gaussian distribution of $\Omega_B$ using Lewis & Challinor's CAMB software. The resulting $C_\ell$ are qualitatively satisfying. We quantify the goodness of fit using a simple $\chi^2$ test. We consider two distinct scenarios in which the fluctuations on $\Omega_B$ are compensated by fluctuations on $\Omega_{CDM}$ to assure a spatially flat $\Omega_\kappa = 0$ universe or not. In both cases, out best fit have $\Delta \chi^2 \gtrsim 2400$ (with respect to a fiducial $\Lambda$CDM model), empirically excluding our model by several tens of standard deviations.
Including the metric fluctuations of a realistic cosmological geometry we reconsider an earlier suggestion that measuring the relative time-of-flight of ultra-relativistic particles can provide interesting constraints on fundamental cosmological and/or particle parameters. Using convenient properties of the geodetic light-cone gauge we first compute, to leading order in the Lorentz factor and for a generic (inhomogeneous, anisotropic) space-time, the relative arrival times of two ultra-relativistic particles as a function of their masses and energies as well as of the details of the large-scale geometry. Remarkably, the result can be written as an integral over the unperturbed line-of-sight of a simple function of the local, inhomogeneous redshift. We then evaluate the irreducible scatter of the expected data-points due to first-order metric perturbations, and discuss, for an ideal source of ultra-relativistic particles, the resulting attainable precision on the determination of different physical parameters.
We consider an effective viscous pressure as the result of a backreaction of inhomogeneities within Buchert's formalism. The use of an effective metric with a time-dependent curvature radius allows us to calculate the luminosity distance of the backreaction model. This quantity is different from its counterpart for a "conventional" spatially flat bulk viscous fluid universe. Both expressions are tested against the SNIa data of the Union2.1 sample with only marginally different results.
In this paper, we investigate the Noether symmetries of a generalized scalar-tensor, Brans-Dicke type cosmological model, in which we consider explicit scalar field dependent couplings to the Ricci scalar, and to the scalar field kinetic energy, respectively. We also include the scalar field self-interaction potential into the gravitational action. From the condition of the vanishing of the Lie derivative of the gravitational cosmological Lagrangian with respect to a given vector field we obtain three cosmological solutions describing the time evolution of a spatially flat Friedman-Robertson-Walker Universe filled with a scalar field. The cosmological properties of the solutions are investigated in detail, and it is shown that they can describe a large variety of cosmological evolutions, including models that experience a smooth transition from a decelerating to an accelerating phase.
Using all-sky maps obtained from COBE/DIRBE at 3.5 and 4.9 um, we present a reanalysis of diffuse sky emissions such as zodiacal light (ZL), diffuse Galactic light (DGL), integrated starlight (ISL), and isotropic residual emission including the extragalactic background light (EBL). Our new analysis, which includes an improved estimate of ISL using the Wide-field Infrared Survey Explorer (WISE) data, enabled us to find the DGL signal in a direct linear correlation between diffuse near-infrared and 100 um emission at high Galactic latitudes (|b| > 35 degree). At 3.5um, the high-latitude DGL result is comparable to the low-latitude value derived from the previous DIRBE analysis. In comparison with models of the DGL spectrum assuming a size distribution of dust grains composed of amorphous silicate, graphite, and polycyclic aromatic hydrocarbon (PAH), the measured DGL values at 3.5 and 4.9 um constrain the mass fraction of PAH particles in the total dust species to be more than ~ 2%. This was consistent with the results of Spitzer/IRAC toward the lower Galactic latitude regions. The derived residual emission of 8.9 +/- 3.4 nW m^{-2} sr^{-1} at 3.5 um is marginally consistent with the level of integrated galaxy light and the EBL constraints from the gamma-ray observations. The residual emission at 4.9 um is not significantly detected due to the large uncertainty in the ZL subtraction, same as previous studies. Combined with our reanalysis of the DIRBE data at 1.25 and 2.2 um, the residual emission in the near-infrared exhibits the Rayleigh-Jeans spectrum.
The nonlinear state of a high-beta collisionless plasma is investigated when an imposed linear shear amplifies or diminishes a uniform magnetic field, driving pressure anisotropies and hence firehose/mirror instabilities. The evolution of the resulting microscale turbulence is considered when the shear is switched off or reversed after one shear time (mimicking local behaviour of a macroscopic flow), so a new macroscale configuration is superimposed on the microscale state left behind by the previous one. There is a threshold value of plasma beta: when $\beta\ll\Omega/S$ (ion cyclotron frequency/shear rate), the emergence of firehose/mirror fluctuations driven unstable by shear and their disappearance when the shear is removed/reversed are quasi-instantaneous compared to the shear time, viz., the decay time of these fluctuations is $\sim\beta/\Omega \ll 1/S$ (this result follows from the free decay of the fluctuations being constrained by the same marginal-stability thresholds as their growth). In contrast, when $\beta\gtrsim\Omega/S$ ("ultra-high" beta), the old microscale state can only be removed on the shear timescale. In this regime, driven firehose fluctuations grow secularly to order-unity amplitudes, compensating for the decay of the mean field and so pinning pressure anisotropy at marginal stability with no appreciable scattering of particles---which is unlike what happens at moderate $\beta$. When the shear reverses, the shearing away of this firehose turbulence compensates for the increase in the mean field and thus prevents growth of the pressure anisotropy, stopping the system from going mirror-unstable. Therefore, at ultra-high beta, the system stays close to the firehose threshold, the mirror instability is largely suppressed, while the mean magnetic energy barely changes at all. Implications for plasma dynamo and thus the origin of cosmic magnetism are discussed.
In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local $f(R)$ gravity, (2) non local ghost free theory of gravity, and (3) non-minimally coupled gravity with SM sector and dilaton field. Next we apply conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory ($\Lambda_{UV}$) as well as the dark matter mass ($M$). We consider two cases- (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM particles. Finally, we propose some different UV complete models from a particle physics point of view, which can give rise to the same effective theory that we have deduced from extended theories of gravity.
Cosmological hysteresis, has interesting and vivid implications in the scenario of a cyclic bouncy universe. This, purely thermodynamical in nature, is caused by the asymmetry in the equation of state parameter during expansion and contraction phase of the universe, due to the presence of a single scalar field. When applied to variants of modified gravity models this phenomenon leads to the increase in amplitude of the consecutive cycles of the universe, provided we have physical mechanisms to make the universe bounce and turnaround. This also shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of $\oint pdV$ and on model parameters.
Links to: arXiv, form interface, find, astro-ph, recent, 1512, contact, help (Access key information)
We show that compatibility between the DAMA modulation result (as well as less statistically significant excesses such as the CDMS Silicon effect and the excess claimed by CRESST) with constraints from other experiments can be achieved by extending the analysis of direct detection data beyond the standard elastic scattering of a WIMP off nuclei with a spin--dependent or a spin--independent cross section and with a velocity distribution as predicted by the Isothermal Sphere model. To do so we discuss several new approaches for the analysis of Dark Matter direct detection data, with the goal to remove or reduce its dependence on specific theoretical assumptions, and to extend its scope: the factorization approach of astrophysics uncertainties, the classification and study of WIMP-nucleon interactions within non--relativistic field theory, inelastic scattering and isovector-coupling cancellations including subdominant two-nucleon NLO effects. Typically, combining two or more of these ingredients can lead to conclusions which are very different to what usually claimed in the literature. This shows that we are only starting now to scratch the surface of the most general WIMP direct detection parameter space.
[Abridged] We analyze the evolution of superhorizon-scale magnetic fields from the end of inflation till today. Whatever is the mechanism responsible for their generation during inflation, we find that a given magnetic mode with wavenumber $k$ evolves, after inflation, according to the values of $k\eta_e$, $n_{\mathbf{k}}$, and $\Omega_k$, where $\eta_e$ is the conformal time at the end of inflation, $n_{\mathbf{k}}$ is the number density spectrum of inflation-produced photons, and $\Omega_k$ is the phase difference between the two Bogolubov coefficients which characterize the state of that mode at the end of inflation. For any realistic inflationary magnetogenesis scenario, we find that $n_{\mathbf{k}}^{-1} \ll |k\eta_e| \ll 1$, and three evolutionary scenarios are possible: ($i$) $|\Omega_k \mp \pi| = \mathcal{O}(1)$, in which case the evolution of the magnetic spectrum $B_k(\eta)$ is adiabatic, $a^2B_k(\eta) = \mbox{const}$, with $a$ being the expansion parameter; ($ii$) $|\Omega_k \mp \pi| \ll |k\eta_e|$, in which case the evolution is superadiabatic, $a^2B_k(\eta) \propto \eta$; ($iii$) $|k\eta_e| \ll |\Omega_k \mp \pi| \ll 1$ or $|k\eta_e| \sim |\Omega_k \mp \pi| \ll 1$, in which case an early phase of adiabatic evolution is followed, after a time $\eta_\star \sim |\Omega_k \mp \pi|/k$, by a superadiabatic evolution. Once a given mode reenters the horizon, it remains frozen into the plasma and then evolves adiabatically till today. As a corollary of our results, we find that inflation-generated magnetic fields evolve adiabatically on all scales and for all times in conformal-invariant free Maxwell theory, while they evolve superadiabatically after inflation on superhorizon scales in the non-conformal-invariant Ratra model. The latter result supports our recent claim that the Ratra model can account for the presence of cosmic magnetic fields.
The bulk flow is a volume average of the peculiar velocities and a useful probe of the mass distribution on large scales. The gravitational instability model views the bulk flow as a potential flow that obeys a Maxwellian Distribution. We use two N-body simulations, the LasDamas Carmen and the Horizon Run, to calculate the bulk flows of various sized volumes in the simulation boxes. Once we have the bulk flow velocities as a function of scale, we investigate the mass and gravitational potential distribution around the volume. We found that matter densities can be asymmetrical and difficult to detect in real surveys, however, the gravitational potential and its gradient may provide better tools to investigate the underlying matter distribution. This study shows that bulk flows are indeed potential flows and thus provides information on the flow sources. We also show that bulk flow magnitudes follow a Maxwellian distribution on scales $>10\ h^{-1}$Mpc.
We investigate the production of a stochastic background of gravitational waves in the electroweak phase transition. We consider a few extensions of the Standard Model which can give very strongly first-order phase transitions. We concentrate on the possibility that the phase transition fronts either propagate as detonations or run away. We compute the bubble wall velocity taking into account the friction and hydrodynamics due to the presence of the plasma, and we track the development of the phase transition up to the percolation time. We calculate the contribution to the gravitational wave spectrum from bubble collisions, magnetohydrodynamic turbulence, and sound waves. For the kinds of models we consider we find parameter regions for which the gravitational waves are potentially observable at the planned space-based interferometer eLISA. The sound waves are generally the strongest source. Since this mechanism is diminished in the presence of runaway walls, the models with the best prospects of detection at eLISA are those which do not have such solutions. In particular, we find that heavy extra bosons provide a stronger signal than tree-level terms.
We study features in the bispectrum of the primordial curvature perturbation correlated with the reconstructed primordial power spectrum from the observed cosmic microwave background temperature data. We first show how the bispectrum can be completely specified in terms of the power spectrum and its first two derivatives, valid for any configuration of interest. Then using a model-independent reconstruction of the primordial power spectrum from the Planck angular power spectrum of temperature anisotropies, we compute the bispectrum in different triangular configurations. We find that in the squeezed limit at k ~ 0.1/Mpc and k ~ 0.013/Mpc there are marginal 2sigma deviations from the standard featureless bispectrum, which meanwhile is consistent with the reconstructed bispectrum in the equilateral configuration.
The Matter Bounce scenario allows for a sizable parameter space where cosmological fluctuations originally exit the Hubble radius when the background energy density was small. In this scenario and its extended versions, the low energy degrees of freedom are likely responsible for the statistical properties of the cosmic microwave background (CMB) power spectrum at large length scales. An interesting consequence is that these modes might be observable only at relatively late times. Therefore low redshift observations could provide evidence for, or even falsify, various bouncing models. We provide an example where a recently hinted potential deviation from $\Lambda$-Cold-Dark-Matter ($\Lambda$CDM) cosmology results from a dark matter (DM) and dark energy (DE) interaction. The same interaction allows Matter Bounce models to generate a red tilt for the primordial curvature perturbations in corroboration with CMB experiments.
The results from Planck2015, when combined with earlier observations from WMAP, ACT, SPT and other experiments, were the first observations to disfavor the "classic" inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness problem.' Some propose turning instead to a "postmodern" inflationary paradigm in which the cosmological properties in our observable universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic cosmology, has been proposed that can produce distinctive predictions.
A probability of distinguishing between $\Lambda$CDM model and modified gravity is studied by using the future observations for the growth rate of cosmic structure (Euclid redshift survey). Adopting extended DGP model, Kinetic Gravity Braiding model, and Galileon model as modified gravity, we compare predicted cosmic growth rate by models to the mock observational data. The growth rate $f\sigma_8$ in the original DGP model is suppressed compared with the $\Lambda$CDM case, for the same value of the current density parameter of matter $\Omega_{m,0}$, because of the suppression of effective gravitational constant. In case of the kinetic gravity braiding model and the Galileon model, the growth rate $f\sigma_8$ is enhanced compared with the $\Lambda$CDM case, for the same value of $\Omega_{m,0}$, because of the enhancement of effective gravitational constant. For future observational data of the cosmic growth rate (Euclid), compatible value of $\Omega_{m,0}$ are different by models, furthermore $\Omega_{m,0}$ can be stringently constrained. Thus, we find the $\Lambda$CDM model is distinguishable from modified gravity by combining the growth rate data of the Euclid with other observations.
We investigate the thermal relics as hot, warm and cold dark matter in $\mathscr{L}=\varepsilon^{2-2\beta}R^\beta+{16\pi}m_{\text{Pl}}^{-2}\mathscr{L}_m$ gravity, where $\varepsilon$ is a constant balancing the dimension of the field equation, and $1<\beta<(4+\sqrt{6})/5$ for the positivity of energy density and temperature. If light neutrinos serve as hot/warm relics, the entropic number of statistical degrees of freedom $g_{*s}$ at freeze-out and thus the predicted fractional energy density $\Omega_\psi h^2$ are $\beta-$dependent, which relaxes the standard mass bound $\Sigma m_\nu$. For cold relics, by exactly solve the simplified Boltzmann equation in both relativistic and nonrelativistic regimes, we show that the Lee-Weinberg bound for the mass of heavy neutrinos can be considerably relaxed, and the 'WIMP miracle" for weakly interacting massive particles (WIMPs) gradually invalidates as $\beta$ deviates from $\beta=1^+$. The whole framework reduces to become that of GR in the limit $\beta\to 1^+$.
We investigate the spatial distribution of satellite galaxies that were obtained from a mock redshift survey of the first Millennium Run simulation. The satellites were identified using typical redshift space criteria and, hence, the sample includes both genuine satellites and a large number of interlopers. As expected from previous work, the 3D locations of the satellites are well-fitted by a combination of a Navarro, Frenk & White (NFW) density profile and a power law. At fixed stellar mass, the NFW scale parameter, r_s, for the satellite distribution of red hosts exceeds that for the satellite distribution of blue hosts. In both cases the dependence of r_s on host stellar mass is well-fitted by a power law. For the satellites of red hosts, r_s^{red} \propto (M_\ast / M_sun)^{0.71 \pm 0.05} while for the satellites of blue hosts, r_s^{blue} \propto (M_\ast / M_sun)^{0.48 \pm 0.07}. For hosts with stellar masses greater than 4.0E+10 M_sun, the satellite distribution around blue hosts is much more concentrated than it is around red hosts with the same stellar mass. We perform model fits to the projected (2D) locations of the satellites and find that, with the exception of the satellites of the most massive red hosts, the 2D analysis accurately recovers the values of r_s obtained from the 3D analysis. Therefore, even in the limit of a large number of interlopers, the 3D distribution can be recovered using 2D information alone. The spatial distribution of the satellites of red hosts traces that of the hosts' halos; however, the spatial distribution of the satellites of blue hosts is more concentrated that of the hosts' halos by a factor of ~2. This calls into question whether observed satellites that are selected from redshift space can be used to directly infer the concentration of the dark matter halos of massive, blue host galaxies in our universe.
We construct spacetimes which provide spherical and nonspherical models of black hole formation in the flat Friedmann-Lemaitre-Robertson-Walker (FLRW) universe with the Lemaitre-Tolman-Bondi solution and the Szekeres quasispherical solution, respectively. These dust solutions may contain both shell-crossing and shell-focusing naked singularities. These singularities can be physically regarded as the breakdown of dust description, where strong pressure gradient force plays a role. We adopt the simultaneous big bang condition to extract a growing mode of adiabatic perturbation in the flat FLRW universe. If the density perturbation has a sufficiently homogeneous central region and a sufficiently sharp transition to the background FLRW universe, its central shell-focusing singularity is globally covered. If the density concentration is {\it sufficiently large}, there appears no shell-crossing singularity and a black hole is formed. If the density concentration is {\it not sufficiently large}, there appears shell-crossing singularity. In this case, large dipole moment significantly advances shell-crossing singularities and they tend to appear before the black hole formation. In contrast, there unavoidably appears a shell-crossing singularity in the spherical and nonspherical evolution of cosmological voids. The present analysis is general and applicable to cosmological nonlinear structure formation described by these dust solutions.
We investigate the Einstein static universe and the emergent universe scenario in the framework of Horava-Lifshitz F(R) gravity. We first perform a dynamical analysis in the phase space, and amongst others we show that a universe filled with usual matter satisfying the strong energy condition can stay in a static phase for very long times, and eventually move away from it giving rise to the usual expanding thermal history of the universe, which is just the scenario of emergent universe. Additionally, we examine the behavior of the scenario under scalar perturbations, extracting the conditions under which it is free of perturbative instabilities. Our analysis reveals that there are large regions in the parameter space that lead to well-behaved perturbations, even in the presence of ordinary dust matter. Hence, the emergent universe scenario can be naturally and safely realized in the framework of Horava-Lifshitz F(R) cosmology.
We report a candidate centi-parsec supermassive black hole binary (SMBHB) in the radio-quiet quasar SDSS J0159+0105 at z=0.217. The 8.1-year Catalina V-band light curve for this quasar reveals two significant (at P>99%) periodic signals at ~741 day and ~1500 day. The period ratio, which is close to 1:2, is typical of a black-hole binary system with a mass ratio of 0.05<q<0.8 according to recent numerical simulations. SDSS J0159+0105 displays unusual properties in its spectral energy distribution: the UV emission has significant excess (by 3.2 times brighter) compared to that of normal quasars. The UV excess indicates the existence of a mini-disk around each BH of the binary. SDSS J0159+0105 also has two SDSS spectroscopic observations separated by ~10 years. There is a significant change in the broad H-beta profile between the two epochs, which can be explained by a single broad-line region (BLR) around the binary system illuminated by the aforementioned mini-disks, or a stream of gas flowing from the circumbinary disk to one of the SMBHs. From the single BLR assumption and the orbital period t_orb ~1500 day, we estimate the total virial masses of M_SMBHB} ~ 1.3x10^8 M_sun, the average distances of BLR of ~0.04pc (~50 light-day, with +/-0.3 dex uncertainty), and a SMBHB separation of d= (0.01pc)M_{8,tot}^{1/3} (T_rest/3.3yr)^{2/3} ~ 0.013 pc (15 light-day). Based on analytical work, the postulated circumbinary disk has an inner radius of 2d = 0.026 pc (30 light-day). The unique properties of SDSS J0159+0105 are consistent with it being a centi-parsec SMBHB.
The fundamental nature of Dark Matter (DM) has not been established. Indeed, beyond its gravitational effects, DM remains undetected by present experiments. In this situation, it is reasonable to wonder if other alternatives can effectively explain the observations usually associated with the existence of DM. The modification of the gravitational interaction has been studied in this context from many different approaches. However, the large amount of different astrophysical evidences makes difficult to think that modified gravity can account for all these observations. On the other hand, if such a modification introduces new degrees of freedom, they may work as DM candidates. We will summarize the phenomenology of these gravitational dark matter candidates by analyzing minimal models.
The inverse seesaw mechanism provides an attractive approach to generate small neutrino mass, which origins from a tiny $U(1)_L$ breaking. In this paper, we work in the supersymmetric version of this mechanism, where the singlet-like sneutrino could be an asymmetric dark matter (ADM) candidate in the maximally $U(1)_{L}$ symmetric limit. However, even a tiny $\delta m$, the mass splitting between sneutrino and anti-sneutrino as a result of the tiny $U(1)_{L}$ breaking effect, could lead to fast oscillation between sneutrino and anti-sneutrino and thus spoils the ADM scenario. We study the evolution of this oscillation and find that a weak scale sneutrino, which tolerates a relatively larger $\delta m\sim 10^{-5}$ eV, is strongly favored. We also investigate possible natural ways to realize that small $\delta m$ in the model.
We study the evolution of giant clumps in high-z disc galaxies using AMR cosmological simulations at redshifts z=6-1. Our sample consists of 34 galaxies, of halo masses 10^{11}-10^{12}M_s at z=2, run with and without radiation pressure (RP) feedback from young stars. While RP has little effect on the sizes and global stability of discs, it reduces the amount of star-forming gas by a factor of ~2, leading to a decrease in stellar mass by a similar factor by z~2. Both samples undergo violent disc instability (VDI) and form giant clumps of masses 10^7-10^9M_s at a similar rate, though RP significantly reduces the number of long-lived clumps. When RP is (not) included, clumps with circular velocity <40(20)km/s, baryonic surface density <200(100)M_s/pc^2 and baryonic mass <10^{8.2}(10^{7.3})M_s are short-lived, disrupted in a few free-fall times. The more massive and dense clumps survive and migrate toward the disc centre over a few disc orbital times. In the RP simulations, the distribution of clump masses and star-formation rates (SFRs) normalized to their host disc is very similar at all redshifts. They exhibit a truncated power-law with a slope slightly shallower than -2. Short-lived clumps preferentially have young stellar ages, low masses, high gas fractions and specific SFRs (sSFR), and they tend to populate the outer disc. The sSFR of massive, long-lived clumps declines with age as they migrate towards the disc centre, producing gradients in mass, stellar age, gas fraction, sSFR and metallicity that distinguish them from short-lived clumps. Ex situ mergers make up ~37% of the mass in clumps and ~29% of the SFR. They are more massive and with older stellar ages than the in situ clumps, especially near the disc edge. Roughly half the galaxies at redshifts z=4-1 are clumpy over a wide range of stellar mass, with clumps accounting for ~3-30% of the SFR but ~0.1-3% of the stellar mass.
Gaia's very accurate astrometric measurements will allow the International
Celestial Reference Frame (ICRF) to be improved by a few orders of magnitude in
the optical. Several sets of quasars are used to define a kinematically stable
non-rotating reference frame with the barycentre of the Solar System as its
origin. Gaia will also observe a large number of galaxies which could obtain
accurate positions and proper motions although they are not point-like.
The optical stability of the quasars is critical and we investigate how
accurately the reference frame can be recovered. Various proper motion patterns
are also present in the data, the best known is caused by the acceleration of
the Solar System Barycentre, presumably, towards the Galactic centre. We review
some other less-well-known effects that are not part of standard astrometric
models.
We model quasars and galaxies using realistic sky distributions, magnitudes
and redshifts. Position variability is introduced using a Markov chain model.
The reference frame is determined using the algorithm developed for the Gaia
mission which also determines the acceleration of the Solar System. We also
test a method to measure the velocity of the Solar System barycentre in a
cosmological frame.
We simulate the recovery of the reference frame and the acceleration of the
Solar System and conclude that they are not significantly disturbed in the
presence of quasar variability which is statistically averaged. However, the
effect of a non-uniform sky distribution of the quasars can result in a
correlation between the reference frame and acceleration which degrades the
solution. Our results suggest that an attempt should be made to astrometrically
determine the redshift dependent apparent drift of galaxies due to our velocity
relative to the CMB, which in principle could allow the determination of the
Hubble parameter.
We briefly review some recent advances in the study of the shadows of rotating black holes in alternative theories. The size and the shape of the shadow depend on the mass and the angular momentum, and they can also depend on other parameters specific of the particular model adopted. As an example, we show the results corresponding to a rotating braneworld black hole.
We investigate the behavior of the entanglement entropy of space in the primordial phase of the universe before the beginning of cosmic inflation. We argue that in this phase the entanglement entropy of a region of space grows from a zero-law to an area-law. This behavior provides a quantum version of the classical BKL conjecture that spatially separated points decouple in the approach to a cosmological singularity. We show that the relational growth of the entanglement entropy with the scale factor provides a new statistical notion of arrow of time in quantum gravity. The growth of entanglement in the pre-inflationary phase provides a mechanism for the production of the quantum correlations present at the beginning of inflation and imprinted in the CMB sky.
We study the possibility of a heavy scalar or pseudoscalar in TeV-scale beyond the Standard Model scenarios being the inflaton of the early universe in light of the recent O(750) GeV diphoton excess at the LHC. We consider a scenario in which the new scalar/pseudoscalar couples to the Standard Model gauge bosons at the loop-level through new massive Standard Model charged vector-like fermions with/without dark fermions. We calculate the renormalization group running of both the Standard Model and the new scalar couplings, and present two different models that are perturbative and with a stabilized vacuum up to near the Planck scale. Thus, the Standard Model Higgs and this possible new resonance may still preserve the minimalist features of Higgs inflation.
The first data from the LHC Run-2 have shown a possible excess in the events containing two photons with invariant mass around 750~GeV, suggesting the existence of a new resonance $\phi$ which decays dominantly into new undetected particles, such as the dark matter (DM) particles. In a simple model where $\phi$ is a pseudo-scalar and couples to a scalar DM particle, we show that the 750 GeV two-photon excess reported by the LHC is consistent with another photon excess, the GeV excess in the cosmic gamma-rays towards the Galactic Center observed by the Fermi-LAT collaboration. Both excesses can be explained by a DM particle with mass around 60~GeV and annihilates dominantly into gluons with a typical thermal annihilation cross section. The predicted cross section for the gamma-ray line in this model can be confirmed or ruled out by the Ferm-LAT and future experiments.
We revisit the analysis made by Hwang and Noh [JCAP 1310 (2013)] aiming the construction of a Newtonian set of equations incorporating pressure effects typical of General Relativity theory. We perform in an explicit way the deduction of the Hwang-Noh equations, comparing it with similar computations found in the literature. Later, we investigate stellar equilibrium and cosmology, at background and perturbative levels, using the new set of equations. It is shown that, in this context, the predictions for the background evolution of the universe are deeply changed with respect to the full relativistic theory: the acceleration of the universe is achieved with positive pressure. The properties of neutron stars are reproduced qualitatively, but the upper mass is at least one order of magnitude higher than that obtained in General Relativity. However, the perturbed cosmological equations at small scales reproduce those found in the relativistic context. We argue that this last result may open new possibilities for numerical simulations for structure formation in the universe.
We have acquired Hubble Space Telescope (HST) and Very Large Telescope near-infrared spectra and images of supernova (SN) Refsdal after its discovery as an Einstein cross in Fall 2014. The HST light curve of SN Refsdal matches the distinctive, slowly rising light curves of SN 1987A-like supernovae (SNe), and we find strong evidence for a broad H-alpha P-Cygni profile in the HST grism spectrum at the redshift (z = 1.49) of the spiral host galaxy. SNe IIn, powered by circumstellar interaction, could provide a good match to the light curve of SN Refsdal, but the spectrum of a SN IIn would not show broad and strong H-alpha absorption. From the grism spectrum, we measure an H-alpha expansion velocity consistent with those of SN 1987A-like SNe at a similar phase. The luminosity, evolution, and Gaussian profile of the H-alpha emission of the WFC3 and X-shooter spectra, separated by ~2.5 months in the rest frame, provide additional evidence that supports the SN 1987A-like classification. In comparison with other examples of SN 1987A-like SNe, SN Refsdal has a blue B-V color and a high luminosity for the assumed range of potential magnifications. If SN Refsdal can be modeled as a scaled version of SN 1987A, we estimate it would have an ejecta mass of 20+-5 solar masses. The evolution of the light curve at late times will provide additional evidence about the potential existence of any substantial circumstellar material (CSM). Using MOSFIRE and X-shooter spectra, we estimate a subsolar host-galaxy metallicity (8.3+-0.1 dex and <8.4 dex, respectively) near the explosion site.
We consider the recently introduced mimetic gravity, which is a Weyl-symmetric extension of the General Relativity and which can play a role of an imperfect fluid-like Dark Matter with a small sound speed. In this paper we discuss in details how this higher- derivative scalar-tensor theory goes beyond the construction by Horndeski, keeping only one scalar degree of freedom on top of two standard graviton polarizations. In particular, we consider representations of the theory in different sets of Weyl-invariant variables and connect this framework to the singular Brans-Dicke theory. Further, we find solution of equations of motion for the mimetic gravity in the synchronous reference frame in a general curved spacetime. This solution is exact in the test-field approximation or in the case of a shear-free spacetime without any other matter.
In supersymmetric theories, topological defects can have nontrivial behaviors determined purely by whether or not supersymmetry is restored in the defect core. A well-known example of this is that some supersymmetric cosmic strings are automatically superconducting, leading to important cosmological effects and constraints. We investigate the impact of nontrivial kinetic interactions, present in a number of particle physics models of interest in cosmology, on the relationship between supersymmetry and supercurrents on strings. We find that in some cases it is possible for superconductivity to be disrupted by the extra interactions.
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For about a decade, the baryon acoustic oscillation (BAO) peak at about 105 Mpc/h has provided a standard ruler test of the LCDM cosmological model, a member of the Friedmann--Lemaitre--Robertson--Walker (FLRW) family of cosmological models---according to which comoving space is rigid. However, general relativity does not require comoving space to be rigid. During the virialisation epoch, when the most massive structures form by gravitational collapse, it should be expected that comoving space evolves inhomogeneous curvature as structure grows. The BAO peak standard ruler should also follow this inhomogeneous evolution if the comoving rigidity assumption is false. This "standard" ruler has now been detected to be flexible, as expected under general relativity.
We give a brief summary of the formalism of invariants in general scalar-tensor and multiscalar-tensor gravities without derivative couplings. By rescaling of the metric and reparametrization of the scalar fields, the theory can be presented in different conformal frames and parametrizations. Due to this freedom in transformations, the scalar fields themselves do not carry independent physical meaning (in a generic parametrization). However, there are functions of the scalar fields and their derivatives which remain invariant under the transformations, providing a set of physical variables for the theory. We indicate how to construct such invariants and show how the observables like parametrized post-Newtonian parameters and characteristics of Friedmann-Lemaitre-Robertson-Walker cosmology can be neatly expressed in terms of the invariants.
If local supersymmetry is the correct extension of the standard model of particle physics, then following Inflation the early universe would have been populated by gravitinos produced from scatterings in the hot plasma during reheating. Their abundance is directly related to the magnitude of the reheating temperature. The gravitino lifetime is fixed as a function of its mass, and for gravitinos with lifetimes longer than the age of the universe at redshift $z\simeq 2\times 10^{6}$ (or roughly $6\times 10^6{\rm s}$), decay products can produce spectral distortion of the cosmic microwave background. Currently available COBE/FIRAS limits on spectral distortion can, in certain cases, already be competitive with respect to cosmological constraints from primordial nucleosynthesis for some gravitino decay scenarios. We show how the sensitivity limits on $\mu$ and \textsl{y} distortions that can be reached with current technology would improve constraints and possibly rule out a significant portion of the parameter space for gravitino masses and Inflation reheating temperatures.
In this paper we demonstrate that in the context of mimetic $F(R)$ gravity with Lagrange multiplier, it is possible to realize cosmologies which are compatible with the recent BICEP2/Keck Array data. We provide some characteristic examples for which the predicted scalar to tensor ratio can be quite smaller in comparison to the upper limit imposed by the BICEP2/Keck Array observations.
We perform a phase space analysis of a generalized modified gravity theory with non-minimal coupling between geometry and matter. We apply the dynamical system approach to this generalized model and find that in the cosmological context, different choices of Lagrangian density will apparently result in different phases of the universe. By carefully choosing the variables, we prove that there is an attractor solution to describe the late time accelerating universe when the modified gravity is chosen in a simple power-law form of the curvature scalar. We further examine the temperature evolution based on the thermodynamic understanding of the model. Confronting the model with temperature-redshift and supernova type Ia data sets, we find that the non-minimally coupled theory of gravity is a viable model to describe the late time universe acceleration.
If the Universe is dominated by cold dark matter and dark energy as in the currently popular LCDM cosmology, it is expected that large scale structures form gradually, with galaxy clusters of mass M > ~10^14 Msun appearing at around 6 Gyrs after the Big Bang (z ~ 1). Here, we report the discovery of 59 massive structures of galaxies with masses greater than a few x 10^13 Msun at redshifts between z=0.6 and 4.5 in the Great Observatories Origins Deep Survey fields. The massive structures are identified by running top-hat filters on the two dimensional spatial distribution of magnitude-limited samples of galaxies using a combination of spectroscopic and photometric redshifts. We analyze the Millennium simulation data in a similar way to the analysis of the observational data in order to test the LCDM cosmology. We find that there are too many massive structures (M > 7 x 10^13 Msun) observed at z > 2 in comparison with the simulation predictions by a factor of a few, giving a probability of < 1/2500 of the observed data being consistent with the simulation. Our result suggests that massive structures have emerged early, but the reason for the discrepancy with the simulation is unclear. It could be due to the limitation of the simulation such as the lack of key, unrecognized ingredients (strong non-Gaussianity or other baryonic physics), or simply a difficulty in the halo mass estimation from observation, or a fundamental problem of the LCDM cosmology. On the other hand, the over-abundance of massive structures at high redshifts does not favor heavy neutrino mass of ~ 0.3 eV or larger, as heavy neutrinos make the discrepancy between the observation and the simulation more pronounced by a factor of 3 or more.
We present a high-precision measurement of the parallax for the 12-day Cepheid SS Canis Majoris, obtained via spatial scanning with the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST). Spatial scanning enables astrometric measurements with a precision of 20-40 muas, an order of magnitude better than pointed observations. SS CMa is the second Cepheid targeted for parallax measurement with HST, and is the first of a sample of eighteen long-period >~ 10 days) Cepheids selected in order to improve the calibration of their period-luminosity relation and eventually permit a determination of the Hubble constant H_0 to better than 2%. The parallax of SS CMa is found to be 348 +/- 38 muas, corresponding to a distance of 2.9 +/- 0.3 kpc. We also present a refinement of the static geometric distortion of WFC3 obtained using spatial scanning observations of calibration fields, with a typical magnitude <~0.01 pixels on scales of 100 pixels.
We study linear scalar perturbations around a flat FLRW background in mimetic Horndeski gravity. In the absence of matter, we show that the Newtonian potential satisfies a second-order differential equation with no spatial derivatives. This implies that the sound speed for scalar perturbations is exactly zero on this background. We also show that in mimetic $G^3$ theories the sound speed is equally zero. We obtain the equation of motion for the comoving curvature perturbation (first order differential equation) and solve it to find that the comoving curvature perturbation is constant on all scales in mimetic Horndeski gravity. We find solutions for the Newtonian potential evolution equation in two simple models. Finally we show that the sound speed is zero on all backgrounds and therefore the system does not have any wave-like scalar degrees of freedom.
In this paper the existence of a stealth field during the evolution of our Universe is studied. With this aim, in the framework of the FRW cosmology, the case of non-conformal non-minimal coupling between a stealth scalar field and gravity is studied. It is shown that de Sitter's are the only backgrounds allowing for a stealth field fully depending on the spacetime coordinates. This way, such a field is not consistent with the present cosmological picture. If the stealth is homogeneous, then its dynamics is restricted by the underlying cosmological evolution. It is shown that homogeneous stealths can coexist with the kind of matter used to describe the matter content of our Universe according to the $\Lambda$CDM model.
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