We present a new version of our racetrack inflation scenario which, unlike our original proposal, is based on an explicit compactification of type IIB string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The axion-dilaton and all complex structure moduli are stabilized by fluxes. The remaining 2 Kahler moduli are stabilized by a nonperturbative superpotential, which has been explicitly computed. For this model we identify situations for which a linear combination of the axionic parts of the two Kahler moduli acts as an inflaton. As in our previous scenario, inflation begins at a saddle point of the scalar potential and proceeds as an eternal topological inflation. For a certain range of inflationary parameters, we obtain the COBE-normalized spectrum of metric perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We discuss possible changes of parameters of our model and argue that anthropic considerations favor those parameters that lead to a nearly flat spectrum of inflationary perturbations, which in our case is characterized by the spectral index n_s = 0.95.
After a brief introduction to the NIST EBIT facility, we present the results of three different types of experiments that have been carried out there recently: EUV and visible spectroscopy in support of the microelectronics industry, laboratory astrophysics using an x-ray microcalorimeter, and charge exchange studies using extracted beams of highly charged ions.
A geometric view of the possible outcomes of elastic collisions of two massive bodies is developed that integrates laboratory, center of mass, and relative body frames in a single diagram. From these diagrams all the scattering properties of binary collisions can be obtained. The particular case of gravitational scattering by a moving massive object corresponds to the slingshot maneuver, and its maximum velocity is obtained.
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Full relativistic simulations in three dimensions invariably develop runaway modes that grow exponentially and are accompanied by violations of the Hamiltonian and momentum constraints. Recently, we introduced a numerical method (Hamiltonian relaxation) that greatly reduces the Hamiltonian constraint violation and helps improve the quality of the numerical model. We present here a method that controls the violation of the momentum constraint. The method is based on the addition of a longitudinal component to the traceless extrinsic curvature generated by a vector potential w_i, as outlined by York. The components of w_i are relaxed to solve approximately the momentum constraint equations, pushing slowly the evolution toward the space of solutions of the constraint equations. We test this method with simulations of binary neutron stars in circular orbits and show that effectively controls the growth of the aforementioned violations. We also show that a full numerical enforcement of the constraints, as opposed to the gentle correction of the momentum relaxation scheme, results in the development of instabilities that stop the runs shortly.
Even when we consider Newtonian stars, i.e., stars with surface gravitational redshift, z << 1, it is well known that, theoretically, it is possible to have stars, supported against self-gravity, almost entirely by radiation pressure. However, such Newtonian stars must necessarily be supermassive. We point out that this requirement for excessive large M, in Newtonian case, is a consequence of the occurrence of low z<< 1. On the other hand, if we remove such restrictions, and allow for possible occurrence of highly general relativistic regime, z >> 1, we show that, it is possible to have radiation pressure supported stars at arbitrary value of M. Since radiation pressure supported stars necessarily radiate at the Eddington limit, in Einstein gravity, they are never in strict hydrodynamical equilibrium. Further, it is believed that sufficiently massive or dense objects undergo continued gravitational collapse to the Black Hole stage characterized by z =infty. Thus, late stages of Black Hole formation, by definition, will have, z >> 1, and hence could be examples of quasi-stable general relativistic radiation pressure supported stars. It is shown that the observed duration of such Eddington limited radiation pressure dominates states is t ~ 5. 10^8 (1+z) yr. Thus, t --> infty as Black Hole formation (z--> infty) would take place. Consequently, such radiation pressure dominated extreme general relativistic stars become Eternally Collapsing Objects and the BH state is preceded by such an eternal radiation pressure supported phase.
The 5D Cosmological General Relativity theory developed by Carmeli reproduces all of the results that have been successfully tested for Einstein's 4D theory. However the Carmeli theory because of its fifth dimension, the velocity of the expanding universe, predicts something different for the propagation of gravity waves on cosmological distance scales. This analysis indicates that gravitational radiation may not propagate as an unattenuated wave where effects of the Hubble expansion are felt. In such cases the energy does not travel over such large length scales but is evanescent and dissipated into the surrounding space as heat.
We study a new field theory effect in the cosmological context in the Two Measures Field Theory (TMT). TMT is an alternative gravity and matter field theory where the gravitational interaction of fermionic matter is reduced to that of General Relativity when the energy density of the fermion matter is much larger than the dark energy density. In this case also the 5-th force problem is solved automatically. In the opposite limit, where the magnitudes of fermionic energy density and scalar field dark energy density become comparable, nonrelativistic fermions can participate in the cosmological expansion in a very unusual manner. Some of the features of such states in a toy model of the late time universe filled with homogeneous scalar field and uniformly distributed nonrelativistic neutrinos: neutrino mass increases as m ~ a^{3/2}; the neutrino gas equation-of-state approaches w=-1, i.e. neutrinos behave as a sort of dark energy; the total (scalar field + neutrino) equation-of-state also approaches w=-1; the total energy density of such universe is less than it would be in the universe filled with the scalar field alone. An analytic solution is presented. A domain structure of the dark energy seems to be possible. We speculate that decays of the CLEP state neutrinos may be both an origin of cosmic rays and responsible for a late super-acceleration of the universe. In this sense the CLEP states exhibit simultaneously new physics at very low densities and for very high particle masses.
PPN-limit of higher order theories of gravity represents a still
controversial matter of debate and no definitive answer has been provided, up
to now, about this issue. By exploiting the analogy between scalar-tensor and
fourth-order theories of gravity, one can generalize the PPN-limit formulation.
By using the definition of the PPN-parameters $\gamma$ and $\beta$ in term of
the $f(R)$ derivatives, we show that a family of third-order polynomial
theories, in the Ricci scalar $R$, turns out to be compatible with the
PPN-limit and the deviation from General Relativity theoretically predicted
agree with experimental data.
We derive new bounds on Lorentz violations in the electron sector from existing data on high-energy astrophysical sources. Synchrotron and inverse Compton data give precisely complementary constraints. The best bound on a specific combination of electron Lorentz-violating coefficients is at the 6 x 10^(-20) level, and independent bounds are available for all the Lorentz-violating c coefficients at the 2 x 10^(-14) level or better. This represents an improvement in some bounds by fourteen orders of magnitude.
Based on the cosmic holographic conjecture of Fischler and Susskind, we point out that the average energy density of the universe is bound from above by its entropy limit. Since Friedmann's equation saturates this relation, the measured value of the cosmological energy density is completely natural in the framework of holographic thermodynamics: vacuum energy density fills the available quantum degrees of freedom allowed by the holographic bound. This is in strong contrast with traditional quantum field theories where, since no similar bound applies, the natural value of the vacuum energy is expected to be 123 orders of magnitude higher than the holographic value. Based on our simple calculation, holographic thermodynamics, and consequently any future holographic quantum (gravity) theory, resolves the vacuum energy puzzle.
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We discuss the possibility of generation of baryon inhomogeneities in a quark-gluon plasma phase due to moving Z(3) interfaces. By modeling the dependence of effective mass of the quarks on the Polyakov loop order parameter, we study the reflection of quarks from collapsing Z(3) interfaces and estimate resulting baryon inhomogeneities in the context of the early universe. We argue that in the context of certain low energy scale inflationary models, it is possible that large Z(3) walls arise at the end of the reheating stage. Collapse of such walls could lead to baryon inhomogeneities which may be separated by large distances near the QCD scale. Importantly, the generation of these inhomogeneities is insensitive to the order, or even the existence, of the quark-hadron phase transition. We also briefly discuss the possibility of formation of quark nuggets in this model, as well as baryon inhomogeneity generation in relativistic heavy-ion collisions.
We study the scalar sector of the Two Measures Field Theory (TMT) model in the context of cosmological dynamics. The scalar sector includes the inflaton \phi and the Higgs \upsilon fields. The model possesses gauge and scale invariance. The latter is spontaneously broken due to intrinsic features of the TMT dynamics. In the model with the inflaton \phi alone, in different regions of the parameter space the following different effects can take place without fine tuning of the parameters and initial conditions: a) Possibility of resolution of the old cosmological constant problem: this is done in a consistent way hinted by S. Weinberg in his comment concerning the question of how one can avoid his no-go theorem. b) The power law inflation without any fine tuning may end with damped oscillations of $\phi$ around the state with zero cosmological constant. c) There are regions of the parameters where the equation-of-state w=p/\rho in the late time universe is w<-1 and w asymptotically (as t\to\infty) approaches -1 from below. This effect is achieved without any exotic term in the action. In a model with both \phi and \upsilon fields, a scenario which resembles the hybrid inflation is realized but there are essential differences, for example: the Higgs field undergos transition to a gauge symmetry broken phase <\upsilon>\neq 0 soon after the end of a power law inflation; there are two oscillatory regimes of \upsilon, one around \upsilon =0 at 50 e-folding before the end of inflation, another - during transition to a gauge symmetry broken phase where the scalar dark energy density approaches zero without fine tuning; the gauge symmetry breakdown is achieved without tachyonic mass term in the action.
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We investigate the relic density n_\chi of non-relativistic long-lived or stable particles \chi in cosmological scenarios in which the temperature T is too low for \chi to achieve full chemical equilibrium. The case with a heavier particle decaying into \chi is also investigated. We derive approximate solutions for n_\chi(T) which accurately reproduce numerical results when full thermal equilibrium is not achieved. If full equilibrium is reached, our ansatz no longer reproduces the correct temperature dependence of the \chi number density. However, it does give the correct final relic density, to an accuracy of about 3% or better, for all cross sections and initial temperatures.
We investigate the dynamics in a galactic potential with two reflection symmetries. The phase-space structure of the real system is approximated with a resonant detuned normal form constructed with the method based on the Lie transform. Attention is focused on the stability properties of the axial periodic orbits that play an important role in galactic models. Using energy and ellipticity as parameters, we find analytical expressions of bifurcations and compare them with numerical results available in the literature.
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We investigate the thermodynamics of static black objects such as black holes, black strings and their generalizations to D dimensions (`black branes') in a gravitational theory containing the four dimensional Gauss-Bonnet term in the action, when D-4 of the dimensions are compactified on a torus. The entropies of black holes and black branes are compared to obtain information on the stability of these objects and to find their phase diagrams. We demonstrate the existence of a critical mass, which depends on the scale of the compactified dimensions, below which the black hole entropy dominates over the entropy of the black membrane.
We argue that, when coupled to Einstein's theory of gravity, the Yukawa
theory may solve the cosmological constant problem in the following sense: The
radiative corrections of fermions generate an effective potential for the
scalar field, such that the effective cosmological term Lambda_eff is
dynamically driven to zero. Thence, for any initial positive cosmological
constant Lambda_0, Lambda_eff = 0 is an attractor of the semiclassical Einstein
theory coupled to fermionic and scalar matter fields. When the initial
cosmological term is negative, Lambda_eff=Lambda_0 does not change. Next we
argue that the dark energy of the Universe may be explained by a GUT scale
fermion with a mass, m = 4.3 * 10^15 (Lambda_0/10^13GeV)^(1/2) GeV.
Finally, we comment on how the inflationary paradigm, BEH mechanism and phase
transitions in the early Universe get modified in the light of our findings.
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