The curvaton reheating in a tachyonic inflationary universe model with an exponential potential is studied. We have found that the energy density in the kinetic epoch, has a complicated dependencies of the scale factor. For different scenarios, the temperature of reheating is computed. These temperature result to be analogous to those obtained in the standard case of the curvaton scenario.

Future missions of gravitational-wave astronomy will be operated by space-based interferometers, covering very wide range of frequency band. Search for stochastic gravitational-wave backgrounds (GWBs) is one of the main target for such missions, and we here discuss the prospects for direct measurement of isotropic and anisotropic components of (primordial) GWBs around the frequency 0.1-10 Hz. After extending the theoretical basis for correlation analysis, we evaluate the sensitivity and the signal-to-noise ratio for the proposed future missions of space interferometers, like Big-Bang Observer (BBO), Deci-Hertz Interferometer Gravitational-wave Observer (DECIGO) and recently proposed Fabry-Perot type DECIGO. The astrophysical foregrounds which are expected at the low frequency may be a big obstacle and significantly reduce the signal-to-noise ratio of GWBs. As a result, minimum detectable amplitude may reach h^2 \Omega = 10^{-15} - 10^{-16}, as long as foreground point sources are properly subtracted. Based on the correlation analysis, we also discuss measurement of anisotropies of GWBs. As an example, sensitivity level required for detecting the dipole moment of GWB induced by the proper motion of our local system is closely examined.

We study the expansion of the universe at late times in the case that the cosmological constant obeys certain scaling laws motivated by renormalisation group running in quantum theories. The renormalisation scale is identified with the Hubble scale and the inverse radii of the event and particle horizon, respectively. We find de Sitter solutions, power-law expansion and super-exponential expansion in addition to future singularities of the Big Rip and Big Crunch type.

In this work, numerical simulations were used to investigate the gravitational stochastic background produced by coalescences occurring up to $z \sim 5$ of double neutron star systems. The cosmic coalescence rate was derived from Monte Carlo methods using the probability distributions for forming a massive binary and to occur a coalescence in a given redshift. A truly continuous background is produced by events located only beyond the critical redshift $z_* = 0.23$. Events occurring in the redshift interval $0.027<z<0.23$ give origin to a "popcorn" noise, while those arising closer than $z = 0.027$ produce a shot noise. The gravitational density parameter $\Omega_{gw}$ for the continuous background reaches a maximum around 670 Hz with an amplitude of $1.1\times 10^{-9}$, while the "popcorn" noise has an amplitude about one order of magnitude higher and the maximum occurs around a frequency of 1.2 kHz. The signal is below the sensitivity of the first generation of detectors but could be detectable by the future generation of ground based interferometers. Correlating two coincident advanced-LIGO detectors or two EGO interferometers, the expected S/N ratio are respectively 0.5 and 10.

We study a particular supersymmetric realization of the Peccei-Quinn symmetry which provides a suitable candidate for the curvaton field. The class of models considered also solves the mu problem, while generating the Peccei-Quinn scale dynamically. The curvaton candidate is a pseudo Nambu-Goldstone boson corresponding to an angular degree of freedom orthogonal to the axion field. Its order parameter increases substantially following a phase transition during inflation. This results in a drastic amplification of the curvaton perturbations. Consequently, the mechanism is able to accommodate low-scale inflation with Hubble parameter at the TeV scale. Hence, we investigate modular inflation using a string axion field as the inflaton with inflation scale determined by gravity mediated soft supersymmetry breaking. We find that modular inflation with the orthogonal axion as curvaton can indeed account for the observations for natural values of the parameters.

We study the influence of nonlocal interactions in two spin one pairing patterns of two-flavor quark matter: the anisotropic blue color paring besides the usual two color superconducting matter (2SCb), in which red and green colors are paired, and the color spin locking phase (CSL). The effect of nonlocality on the gaps is rather large and the pairings exhibit a strong dependence on the form factor of the interaction, especially in the low density region. The application of these small spin-one condensates for compact stars is analyzed: the early onset of quark matter of the nonlocal models may help to stabilize hybrid star configurations. While the anisotropic blue quark pairing does not survive a big asymmetry in the flavor space as imposed by the charge neutrality condition, the nonlocality makes the diquark pairing gaps in the CSL phase too small to be a good candidate for hybrid star cooling phenomenology. Therefore, if nonlocal effects are taken into account, both phases seem to be unlikely to occur in the interior of compact stars.

The curvaton reheating in a tachyonic braneworld inflationary universe model with an exponential potential is studied. We have found that the energy density in the kinetic epoch, has a complicated dependencies of the scale factor. For different scenarios the temperature of reheating is computed, finding an upper limit that lies in the range $10^{14}$--$10^{16}$GeV.

Integral Field Spectroscopy (IFS) provides a spectrum simultaneously for each spatial sample of an extended, two-dimensional field. It consists of an Integral Field Unit (IFU) which slices and re-arranges the initial field along the entrance slit of a spectrograph. This article presents an original design of IFU based on the advanced image slicer concept. To reduce optical aberrations, pupil and slit mirrors are disposed in a fan-shaped configuration that means that angles between incident and reflected beams on each elements are minimized. The fan-shaped image slicer improves image quality in terms of wavefront error by a factor 2 comparing with classical image slicer and, furthermore it guaranties a negligible level of differential aberration in the field. As an exemple, we are presenting the design LAM used for its proposal at the NIRSPEC/IFU invitation of tender.

Self-similar models are important in general relativity and other fundamental theories. In this paper we shall discuss the ``similarity hypothesis'', which asserts that under a variety of physical circumstances solutions of these theories will naturally evolve to a self-similar form. We will find there is good evidence for this in the context of both spatially homogenous and inhomogeneous cosmological models, although in some cases the self-similar model is only an intermediate attractor. There are also a wide variety of situations, including critical pheneomena, in which spherically symmetric models tend towards self-similarity. However, this does not happen in all cases and it is it is important to understand the prerequisites for the conjecture.

In models with extra dimensions, a black hole evaporates both in the bulk and on the visible brane, where standard model fields live. The exact emissivities of each particle species are needed to determine how the black hole decay proceeds. We compute and discuss the absorption cross-sections, the relative emissivities and the total power output of all known fields in the evaporation phase. Graviton emissivity is highly enhanced as the spacetime dimensionality increases. Therefore, a black hole loses a significant fraction of its mass in the bulk. This result has important consequences for the phenomenology of black holes in models with extra dimensions and black hole detection in particle colliders.

We present a fully model-independent analysis of the extensive observations reported by a recent ether-drift experiment in Berlin. No a priori assumption is made on the nature of a hypothetical preferred frame. We find a remarkable consistency with an Earth's cosmic motion exhibiting an average declination angle |\gamma|\sim 43^o and with values of the RMS anisotropy parameter (1/2-\beta+\delta) that are one order of magnitude larger than the presently quoted ones. This might represent the first modern indication for a preferred frame and for a non-zero anisotropy of the speed of light.

Although several models of $f(R)$ theories of gravity within the Palatini approach have been studied already, the interest was concentrated on those that have an effect on the late-time evolution of the universe, by the inclusion for example of terms inversely proportional to the scalar curvature in the gravitational action. However, additional positive powers of the curvature also provide interesting early-time phenomenology, like inflation, and the presence of such terms in the action is equally, if not more, probable. In the present paper models with both additional positive and negative powers of the scalar curvature are studied. Their effect on the evolution of the universe is investigated for all cosmological eras, and various constraints are put on the extra terms in the actions. Additionally, we examine the extent to which the new terms in positive powers affect the late-time evolution of the universe and the related observables, which also determines our ability to probe their presence in the gravitational action.

Because the equivalence principle holds as a theorem (of Iliev gr-qc/9709053) in the general theory of relativity along any non-self-intersecting curve, gravitational time dilation of 1/(1-v^2)^(1/2) is indistinguishable (along a curve) from time dilation caused by a relative velocity of v; time dilation and relative velocity are two sides of the same coin even in the general theory. Therefore, Einstein's velocity composition law u=(v+w)/(1+vw) can be rewritten to accumulate time dilation in the general theory according to 1/(1-u^2)^(1/2)=(1+vw)/[(1-v^2)(1-w^2)]^(1/2), not by direct multiplication of time dilation factors 1/(1-u^2)^(1/2)=1/[(1-v^2)(1-w^2)]^(1/2). The unbounded intensification of time dilation observed as an event horizon emerges at the center of a collapsing star is therefore indistinguishable (along a curve) from a relative velocity of the center approaching the speed of light, implying a bubble-like local inflation of the star's interior as the center recedes toward infinity even as the star continues to collapse as seen from the outside (as conjectured by Shatskiy astro-ph/0407222). This potentially provides a generic mechanism through which trapped surfaces and therefore singularities do not occur after gravitational collapse and before the big bang.

We apply the method of matched asymptotic expansions to analyse whether cosmological variations in physical `constants' and scalar fields are detectable, locally, on the surface of local gravitationally bound systems such as planets and stars, or inside virialised systems like galaxies and clusters. We assume spherical symmetry and derive a sufficient condition for the local time variation of the scalar fields that drive varying constants to track the cosmological one. We calculate under number of specific examples in detail by matching the Schwarzschild spacetime to spherically symmetric inhomogeneous Tolman-Bondi metrics in an intermediate region by rigorously construction matched asymptotic expansions on cosmological and local astronomical scales which overlap in an intermediate domain. We conclude that, independent of the details of the scalar-field theory describing the varying 'constant', the condition for cosmological variations to be measured locally is almost always satisfied in physically realistic situations. The proof of this statement provides a rigorous justification for using terrestrial experiments and solar system observations to constraint or detect any cosmological time variations in the traditional `constants' of Nature.

Standard Big Bang nucleosynthesis at baryonic density as inferred by WMAP implies a primordial Li7 abundance factor of two to three larger than that inferred by observations of low--metallicity halo stars. Recent observations of Li6 in halo stars suggest a pre--galactic origin of this isotope, which is exceedingly difficult to explain by putative high redshift cosmic ray populations. We investigate if one or both of these lithium problems may be solved by late decaying relic particles in the Constrained Minimal Supersymmetric Standard Model (CMSSM) coupled to gravity. Assuming that the gravitino is the lightest supersymmetric particle (LSP) we find that in large parts of the CMSSM parameter space either of these problems can be potentially solved. In particular, we also find solutions where both lithium problems may be solved simultaneously. These entail the hadronic decay of relic 1 TeV staus into 100 GeV gravitinos at 1000 sec after the Big Bang, as proposed by one of us before. Moreover, the produced gravitinos naturally contribute a large fraction, or all, to the by WMAP required dark matter density. A prediction of this model is the dark matter to be lukewarm with free--streaming lengths of the order of a 4 keV early freezing--out relic particle. Such lukewarm gravitino dark matter may have beneficial effects to the formation of galactic structures and may be constrained by the reionisation history of the Universe.

Several phenomenological and cosmological aspects of a minimal extension of the Georgi-Glashow model, where the Higgs sector is composed by 5_H, 15_H, and 24_H, are studied. It is shown that the constraints coming from the unification of gauge interactions up to two-loop level predict light scalar leptoquarks. In this GUT scenario, the upper bound on the total proton decay lifetime is tau_p < 1.4 x 10^36 years. The possibility to explain the matter-antimatter asymmetry in the universe through the decays of SU(2)_L scalar triplets is also studied. We find that a successful triplet seesaw leptogenesis implies an upper bound on the scalar leptoquark mass, M_Phib < 10^{6-7} GeV. We conclude that this GUT scenario can be tested at the next generation of proton decay experiments and future colliders through the production of scalar leptoquarks.

Taking seriously the interpretation of black hole entropy as the logarithm of the number of microstates, we argue that thermal gravitons may undergo a phase transition to a kind of black hole condensate. The phase transition proceeds via nucleation of black holes at a rate governed by a saddlepoint configuration whose free energy is of order the inverse temperature in Planck units. Whether the universe remains in a low entropy state as opposed to the high entropy black hole condensate depends sensitively on its thermal history. Our results may clarify an old observation of Penrose regarding the very low entropy state of the universe.

We address the emerging discrepancy between the Big Bang Nucleosynthesis data and standard cosmology, which asks for a bit longer evolution time. If this effect is real, one possible implication (in a framework of brane cosmology model) is that there is a ``dark radiation'' component which is negative and makes few percents of ordinary matter density. If so, all scales of this model can be fixed, provided brane-to-bulk leakage problem is solved.

We study the finite temperature-density phase diagram of an attractive fermionic system that supports two-body (dimer) and three-body (trimer) bound states in free space. Using interactions characteristic for nuclear systems, we obtain the critical temperature T_c2 for the superfluid phase transition and the limiting temperature T_c3 for the extinction of trimers. The phase diagram features a Cooper-pair condensate in the high-density, low-temperature domain which, with decreasing density, crosses over to a Bose condensate of strongly bound dimers. The high-temperature, low-density domain is populated by trimers whose binding energy decreases toward the density-temperature domain occupied by the superfluid and vanishes at a critical temperature T_c3 > T_c2.

We present a numerical model of a collapsing radiating sphere, whose boundary surface undergoes bouncing due to a decreasing of its inertial mass density (and, as expected from the equivalence principle, also of the ``gravitational'' force term) produced by the ``inertial'' term of the transport equation. This model exhibits for the first time the consequences of such an effect, and shows that under physically reasonable conditions this decreasing of the gravitational term in the dynamic equation may be large enough as to revert the collapse and produce a bouncing of the boundary surface of the sphere.

Inspired by the generalization of quantum theory for the case of non-Hermitian Hamiltonians with CPT symmetry, we construct a simple classical cosmological scalar field based model describing a smooth transition from ordinary dark energy to the phantom one.

We propose a mechanism for solving the horizon and entropy problems of standard cosmology which does not make use of cosmological inflation. Crucial ingredients of our scenario are brane gases, extra dimensions, and a confining potential due to string gas effects which becomes dominant at string-scale brane separations. The initial conditions are taken to be a statistically homogeneous and isotropic hot brane gas in a space in which all spatial dimensions are of string scale. The extra dimensions which end up as the internal ones are orbifolded. The hot brane gas leads to an initial phase (Phase 1) of isotropic expansion. Once the bulk energy density has decreased sufficiently, a weak confining potential between the two orbifold fixed planes begins to dominate, leading to a contraction of the extra spatial dimensions (Phase 2). String modes which contain momentum about the dimensions perpendicular to the orbifold fixed planes provide a repulsive potential which prevents the two orbifold fixed planes from colliding. The radii of the extra dimensions stabilize, and thereafter our three spatial dimensions expand as in standard cosmology. The energy density after the stabilization of the extra dimensions is of string scale, whereas the spatial volume has greatly increased during Phases 1 and 2, thus leading to a non-inflationary solution of the horizon and entropy problems.

In cores of supernovae and crusts of neutron stars, nuclei can adopt interesting shapes, such as rods or slabs, etc., which are referred to as nuclear "pasta." Recently, we have been studying the pasta phases focusing on their dynamical aspects with quantum molecular dynamic (QMD) approach. We review our findings on the following topics: dynamical formation of the pasta phases by cooling down the hot uniform nuclear matter; a phase diagram on the density versus temperature plane; structural transitions between the pasta phases induced by compression and their mechanism. Properties of the nuclear interaction used in our works are also discussed.

The experimental evidence that the equation of state (EOS) of the dark energy (DE) could be evolving with time/redshift (including the possibility that it might behave phantom-like near our time) suggests that there might be dynamical DE fields that could explain this behavior. We propose, instead, that a variable cosmological term (including perhaps a variable Newton's gravitational coupling too) may account in a natural way for all these features.

We investigate the formation via tunneling of inflating (false-vacuum) bubbles in a true-vacuum background, and the reverse process. Using effective potentials from the junction condition formalism, all true- and false-vacuum bubble solutions with positive interior and exterior cosmological constant, and arbitrary mass are catalogued. We find that tunneling through the same effective potential appears to describe two distinct processes: one in which the initial and final states are separated by a wormhole (the Farhi-Guth-Guven mechanism), and one in which they are separated by a cosmological horizon. In the zero-mass limit, the first process corresponds to the creation of an inhomogenous universe from nothing, while the second mechanism is equivalent to the nucleation of true- or false-vacuum Coleman-De Luccia bubbles. Known pathologies that arise in the path integral for the first (wormhole) process are shown not to appear in the second. We compute the probabilities of both mechanisms in the WKB approximation using semi-classical Hamiltonian methods, and find that -- assuming both process are allowed -- neither mechanism dominates in all regimes.

Astrophysical observations suggest that the fine structure constant (alpha) may (or may not) be evolving over the cosmological time scale. This raises a much debated question: is alpha variation due to the variation of the speed of light (c), elementary electric charge (e), or the Planck constant (h)?
Previously, we proposed the metrological approach based on the analysis of the relationships between the fundamental units (e.g. of the length and time) and the fundamental constants. Our methodology allows one to find how each of the fundamental constants e, c, h evolves in time and offers a new outlook for this area. Here we give a brief outline of this approach and the main results it produces.

We propose a new way of obtaining slow-roll inflation in the context of higher dimensional models motivated by string and M theory. In our model, all extra spatial dimensions are orbifolded. The initial conditions are taken to be a hot dense bulk brane gas which drives an initial phase of isotropic bulk expansion. This phase ends when a weak potential between the orbifold fixed planes begins to dominate. For a wide class of potentials, a period during which the bulk dimensions decrease sufficiently slowly to lead to slow-roll inflation of the three dimensions parallel to the orbifold fixed planes will result. Once the separation between the orbifold fixed planes becomes of the string scale, a repulsive potential due to string effects takes over and leads to a stabilization of the radion modes. The conversion of bulk branes into radiation during the phase of bulk contraction leads to reheating.

We have in earlier work (Basse N P 2005, Phys. Lett. A vol. 340 p. 456) reported on intriguing similarities between density fluctuation power versus wavenumber on small (mm) and large (Mpc) scales. In this paper we expand upon our previous studies of small and large scale measurements made in fusion plasmas and using cosmological data, respectively. The measurements are compared to predictions from classical fluid turbulence theory. Both small and large scale data can be fitted to a functional form that is consistent with the dissipation range of turbulence. The comparable dependency of density fluctuation power on wavenumber in fusion plasmas and cosmology might indicate a common origin of these fluctuations.