Radiation-dominated Era Research Articles

Dynamics of massive interacting scalar fields in Bekenstein- Sandvik-Barrow-Magueijo theory

We examine the dynamical characteristics of massive interacting scalar field introduced in the Bekenstein-Sandvik-Barrow-Magueijo (BSBM) theory. Based on the classification of matter- and radiation-dominated cosmological eras, we consider three possible physical scenarios that allowed by the theory. We present the analysis of its dynamics in terms of phase space of the corresponding massive scalar field. The results demonstrate distinct characteristics between those eras. Characteristic of the related fine structure constant is also discussed.

Gauss–Bonnet gravitational baryogenesis

In this letter we study some variant forms of gravitational baryogenesis by using higher order terms containing the partial derivative of the Gauss-Bonnet scalar coupled to the baryonic current. This scenario extends the well known theory that uses a similar coupling between the Ricci scalar and the baryonic current. One appealing feature of the scenario we study is that the predicted baryon asymmetry during a radiation domination era is non-zero. We calculate the baryon to entropy ratio for the Gauss-Bonnet term and by using the observational constraints we investigate which are the allowed forms of the $R+F(\mathcal{G})$ gravity controlling the evolution. Also we briefly discuss some alternative higher order terms that can generate a non-zero baryon asymmetry, even in the conformal invariance limit.

Gauss-Bonnet cosmology unifying late and early-time acceleration eras with intermediate eras

In this paper we demonstrate that with vacuum $F(G)$ gravity it is possible to describe the unification of late and early-time acceleration eras with the radiation and matter domination era. The Hubble rate of the unified evolution contains two mild singularities, so called Type IV singularities, and the evolution itself has some appealing features, such as the existence of a deceleration-acceleration transition at late times. We also address quantitatively a fundamental question related to modified gravity models description of cosmological evolution: Is it possible for all modified gravity descriptions of our Universe evolution, to produce a nearly scale invariant spectrum of primordial curvature perturbations? As we demonstrate, the answer for the $F(G)$ description is no, since the resulting power spectrum is not scale invariant, in contrast to the $F(R)$ description studied in the literature. Therefore, although the cosmological evolution can be realized in the context of vacuum $F(G)$ gravity, the evolution is not compatible with the observational data, in contrast to the $F(R)$ gravity description of the same cosmological evolution.

Inflaton dark matter from incomplete decay

We show that the decay of the inflaton field may be incomplete, while nevertheless successfully reheating the universe and leaving a stable remnant that accounts for the present dark matter abundance. We note, in particular, that since the mass of the inflaton decay products is field-dependent, one can construct models, endowed with an appropriate discrete symmetry, where inflaton decay is kinematically forbidden at late times and only occurs during the initial stages of field oscillations after inflation. We show that this is sufficient to ensure the transition to a radiation-dominated era and that inflaton particles typically thermalize in the process. They eventually decouple and freeze out, yielding a thermal dark matter relic. We discuss possible implementations of this generic mechanism within consistent cosmological and particle physics scenarios, for both single-field and hybrid inflation.

Singular F(R) cosmology unifying early- and late-time acceleration with matter and radiation domination era

We present some cosmological models which unify the late- and early-time acceleration eras with the radiation and the matter domination era, and we realize the cosmological models by using the theoretical framework of gravity. Particularly, the first model unifies the late- and early-time acceleration with the matter domination era, and the second model unifies all the evolution eras of our Universe. The two models are described in the same way at early and late times, and only the intermediate stages of the evolution have some differences. Each cosmological model contains two Type IV singularities which are chosen to occur one at the end of the inflationary era and one at the end of the matter domination era. The cosmological models at early times are approximately identical to the R2 inflation model, so these describe a slow-roll inflationary era which ends when the slow-roll parameters become of order one. The inflationary era is followed by the radiation era and after that the matter domination era follows, which lasts until the second Type IV singularity, and then the late-time acceleration era follows. The models have two appealing features: firstly they produce a nearly scale invariant power spectrum of primordial curvature perturbations and a scalar-to-tensor ratio which are compatible with the most recent observational data and secondly, it seems that the deceleration–acceleration transition is crucially affected by the presence of the second Type IV singularity which occurs at the end of the matter domination era. As we demonstrate, the Hubble horizon at early times shrinks, as expected for an initially accelerating Universe, then during the matter domination era, it expands and finally after the Type IV singularity, the Hubble horizon starts to shrink again, during the late-time acceleration era. Intriguingly enough, the deceleration–acceleration transition, occurs after the second Type IV singularity. In addition, we investigate which gravity can successfully realize each of the four cosmological epochs.

Constraints on singular evolution from gravitational baryogenesis

We investigate how the gravitational baryogenesis mechanism can potentially constrain the form of a Type IV singularity. Specifically, we study two different models with interesting phenomenology, that realize two distinct Type IV singularities, one occurring at the end of inflation and one during the radiation domination era or during the matter domination era. As we demonstrate, the Type IV singularities occurring at the matter domination era or during the radiation domination era are constrained by the gravitational baryogenesis, in such a way so that these do not render the baryon to entropy ratio singular. Both the cosmological models we study cannot be realized in the context of ordinary Einstein–Hilbert gravity, and hence our work can only be realized in the context of [Formula: see text] gravity and more generally in the context of modified gravity only.

Accretion of radiation and rotating primordial black holes

We consider rotating primordial black holes (PBHs) and study the effect of accretion of radiation in the radiation-dominated era. The central part of our analysis deals with the role of the angular momentum parameter on the evolution of PBHs. We find that both the accretion and evaporation rates decrease with an increase in the angular momentum parameter, but the rate of evaporation decreases more rapidly than the rate of accretion. This shows that the evaporation time of PBHs is prolonged with an increase in the angular momentum parameter. We also note that the lifetime of rotating PBHs increases with an increase in the accretion efficiency of radiation as in the case of nonrotating PBHs.

A complete cosmological scenario from $$f(R,T^{\phi })$$ f ( R , T ϕ ) gravity theory

Recent elaborated by T. Harko and collaborators, the $f(R,T)$ theories of gravity contemplate an optimistic alternative to dark energy, for which $R$ and $T$ stand for the Ricci scalar and the trace of the energy-momentum tensor, respectively. Although the literature has shown that the $T$ dependence on the gravitational part of the action - which is due to the consideration of quantum effects - may induce some novel features in the scope of late-time cosmological dynamics, in the radiation-dominated universe, when $T=0$, no contributions seem to rise from such theories. Apparently, $f(R,T)$ contributions to a radiation-dominated universe may rise only from the $f(R,T^\varphi)$ approach, which is nothing but the $f(R,T)$ gravity in the case of a self-interacting scalar field whose trace of the energy-momentum tensor is $T^\varphi$. We intend, in this article, to show how $f(R,T^\varphi)$ theories of gravity can contribute to the study of the primordial stages of the universe. Our results predict a graceful exit from inflationary stage to a radiation-dominated era. They also predict a late-time cosmic acceleration after a matter-dominated phase, making the $f(R,T^\varphi)$ theories able to describe, in a self-consistent way, all the different stages of the universe dynamics.

New massive bigravity cosmologies with double matter coupling

We study a previously largely unexplored branch of homogeneous and isotropic background solutions in ghost-free massive bigravity with consistent double matter coupling. For a certain family of parameters we find `self-inflated' FLRW cosmologies, i.e. solutions with an accelerated early-time period during the radiation-dominated era. In addition, these solutions also display an accelerated late-time period closely mimicking GR with a cosmological constant. Interestingly, within this family, the particular case of β1=β3=0 gives bouncing cosmologies, where there is an infinite contracting past, a non-zero minimum value of the scale factor at the bounce, and an infinite expanding future.

Towards realisticf(T)models with nonminimal torsion-matter coupling extension

Using the observation data of SNeIa, CMB and BAO, we establish two concrete $f(T)$ models with nonminimal torsion-matter coupling extension. We study in detail the cosmological implication of our models and find they are successful in describing the observation of the Universe, its large scale structure and evolution. In other words, these models do not change the successful aspects of $\Lambda$CDM scenario under the error band of fitting values as describing the evolution history of the Universe including radiation-dominated era, matter-dominated era and the present accelerating expansion. Meanwhile, the significant advantage of these models is that they could avoid the cosmological constant problem of $\Lambda$CDM. A joint analysis is performed by using the data of CMB+BAO+JLA, which leads to $\Omega_{m0}=0.255\pm 0.010, \Omega_{b0}h^2=0.0221\pm 0.0003$ and $H_0=68.54\pm 1.27$ for model I and $\Omega_{m0}=0.306\pm 0.010, \Omega_{b0}h^2=0.0225\pm 0.0003$ and $H_0=60.97\pm 0.44$ for model II at 1$\sigma$ confidence level. The evolution of the decelaration parameter $q(a)$ and the effective equation of state $w_{DE}(a)$ are displayed. Furthermore, The resulted age of the Universe from our models is consistent with the ages of the oldest globular clusters. As for the fate of the Universe, model I results in a de Sitter accelerating phase while model II appears a power-law one, even though $w_{DE0}< -1$ makes model I look like a phantom at present time.

σCDM coupled to radiation: Dark energy and Universe acceleration

Recently, the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as [Formula: see text]CDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann–Robertson–Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two-fold: To extend “life” of the [Formula: see text]CDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential [Formula: see text] via variation of the interaction parameter [Formula: see text]. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state (EoS) and evolution of DE EoS with variation of coupling constant [Formula: see text]. A comparison with the [Formula: see text]CDM model was performed. A new feature of the model is the existence of some values of potential coupling constant, leading to a [Formula: see text]CDM solution without transition into accelerated expansion epoch.

Primordial black holes as biased tracers

Primordial black holes (PBHs) are theoretical black holes which may be formed during the radiation dominant era and, basically, caused by the gravitational collapse of radiational overdensities. It has been well known that in the context of the structure formation in our Universe such collapsed objects, e.g., halos/galaxies, could be considered as bias tracers of underlying matter fluctuations and the halo/galaxy bias has been studied well. Employing a peak-background split picture which is known to be a useful tool to discuss the halo bias, we consider the large scale clustering behavior of the PBH and propose an almost mass-independent constraint to the scenario that dark matters (DMs) consist of PBHs. We consider the case where the statistics of the primordial curvature perturbations is almost Gaussian, but with small local-type non-Gaussianity. If PBHs account for the DM abundance, such a large scale clustering of PBHs behaves as nothing but the matter isocurvature perturbation and constrained strictly by the observations of cosmic microwave backgrounds (CMB). From this constraint, we show that, in the case a certain single field causes both CMB temperature perturbations and PBH formations, the PBH-DM scenario is excluded even with quite small local-type non-Gaussianity, $|f_\mathrm{NL}|\sim\mathcal{O}(0.01)$, while we give the constraints to parameters in the case where the source field of PBHs is different from CMB perturbations.

The Higgs boson and cosmology

I will discuss how the Higgs field of the Standard Model may have played an important role in cosmology, leading to the homogeneity, isotropy and flatness of the Universe; producing the quantum fluctuations that seed structure formation; triggering the radiation-dominated era of the hot Big Bang; and contributing to the processes of baryogenesis and dark matter production.

Scalar-Torsion Cosmology in the Poincaré Gauge Theory of Gravity

We investigate the cosmological effect of the scalar-torsion (0+) mode in Poincaré gauge theory of gravity. We focus on two types of solutions distinguished by the constant curvature and kinetic energy. In the former, we find that the torsion EoS (w) varies with the background stage of the universe. In particular, it behaves like radiation (matter) of w=1/3 (w=0) in the radiation (matter) dominant era. But eventually in the late time the torsion density becomes a de Sitter universe for the acceleration universe. In the latter, our numerical analysis indicates that the EoS has an asymptotic behavior in the high redshift regime. We also employ theoretical calculations together with numerical computations in accordance with such asymptotic phenomenon.

Acceleration of the Universe in Matter Dominant Era by Conformal Symmetry Breaking

We introduce a scenario in which the breakdown of conformal symmetry is responsible for the acceleration of universe in the matter dominant era. In this regard, we consider a self interacting scalar field non-minimally coupled to the Ricci scalar and the trace of energy-momentum tensor. For a traceless energy-momentum tensor in radiation dominant era, the coupling to matter vanishes and we are left with a conformal invariant gravitational action of Deser, where the universe may experience a decelerating phase in agreement with observations. In matter dominant era, the coupling to matter no longer vanishes, the conformal symmetry is broken down, and the matter inevitably becomes pressureless. The corresponding field equations are obtained and it is shown that the universe may have an accelerating phase in this era, provided that the value of self interaction coupling constant satisfies an specific lower bound. Moreover, we provide a reasonable solution to the coincidence problem.

Hubble-induced mass from MSSM plasma

We evaluate the effective mass of a scalar field ϕ coupled to thermal plasma through Planck-suppressed interactions.We find it useful to rescale the coupled fields so that all the ϕ-dependences are absorbed into the yukawa and gauge couplings,which allows us to read off the leading order contributions to the effective mass m̃ϕ from the 2-loop free energy calculatedwith the rescaled couplings. We give an analytical expression for m̃ϕ at a sufficiently high temperaturein the case where ϕ is coupled to the MSSM chiral superfields through non-minimal Kähler potential.We find that |m̃ϕ2| is about 10−3H2 ∼ 10−2H2 at the leading order in terms of the couplings for typical parameter sets, where H is the Hubble expansion rate in the radiation-dominated era.

SU(1,1) Lie algebraic approach for the evolution of the quantum inflationary universe

Abstract Quantum behavior of scalar fields and vacuum energy density in the inflationary universe are investigated using SU(1,1) Lie algebraic approach. Wave functions describing the evolution of scalar fields that have been thought to have driven cosmic inflation are identified in several possible quantum states at the early stage of the universe, such as the Fock state, the Glauber coherent state, and the SU(1,1) coherent states. In particular, we focus in this research on two important classes of the SU(1,1) coherent states, which are the so-called even and odd coherent states and the Perelomov coherent state. It is shown in the spatially flat universe driven by a single scalar field that the probability densities in all these states have converged to the origin (ϕ = 0, where ϕ is the scalar field) as time goes by. This outcome implies that the vacuum energy density characterized by the scalar field dissipates with time. The probability density in the matter-dominated era converged more rapidly than that in the radiation-dominated era. Hence, we can confirm that the progress of dissipation for the vacuum energy density became faster as the matter era began after the end of the early dominance of radiation. This consequence is, indeed, in agreement with the results of our previous researches in cosmology (for example, see [Chin. Phys. C 35 (2011) 233] and references there in).

The matter bounce scenario in loop quantum cosmology

In the matter bounce scenario, a dust-dominatedcontracting space-time generates scale-invariantperturbations that, assuming a nonsingularbouncing cosmology, propagate to the expandingbranch and set appropriate initial conditionsfor the radiation-dominated era. Since thisscenario depends on the presence of a bounce,it seems appropriate to consider it in thecontext of loop quantum cosmology where a bouncinguniverse naturally arises. For a pressurelesscollapsing universe in loop quantum cosmology, thepredicted power spectrum of the scalar perturbationsafter the bounce is scale-invariant and the tensorto scalar ratio is negligibly small. A slight redtilt can be given to the scale-invariance ofthe scalar perturbations by a scalar field whoseequation of state is P = −ϵρ, whereϵ is a small positive number. Then, thepower spectrum for tensor perturbations is alsoalmost scale-invariant with the same red tilt asthe scalar perturbations, and the tensor to scalarratio is expected to be r ≈ 9 × 10−4.Finally, for the predicted amplitude of the scalarperturbations to agree with observations, the criticaldensity in loop quantum cosmology must be of the orderρc ∼ 10−9ρPl.

Gravitino cosmology in supersymmetric warm inflation

In supersymmetric models of warm inflation, the large temperature of the radiation bath produced by the dissipative motion of the inflaton field may induce a significant thermal abundance of potentially dangerous gravitinos. While previous discussions of this problem focused on gravitino production only at the end of warm inflation, similarly to conventional reheating scenarios, we study the full evolution of the gravitino abundance during and after inflation for simple monomial potentials, taking into account the enhanced gravitino and possibly gaugino masses due to supersymmetry breaking during inflation and the smooth transition into a radiation-dominated era. We find, on one hand, that the continuous thermal production increases the gravitino yield, although, on the other hand, ``freeze-out'' occurs at temperatures much lower than previously estimated. Moreover, for sufficiently strong dissipation, which allows for sub-Planckian inflaton values, the lower radiation temperature significantly alleviates and possibly solves the gravitino problem, with a baryon asymmetry being nevertheless produced through dissipative effects. Our analysis may also be relevant to standard reheating as an oscillating inflaton will also change the gravitino mass, potentially modifying the produced gravitino yield.

Remarks on Hubble induced mass from fermion kinetic term

We evaluate the effective mass of a scalar field which interacts with visible sector via Planck-suppressed coupling in supergravity framework. We focus on the radiation-dominated (RD) era after inflation and the contribution from a fermionic field in the thermal bath. We find that, in RD era, the fermion kinetic term gives the effective mass of the order of Hubble scale to the scalar field.