Warm Inflation Research Articles

Dirac-Born-Infeld warm inflation realization in the strong dissipation regime

We consider warm inflation with a Dirac-Born-Infeld (DBI) kinetic term in which both the nonequilibrium dissipative particle production and the sound speed parameter slow the motion of the inflaton field. We find that a low sound speed parameter removes, or at least strongly suppresses, the growing function appearing in the scalar of curvature power spectrum of warm inflation, which appears due to the temperature dependence in the dissipation coefficient. As a consequence of that, a low sound speed helps to push warm inflation into the strong dissipation regime, which is an attractive regime from a model building and phenomenological perspective. In turn, the strong dissipation regime of warm inflation softens the microscopic theoretical constraints on cold DBI inflation. The present findings, along with the recent results from swampland criteria, give a strong hint that warm inflation may consistently be embedded into string theory.

Constant-roll inflation driven by q-de Sitter

We have studied constant-roll inflation using the q-de Sitter scale factor. Both the cold and warm inflation have been considered, and the scalar potential and inflaton field have been determined. Also tensor to scalar ratio and the spectral index are obtained. In the cold inflation case, the perturbations have been investigated using Mukhanov–Sasaki equation, and the results determined for the spectral index and tensor to scalar ration are consistent with observations. In the warm inflation two cases of constant damping ([Formula: see text]) and the field dependent damping ([Formula: see text]) have been studied. In both cases the power spectrum and the tensor to scalar ratio are determined as a function of the inflaton field. It has been shown that in both cases the spectral index is independent of the inflaton field. In the case of constant damping the obtained value for the spectral index is inconsistent with observations but for the case of field dependent damping the parameter [Formula: see text] can be chosen such that the value obtained for all the physical quantities including the spectral index be consistent with present cosmological observations.

Inflationary anisotropic phases with bianchi-I cosmic model

This paper is devoted to studying warm anisotropic inflation using modified Chaplygin gas in the context of the Bianchi-I comic model. We investigate the dynamics of the warm intermediate universe model in two distinct regimes, i.e., weak and strong regimes in the context of generalized dissipative coefficient. We formulate solutions of dissipation coefficient, inflaton field, scalar & tensor (S/T) power spectra, spectral index in an environment of slow-roll approximation to discuss the existence of warm weak and strong inflation and checked their viability in view of 2018 Planck data. It is seen through graphical representation that the condition for the existence of warm weak inflation is preserved only for z=0 and z=1 whereas in the case of the strong dissipative regime, the compatibility is achieved for z=3. The corresponding decay rates and the S/T are found to be consistent with the current observations.

Graceful exit problem in warm inflation

A seemingly simple question, how does warm inflation exit gracefully?, has a more complex answer than in a cold paradigm. It has been highlighted here that whether warm inflation exits gracefully depends on three independent choices: The form of the potential, the choice of the warm inflation model (i.e., on the form of its dissipative coefficient) and the regime, of weak or strong dissipation, characterizing the warm inflation dynamics. Generic conditions on slow-roll parameters and several constraints on the different model parameters required for warm inflation to exit gracefully are derived.

Does cold inflation with dissipation mechanism in nonequilibrium thermodynamic prescription imply warm inflation?

The present work is an attempt to find inter relationship between the cold and warm inflationary scenarios. Here cold inflation is described by a single scalar field (inflaton) and nonequilibrium thermodynamical prescription is imposed. It is found that this quasi-de-Sitter phase of evolution is equivalent to warm inflation. The present work also addresses the question whether the dissipation is Hawking-type or not.

Intermediate class of warm pseudoscalar inflation

High dissipative regime of warm pseudoscalar inflation model (Kamali in Phys Rev D 100:043520, arXiv:1901.01897 [gr-qc], 2019) with an approximately constant value of dissipation parameter Q is studied. Intermediate solution of the scale-factor related to the accelerated expansion of the Universe which is rolled out by observational data in the context of standard (cold) model of inflation is used. There is a region of free parameters phase-space of the model which is interestingly compatible with recent observational data. It is discussed that the model is also compatible with the swampland criteria in a broad range of parameters phase-space and TCC in a limited area of parameters.

Minimal warm inflation with complete medium response

If a homogeneous field evolves within a medium, with the lattergradually picking up a temperature, then the friction felt by thefield depends on how its evolution rate compares with medium timescales. We suggest a framework which permits toincorporate the contributions from all medium time scales. As anexample, we illustrate how warm axion inflation can be described byinputting the retarded pseudoscalarcorrelator of a thermal Yang-Mills plasma.Adopting a semi-realistic model for the latter,and starting the evolution at almost vanishing temperature,we show how the system heats up and then entersthe “weak” or “strong” regime of warm inflation.Previous approximate treatments are scrutinized.

A study of warm inflation model inspired by some inhomogeneous dark energy fluids

A study of warm inflation model inspired by some inhomogeneous dark energy fluids

Constant-roll warm inflation and the β -function approach

We propose a new approach to constant-roll warm inflation as a generalization of constant-roll inflation. Based on the $\beta$-function formalism, it is shown that constant-roll warm inflation models with a natural end fall into universality classes defined by three different types of $\beta$-functions, under the assumption that radiation energy density is quasi-stable. Given that warm inflation is completely specified by the $\beta$-function and dissipation coefficient ratio, we investigate whether or not the inflation can physically be realized for enough number of e-foldings at the background level for some combinations of the $\beta$-functions and non-trivial dissipation coefficient ratios.

Warm-assisted natural inflation

We consider natural inflation in a warm inflation framework with a temperature-dependent dissipative coefficient Γ∝ T3. Natural inflation can be compatible with the Planck 2018 results with such warm assistance. With no a priori assumptions on the dissipative effect's magnitude, we find that the Planck results prefer a weak dissipative regime for our benchmark scale f=5 Mpl, which lies outside the 2σ region in the cold case. The inflation starts in the cold regime and evolves with a growing thermal fluctuation that dominates over quantum fluctuation before the end of the inflation. The observed spectral tilt puts stringent constraints on the model's parameter space. We find that f< 1 M_ pl is excluded. A possible origin of such dissipative coefficient from axion-like coupling to gauge fields and tests of the model are also discussed.

Paradigm of warm quintessential inflation and production of relic gravity waves

We consider the framework of quintessential inflation in the warm background which is caused by the dissipation of the scalar field energy density into relativistic degrees of freedom. The dissipation process has important consequences for the evolution both at the levels of background as well as perturbation and allows us to easily satisfy the observational constraints.~Our numerical analysis confirms that the model conforms to observational constraints even if the field-radiation coupling strength is weak. In the warm background, we investigate the post inflationary evolution of relic gravity waves produced during inflation whose amplitude is constrained by the Big Bang Nucleosynthesis constraint. Further, we investigate the effect of coupling on the amplitude of gravity waves and obtain the allowed phase space between the model parameters. The mechanism of quintessential inflation gives rise to the blue spectrum of gravitational wave background at high frequencies. We discuss the perspectives of detection of the signal of relic gravity waves by future proposed missions. Improvements of their sensitivities in the high-frequency regime, in the future, might allow us to probe the blue tilt of the spectrum caused by the presence of a kinetic regime in the underlying framework of inflation.

Warm inflation with non-comoving scalar field and radiation fluid

We consider a warm inflationary scenario in which the two major fluid components of the early Universe, the scalar field and the radiation fluid, evolve with distinct four-velocities. This cosmological configuration is equivalent to a single anisotropic fluid, expanding with a four-velocity that is a combination of the two fluid four-velocities. Due to the presence of anisotropies the overall cosmological evolution is also anisotropic. We obtain the gravitational field equations of the non-comoving scalar field–radiation mixture for a Bianchi Type I geometry. By assuming the decay of the scalar field, accompanied by a corresponding radiation generation, we formulate the basic equations of the warm inflationary model in the presence of two non-comoving components. By adopting the slow-roll approximation the theoretical predictions of the warm inflationary scenario with non-comoving scalar field and radiation fluid are compared in detail with the observational data obtained by the Planck satellite in both weak dissipation and strong dissipation limits, and constraints on the free parameters of the model are obtained. The functional forms of the scalar field potentials compatible with the non-comoving nature of warm inflation are also obtained.

Consistency of a kind of general noncanonical warm inflation

The framework of a kind of noncanonical warm inflation is introduced, and the dynamical equations of this scenario are presented. We propose the slow roll approximations and give some redefining slow roll parameters in this scenario which remain dimensionless. Performing systemic stability analysis, we calculate the slow roll conditions to guarantee that slow roll approximations hold. The slow roll conditions suggest slow roll inflation in general noncanonical warm inflationary scenario can still exist, and in addition, the slow roll approximations are more easily to be satisfied. Then, a concrete Dirac-Born-Infeld warm inflationary model is studied.

Towards a reliable effective field theory of inflation

We present the first quantum field theory model of inflation that is renormalizable in the matter sector, with a super-Hubble inflaton mass and sub-Planckian field excursions, which is thus technically natural and consistent with a high-energy completion within a theory of quantum gravity. This is done in the framework of warm inflation, where we show, for the first time, that strong dissipation can fully sustain a slow-roll trajectory with slow-roll parameters larger than unity in a way that is both theoretically and observationally consistent. The inflaton field corresponds to the relative phase between two complex scalar fields that collectively break a U(1) gauge symmetry, and dissipates its energy into scalar degrees of freedom in the warm cosmic heat bath. A discrete interchange symmetry protects the inflaton mass from large thermal corrections. We further show that the dissipation coefficient decreases with temperature in certain parametric regimes, which prevents a large growth of thermal inflaton fluctuations. We find, in particular, a very good agreement with the Planck legacy data for a simple quadratic inflaton potential, predicting a low tensor-to-scalar ratio r≲10−5.

Runaway potentials in warm inflation satisfying the swampland conjectures

The runaway potentials, which do not possess any critical points, are viable potentials which befit the recently proposed de Sitter swampland conjecture very well. In this work, we embed such potentials in the warm inflation scenario motivated by quantum field theory models generating a dissipation coefficient with a dependence cubic in the temperature. It is demonstrated that such models are able to remain in tune with the present observations and they can also satisfy all the three Swampland conjectures, namely the Swampland Distance conjecture, the de Sitter conjecture and the Transplackian Censorship Conjecture, simultaneously. These features make such models viable from the point of view of effective field theory models in quantum gravity and string theory, away from the Swampland.

Weak and strong warm logamediate anisotropic inflationary universe model

In this paper we investigate a warm inflation scenario of a locally rotationally symmetric Bianchi type-I model using a background of modified Chaplygin gas. We determine the field equations and perturbations parameters, such as the scalar power spectrum, scalar spectral index, scalar potential, and tensor-to-scalar ratio under the slow roll approximation. We determine these parameters in the direction of the Hubble parameter during both the weak and strong logamediate inflationary regimes. These cosmological parameters show that the anisotropic model is compatible with WMAP 7 from the 2018 Planck observational data.

Formation of primordial black holes from warm inflation

Primordial Black Holes (PBHs) serve as a unique probe to the physics of the early Universe, particularly inflation. In light of this, we study the formation of PBHs by the collapse of overdense perturbations generated during a model of warm inflation. For our model, we find that the primordial curvature power spectrum is red-tilted (spectral index ns<1) at the large scales (small k) and is consistent with the ns−r values allowed from the CMB observations. Along with that, it has a blue-tilt (ns>1) for the small PBH scales (large k), with a sufficiently large amplitude of the primordial curvature power spectrum required to form PBHs. These features originate because of the inflaton's coupling with the other fields during warm inflation. We discuss the role of the inflaton dissipation to the enhancement in the primordial power spectrum at the PBH scales. We find that for some parameter range of our warm inflation model, PBHs with mass ∼ 103 g can be formed with significant abundance. Such tiny mass PBHs have a short lifetime ∼ 10−19 s and would have evaporated into Hawking radiation in the early Universe. Further in this study, we discuss the evaporation constraints on the initial mass fraction of the generated PBHs and the possibility of Planck mass PBH relics to constitute the dark matter.

Power law plateau inflation potential in the RS II braneworld evading swampland conjecture

In the recent time, inflationary cosmology is facing an existential crisis due to the proposed Swampland criterion which aims to evade any (meta-)stable de Sitter construction within the String landscape. It is been realised that a single field slow roll inflation is inconsistent with the Swampland criterion unless the inflationary model is realised in some non-standard scenario such as Warm inflation or the Braneworld scenario. Dimopoulos and Owen (Phys Rev D 94(6): 063518, 2016) introduced a new class of model of inflation dubbed as the power law plateau inflation in the standard cold inflationary scenario. But to realise this model in the standard scenario consistent with observation, they had to introduce a phase of thermal inflation. In this paper we have analysed this model in the braneworld scenario to show that for some choice of the parameters defining the model class, one can have an observationally consistent power law plateau without any phase of thermal inflation. We have also shown that, for the correct choice of model parameters, one can easily satisfy the Swampland criterion. Besides, for correct choice of equation of states (w_{re}), one can also satisfy the recently proposed Trans–Planckian Censorship Conjecture (TCC).

Pre-inflation dynamical behavior of warm inflation in loop quantum cosmology

Considering a constant dissipative coefficient [Formula: see text], the pre-inflation dynamical behaviors of warm inflation in the loop quantum cosmology scenario are discussed. We consider three sets of initial conditions. The evolution of the background can always be divided into three phases, namely super-inflation, damping, and slow-roll inflation phases, with the duration of each phase depending on the initial conditions. As an example, we compare the background evolution between [Formula: see text] and [Formula: see text] under special initial conditions and find that there is no slow-roll inflation phase for [Formula: see text] while the number of e-folds is about 60.209 for [Formula: see text].

Reconstruction of warm Chaplygin gas inflationary models

By assuming the specific Chaplygin gas model, we study the reconstruction of warm inflation model with the help of tensor-to-scalar ratio [Formula: see text] and scalar spectral index [Formula: see text]. In this regard, we take flat Friedmann–Robertson–Walker (FRW) metric and discuss the general forms of dissipative coefficient [Formula: see text] as well as effective potential [Formula: see text] for two dissipative regimes i.e., the weak and strong. We use inflationary parameters such as slow-roll parameters, power spectrum of the curvature perturbation, tensor spectrum, spectral index, scalar-to-tensor ratio and Hubble parameter to find the generalized form of dissipative coefficient and effective potential. We discuss the results of dissipative coefficient and reconstructed potential in detail for the specific choice of tensor-to-scalar ratio [Formula: see text] and scalar spectral index [Formula: see text].