Strong Dissipative Regimes Research Articles

Perturbation Spectra of Warm Inflation in f(Q, T) Gravity

We investigate the warm inflationary scenario within the context of the linear version of f(Q, T) gravity, coupled with both the inflaton scalar field and the radiation field, under the conditions of the strong dissipation regime. First, we calculate the modified Friedmann equations and the modified slow-roll parameters. Subsequently, we apply the slow-roll approximations to derive the scalar power spectrum and the tensor power spectrum. Also, we develop formulations of the scalar and tensor perturbations for the f(Q, T) gravity with the warm inflation scenario. Furthermore, we scrutinize two different forms of the dissipation coefficient, a constant and a function of the inflaton field, to determine the scalar spectral index, the tensor-to-scalar ratio, and the temperature for the power-law potential case. By imposing some constraints on the free parameters of the model, we attain results in good agreement with both the Planck 2018 data and the joint Planck, BK15, and baryon acoustic oscillation data for the tensor-to-scalar ratio, and consistent results aligned with the Planck 2018 data for the scalar spectral index. In addition, the obtained results are within the range of observational data for the amplitude of the scalar power spectrum. Consequently, we are able to revive the power-law potential that was previously ruled out by observational data. Moreover, for both dissipation coefficients, the model leads to a scalar spectral index with the blue and red tilts in agreement with the Wilkinson Microwave Anisotropy Probe 3 yr data.

Theoretical and observational prescription of warm-inflation in FLRW universe with torsion

The paper deals with Warm Inflationary scenario in FLRW with torsion both from theoretical and observational point of view. In the background of flat FLRW model the Hubble parameter is found to be proportional to the torsion function and warm inflation is examined both in weak and strong dissipation regimes for the power law choice of potential using slow-roll approximation with quasi-stable criteria for radiation. The slow-roll parameters, no.of e-folds, scalar spectral index, and tensor-to-scalar ratio are determined in the present model for mainly three choices of the dissipation coefficient Gamma using the Planck data set. Finally, we focus on single-field chaotic quartic potential with the above choices of the dissipation coefficient to confront the warm inflation observational predictions directly with the latest observational data set.

Warm inflation driven by complex quintessence field within rastall gravity

This manuscript is devoted to examining the role of the “complex quintessence field” (CQF) in driving warm inflation (WI) within the Rastall theory of gravity (RTG). Recently, the accelerating cosmic expansion has been described by CQF, which is linked to several other cosmic scenarios. In this approach, we construct the corresponding dynamical equations for inflation using the flat Friedmann–Robertson–Walker (FRW) spacetime. We begin with a fundamental approach of selecting intermediate, logamediate, and power-law models to study how inflation is realized from these models. For each model, we find analytic solutions of the scalar field and corresponding effective potential necessary to produce inflation under slow-roll (SR) conditions. These solutions allow us to develop inflationary observable in the strong dissipative regime, including the SR parameters, e-folding number, scalar/tensor power spectra, scalar spectral index (ns) and its running (αs) and finally tensor to scalar ratio (r). We checked the impact of additional theory parameter λ on the evolutionary trajectories in ns−r and ns−αs planes for the underlying inflationary models. For all three models, it is concluded that CQF-inspired inflation in RTG provides interesting and feasible results which fully satisfy the Planck constraints.

Warm inflation in [formula omitted] gravity

In this work, we explored warm inflation in the background of f(R,T) gravity in the strong dissipation regime. Considering scalar field for FLRW universe, we derived modified field equations. We then deduced slow-roll parameters under slow-roll approximations followed by power spectrum for scalar and tensor perturbations and their corresponding spectral indices. We have considered Chaotic and Natural potentials and estimated scalar spectral index and tensor-to-scalar ratio for constant as well as variable dissipation factor Γ. We found that both the rejected potentials can be revived under the context of f(R,T) gravity with suitable choice of the model parameters. Further, it is seen that within the warm inflationary scenario both the potentials can yield result consistent with Planck 2018 and BICEP/Keck bounds at the Planckian and sub-Planckian energy scales.

Looking inside the Swampland from Warm Inflation: Dissipative Effects in De Sitter Expansion

This paper reviews the theoretical and phenomenological implications of the swampland conjectures from the perspective of inflationary cosmology, focusing on warm inflation. We demonstrate how the swampland conjectures appear to favor the strong dissipative regime, giving warm inflation a competitive edge over standard inflation. Additionally, we ponder the possible deeper implications of dissipation for constructing successful inflation models from string theory.

Recent Developments in Warm Inflation

Warm inflation, its different particle physics model implementations, and the implications of dissipative particle production for its cosmology are reviewed. First, we briefly present the background dynamics of warm inflation and contrast it with the cold inflation picture. An exposition of the space of parameters for different well-motivated potentials, which are ruled out, or severely constrained in the cold inflation scenario, but not necessarily in warm inflation, is provided. Next, the quantum field theory aspects in realizing explicit microscopic models for warm inflation are given. This includes the derivation of dissipation coefficients relevant in warm inflation for different particle field theory models. The dynamics of cosmological perturbations in warm inflation are then described. The general expression for the curvature scalar power spectrum is shown. We then discuss in detail the relevant regimes of warm inflation, the weak and strong dissipative regimes. We also discuss the results predicted in these regimes of warm inflation and how they are confronted with the observational data. We explain how the dissipative dynamics in warm inflation can address several long-standing issues related to (post-) inflationary cosmology. This includes recent discussions concerning the so-called swampland criteria and how warm inflation can belong to the landscape of string theory.

Warm beta -exponential inflation and the swampland conjectures

We investigate theoretical and observational aspects of a warm inflation scenario driven by the beta -exponential potential, which generalizes the well-known power law inflation. In such a scenario, the decay of the inflaton field into radiation happens during the inflationary phase. In our study, we consider a dissipation coefficient (varGamma ) with cubic dependence on the temperature (T) and investigate the consequences in the inflationary dynamics, focusing on the impact on the spectral index n_s, its running n_{run} and tensor-to-scalar ratio r. We find it possible to realize inflation in agreement with current cosmic microwave background data in weak and strong dissipation regimes. We also investigate theoretical aspects of the model in light of the swampland conjectures, as warm inflation in the strong dissipation regime has been known as a way to satisfy the three conditions currently discussed in the literature. We find that when varGamma propto T^3, the beta -exponential model can be accommodated into the conjectures.

Adiabatic quantum Zeno dynamics of bosonic atom pairs with large inelastic losses

We report on experiments exploring the non-Hermitian dynamics of pairs of two-level atoms tightly confined in an optical lattice and driven by a near-resonant laser. Although spontaneous emission is negligible for the long-lived excited state, two-body dissipation arises from strong inelastic collisions between two atoms in the excited state. We demonstrate quasi-adiabatic control of the internal state of the pairs in the quantum Zeno regime where inelastic losses dominate. Preparing each atom pair in the longest-lived eigenstate of the non-Hermitian Hamiltonian describing the dissipative dynamics, we measure a lifetime enhanced by more than two orders of magnitude in comparison to the bare two-body lifetime. The measured enhancement factor is in quantitative agreement with the expected lifetime of the prepared ``non-Hermitian dressed state''.

Multi-field cold and warm inflation and the de Sitter swampland conjectures

We discuss under which conditions multi-field cold and warminflationary models with canonical kinetic energy terms are compatiblewith the swampland conjectures about the emergence of de Sitter solutionsin string theory. We find that under quite general conditions the slow-rollconditions for multi-field cold inflation are at odds with the swamplandconjectures for an arbitrary number of scalar fields driving inflation.However, slow-roll conditions can be reconciled with the swampland conjecturesin the strong dissipative regime of warm inflation.

Does fractal universe favour warm inflation: Observational support?

The present work examines the possibility of warm inflationary paradigm in the modified gravity theory with fractal geometry. By choosing the normal fluid as radiation fluid and the effective fluid (with the extra term in modified field equation) as the inflaton field both strong and weak dissipative regimes have been studied using slow roll approximation with quasi-stable criteria for radiation. Finally, using the Planck data set, the present model has been analyzed for various choices of the fractal function and the dissipation parameter.

Scalar warm inflation in holographic cosmology

We consider warm inflation in the context of holographic cosmology. The weak and the strong dissipative regime are analysed in the slow-roll approximation and within what is known as intermediate inflation. For an appropriate choice of the equation of state, the intermediate inflation is not only an exact solution in general relativity, but also in the holographic setup considered in this paper. Within this approach several dissipative and physically relevant functions are considered. We constrain our model using the latest Planck data. We conclude that three of the models analysed are consistent with Planck data for some ranges of the model parameters. However, one of them is ruled out by the observations.

Rényi entropy dynamics and Lindblad spectrum for open quantum systems

In this letter we point out that the Lindblad spectrum of a quantum many-body system displays a segment structure and exhibits two different energy scales in the strong dissipation regime. One energy scale determines the separation between different segments, being proportional to the dissipation strength, and the other energy scale determines the broadening of each segment, being inversely proportional to the dissipation strength. Ultilizing a relation between the dynamics of the second R\'enyi entropy and the Lindblad spectrum, we show that these two energy scales respectively determine the short- and the long-time dynamics of the second R\'enyi entropy starting from a generic initial state. This gives rise to opposite behaviors, that is, as the dissipation strength increases, the short-time dynamics becomes faster and the long-time dynamics becomes slower. We also interpret the quantum Zeno effect as specific initial states that only occupy the Lindblad spectrum around zero, for which only the broadening energy scale of the Lindblad spectrum matters and gives rise to suppressed dynamics with stronger dissipation. We illustrate our theory with two concrete models that can be experimentally verified.

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.

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.

Warm intermediate and logamediate cosmic inflation with a constant ‎dissipation coefficient in loop quantum gravity

Warm inflationary model in the context of loop quantum cosmology is investigated. To this aim we consider two cases intermediate inflation and logamediate inflation. In both the cases, assuming a constant dissipation coefficient, we study the model under consideration in weak dissipation regime and also in strong dissipation regime. In each of these cases, we obtain various parameters such as potential function of inflationary scalar field and slow-roll parameters. Perturbation theory and also finding relations between perturbative parameters is studied.

Quantum speedup in noninertial frames

We investigate the speedup evolution of the system under the influence of the Unruh effect, where one of the observers (e.g., Bob) is uniformly accelerated. We show that acceleration can be beneficial to the evolution speed of the system, even in the presence of noise. Here two distinct dissipation mechanisms are considered, one where the total system is in a noise channel and the second where only Bob’s qubit is in a noisy channel. Interestingly, for the total system in the amplitude damping channel and depolarizing channel, the evolution speed of the system may increase monotonously with the increase of acceleration, which is in stark contrast to the case where only Bob’s qubit undergoing a noise channel. We find that the reason behind these behaviors are due to the competition mechanism between the Unruh effect and the dissipation effect, illustrated by the analytical formula of quantum speed limit time derived under quasi-inertial frame and strong dissipation regime.

Confronting the warm vector inflation in Rastall theory of gravity with Planck 2018 data

Abstract The main focus of this manuscript is to explore the effectiveness of Rastall theory of gravity in describing very early epoch of the universe, called cosmic inflation. In this framework, we develop the basic inflationary dynamical equations for flat FRW metric. To find out the exact solutions of inflaton field and corresponding potentials, we start with a basic technique of choosing a known solution of the scale factor, i.e., intermediate and logamediate forms and then extracted the effective potential necessary to support the inflation under slow-roll condition. Via these solutions, we calculate the inflationary observable such as the slow-roll parameters, e-folding number, scalar/tensor power spectra, scalar spectral index and tensor–scalar ratio in both strong and weak dissipative regimes. The recent Planck 2018 data sets bounds for scalar power spectrum, scalar spectral index, n s = 0 . 966 and tensor–scalar ratio, R 0 . 16 . We have plotted graphical trajectories of R − n s by constraining the model parameters, which show that Planck bounds are fully satisfied by Rastall theory of gravity. Hence, this modified gravity theory has ability to describe the early as well as the late-time cosmic eras elegantly.

Cosmology of a generalised version of holographic dark energy in presence of bulk viscosity and its inflationary dynamics through slow roll parameters

This study reports a reconstruction scheme of a Dark Energy (DE) model with higher-order derivative of Hubble parameter, which is a particular case of Nojiri–Odintsov holographic DE (HDE) [S. Nojiri and S. D. Odintsov, Gen. Relativ. Gravit. 38 (2006) 1285.] that unifies phantom inflation with the acceleration of the universe on late-time. The reconstruction has been carried out in the presence of bulk viscosity, where the bulk-viscous pressure has been taken as a function of Hubble parameter. Ranges of cosmic time [Formula: see text] have been derived for quintessence, cosmological constant and phantom behaviour of the equation-of-state (EoS) parameter. In the viscous scenario, the reconstruction has been carried out in an interacting and noninteracting situations and in both the cases stability against small perturbations has been observed. Finally, the slow roll parameters have been studied and a scope of exit from inflation has been observed. Also, the availability of quasi-exponential expansion has been demonstrated for interacting viscous scenario and a study through tensor-to-scalar ratio has ensured consistency of the model with the observational bound by Planck. Alongwith primordial fluctuations, the interacting scenario has been found to generate strong dissipative regime.

Warm brane inflation with an exponential potential: A consistent realization away from the swampland

It has very recently been realized that coupling branes to higher dimensional quantum gravity theories and considering the consistency of what lives on the branes, one is able to understand whether such theories can belong either to the swampland or to the landscape. In this regard, in the present work, we study a warm inflation model embedded in the Randall-Sundrum braneworld scenario. It is explicitly shown that this model belongs to the landscape by supporting a strong dissipative regime with an inflaton steep exponential potential. The presence of extra dimension effects from the braneworld allow achieving this strong dissipative regime, which is shown to be both theoretically and observationally consistent. In fact, such strong dissipation effects, which decrease towards the end of inflation, together with the extra dimension effect, allow the present realization to simultaneously satisfy all previous restrictions imposed on such a model and to evade the recently proposed swampland conjectures. The present implementation of this model, in terms of an exponential potential for the scalar field, makes it also a possible candidate for describing the late-time Universe in the context of a dissipative quintessential inflation model and we discuss this possibility in the Conclusions.

Constraints on warm power-law inflation in light of Planck results

The constraints on a general form of the power-law potential and the dissipation coefficient in the framework of warm single field inflation imposed by Planck data will be investigated. By considering a quasi-static Universe, besides a slow-roll condition, the suitable regions in which a pair of theoretical free parameters are in good agreement with Planck results will be estimated. In this method, instead of a set of free parameters, we can visualize a region of free parameters that can satisfy the precision limits on theoretical results. On the other side, when we consider the preformed quantity for the amplitude of scalar perturbations, the conflict between obtained results for free parameters in different steps will be dramatically decreased. As done in prominent literature, based on the friction of the environment, we can divide the primordial Universe into two different epochs, namely weak and strong dissipative regimes. For the aforementioned eras, the free parameters of the model will be constrained and the best regions will be obtained. To do so, the main inflationary observables such as tensor-to-scalar ratio, power-spectra of density perturbations and gravitational waves, scalar and tensor spectral indices, running spectral index and the number of e-folds in both weak and strong regimes will be obtained. Ultimately, it can be visualized, this model can make concord between theoretical results and data originated from cosmic microwave background and Planck 2013, 2015 and 2018.