arXiv subjects

Suratna Das

Publications and source records attributed to Suratna Das.

At least 37 records · Page 2Linked to original sources

arXiv2019

Warm Inflation in the light of Swampland Criteria

Warm Inflation seems to be the most befitting single-field slow-roll inflation scenario in the context of the recently proposed Swampland Criteria. We investigate the constraints these Swampland Criteria impose on Warm Inflation parameters and show that Warm Inflation is in accordance with both the current cosmological observations and the proposed Swampland Criteria in both weak and strong dissipative regimes depending on the value of the parameter $c$ which limits the slope of the inflaton potential according to the criteria.

hep-th↗

arXiv2018

The `unitarity problem' of Higgs inflation in the light of collapse dynamics

Higgs inflation scenario is one of the most compelling models of inflation at present time. It not only explains the observed data well, but also provides means to include the inflaton field within the well understood Standard Model of particle physics, without invoking any need for its extension. Despite this, due to the requirement of large non-minimal coupling to the curvature scalar of the inflaton field, or in this case the Higgs field, this model suffers from a problem often called as the `unitarity' or the `naturalness' problem. On the other hand, to address the longstanding `interpretational issue' of quantum to classical transition of the primordial modes, the collapse dynamics of quantum mechanics has recently been included into the inflationary mechanism. We show that inclusion of such collapse mechanism in Higgs inflation helps alleviate the `unitarity problem' to a great deal.

astro-ph.CO↗

arXiv2017

Resurrecting Quartic and Quadratic inflaton potentials in two-field inflationary model

After the release of the PLANCK data, it is evident that inflationary paradigm has stood the test of time. Even though, it is difficult to realise inflationary paradigm in a particle physics model as the present observations have ruled out the simplest quartic and quadratic inflationary potentials, which generically arise in particle physics. We would show that such simplest inflationary potentials can evade discrepancies with observations, if the inflaton field is assisted by another scalar during inflation. Moreover, unlike other multifield models, our model yields no isocurvature perturbations and negligible non-Gaussianity, making it more compatible with the present data. Above all, our model can also be realised in the framework of SUGRA.

astro-ph.CO↗

arXiv2017

On signatures of spontaneous collapse dynamics modified single field inflation

The observed classicality of primordial perturbations, despite their quantum origin during inflation, calls for a mechanism for quantum-to-classical transition of these initial fluctuations. As literature suggests a number of plausible mechanisms which try to address this issue, it is of importance to seek for concrete observational signatures of these several approaches in order to have a better understanding of the early universe dynamics. Among these several approaches, it is the spontaneous collapse dynamics of Quantum Mechanics which is most viable of leaving discrete observational signatures as collapse mechanism inherently changes the generic Quantum dynamics. We observe in this study that the observables from the scalar sector, i.e. scalar tilt $n_s$, running of scalar tilt $α_s$ and running of running of scalar tilt $β_s$, can not potentially distinguish a collapse modified inflationary dynamics in the realm of canonical scalar field and $k-$inflationary scenarios. The only distinguishable imprint of collapse mechanism lies in the observables of tensor sector in the form of modified consistency relation and a blue-tilted tensor spectrum only when the collapse parameter $δ$ is non-zero and positive.

astro-ph.CO↗

arXiv2016

Dilaton assisted two-field inflation from no-scale supergravity

We present a two-field inflation model where inflaton field has a non-canonical kinetic term due to the presence of a dilaton field. It is a two-parameter generalization of one-parameter Brans-Dicke gravity in the Einstein frame. We show that in such an inflation model the quartic and quadratic inflaton potentials, which are otherwise ruled out by the present Planck-{\it Keck}/BICEP2 data, yield scalar spectral index and tensor-to-scalar ratio in accordance with the present data. Such a model yield tensor-to-scalar ratio of the order of $10^{-2}$ which is within the reach of $B-$mode experiments like {\it Keck}/BICEP3, CMBPol and thus can be put to test in the near future. This model yields negligible non-Gaussianity and no isocurvature perturbations upto slow-roll approximation. Finally, we show that such a model can be realised in the realm of no-scale supergravity.

hep-ph↗

arXiv2016

Non-slow-roll dynamics in $α-$attractors

In this paper we consider the $α-$attractor model and study inflation under a non-slow-roll dynamics. More precisely, we follow the approach recently proposed by Gong and Sasaki \cite{Gong:2015ypa} by means of assuming $N=N\left(ϕ\right)$. Within this framework we obtain a family of functions describing the local shape of the potential during inflation. We study a specific model and find an inflationary scenario predicting an attractor at $n_{s}\approx0.967$ and $r\approx5.5\times10^{-4}$. We further show that considering a non-slow-roll dynamics, the $α-$attractor model can be broaden to a wider class of models that remain compatible with value of $r<0.1$. We further explore the model parameter space with respect to large and small field inflation and conclude that the inflaton dynamics is connected to the $ α- $ parameter, which is also related to the Kähler manifold curvature in the supergravity (SUGRA) embedding of this model. We also comment on the stabilization of the inflaton's trajectory.

gr-qc↗

arXiv2016

Constraints on just enough inflation preceded by a thermal era

If the inflationary era is preceded by a radiation dominated era in which the inflaton too was in thermal equilibrium at some very early time then the CMB data places an upper bound on the comoving temperature of the (decoupled) inflaton quanta. In addition, if one considers models of "just enough" inflation, where the number of e-foldings of inflation is just enough to solve the horizon and flatness problems, then we get a lower bound on the Hubble parameter during inflation, $H_{\rm inf}$, which is in severe conflict with the upper bound from tensor perturbations. Alternatively, imposing the upper bound on $H_{\rm inf}$ implies that such scenarios are compatible with the data only if the number of relativistic degrees of freedom in the thermal bath in the pre-inflationary Universe is extremely large (greater than $10^9$ or $10^{11})$. We are not aware of scenarios in which this can be satisfied.

hep-ph↗

arXiv2015

Gravitational waves in $α-$attractors

We study inflation in the $α-$attractor model under a non-slow-roll dynamics with an ansatz proposed by Gong \& Sasaki \cite{Gong:2015ypa} of assuming $N=N\left(ϕ\right)$. Under this approach, we construct a class of local shapes of inflaton potential that are different from the T-models. We find this type of inflationary scenario predicts an attractor at $n_{s}\sim0.967$ and $r\sim0.00055$. In our approach, the non-slow-roll inflaton dynamics are related to the $α-$parameter which is the curvature of Kähler geometry in the SUGRA embedding of this model.

gr-qc↗

arXiv2015

Revisiting a pre-inflationary radiation era and its effect on the CMB power spectrum

We revisit the scenario where inflation is preceded by a radiation era by considering that the inflaton too could have been in thermal equilibrium early in the radiation era. Hence we take into account not only the effect of a pre-inflationary era on the inflaton mode functions but also that of a frozen thermal distribution of inflaton quanta. We initially discuss in detail the issues relevant to our scenario of a pre-inflationary radiation dominated era and then obtain the scalar power spectrum for this scenario. We find that the power spectrum is free from infrared divergences. We then use the WMAP and Planck data to determine the constraints on the inflaton comoving `temperature' and on the duration of inflation. We find that the best fit value of the duration of inflation is less than 1 e-folding more than what is required to solve cosmological problems, while only an upper bound on the inflaton temperature can be obtained.

astro-ph.CO↗

arXiv2014

Higgs vacuum stability and inflationary dynamics after BICEP2 and PLANCK dust polarisation data

If the recent detection of $B-$mode polarization of the Cosmic Microwave Background by BICEP2 observations, withstand the test of time after the release of recent PLANCK dust polarisation data, then it would surprisingly put the inflationary scale near Grand Unification scale if one considers single-field inflationary models. On the other hand, Large Hadron Collider has observed the elusive Higgs particle whose presently observed mass can lead to electroweak vacuum instability at high scale $(\sim{\mathcal O}(10^{10})$ GeV). In this article, we seek for a simple particle physics model which can simultaneously keep the vacuum of the theory stable and yield high-scale inflation successfully. To serve our purpose, we extend the Standard Model of particle physics with a $U(1)_{B-L}$ gauged symmetry which spontaneously breaks down just above the inflationary scale. Such a scenario provides a constrained parameter space where both the issues of vacuum stability and high-scale inflation can be successfully accommodated. The threshold effect on the Higgs quartic coupling due to the presence of the heavy inflaton field plays an important role in keeping the electroweak vacuum stable. Furthermore, this scenario is also capable of reheating the universe at the end of inflation. Though the issues of Dark Matter and Dark Energy, which dominate the late-time evolution of our universe, cannot be addressed within this framework, this model successfully describes the early universe dynamics according to the Big Bang model.

hep-ph↗

arXiv2014

Classicalization of inflationary perturbations by collapse models in the light of BICEP2

Inflationary and hence quantum origin of primordial perturbations is on a firmer ground than ever post the BICEP2 observations of primordial gravitational waves. One crucial ingredient of success of this paradigm rests on explaining the observed classicality of cosmological inhomogeinities despite their quantum origin. Although decoherence provides a partial understanding of this issue, the question of single outcome motivates the analysis of quantum collapse models in cosmological context which generically modify the dynamics of primordial perturbations and hence can leave their imprints on observables. We revisit one such recently proposed working model of classicalization by spontaneous collapse \cite{Das:2013qwa} in the light of BICEP2 observations to look for possible modifications to tensor power spectra and their implications. We show that it can potentially change the consistency relation of single-field models and a precise measurement of $n_T$ and its running could serve as a test of such dynamics in the early universe.

astro-ph.CO↗

arXiv2013

Quantum to Classical Transition of Inflationary Perturbations - Continuous Spontaneous Localization as a Possible Mechanism -

The inflationary paradigm provides a mechanism to generate the primordial perturbations needed to explain the observed large scale structures in the universe. Inflation traces back all the inhomogeneities to quantum fluctuations although the structures look classical today. Squeezing of primordial quantum fluctuations along with the mechanism of decoherence accounts for many aspects of this quantum to classical transition, although it remains a matter of debate as to whether this is sufficient to explain the issue of realization of a single outcome (i.e. the issue of macro-objectification) from a quantum ensemble given that the universe is a closed system. A similar question of emergence of classical behavior of macroscopic objects exists also for laboratory systems and apart from decoherence there have been attempts to resolve this issue through Continuous Spontaneous Localization (CSL), which is a stochastic nonlinear modification of the non-relativistic Schrödinger equation. Recently, Martin {\it et al.} have investigated whether a CSL-like mechanism with a constant strength parameter, when the Mukhanov-Sasaki variable is taken as the "collapse-operator", can explain how the primordial quantum perturbations generated during inflation become classical. Within the scope of their assumptions they essentially come to a negative conclusion. In the present work, we generalize their analysis by allowing the CSL strength parameter to depend on physical scales so as to capture the CSL amplification mechanism. We show that such a generalization provides a mechanism for macro-objectification (i.e. classicalization) of the inflationary quantum perturbations, while also preserving scale invariance of the power spectrum and phase coherence of super-horizon perturbation modes in a particular class of these models.

astro-ph.CO↗

arXiv2013

Lee-Wick radiation induced bouncing universe models

The present article discusses about the effect of a Lee-Wick partner infested radiation phase of the early universe. As Lee-Wick partners can contribute negative energy density so it is always possible that at some early phase of the universe when the Lee-Wick partners were thermalized the total energy density of the universe became very small making the effective Hubble radius very big. This possibility gives rise to the probability of a bouncing universe. As will be shown in the article that a simple Lee-Wick radiation is not enough to produce a bounce. There can be two possibilities which can produce a bounce in the Lee-Wick radiation phase. One requires a cold dark matter candidate to trigger the bounce and the other possibility requires the bouncing temperature to be fine tuned such as all the Lee-Wick partners of the standard fields are not thermalized at the bounce temperature. Both the possibilities give rise to blue-tilted power spectrum of metric perturbations. Moreover the bouncing universe model can predict the lower limit of the masses of the Lee-Wick partners of chiral fermions and massless gauge bosons. The mass limit intrinsically depends upon the bounce temperature.

hep-th↗

arXiv2013

Bounds on Spontaneous Collapse model of Quantum Mechanics from formation of CMBR and Standard Cosmology

Continuous Spontaneous Localization (CSL) model of Quantum Mechanics modifies Schrödinger equation by adding non-linear stochastic terms due to which the total energy of a system increases with a constant rate which is proportional to the collapse rate $λ$. Thus applying CSL model to cosmological scenarios can change the thermal behaviour of the particles during evolution and we will put constraints on $λ$ by considering several cosmological scenarios.

astro-ph.CO↗

arXiv2013

Primordial non-Gaussianity as a signature of pre-inflationary radiation era

Primordial non-Gaussianity generated in an inflationary model where inflation is preceded by a radiation era is discussed. It is shown that both bispectrum and trispectrum non-Gaussianities are enhanced due to the presence of pre-inflationary radiation era. One distinguishing feature of such a scenario is that the trispectrum non-Gaussianity is larger than the bispectrum one.

astro-ph.CO↗

arXiv2012

Effect of Lee-Wick thermodynamics in the cosmology of the early universe

The Lee-Wick theories require unusual Lee-Wick (LW) partners to the standard model (SM) particles. The excitations of the unusual fields may have indefinite norms in the Hilbert space. In the present talk the thermodynamic results of a toy LW (where each normal particle has only one LW partner and the standard massless gauge fields do not appear in the normal particle spectrum as their LW partners has the potential to produce negative energy density) as well as a realistic LW universe (where the above restrictions are not present) will be discussed.

hep-ph↗

arXiv2012

Constraining CSL strength parameter $λ$ from standard cosmology and spectral distortions of CMBR

Models of spontaneous wave function collapse modify the linear Schrödinger equation of standard Quantum Mechanics by adding stochastic non-linear terms to it. The aim of such models is to describe the quantum (linear) nature of microsystems along with the classical nature (violation of superposition principle) of macroscopic ones. The addition of such non-linear terms in the Schrödinger equation leads to non-conservation of energy of the system under consideration. Thus, a striking feature of collapse models is to heat non-relativistic particles with a constant rate. If such a process is physical, then it has the ability to perturb the well-understood thermal history of the universe. In this article we will try to investigate the impacts of such heating terms on standard evolution of non-relativistic matter and on the formation of CMBR. We will use the CSL model, the most widely used collapse model. We will also put constraints on the CSL collapse rate $λ$ by considering that the standard evolution of non-relativistic matter is not hampered and the observed precise blackbody spectrum of CMBR would not get distorted (in the form of $μ-$type and $y-$type distortions) so as to violate the observed bounds.

astro-ph.CO↗

arXiv2012

A toy model based analysis on the effect of the Lee-Wick partners in the evolution of the early universe

In the present article the thermodynamic results of the Lee-Wick partner infested universe have been applied in a toy model where there is one Lee-Wick partner to each of the standard model particle and more over the longitudinal degrees of freedom of the massive partners of the standard massless gauge bosons are neglected at high temperatures. For practical purposes, the chiral fermionic sector of Lee-wick theories requires two Lee-Wick partners per fermion which opens up the possibility for a negative energy density of the early universe. A toy Lee-Wick model with one fermionic partner relaxes such oddities and hence easy to deal with. In a similar way, the longitudinal degrees of freedom of the massive gauge boson partners also have the potential to yield negative energy densities and thus those will be neglected in a toy model study. In such a toy model one can analytically calculate the time-temperature relation in the very early radiation dominated universe which shows interesting new physics. The article also tries to point out how a Lee-Wick particle dominated early cosmology transforms into the standard cosmological model. Based on the results of this toy model analysis a brief discussion on the more realistic model, which can accommodate two Lee-Wick partners for each standard fermionic field and the longitudinal degree of freedom of partners of the gauge fields, is presented. It has been shown that such an universe is mostly very difficult to attain but there are certain conditions where one can indeed think of such an universe which can evolve into the standard cosmological universe in a short time duration.

hep-ph↗