A note on Single-field Inflation and the Swampland Criteria

The recently proposed Swampland Criteria aim to evade any (meta-)stable de Sitter constructions within String landscapes, making it difficult to accommodate accelerating phases, like dark energy domination and inflationary epoch, in cosmology. In this note, we analyse the status of various models of single field slow-roll inflation given the old as well as the refined Swampland conjectures, which constrain the form of scalar potentials in any low energy effective field theory residing in the landscapes. In particular, we note that Warm Inflation turns out to be the most befitting scenario as long as lifting the tensions with Swampland Criteria are concerned.Comment: 4 pages, no figure, revtex4, v2: 6 pages, no figure, discussion on refined Swampland criteria added, conclusion unchanged, references added. Accepted for publication in Physical Review

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.Comment: 5 pages, no figure, v2: references added, accepted for publication in PR

Effects of Radiation on Primordial Non-Gaussianity

We study the non-Gaussian features in single-field slow-roll inflationary scenario where inflation is preceded by a radiation era. In such a scenario both bispectrum and trispectrum non-Gaussianities are enhanced. Interestingly, the trispectrum in this scenario does not depend up on the slow-roll parameters and thus $\tau_{NL}$ is larger than $f_{NL}$ which can be a signature of such a pre-inflationary radiation era.Comment: Based on the talk presented in the ICGC - 2011, held at Goa during December 14 - 19, 2011 : Contribution to the proceedings for the sam

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.Comment: 3 pages, Submitted to Proceedings of 13th Marcel Grossmann Meeting, Stockholm, July 201

VSR is incompatible with Thomas precession

Glashow and Cohen make the interesting observation that certain proper subgroups of the Lorentz group like HOM(2) or SIM(2) can explain many results of special relativity like time dilation, relativistic velocity addition and a maximal isotropic speed of light. We show here that such SIM(2) and HOM(2) based VSR theories predict an incorrect value for the Thomas precession and are therefore ruled out by observations. In VSR theories the spin-orbital coupling in atoms turn out to be too large by a factor of 2. The Thomas-BMT equation derived from VSR predicts a precession of electrons and muons in storage rings which is too large by a factor of $10^3$. VSR theories are therefore ruled out by observations.Comment: 14 pages, LaTeX file, no figures, v2: Journal Version, Accepted for publication in Mod. Phys. Lett.

Thermodynamics of the Pauli oscillators and Lee-Wick partners of the Standard Model particles

The present article is about the statistical mechanics of non-trivial field configurations. The non-trivial fields arise from the negative sign of the commutators and the anticommutators of the bosonic and fermionic field excitations. These kinds of fields were previously studied by Pauli and Lee and Wick. The thermal distribution function of the above mentioned fields are calculated in the article and using the thermal distribution functions the energy density, pressure and entropy density of the non-trivial field configurations are found out. The results match exactly with a previous calculation done by Fornal et. al. for higher derivative Lee-Wick theories showing a deeper similarity with the earlier work. It is assumed that such kinds of non-trivial fields may have existed in the early universe and may have some cosmological relevance.Comment: 8 pages, 2 figures, For a more detailed version refer to arXiv:1108.048

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.Comment: 14 pgs, no figure, v2 & v3: Discussion of Sec 3.3 slightly modified, changes have been made in the 'Discussion and Conclusion' section accordingly, main conclusion unchanged, references added, accepted for publication in JCA

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.Comment: 3 Pages, 2 figures, Latex file. Talk given in the thirteenth Marcel Grossmann meeting (MG13), Stockholm, held during 1st-7th July 2012. The new version is a shortened form of the earlier submissio

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.Comment: v2: 23 pages, 2 figures, Title changed, Accepted for publication in PR

On the 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.Comment: 8 pages, 4 figures, double column, v2: 12 pages, 5 figures, version matched with the published version in PR