Search

In this work, our prime objective is to study non-locality and long-range effects of two-body correlation using quantum entanglement from the various information-theoretic measures in the static patch of de Sitter space using a two-body Open Quantum System (OQS). The OQS is described by a system of two entangled atoms, surrounded by a thermal bath, which is modelled by a massless probe scalar field. Firstly, we partially trace over the bath field and construct the Gorini Kossakowski Sudarshan Lindblad (GSKL) master equation, which describes the time evolution of the reduced subsystem density matrix. This GSKL master equation is characterized by two components, these are-Spin chain interaction Hamiltonian and the Lindbladian. To fix the form of both of them, we compute the Wightman functions for probe massless scalar field. Using this result along with the large time equilibrium behaviour we obtain the analytical solution for reduced density matrix. Further using this solution we evaluate various entanglement measures, namely Von-Neumann entropy, R$e'$nyi entropy, logarithmic negativity, entanglement of formation, concurrence and quantum discord for the two atomic subsystems on the static patch of De-Sitter space. Finally, we have studied the violation of Bell-CHSH inequality, which is the key ingredient to study non-locality in primordial cosmology., Comment: 52 pages (41 pages paper + 11 pages Appendix and references), 18 figures, 2 tables, This project is the part of the non-profit virtual international research consortium "Quantum Aspects of the Space-Time & Matter", Accepted for publication in European Physical Journal C, Matched with the published version

In this paper, we explore the connection between the curvature of the background De Sitter space-time with the spectroscopic study of entanglement of two atoms. Our set up is in the context of an Open Quantum System (OQS), where the two atoms, each having two energy levels and represented by Pauli spin tensor operators projected along any arbitrary direction. The system mimics the role of a pair of freely falling Unruh De-Witt detectors, which are allowed to non-adiabatically interact with a conformally coupled massless probe scalar field which has the role of background thermal bath. The effective dynamics of this combined system takes into account of the non-adiabatic interaction, which is commonly known as the Resonant Casimir Polder Interaction (RCPI) with the thermal bath. Our analysis reveals that the RCPI of two stable entangled atoms in the quantum vacuum states in OQS depends on the de Sitter space-time curvature relevant to the temperature of the thermal bath felt by the static observer. We also find that, in OQS, RCPI produces a new significant contribution appearing in the effective Hamiltonian of the total system and thermal bath under consideration. We find that the Lamb Shift is characterized by a decreasing inverse square power-law behavior, $L^{-2}$, when inter atomic Euclidean distance, $L$, is much larger than a characteristic length scale, $k$, which is the inverse surface gravity of the background De Sitter space. If the background space-time would have been Minkowskian this shift decreases as, $L^{-1}$, and is independent of temperature. Thus, we establish a connection between the curvature of the De Sitter space-time with the Lamb Shift spectroscopy., Comment: 65 pages, 3 figures, 1 Table, This project is the part of the non-profit virtual international research consortium "Quantum Structures of the Space-Time & Matter". Accepted for publication in European Physical Journal C

In this article, we study quantum randomness of stochastic cosmological particle production scenario using quantum corrected higher order Fokker Planck equation. Using the one to one correspondence between particle production in presence of scatterers and electron transport in conduction wire with impurities we compute the quantum corrections of Fokker Planck Equation at different orders. Finally, we estimate Gaussian and non-Gaussian statistical moments to verify our result derived to explain stochastic particle production probability distribution profile., Comment: 6 pages, 4 figures, Accepted for publication in European Physical Journal C

In this article, using the principles of Random Matrix Theory (RMT), we give a measure of quantum chaos by quantifying Spectral From Factor (SFF) appearing from the computation of two-point Out of Time Order Correlation function (OTOC) expressed in terms of square of the commutator bracket of quantum operators which are separated in time. We also provide a strict model independent bound on the measure of quantum chaos, $-1/N(1-1/\pi)\leq {\bf SFF}\leq 0$ and $0\leq {\bf SFF}\leq 1/\pi N$, valid for thermal systems with a large and small number of degrees of freedom respectively. Based on the appropriate physical arguments we give a precise mathematical derivation to establish this alternative strict bound of quantum chaos., Comment: 4 pages, 2 figures

In this work, we study the impact of quantum entanglement on the two-point correlation function and the associated primordial power spectrum of mean square vacuum fluctuation in a bipartite quantum field theoretic system. The field theory that we consider is the effective theory of axion field arising from Type IIB string theory compactified to four dimensions. We compute the expression for the power spectrum of vacuum fluctuation in three different approaches, namely (1) field operator expansion (FOE) technique with the quantum entangled state, (2) reduced density matrix (RDM) formalism with mixed quantum state and (3) the method of non-entangled state (NES). For massless axion field, in all these three formalism, we reproduce, at the leading order, the exact scale-invariant power spectrum which is well known in the literature. We observe that due to quantum entanglement, the sub-leading terms for these thee formalisms are different. Thus, such correction terms break the degeneracy among the analysis of the FOE, RDM and NES formalisms in the super-horizon limit. On the other hand, for massive axion field, we get a slight deviation from scale invariance and exactly quantify the spectral tilt of the power spectrum in small scales. Apart from that, for massless and massive axion field, we find distinguishable features of the power spectrum for the FOE, RDM, and NES on the large scales, which is the result of quantum entanglement. We also find that such large-scale effects are comparable to or greater than the curvature radius of the de Sitter space. Most importantly, in the near future, if experiments probe for early universe phenomena, one can detect such small quantum effects. In such a scenario, it is possible to test the implications of quantum entanglement in primordial cosmology., Comment: 75 pages, 13 figures, 1 table, Revised version, This work published is published in Universe as part of the Special Issue "Cosmic String Theory and Observations"

In this work, our prime focus is to study the one to one correspondence between the conduction phenomena in electrical wires with impurity and the scattering events responsible for particle production during stochastic inflation and reheating implemented under a closed quantum mechanical system in early universe cosmology. In this connection, we also present a derivation of fourth order corrected version of the Fokker Planck equation and its analytical solution for studying the dynamical features of the particle creation events in the stochastic inflation and reheating stage of the universe. It is explicitly shown from our computation that quantum corrected Fokker Planck equation describe the particle creation phenomena better for Dirac delta type of scatterer. In this connection, we additionally discuss It$\hat{o}$, Stratonovich prescription and the explicit role of finite temperature effective potential for solving the probability distribution profile. Furthermore, we extend our discussion to describe the quantum description of randomness involved in the dynamics. We also present a computation to derive the expression for the measure of the stochastic non-linearity arising in the stochastic inflation and reheating epoch of the universe, often described by Lyapunov Exponent. Apart from that, we quantify the quantum chaos arising in a closed system by a more strong measure, commonly known as Spectral Form Factor using the principles of Random Matrix Theory (RMT). Additionally, we discuss the role of out of time order correlation (OTOC) function to describe quantum chaos in the present non-equilibrium field theoretic setup. Finally, for completeness, we also provide a bound on the measure of quantum chaos arising due to the presence of stochastic non-linear dynamical interactions into the closed quantum system of the early universe in a completely model-independent way., Comment: 177 pages, 58 figures, 4 tables, Accepted for publication in European Physical Journal C

It has been conjectured that fermions minimally coupled to a Chern-Simons gauge field define a conformal field theory (CFT) that is level-rank dual to Chern-Simons gauged Wilson-Fisher Bosons. The CFTs in question admit relevant deformations parametrized by a real mass. When the mass deformation is positive, the duality of the two deformed theories has previously been checked in detail in the large $N$ limit by comparing explicit all orders results on both sides of the duality. In this paper we perform a similar check for the case of negative mass deformations. In this case the bosonic field condenses triggering the Higgs mechanism. The effective excitations in this phase are massive $W$ bosons. By summing all leading large $N$ graphs involving these $W$ bosons we find an all orders (in the 't Hooft coupling) result for the thermal free energy of the bosonic theory in the condensed phase. Our final answer perfectly matches the previously obtained fermionic free energy under the conjectured duality map., Comment: 48 pages, Minor modifications added in revised version

In this work, we study the phenomena of quantum entanglement by computing de Sitter entanglement entropy from von Neumann measure. For this purpose we consider a bipartite quantum field theoretic setup in presence of axion originating from ${\bf Type~ II~B}$ string theory. We consider the initial vacuum to be CPT invariant non-adiabatic $\alpha$ vacua state under ${\bf SO(1,4)}$ ismometry, which is characterized by a real one-parameter family. To implement this technique we use a ${\bf S^2}$ which divide the de Sitter into two exterior and interior sub-regions. First, we derive the wave function of axion in an open chart for $\alpha$ vacua by applying Bogoliubov transformation on the solution for Bunch-Davies vacuum state. Further, we quantify the density matrix by tracing over the contribution from the exterior region. Using this result we derive entanglement entropy, R$\acute{e}$nyi entropy and explain the long-range quantum effects in primordial cosmological correlations. We also provide a comparison between the results obtained from Bunch-Davies vacuum and the generalized $\alpha$ vacua, which implies that the amount of quantum entanglement and the long-range effects are larger for non zero value of the parameter $\alpha$. Most significantly, our derived results for $\alpha$ vacua provides the necessary condition for generating non zero entanglement entropy in primordial cosmology., Comment: 31 pages, 13 figures, Revised version, Accepted for publication in Nuclear Physics B

In this work, we study the key role of generic Effective Field Theory (EFT) framework to quantify the correlation functions in a quasi de Sitter background for an arbitrary initial choice of the quantum vacuum state. We perform the computation in unitary gauge, in which we apply the St$\ddot{\text{u}}$ckelberg trick in lowest dimensional EFT operators which are broken under time diffeomorphism. In particular, using this non-linear realization of broken time diffeomorphism and truncating the action by considering the contribution from two derivative terms in the metric, we compute the two-point and three-point correlations from scalar perturbations and two-point correlation from tensor perturbations to quantify the quantum fluctuations observed in the Cosmic Microwave Background (CMB) map. We also use equilateral limit and squeezed limit configurations for the scalar three-point correlations in Fourier space. To give future predictions from EFT setup and to check the consistency of our derived results for correlations, we use the results obtained from all classes of the canonical single-field and general single-field $P(X,\phi)$ model. This analysis helps us to fix the coefficients of the relevant operators in EFT in terms of the slow-roll parameters and effective sound speed. Finally, using CMB observations from Planck we constrain all these coefficients of EFT operators for the single-field slow-roll inflationary paradigm., Comment: 81 pages, Revised version, Accepted for publication in Universe. This is an invited article which is explicitly written for a special issue "Cosmological Constant Puzzle" of Universe. This project is the part of the non-profit virtual international research consortium "Quantum Structures of the Space-Time & Matter''

In this work, we study the quantum entanglement and compute entanglement entropy in de Sitter space for a bipartite quantum field theory driven by axion originating from ${\bf Type~ IIB}$ string compactification on a Calabi Yau three fold (${\bf CY^3}$) and in presence of ${\bf NS5}$ brane. For this compuation, we consider a spherical surface ${\bf S}^2$, which divide the spatial slice of de Sitter (${\bf dS_4}$) into exterior and interior sub regions. We also consider the initial choice of vaccum to be Bunch Davies state. First we derive the solution of the wave function of axion in a hyperbolic open chart by constructing a suitable basis for Bunch Davies vacuum state using Bogoliubov transformation. We then, derive the expression for density matrix by tracing over the exterior region. This allows us to compute entanglement entropy and R$\acute{e}$nyi entropy in $3+1$ dimension. Further we quantify the UV finite contribution of entanglement entropy which contain the physics of long range quantum correlations of our expanding universe. Finally, our analysis compliments the necessary condition for the violation of Bell's inequality in primordial cosmology due to the non vanishing entanglement entropy for axionic Bell pair., Comment: 51 pages, 10 figures, Revised version, Accepted for publication in European Physical Journal C

It has recently been demonstrated that the large N limit of a model of fermions charged under the global/gauge symmetry group $O(N)^{q-1}$ agrees with the large $N$ limit of the SYK model. In these notes we investigate aspects of the dynamics of the $O(N)^{q-1}$ theories that differ from their SYK counterparts. We argue that the spectrum of fluctuations about the finite temperature saddle point in these theories has $(q-1)\frac{N^2}{2}$ new light modes in addition to the light Schwarzian mode that exists even in the SYK model, suggesting that the bulk dual description of theories differ significantly if they both exist. We also study the thermal partition function of a mass deformed version of the SYK model. At large mass we show that the effective entropy of this theory grows with energy like $E \ln E$ (i.e. faster than Hagedorn) up to energies of order $N^2$. The canonical partition function of the model displays a deconfinement or Hawking Page type phase transition at temperatures of order $1/\ln N$. We derive these results in the large mass limit but argue that they are qualitatively robust to small corrections in $J/m$., Comment: 60 pages, 7 figures

We investigate the possibility of constraining parameters of Effective Field Theory (EFT) of inflation with upcoming Large Scale Structure (LSS) surveys in order to have a better understanding of inflationary dynamics. With the development of the construction algorithm of EFT, we arrive at a properly truncated action for the entire scenario. Using this, we compute the two-point correlation function for quantum fluctuations from Goldstone modes and related inflationary observables in terms of coefficients of relevant EFT operators. We then perform Fisher matrix forecast analysis to estimate the possible error bars on the parameters of EFT as well as on the inflationary parameters using two upcoming LSS surveys, namely, LSST and EUCLID., Comment: 23 pages, 5 tables, Substantially modified version. Major changes appear in the analysis and interpretation with a forecast on upcoming LSS missions

In this work, we have developed an elegant algorithm to study the cosmological consequences from a huge class of quantum field theories (i.e. superstring theory, supergravity, extra dimensional theory, modified gravity etc.), which are equivalently described by soft attractors in the effective field theory framework. In this description we have restricted our analysis for two scalar fields - dilaton and Higgsotic fields minimally coupled with Einstein gravity, which can be generalized for any arbitrary number of scalar field contents with generalized non-canonical and non-minimal interactions. We have explicitly used $R^2$ gravity, from which we have studied the attractor and non-attractor phase by exactly computing two point, three point and four point correlation functions from scalar fluctuations using In-In (Schwinger-Keldysh) and $\delta {\cal N}$ formalism. We have also presented theoretical bounds on the amplitude, tilt and running of the primordial power spectrum, various shapes (equilateral, squeezed, folded kite or counter collinear) of the amplitude as obtained from three and four point scalar functions, which are consistent with observed data. Also the results from two point tensor fluctuations and field excursion formula are explicitly presented for attractor and non-attractor phase. Further, reheating constraints, scale dependent behaviour of the couplings and the dynamical solution for the dilaton and Higgsotic fields are also presented. New sets of consistency relations between two, three and four point observables are also presented, which shows significant deviation from canonical slow roll models. Additionally, three possible theoretical proposals have presented to overcome the tachyonic instability at the time of late time acceleration. Finally, we have also provided the bulk interpretation from the three and four point scalar correlation functions for completeness., Comment: 106 pages, 33 figures, 6 tables, Accepted for publication in European Physical Journal C

In this paper, we have worked on the possibility of setting up an Bell's inequality violating experiment in the context of primordial cosmology following the fundamental principles of quantum mechanics. To set up this proposal we have introduced a model independent theoretical framework using which we have studied the creation of new massive particles for the scalar fluctuations in the presence of additional time dependent mass parameter. Next we explicitly computed the one point and two point correlation functions from this setup. Then we comment on the measurement techniques of isospin breaking interactions of newly introduced massive particles and its further prospects. After that, we give an example of string theory originated axion monodromy model in this context. Finally, we provide a bound on the heavy particle mass parameter for any arbitrary spin field., Comment: 10 pages, 6 figures, 1 table, Shorter version of arXiv:1607.00237, "Talk presented at Varying Constants and Fundamental Cosmology-VARCOSMOFUN'16. To appear in a special issue of Universe."

In this work, we have studied the possibility of setting up Bell's inequality violating experiment in the context of cosmology, based on the basic principles of quantum mechanics. First we start with the physical motivation of implementing the Bell's inequality violation in the context of cosmology. Then to set up the cosmological Bell violating test experiment we introduce a model independent theoretical framework using which we have studied the creation of new massive particles by implementing the WKB approximation method for the scalar fluctuations in presence of additional time dependent mass contribution. Next using the background scalar fluctuation in presence of new time dependent mass contribution, we explicitly compute the expression for the one point and two point correlation functions. Furthermore, using the results for one point function we introduce a new theoretical cosmological parameter which can be expressed in terms of the other known inflationary observables and can also be treated as a future theoretical probe to break the degeneracy amongst various models of inflation. Additionally, we also fix the scale of inflation in a model independent way without any prior knowledge of primordial gravitational waves. Next, we also comment on the technicalities of measurements from isospin breaking interactions and the future prospects of newly introduced massive particles in cosmological Bell violating test experiment. Further, we cite a precise example of this set up applicable in the context of string theory motivated axion monodromy model. Then we comment on the explicit role of decoherence effect and high spin on cosmological Bell violating test experiment. In fine, we provide a theoretical bound on the heavy particle mass parameter for scalar fields, graviton and other high spin fields from our proposed setup., Comment: 202 pages, 16 figures, 1 table, Accepted for publication in European Physical Journal C

In this work, we propose different models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of a dark matter (DM) candidate, without ad-hoc additions to the Standard Model (SM). We modify the gravity sector by allowing quantum corrections motivated from local $f(R)$ gravity, and non-minimally coupled gravity with SM sector and dilaton field. Using an effective field theory (EFT) framework, we constrain the scale of the EFT and DM mass. We consider two cases-Light DM (LDM) and Heavy DM (HDM), and deduce upper bounds on the DM annihilation cross section to SM particles., Comment: 2 pages, 3 figures, "Presented at the 52nd Winter School of Theoretical Physics (Ladek Zdroj, Poland). To appear in a special issue of Acta Physica Polonica B"

This thesis compiles the results of six works which deal with - inflationary model building and estimation of cosmological parameters from various field theoretic setup, quantification of reheating temperature, studies of leptogenesis in braneworld and estimation of primordial non-Gaussianity from ${\cal N}=1$ supergravity using $\delta N$ formalism. We start our discussion with exploring the possibility of MSSM inflation in the light of recent observed data from various D -flat directions using the saddle and inflection point techniques. The effective inflaton potential around saddle point and inflection point have been utilized in estimating the observable parameters and confronting them with WMAP7 and Planck dataset. Next we explore the possibility of inflation from the five dimensional ${\cal N} = 2$ supergravity setup by deriving the effective potential in the context of RS like braneworld model and DBI Galileon. After deriving an four dimensional effective potential, we obtain the inflationary observables from both the scenarios and confront them with the WMAP data. Further we fit the CMB angular power spectra from TT anisotropy and other polarization data obtained from WMAP. Further, we discuss the non-trivial features of reheating from supergravity inspired braneworld model, where the results are to some extent different from that of the usual low energy GR counterpart, because of the modified Friedmann equations in this setup. We explicitly derive the analytical expressions for the reheating temperature and further solve the evolution equation of the number density of thermal gravitino which results in the gravitino abundance. Finally, we study the primordial local type of non-Gaussian features using $\delta N$ formalism for a generic class of sub-Planckian models dominated by the Hubble-induced corrections within ${\cal N} = 1$ supergravity framework., Comment: 164 pages, 25 figures, 13 tables, Ph.D. thesis, Work done at Physics and Applied Mathematics Unit, Indian Statistical Institute, Kolkata, Thesis successfully defended on 03/03/2016 at PAMU, ISI, Kolkata, Supervisor: Dr. Supratik Pal. Thesis is based on the works arXiv:1102.4206, arXiv:1108.5676, arXiv:1111.3441, arXiv:1208.4433, arXiv:1209.5883, arXiv:1305.6398, arXiv:1402.1227, arXiv:1402.1251

Cosmological hysteresis is a purely thermodynamical phenomenon caused by the gradient in pressure, hence the characteristic equation of state during the expansion and contraction phases of the universe are different, provided that the universe bounces and recollapses. During hysteresis pressure asymmetry is created due to the presence of a single scalar field in the dynamical process. Also such an interesting scenario has vivid implications in cosmology when applied to variants of modified gravity models described within the framework of membrane paradigm. Cyclic universe along with scalar field leads to the increase in the amplitude of the cosmological scale factor at each consecutive cycles of the universe. Detailed analysis shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of the hysteresis loop integral $\oint pdV$ and on membrane model parameters., Comment: 12 pages, 6 figures. arXiv admin note: substantial text overlap with arXiv:1506.02260

Cosmological hysteresis, has interesting and vivid implications in the scenario of a cyclic bouncy universe. This, purely thermodynamical in nature, is caused by the asymmetry in the equation of state parameter during expansion and contraction phase of the universe, due to the presence of a single scalar field. When applied to variants of modified gravity models this phenomenon leads to the increase in amplitude of the consecutive cycles of the universe, provided we have physical mechanisms to make the universe bounce and turnaround. This also shows that the conditions which creates a universe with an ever increasing expansion, depend on the signature of $\oint pdV$ and on model parameters., Comment: 6 pages, 3 figures, To appear in the Proceedings of the Fourteenth Marcel Grossman Meeting on General Relativity at University of Rome "La Sapienza" - Rome, July 12-18, 2015

In this article, we propose different background models of extended theories of gravity, which are minimally coupled to the SM fields, to explain the possibility of genesis of dark matter without affecting the SM particle sector. We modify the gravity sector by allowing quantum corrections motivated from (1) local $f(R)$ gravity and (2) non-minimally coupled gravity with SM sector and dilaton field. Next we apply conformal transformation on the metric to transform the action back to the Einstein frame. We also show that an effective theory constructed from these extended theories of gravity and SM sector looks exactly the same. Using the relic constraint observed by Planck 2015, we constrain the scale of the effective field theory ($\Lambda_{UV}$) as well as the dark matter mass ($M$). We consider two cases- (1) light dark matter (LDM) and (2) heavy dark matter (HDM), and deduce upper bounds on thermally averaged cross section of dark matter annihilating to SM particles. Further we show that our model naturally incorporates self interactions of dark matter. Using these self interactions, we derive the constraints on the parameters of the (1) local $f(R)$ gravity and (2) non-minimally coupled gravity from dark matter self interaction. Finally, we propose some different UV complete models from a particle physics point of view, which can give rise to the same effective theory that we have deduced from extended theories of gravity., Comment: 45 pages, 8 figures, Accepted for publication in European Physical Journal C

In this article, our prime objective is to study the inflationary paradigm from generalized tachyon (GTachyon) living on the world volume of a non-BPS string theory. The tachyon action is considered here is getting modified compared to the original action. One can quantify the amount of the modification via a power $q$ instead of $1/2$ in the effective action. Using this set up we study inflation from various types of tachyonic potentials, using which we constrain the index $q$ within, $1/2

In this article, we have studied the cosmological and particle physics constraints on dark matter relic abundance from effective field theory of inflation using tensor-to-scalar ratio ($r$), in case of Randall-Sundrum single membrane (RSII) paradigm. Using semi-analytical approach we establish a direct connection between the dark matter relic abundance ($\Omega_{DM}h^2$) and primordial gravity waves ($r$), which establishes a precise connection between inflation and generation of dark matter within the framework of effective field theory in RSII membrane. Further assuming the UV completeness of the effective field theory perfectly holds good in the prescribed framework, we have explicitly shown that the membrane tension, $\sigma$, bulk mass scale $M_5$, and cosmological constant $\tilde{\Lambda}_{5}$, in RSII membrane plays the most significant role to establish the connection between dark matter and inflation, using which we have studied the features of various mediator mass scale suppressed effective field theory "relevant operators" induced from the localized $s$, $t$ and $u$ channel interactions. Taking a completely model independent approach, we have studied an exhaustive list of tree-level Feynman diagrams for dark matter annihilation within the prescribed setup and to check the consistency of the obtained results, further we apply the constraints as obtained from recently observed Planck 2015 data and Planck+BICEP2+Keck Array joint datasets. Using all of these derived results we have shown that to satisfy the bound on, $\Omega_{DM}h^2=0.1187\pm 0.0017$, as from Planck 2015 data, it is possible to put further stringent constraint on $r$ within, $0.01\leq r\leq 0.12$, for thermally averaged annihilation cross-section of dark matter, $\langle \sigma v\rangle\approx {\cal O}(10^{-28}-10^{-27}){\rm cm^3 /s}$, which are very useful to constrain various membrane inflationary models., Comment: 67 pages, 27 figures, 1 table, Final version, Accepted for publication in Physics of the Dark Universe

In this paper my prime objective is to analyze the constraints on a sub-Planckian excursion of a single inflaton field within Effective Field Theory framework in a model independent fashion. For a generic single field inflationary potential, using the various parameterization of the primordial power spectrum I have derived the most general expression for the field excursion in terms of various inflationary observables, applying the observational constraints obtained from recent Planck 2015 and Planck 2015 +BICEP2/Keck Array data. By explicit computation I have reconstructed the structural form of the inflationary potential by constraining the Taylor expansion coefficients appearing in the generic expansion of the potential within the Effective Field Theory. Next I have explicitly derived, a set of higher order inflationary consistency relationships, which would help us to break the degeneracy between various class of inflationary models by differentiating them. I also provided two simple examples of Effective Theory of inflation- inflection-point model and saddle-point model to check the compatibility of the prescribed methodology in the light of Planck 2015 and Planck 2015 +BICEP2/Keck Array data. Finally, I have also checked the validity of the prescription by estimating the cosmological parameters and fitting the theoretical CMB TT, TE and EE angular power spectra with the observed data within the multipole range $2

Hysteresis is a phenomenon occurring naturally in several magnetic and electric materials in condensed matter physics. When applied to cosmology, aka cosmological hysteresis, has interesting and vivid implications in the scenario of a cyclic bouncy universe. Most importantly, this physical prescription can be treated as an alternative proposal to inflationary paradigm. Cosmological hysteresis is caused by the asymmetry in the equation of state parameter during expansion and contraction phase of the universe, due to the presence of a single scalar field. This process is purely thermodynamical in nature, results in a non-vanishing hysteresis loop integral $(\oint pdV)$ in cosmology. When applied to variants of modified gravity models -1) Dvali-Gabadadze-Porrati (DGP) brane world gravity, 2) Cosmological constant dominated Einstein gravity, 3) Loop Quantum Gravity (LQG), 4) Einstien-Gauss-Bonnet brane world gravity and 5) Randall Sundrum single brane world gravity (RSII), under certain circumstances, this phenomenon leads to the increase in amplitude of the consecutive cycles and to a universe with older and larger successive cycles, provided we have physical mechanisms to make the universe bounce and turnaround. This inculcates an arrow of time in a dissipationless cosmology. Remarkably, this phenomenon appears to be widespread in several cosmological potentials in variants of modified gravity background, which we explicitly study for- i) Hilltop, ii) Natural and iii) Colemann-Weinberg potentials, in this paper. Semi-analytical analysis of these models, for different potentials with minimum/minima, show that the conditions which creates a universe with an ever increasing expansion, depend on the signature of the hysteresis loop integral $(\oint pdV)$ as well as on the variants of model parameters., Comment: 180 pages, 31 figures, 1 table, Final version, Accepted for publication in Astroparticle Physics

In this article, I have studied the cosmological and particle physics constraints on a generic class of large field ($|\Delta\phi|>M_{p}$) and small field ($|\Delta\phi

Fermion localization in a braneworld model in presence of dilaton coupled higher curvature Gauss-Bonnet bulk gravity is discussed. It is shown that the lowest mode of left handed fermions can be naturally localized on the visible brane due to the dilaton coupled higher curvature term without the necessity of any external localizing bulk field., Comment: 18 pages, 1 figure, 2 tables, Accepted for publication in Classical and Quantum Gravity

We have derived an effective potential for inflationary scenario from torsion and quantum gravity correction in terms of the scalar field hidden in torsion. A strict bound on the CP violating $\theta$ parameter, ${\cal O}(10^{-10})<\theta<{\cal O}(10^{-9})$ has been obtained, using {\tt Planck+WMAP9} best fit cosmological parameters., Comment: 8 pages, 1 figure, Accepted for publication in JHEP

In this paper my prime objective is to explain the generation of large tensor-to-scalar ratio from the single field sub-Planckian inflationary paradigm within Randall Sundrum (RS) single braneworld scenario in a model independent fashion. By explicit computation I have shown that the effective field theory prescription of brane inflation within RS single brane setup is consistent with sub- Planckian excursion of the inflaton field, which will further generate large value of tensor-to-scalar ratio, provided the energy density for inflaton degrees of freedom is high enough compared to the brane tension in high energy regime. Finally, I have mentioned the stringent theoretical constraint on positive brane tension, cut-off of the quantum gravity scale and bulk cosmological constant to get sub-Planckian field excursion along with large tensor-to-scalar ratio as recently observed by BICEP2 or at least generates the tensor-to-scalar ratio consistent with the upper bound of Planck (2013 and 2015) data and Planck+BICEP2+Keck Array joint constraint., Comment: 20 pages, Revision accepted by Nuclear Physics B

We propose a framework of modulus stabilization in two brane warped geometry scenario in presence of higher curvature gravity and dilaton in bulk space-time. In the prescribed setup we study various features of the stabilized potential for the modulus field, generated by a bulk scalar degrees of freedom with quartic interactions localized on the two 3-branes placed at the orbifold fixed points. We determine the parameter space for the gravidilaton and Gauss-Bonnet required to stabilize the modulus in such higher curvature dilaton gravity setup., Comment: 20 pages, 4 figures, 1 table, Revision accepted by JHEP

We categorically point out why the analysis of arXiv:1404.1821 [hep-ph] is incorrect. Here we explicitly show why the sub-Planckian field excursion of the inflaton field can yield large observable tensor-to-scalar ratio, which satisfies both Planck and BICEP constraints., Comment: 6 pages, 1 figure, Comment on arXiv:1404.1821 [hep-ph]. Computational error corrected in Eq(7). But conclusion remains unchanged as it completely nullifies the added claim of arXiv:1404.1821 [hep-ph]

In this paper we will analyse the constraints on a sub-Planckian excursion of a single inflaton field, which would yield a large tensor to scalar ratio, while explaining the temperature anisotropy of the cosmic microwave background (CMB) radiation. In particular, our attempt will be to reconstruct the inflationary potential by constraining, $V(\phi_0), V^{\prime}(\phi_0), V^{\prime\prime}(\phi_0), V^{\prime\prime\prime}(\phi_0)$ and $V^{\prime\prime\prime\prime}(\phi_0)$, in the vicinity of the field, $\phi_0\ll M_p$, and the field displacement, $\Delta \phi \ll M_p$, where $M_p$ is the reduced Planck mass. We will provide, for the first time, a set of new {\it consistency} relationships for sub-Planckian excursion of the inflaton field, which would help us to differentiate sub-versus-super Planckian models of inflation. For a generic single field inflationary potential, we will be able to put a stringent bound on the potential energy density: $2.07\times10^{16} {\rm GeV}\leq\sqrt[4]{V_{\star}}\leq 2.40\times 10^{16} {\rm GeV}$, where inflation can occur on the flat potential within, $0.066 \leq\frac{\left |\Delta\phi\right|}{M_p}\,\leq 0.092$, for the following observational constraints: (Planck+WMAP-9+high L+BICEP2). We then provide a prediction for the spectral tilt ($n_{T}$), running ($\alpha_{T}$) and running of running ($\kappa_{T}$) of the tensor modes within the window, $-0.019

In this paper I introduce a precise constraint on primordial magnetogenesis, for a generic class of single-field inflationary model followed by small field excursion below the Planck scale. I also establish a connection between the magnetic field at the present epoch and primordial gravity waves ($r$) via non-vanishing CP asymmetry parameter ($\epsilon_{\bf CP}$), which triggers the leptogenesis scenario. Finally, I explore various hidden cosmophenomenological features of theoretical CMB B-mode polarization spectra, which can be treated as a significant probe to put further stringent constraint on low and high scale small field inflationary models after releasing the Planck B-mode polarization data., Comment: 9 pages, 3 figures, Revision accepted by Physics Letters B

In this paper I provide a general framework based on $\delta N$ formalism to study the features of unavoidable higher dimensional non-renormalizable K\"ahler operators for ${\cal N}=1$ supergravity (SUGRA) during primordial inflation from the combined constraint on non-Gaussianity, sound speed and CMB dipolar asymmetry as obtained from the recent Planck data. In particular I study the nonlinear evolution of cosmological perturbations on large scales which enables us to compute the curvature perturbation, $\zeta$, without solving the exact perturbed field equations. Further I compute the non-Gaussian parameters $f_{NL}$, $\tau_{NL}$ and $g_{NL}$ for local type of non-Gaussianities and CMB dipolar asymmetry parameter, $ A_{CMB}$, using the $\delta N$ formalism for a generic class of sub-Planckian models induced by the Hubble-induced corrections for a minimal supersymmetric D-flat direction where inflation occurs at the point of inflection within the visible sector. Hence by using multi parameter scan I constrain the non-minimal couplings appearing in non-renormalizable K\"ahler operators within, ${\cal O}(1)$, for the speed of sound, $0.02\leq c_s\leq 1$, and tensor to scalar, $10^{-22} \leq r_{\star} \leq 0.12$. Finally applying all of these constraints I will fix the lower as well as the upper bound of the non-Gaussian parameters within, ${\cal O}(1-5)\leq f_{NL}\leq 8.5$, ${\cal O}(75-150)\leq\tau_{NL}\leq 2800$ and ${\cal O}(17.4-34.7)\leq g_{NL}\leq 648.2$, and CMB dipolar asymmetry parameter within the range, $0.05\leq A_{CMB}\leq 0.09$., Comment: 26 pages, 5 figures, Accepted for publication in JHEP

In this paper we will illustrate how to constrain unavoidable K\"ahler corrections for ${\cal N}=1$ supergravity (SUGRA) inflation from the recent Planck data. We will show that the non-renormalizable K\"ahler operators will induce in general non-minimal kinetic term for the inflaton field, and two types of SUGRA corrections in the potential - the Hubble-induced mass ($c_{H}$), and the Hubble-induced A-term ($a_{H}$) correction. The entire SUGRA inflationary framework can now be constrained from (i) the speed of sound, $c_s$, and (ii) from the upper bound on the tensor to scalar ratio, $r_{\star}$. We will illustrate this by considering a heavy scalar degree of freedom at a scale, $M_s$, and a light inflationary field which is responsible for a slow-roll inflation. We will compute the corrections to the kinetic term and the potential for the light field explicitly. As an example, we will consider a visible sector inflationary model of inflation where inflation occurs at the point of inflection, which can match the density perturbations for the cosmic microwave background radiation, and also explain why the universe is filled with the Standard Model degrees of freedom. We will scan the parameter space of the non-renormalizable K\"ahler operators, which we find them to be order ${\cal O}(1)$, consistent with physical arguments. While the scale of heavy physics is found to be bounded by the tensor-to scalar ratio, and the speed of sound, $ {\cal O}(10^{11}\leq M_s\leq 10^{16}) $GeV, for $0.02\leq c_s\leq 1$ and $10^{-22}\leq r_\star \leq 0.12$., Comment: 28 pages, 3 figures, Accepted for publication in JHEP

In this paper we study the role of the 5D Gauss-Bonnet corrections and two loop higher genus contribution to the gravity action in type IIB string theory inspired low energy supergravity theory in the light of gravidilatonic interactions on the lightest Kaluza-Klein graviton mass spectrum. From the latest constraints on the lightest Kaluza-Klein graviton mass as obtained from the ATLAS dilepton search in 7 TeV proton-proton collision, we have shown that due to the presence of Gauss-Bonnet and string loop corrections, the warping solution in an ${\bf AdS_{5}}$ bulk is quite distinct from Randall-Sundrum scenario. We discuss the constraints on the model parameters to fit with present ATLAS data., Comment: 11 pages, 4 figures, Revision accepted by European Physical Journal C

In this paper we introduce an idea of leptogenesis scenario in higher derivative gravity induced DBI Galileon framework {\it aka Galileogenesis} in presence of one-loop R-parity violating couplings in the background of a low energy effective supergravity setup. We have studied extensively the detailed feature of reheating constraints and the cosmophenomenological consequences of thermal gravitino dark matter in light of PLANCK and PDG data. Finally we have also established a direct cosmological connection among dark matter relic abundance, reheating temperature and tensor-to-scalar ratio in the context of DBI Galileon inflation., Comment: 8 pages, 2 figures, Revision accepted by Nuclear Physics B

In this paper the requirement of a warp solution in an Einstein-Gauss-Bonnet 5D warped geometry is shown to fix the signature of Gauss-Bonnet coupling ($\alpha_{5}$). Further, imposing the phenomenological constraints, obtained from the recently observed Higgs like scalar mass as well as $\mu$ parameter of the decay channels ${H}_{0}\rightarrow\gamma\gamma,\tau{\bar \tau}$ explored in ATLAS and CMS detectors, we obtain a stringent bound on $\alpha_{5}$ within $(4.8 - 5.1)\times 10^{-7}$., Comment: 6 pages, 3 figures, Revised version

In this article we provide a new closed relationship between cosmic abundance of primordial gravitational waves and primordial blackholes originated from initial inflationary perturbations for inflection-point models of inflation where inflation occurs below the Planck scale. The current Planck constraint on tensor-to-scalar ratio, running of the spectral tilt, and from the abundance of dark matter content in the universe, we can deduce a strict bound on the current abundance of primordial blackholes to be within a range, $9.99712\times 10^{-3}<\Omega_{PBH}h^{2}<9.99736\times 10^{-3}$., Comment: 7 pages, 3 figures, Revision accepted by Physics Letters B

In this paper we provide an accurate bound on primordial gravitational waves, i.e. tensor-to-scalar ratio $(r)$ for a general class of single-field models of inflation where inflation occurs always below the Planck scale, and the field displacement during inflation remains sub-Planckian. If inflation has to make connection with the real particle physics framework then it must be explained within an effective field theory description where it can be trustable below the UV cut-off of the scale of gravity. We provide an analytical estimation and estimate the largest possible $r$, i.e. $r\leq 0.12$, for the field displacement less than the Planck cut-off., Comment: 13 pages, Revised version, Accepted for publication in Nuclear Physics B

We study the role of the Gauss-Bonnet corrections to the gravity action on the charged AdS black hole in presence of rank 3 antisymmetric Kalb Ramond tensor field strength. Analyzing the branch singularity and the killing horizon, we explicitly derive various thermodynamic parameters and study their behaviour in presence of five dimensional Gauss-Bonnet coupling in AdS space-time. The possibility of a second order phase transition is explored in the light of AdS/CMT correspondence and various critical exponents associated with the discontinuities of the various thermodynamic parameters are determined. We further comment on the universality of the well known Rushbrooke Josephson scaling law and derive a relation between the degree of homogeneity appearing in various free energies and the critical exponents by homogeneous hypothesis test. By making use of the constraints appearing from Hawking temperature and Gauss-Bonnet extended gravity version of Kubo formula we introduce a bound on the five dimensional Gauss-Bonnet coupling and the viscosity entropy ratio in the four dimensional holographic Conformal Field Theory (CFT) dual. This yields a fractional deviation in viscosity entropy ratio from the result obtained from Einstein gravity., Comment: 34 pages, 15 figures, Revised version, references added

In this paper we will analyze generic predictions of an inflection-point model of inflation with Hubble-induced corrections and study them in light of the Planck data. Typically inflection-point models of inflation can be embedded within Minimal Supersymmetric Standard Model (MSSM) where inflation can occur below the Planck scale. The flexibility of the potential allows us to match the observed amplitude of the TT-power spectrum of the cosmic microwave background radiation with low and high multipoles, spectral tilt, and virtually mild running of the spectral tilt, which can put a bound on an upper limit on the tensor-to-scalar ratio, $r \leq 0.12$. Since the inflaton within MSSM carries the Standard Model charges, therefore it is the minimal model of inflation beyond the Standard Model which can reheat the universe with the right thermal degrees of freedom without any dark-radiation., Comment: 11 pages, 6 figures, Accepted for publication in JCAP

We introduce a new class of models of Higgs inflation using the superconformal approach to supergravity by modifying the K$\ddot{a}$hler geometry. Using such a mechanism, we construct a phenomenological functional form of a new K$\ddot{a}$hler potential. From this we construct various types of models which are characterized by a superconformal symmetry breaking parameter $\chi$, and depending on the numerical values of $\chi$ we classify all of the proposed models into three categories. Models with minimal coupling are identified by $\chi=\pm\frac{2}{3}$ branch which are made up of shift symmetry preserving flat directions. We also propose various other models by introducing a non-minimal coupling of the inflaton field to gravity described by $\chi\neq\frac{2}{3}$ branch. We employ all these proposed models to study the inflationary paradigm by estimating the major cosmological observables and confront them with recent observational data from WMAP9 along with other complementary data sets, as well as independently with PLANCK. We also mention an allowed range of non-minimal couplings and the {\it Yukawa} type of couplings appearing in the proposed models used for cosmological parameter estimation., Comment: 13 pages, 6 figures, version to appear in Nuclear Physics B

We study the role of the Gauss-Bonnet corrections and two loop higher genus contribution to the gravity action on the Kaluza-Klien modes and their interactions for different bulk fields which enable one to study various phenomenological implications of string loop corrected Gauss-Bonnet modified warped geometry model in one canvas. We have explicitly derived a phenomenological bound on the Gauss-Bonnet parameter so that the required Planck to TeV scale hierarchy can be achieved through the warp factor in the light of recently discovered Higgs like boson at 125 GeV. Moreover due to the presence of small perturbative Gauss-Bonnet as well as string loop corrections we have shown that the warping solution can be obtained for both de-Sitter and anti-de-Sitter bulk which is quite distinct from Randall-Sundrum scenario. Finally we have evaluated various interactions among these bulk fields and determined the coupling parameters and the Kaluza- Klien mode masses which is crucial to understand the phenomenology of a string two loop corrected Einstein-Gauss-Bonnet warp geometry., Comment: 48 pages, 13 figures, Final version, Accepted for publication in JHEP