arXiv subjects

Anupam Mazumdar

Publications and source records attributed to Anupam Mazumdar.

At least 199 records · Page 11Linked to original sources

arXiv2010

Reheating for Closed String Inflation

We point out some of the outstanding challenges for embedding inflationary cosmology within string theory studying the process of reheating for models where the inflaton is a closed string mode parameterising the size of an internal cycle of the compactification manifold. A realistic model of inflation must explain the tiny perturbations in the cosmic microwave background radiation and also how to excite the ordinary matter degrees of freedom after inflation, required for the success of Big Bang Nucleosynthesis. We study these issues focusing on two promising inflationary models embedded in LARGE volume type IIB flux compactifications. We show that phenomenological requirements and consistency of the effective field theory treatment imply the presence at low energies of a hidden sector together with a visible sector, where the Minimal Supersymmetric Standard Model fields are residing. A detailed calculation of the inflaton coupling to the fields of the hidden sector, visible sector, and moduli sector, reveals that the inflaton fails to excite primarily the visible sector fields, instead hidden sector fields are excited copiously after the end of inflation. This sets severe constraints on hidden sector model building where the most promising scenario emerges as a pure N=1 SYM theory, forbidding the kinematical decay of the inflaton to the hidden sector. In this case it is possible to reheat the Universe with the visible degrees of freedom even though in some cases we discover a new tension between TeV scale SUSY and reheating on top of the well-known tension between TeV scale SUSY and inflation.

hep-th↗

arXiv2010

Inflection point inflation within supersymmetry

We propose to address the fine tuning problem of inflection point inflation by the addition of extra vacuum energy that is present during inflation but disappears afterwards. We show that in such a case, the required amount of fine tuning is greatly reduced. We suggest that the extra vacuum energy can be associated with an earlier phase transition and provide a simple model, based on extending the SM gauge group to SU(3)_C \times SU(2)_L\times U(1)_Y\times U(1)_{B-L}, where the Higgs field of U(1)_{B-L} is in a false vacuum during inflation. In this case, there is virtually no fine tuning of the soft SUSY breaking parameters of the flat direction which serves as the inflaton. However, the absence of radiative corrections which would spoil the flatness of the inflaton potential requires that the U(1)_{B-L} gauge coupling should be small with g_{B-L}\leq 10^{-4}.

hep-ph↗

arXiv2010

Reheating in Inflationary Cosmology: Theory and Applications

Reheating is an important part of inflationary cosmology. It describes the production of Standard Matter particles after the phase of accelerated expansion. We give a review of the reheating process, focusing on an in-depth discussion of the preheating stage which is characterized by exponential particle production due to a parametric resonance or tachyonic instability. We give a brief overview of the thermalization process after preheating and end with a survey of some applications to supersymmetric theories and to other issues in cosmology such as baryogenesis, dark matter and metric preheating.

hep-th↗

arXiv2010

Particle physics models of inflation and curvaton scenarios

We review the particle theory origin of inflation and curvaton mechanisms for generating large scale structures and the observed temperature anisotropy in the cosmic microwave background (CMB) radiation. Since inflaton or curvaton energy density creates all matter, it is important to understand the process of reheating and preheating into the relevant degrees of freedom required for the success of Big Bang Nucleosynthesis. We discuss two distinct classes of models, one where inflaton and curvaton belong to the hidden sector, which are coupled to the Standard Model gauge sector very weakly. There is another class of models of inflaton and curvaton, which are embedded within Minimal Supersymmetric Standard Model (MSSM) gauge group and beyond, and whose origins lie within gauge invariant combinations of supersymmetric quarks and leptons. Their masses and couplings are all well motivated from low energy physics, therefore such models provide us with a unique opportunity that they can be verified/falsified by the CMB data and also by the future collider and non-collider based experiments. We then briefly discuss stringy origin of inflation, alternative cosmological scenarios, and bouncing universes.

hep-ph↗

arXiv2009

Probing Unified Origin of Dark Matter and Baryon Asymmetry at PAMELA/Fermi

We propose an unified model of dark matter and baryon asymmetry in a lepto-philic world above the electroweak scale. We provide an example where the inflaton decay products subsequently generate a lepton asymmetry and a dark matter abundance with an unique coupling in the early universe, while the present day decay of the dark matter through the same coupling gives rise the observed cosmic ray anomalies at PAMELA and Fermi Large Area Telescope.

hep-ph↗

arXiv2009

Inflation with a Negative Cosmological Constant

We find a unique way of realizing inflation through cyclic phases in an universe with negative vacuum energy. According to the second law of thermodynamics entropy monotonically increases from cycle to cycle, typically by a constant factor. This means that the scale factor at the same energy density in consecutive cycles also increases by a constant factor. If the time period of the oscillations remain approximately constant then this leads to an ``over all'' exponential growth of the scale factor, mimicking inflation. A graceful exit from this inflationary phase is possible as a dynamical scalar field can take us from the negative to a positive energy vacuum during the last contracting phase.

hep-th↗

arXiv2009

Gravitational waves from the fragmentation of a supersymmetric condensate

We discuss the production of gravity waves from the fragmentation of a supersymmetric condensate in the early universe. Supersymmetry predicts the existence of flat directions in the potential. At the end of inflation, the scalar fields develop large time-dependent vacuum expectation values along these flat directions. Under some general conditions, the scalar condensates undergo a fragmentation into non-topological solitons, Q-balls. We study this process numerically and confirm the recent analytical calculations showing that it can produce gravity waves observable by Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), Laser Interferometer Space Antenna (LISA), and Big Bang Observer (BBO). The fragmentation can generate gravity waves with an amplitude as large as Omega_{GW}~10^{-11} and with a peak frequency ranging from mHz to 10 Hz, depending on the parameters. The discovery of such a relic gravitational background radiation can open a new window on the physics at the high scales, even if supersymmetry is broken well above the electroweak scale.

astro-ph.CO↗

arXiv2009

Inflation, baryogenesis and gravitino dark matter at ultra low reheat temperatures

It is quite possible that the reheat temperature of the universe is extremely low close to the scale of Big Bang nucleosynthesis, i.e. $T_{R}\sim 1-10$ MeV. At such low reheat temperatures generating matter anti-matter asymmetry and synthesizing dark matter particles are challenging issues which need to be addressed within a framework of beyond the Standard Model physics. In this paper we point out that a successful cosmology can emerge naturally provided the R-parity violating interactions are responsible for the excess in baryons over anti-baryons and at the same time they can explain the longevity of dark matter with the right abundance.

hep-ph↗

arXiv2009

Newton's constant in f(R,R_{μν}R^{μν},\Box R) theories of gravity and constraints from BBN

We consider corrections to the Einstein-Hilbert action which contain both higher order and nonlocal terms. We derive an effective Newtonian gravitational constant applicable at the weak field limit and use the primordial nucleosynthesis (BBN) bound and the local gravity constraints on $G_{eff}$ in order to test the viability of several cases of our general Lagrangian. We will also provide a BBN constrain on the $\Box R$ gravitational correction.

astro-ph.CO↗

arXiv2008

Gravitational waves from fragmentation of a primordial scalar condensate into Q-balls

A generic consequence of supersymmetry is formation of a scalar condensate along the flat directions of the potential at the end of cosmological inflation. This condensate is usually unstable, and it can fragment into non-topological solitons, Q-balls. The gravitational waves produced by the fragmentation can be detected by Laser Interferometer Space Antenna (LISA), Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), and Big Bang Observer (BBO), which can offer an important window on the early universe and the physics at some very high energy scales.

astro-ph↗

arXiv2008

Attraction towards an inflection point inflation

Many models of high energy physics possess metastable vacua. It is conceivable that the universe can get trapped in such a false vacuum, irrespective of its origin and prior history, at an earlier stage during its evolution. The ensuing false vacuum inflation results in a cold and empty universe and has a generic graceful exit problem. We show that an inflection point inflation along the flat directions of the Minimal Supersymmetric Standard Model (MSSM) can resolve this graceful exit problem by inflating the bubble which nucleate out of a false vacuum. The important point is that the initial condition for an MSSM inflation can be naturally realized, due to an attractor behavior towards the inflection point. We investigate these issues in detail and also present an example where metastable vacua, hence the false vacuum inflation, can happen within the MSSM.

hep-ph↗

arXiv2008

Affleck-Dine condensate, late thermalization and the gravitino problem

In this clarifying note we discuss the late decay of an Affleck-Dine condensate by providing a no-go theorem that attributes to conserved global charges which are identified by the net particle number in fields which are included in the flat direction(s). For a rotating condensate, this implies that: (1) the net baryon/lepton number density stored in the condensate is always conserved, and (2) the total particle number density in the condensate cannot decrease. This reiterates that, irrespective of possible non-perturbative particle production due to $D$-terms in a multiple flat direction case, the prime decay mode of an Affleck-Dine condensate will be perturbative as originally envisaged. As a result, cosmological consequences of flat directions such as delayed thermalization as a novel solution to the gravitino overproduction problem will remain virtually intact.

hep-ph↗

arXiv2008

Large tensor-to-scalar ratio and low scale inflation

It is plausible that the scalar density perturbations are created by a relatively low scale model of inflation which predicts the CMB anisotropy and excites Standard Model baryon and cold dark matter, but negligible gravity waves. Nevertheless a significantly large tensor perturbations can be observed if there exists a prior phase of high scale inflation separated by a matter or radiation dominated epoch. In this paper we provide a simple example when the gravity waves generated at high scales trickle through the horizon of the second phase of inflation and leave a distinct imprint in the spectrum of the tensor modes. For a high scale inflation occurring at $H\sim 10^{13}$ GeV while the second phase of inflation happening at $H\sim 1$ GeV, the largest tensor to scalar ratio is bounded by $r_{\rm observed}\leq0.8$.

astro-ph↗

arXiv2008

Emergence of a Big Bang singularity in an exact string background

The origin of Big Bang singularity in 3+1 dimensions can be understood in an exact string theory background obtained by an analytic continuation of a cigar like geometry with a nontrivial dilaton. In a T-dual conformal field theory picture there exists a closed string tachyon potential which excises the singular space-time of a strongly coupled regime to ensure that a higher dimensional universe has no curvature singularity. However in 3+1 dimensions the universe exhibits all the pathology of a standard Big Bang cosmology. The emergence of a singularity now owes to a higher dimensional orbifold singularity which does not have a curvature singularity in higher dimensions, suggesting that close to the compactification scale an effective description of 3+1 dimensions breaks down and bouncing universe emerges in 5 and higher dimensions.

hep-th↗

arXiv2007

Reheating in supersymmetric high scale inflation

Motivated by Refs \cite{am1,am2}, we analyze how the inflaton decay reheats the Universe within supersymmetry. In a non-supersymmetric case the inflaton usually decays via preheating unless its couplings to other fields are very small. Naively one would expect that supersymmetry enhances bosonic preheating as it introduces new scalars such as squarks and sleptons. On the contrary, we point out that preheating is unlikely within supersymmetry. The reason is that flat directions in the scalar potential, classified by gauge invariant combinations of slepton and squark fields, are generically displaced towards a large vacuum expectation value (VEV) in the early Universe. They induce supersymmetry preserving masses to the inflaton decay products through the Standard Model Yukawa couplings, which kinematically blocks preheating for VEVs $> 10^{13}$ GeV. The decay will become allowed only after the flat directions start oscillating, and once the flat direction VEV is sufficiently redshifted. For models with weak scale supersymmetry, this generically happens at a Hubble expansion rate: $H \simeq (10^{-3}-10^{-1}) {\rm TeV}$, at which time the inflaton decays in the perturbative regime. This is to our knowledge first analysis where the inflaton decay to the Standard Model particles is treated properly within supersymmetry. There are number of important consequences: no overproduction of dangerous supersymmetric relics (particularly gravitinos), no resonant excitation of superheavy dark matter, and no non-thermal leptogenesis through non-perturbative creation of the right-handed (s)neutrinos. Finally supersymmetric flat directions can even spoil hybrid inflation all together by not allowing the auxiliary field become tachyonic.

hep-ph↗

arXiv2007

Unifying inflation and dark matter with neutrino masses

We propose a simple model where a {\it gauge invariant inflaton} is responsible for cosmic inflation and generates the seed for structure formation, while its relic {\it thermal} abundance explains the missing matter of the universe in the form of cold dark matter. The inflaton self-coupling also explains the observed neutrino masses. All the virtues can be attained in a minimal extension of the Standard Model gauge group around the TeV scale. We can also unveil these properties of an inflaton in forthcoming space and ground based experiments.

hep-ph↗

arXiv2007

MSSM flat direction inflation: slow roll, stability, fine tunning and reheating

We consider low scale slow roll inflation driven by the gauge invariant flat directions {\bf udd} and {\bf LLe} of the Minimally Supersymmetric Standard Model at the vicinity of a saddle point of the scalar potential. We study the stability of saddle point and the slow roll regime by considering radiative and supergravity corrections. The latter are found to be harmless, but the former require a modest finetuning of the saddle point condition. We show that while the inflaton decays almost instantly, full thermalization occurs late, typically at a temperature $T\approx 10^{7}$ GeV, so that there is no gravitino problem. We also compute the renormalization group running of the inflaton mass and relate it to slepton masses that may be within the reach of LHC and could be precisely determined in a future Linear Collider experiment.

hep-ph↗

arXiv2007

A-term inflation and the smallness of the neutrino masses

The smallness of the neutrino masses may be related to inflation. The minimal supersymmetric Standard Model (MSSM) with small Dirac neutrino masses already has all the necessary ingredients for a successful inflation. In this model the inflaton is a gauge-invariant combination of the right-handed sneutrino, the slepton, and the Higgs field, which generate a flat direction suitable for inflation if the Yukawa coupling is small enough. In a class of models, the observed microwave background anisotropy and the tilted power spectrum are related to the neutrino masses.

hep-ph↗