arXiv subjects

Rouzbeh Allahverdi

Publications and source records attributed to Rouzbeh Allahverdi.

At least 55 records · Page 3Linked to original sources

arXiv2011

Non-perturbative production of matter and rapid thermalization after MSSM inflation

A {\it gauge invariant} combination of LLe {\it sleptons} within the Minimal Supersymmetric Standard Model is one of the few inflaton candidates that can naturally explain population of the observable sector and creation of matter after inflation. After the end of inflation, the inflaton oscillates coherently about the minimum of its potential, which is a point of {\it enhanced gauged symmetry}. This results in bursts of non-perturbative production of the gauge/gaugino and (s)lepton quanta. The subsequent decay of these quanta is very fast and leads to an extremely efficient transfer of the inflaton energy to (s)quarks via {\it instant} preheating. Around 20% of the inflaton energy density is drained during every inflaton oscillation. However, all of the Standard Model degrees of freedom (and their supersymmetric partners) {\it do not} thermalize immediately, since the large inflaton vacuum expectation value breaks the electroweak symmetry. After about 100 oscillations -- albeit within one Hubble time -- the amplitude of inflaton oscillations becomes sufficiently small, and all of the degrees of freedom will thermalize. This provides by far the most efficient reheating of the universe with the observed degrees of freedom.

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arXiv2010

Cladogenesis: Baryon-Dark Matter Coincidence from Branchings in Moduli Decay

We propose late-time moduli decay as the common origin of baryons and dark matter. The baryon asymmetry is produced from the decay of new TeV scale particles, while dark matter is created from the (chain) decay of R-parity odd particles without undergoing any annihilation. The baryon and dark matter abundances are mainly controlled by the dilution factor from moduli decay, which is typically in the range 10^{-9}-10^{-7}. The exact number densities are determined by simple branching fractions from modulus decay, which are expected to be of similar order in the absence of symmetries. This scenario can naturally lead to the observed baryon asymmetry and, for moderate suppression of the two-body decays of the modulus to R-parity odd particles, can also yield the correct dark matter abundance for a dark matter mass in the (5-500) GeV range.

hep-ph↗

arXiv2010

Schizophrenic Neutrinos and $ν$-less Double Beta Decay

We point out a novel possibility for neutrinos where all neutrino flavors can be part Dirac and part Majorana. Our primary motivation for this model comes from an attempt to use supersymmetric see-saw models to tie inflation, baryon asymmetry of the Universe and dark matter to the neutrino sector. The idea however could stand on its own, with or without supersymmetry. We present a realization of this possibility within an $S_3$ family symmetry for neutrino masses, where we obtain tri-bi-maximal mixing for neutrinos to the leading order. The model predicts that for the case of inverted hierarchy, the lower limit on the neutrino mass measured in neutrinoless double beta decay experiments is about a factor of two larger than the usual case.

hep-ph↗

arXiv2010

Baryogenesis and Late-Decaying Moduli

Late-decaying string moduli dilute the baryon asymmetry of the universe created in any previous era. The reheat temperature for such moduli is below a GeV, thus motivating baryogenesis at very low temperatures. We present an extension of the minimal supersymmetric standard model with TeV-scale colored fields that can yield the correct baryon asymmetry of the universe in this context. Modulus decay, which reheats the universe at a temperature below GeV, produces the visible sector fields and neutralino dark matter in non-thermal fashion. We discuss various possibilities for baryogenesis from TeV scale colored fields and show that they can generate an acceptable baryon asymmetry, while being compatible with phenomenological constraints like neutron-antineutron oscillation.

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arXiv2010

MSSM inflation, dark matter, and the LHC

Inflation can occur near a point of inflection in the potential of flat directions of the Minimal Supersymmetric Standard Model. In this paper we elaborate on the complementarity between the bounds from Cosmic Microwave Background measurements, dark matter and particle physics phenomenology in determining the underlying parameters of MSSM inflation by specializing to the Minimal Supergravity scenario. We show that the future measurements from the Large Hadron Collider in tandem with all these constraints will significantly restrict the allowed parameter space. We also suggest a new perspective on the fine tuning issue of MSSM inflation. With quantum corrections taken into account, the necessary condition between the soft supersymmetry breaking parameters in the inflaton potential can be satisfied at scales of interest without a fine tuning of their boundary values at a high scale. The requirement that this happens at the inflection point determines a dimensionless coupling, which is associated with a non-renormalizable interaction term in the Lagrangian and has no bearing for phenomenology, to very high accuracy.

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arXiv2010

Models of supersymmetric dark matter and their predictions in light of CDMS

We consider the prospects of supersymmetric dark matter in light of the recent results announced by the CDMS experiments. In this paper, we investigate the status of: (i) neutralino dark matter in models of minimal supergravity, (ii) neutralino dark matter in models with nonuniversal Higgs masses, and (iii) sneutrino dark matter in the U(1)_{B-L} extension of the minimal supersymmetric standard model; and discuss the predictions of these models for the LHC, Tevatron, IceCube and PAMELA.

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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↗

arXiv2009

Low-scale Inflation and Supersymmetry Breaking in Racetrack Models

In many moduli stabilization schemes in string theory, the scale of inflation appears to be of the same order as the scale of supersymmetry breaking. For low-scale supersymmetry breaking, therefore, the scale of inflation should also be low, unless this correlation is avoided in specific models. We explore such a low-scale inflationary scenario in a racetrack model with a single modulus in type IIB string theory. Inflation occurs near a point of inflection in the Kähler modulus potential. Obtaining acceptable cosmological density perturbations leads to the introduction of magnetized D7-branes sourcing non-perturbative superpotentials. The gravitino mass, m_{3/2}, is chosen to be around 30 TeV, so that gravitinos that are produced in the inflaton decay do not affect big-bang nucleosynthesis. Supersymmetry is communicated to the visible sector by a mixture of anomaly and modulus mediation. We find that the two sources contribute equally to the gaugino masses, while scalar masses are decided mainly by anomaly contribution. This happens as a result of the low scale of inflation and can be probed at the LHC.

hep-th↗

arXiv2009

Sneutrino dark matter in light of PAMELA

In the U(1)_{B-L} extension of the minimal supersymmetric standard model the right-handed sneutrino is a natural candidate for thermal dark matter. Sneutrino annihilation at the present time can be considerably enhanced due to the exchange of the lightest field in the Higgs sector that breaks U(1)_{B-L}. The annihilation mainly produces taus (or muons) by the virtue of B-L charge assignments. A sneutrino mass of 1-2 TeV provides a good fit to the PAMELA and is compatible with the latest results from the FERMI experiment. In addition, the sneutrino-nucleon elastic scattering cross section is within the reach of the upcoming and future direct detection experiments.

hep-ph↗

arXiv2009

Prospects for Indirect Detection of Sneutrino Dark Matter with IceCube

We investigate the prospects for indirect detection of right-handed sneutrino dark matter at the IceCube neutrino telescope in a $U(1)_{B-L}$ extension of the MSSM. The capture and annihilation of sneutrinos inside the Sun reach equilibrium, and the flux of produced neutrinos is governed by the sneutrino-proton elastic scattering cross section, which has an upper bound of $8 \times 10^{-9}$ pb from the $Z^{\prime}$ mass limits in the $B-L$ model. Despite the absence of any spin-dependent contribution, the muon event rates predicted by this model can be detected at IceCube since sneutrinos mainly annihilate into leptonic final states by virtue of the fermion $B-L$ charges. These subsequently decay to neutrinos with 100% efficiency. The Earth muon event rates are too small to be detected for the standard halo model irrespective of an enhanced sneutrino annihilation cross section that can explain the recent PAMELA data. For modified velocity distributions, the Earth muon events increase substantially and can be greater than the IceCube detection threshold of 12 events $\mathrm{km}^{-2}$ $\mathrm{yr}^{-1}$. However, this only leads to a mild increase of about 30% for the Sun muon events. The number of muon events from the Sun can be as large as roughly 100 events $\mathrm{km}^{-2}$ $\mathrm{yr}^{-1}$ for this model.

hep-ph↗

arXiv2009

Sneutrino Dark Matter and the Observed Anomalies in Cosmic Rays

We revisit sneutrino dark matter in light of the recent results from the PAMELA and ATIC experiments. In the U(1)_B-L extension of the minimal supersymmetric standard model the right-handed sneutrino is a natural candidate for thermal dark matter. Sneutrino annihilation at the present time can be considerably enhanced due to the exchange of the lightest field in the Higgs sector that breaks U(1)_B-L. The annihilation mainly produces taus (or muons) by the virtue of B-L charges. A sneutrino mass in the 1-2 TeV range provides a good fit to the PAMELA data and a reasonable fit to the ATIC data. Within this mass range the sneutrino-nucleon elastic scattering cross section is 10^(-11) - 10^(-9) pb, which might be probed by upcoming and future direct detection experiments. In addition, if (at least) one of the neutrinos is dominantly a Dirac fermion, the sneutrino can provide a unified picture of dark matter and inflation.

hep-ph↗

arXiv2009

Unifying inflation and dark matter

We present a simple model where a scalar field is responsible for cosmic inflation and generates the seed for structure formation, while its thermal relic abundance explains dark matter in the universe. 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 in the forthcoming ground based experiments.

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arXiv2008

Inflation and The Minimal Supersymmetric Standard Model

There is strong evidence from cosmological data that the universe underwent an epoch of superluminal expansion called inflation. A satisfactory embedding of inflation in fundamental physics has been an outstanding problem at the interface of cosmology and high energy physics. We show how inflation can be realized within the Minimal Supersymmetric Standard Model (MSSM). The inflaton candidates are two specific combinations of supersymmetric partners of quarks and leptons. MSSM inflation occurs at a low scale and generates perturbations in the range experimentally allowed by the latest data from Wilkinson Microwave Anisotropy Probe (WMAP). The parameter space for inflation is compatible with supersymmetric dark matter, and the Large Hadron Collider (LHC) is capable of discovering the inflaton candidates in the allowed regions of parameter space.

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arXiv2008

A Supersymmetric B-L Dark Matter Model and the Observed Anomalies in the Cosmic Rays

We propose a simple model of supersymmetric dark matter that can explain recent results from PAMELA and ATIC experiments. It is based on a U(1)_B-L extension of the minimal supersymmetric standard model. The dark matter particle is a linear combination of the U(1)_B-L gaugino and Higgsino partners of Higgs fields that break the B-L around one TeV. The dominant mode of dark matter annihilation is to the lightest of the new Higgs fields, which has a mass in the GeV range, and its subsequent decay mainly produces taus or muons by the virtue of B-L charges. This light Higgs also results in Sommerfeld enhancement of the dark matter annihilation cross section, which can be >~ 10^3. For a dark matter mass in the 1-2 TeV range, the model provides a good fit to the PAMELA data and a reasonable fit to the ATIC data. We also briefly discuss the prospects of this model for direct detection experiments and the LHC.

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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↗

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.

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