Low Reheat Temperature Research Articles

Multi-component Dark Matter and small scale structure formation

We consider the evolution of non-thermal dark matter perturbations in models which contain both Weakly Interacting Massive Particles (WIMPs) and axions. Using constraints from existing observations we examine the percentage of WIMPs and axions that may comprise the cosmological dark matter budget in models with an Early Matter Dominated Epoch (EMDE) — where entropy production is important. After carefully tracking the thermal evolution of the various species by solving the Boltzmann equations, we consider the enhancement of perturbations that may have led to early structure formation for axions and WIMPs. We investigate the impact of enhanced perturbations on the parameter space of both species, after imposing existing constraints from indirect detection experiments. Given these constraints we establish the feasibility of axions to form miniclusters in the early universe in EMDEs for a given percentage of allowed WIMPs. We find that EMDEs with low reheat temperatures near the BBN limit are preferred for axion minicluster formation. When the EMDE is caused by string moduli, the WIMP contribution to the relic density is set by the moduli branching to dark matter at the level of ≲ O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\mathcal{O} $$\\end{document}(10−4).

Smooth hybrid inflation with low reheat temperature and observable gravity waves in SU(5) × U(1)χ super-GUT

We realize smooth hybrid inflation in the framework of supersymmetric SU(5) × U(1)χ ⊂ SO(10) model which provides a natural solution to the monopole problem appearing in the spontaneous symmetry breaking of SU(5). The breaking of U(1)χ symmetry leaves a residual discrete Z 2 symmetry, that serves as the MSSM matter parity, realizing the possibility of the lightest supersymmetric particle as a cold dark matter candidate. The d = 5 proton lifetime for the decay p ⟶ K +ν̅, mediated by color-triplet Higgsinos is found to satisfy current experimental bounds if split-high scale SUSY scenario is employed. We show that with minimal Kähler potential, the soft supersymmetry breaking terms play a vital rôle in bringing the scalar spectral index ns within the Planck's latest bounds. In a minimal Kähler potential setup, small values of tensor-to-scalar ratio r ≲ 3.5 × 10-7 are obtained, whereas the gravitino mass turns out to be in the range that favors PeV scale SUSY but is not sufficiently high to avoid the d = 5 proton decay. A non-minimal Kähler potential including higher order corrections is required to realize successful inflation with central value of scalar spectral index ns = 0.9655, large tensor modes r ≲ 0.056 and a low reheat temperature (3 × 106 ≲ Tr ≲ 6.5 × 107) GeV consistent with leptogenesis and baryogenesis.

Dark matter, dark radiation and gravitational waves from mirror Higgs parity

An exact parity replicates the Standard Model giving a Mirror Standard Model, SM ↔ SM′. This “Higgs Parity” and the mirror electroweak symmetry are spontaneously broken by the mirror Higgs, 〈H′〉 = v′ ≫ 〈H〉, yielding the Standard Model Higgs as a Pseudo-Nambu-Goldstone Boson of an approximate SU (4) symmetry, with a quartic coupling λSM(v′) ∼ 10−3. Mirror electromagnetism is unbroken and dark matter is composed of e′ and {overline{e}}^{prime } . Direct detection may be possible via the kinetic mixing portal, and in unified theories this rate is correlated with the proton decay rate. With a high reheat temperature after inflation, the et dark matter abundance is determined by freeze-out followed by dilution from decays of mirror neutrinos, ν′→ ℓH . Remarkably, this requires v′∼ (108–1010) GeV, predicting a Higgs mass of 123 ± 3 GeV at 1σ and a Standard Model neutrino mass of (10−2–10−1) eV, consistent with observed neutrino masses. The mirror QCD sector exhibits a first order phase transition producing gravitational waves that may be detected by future observations. Mirror glueballs decay to mirror photons giving dark radiation with ∆Neff∼ 0.03–0.4. With a low reheat temperature after inflation, the e′ dark matter abundance is determined by freeze-in from the SM sector by either the Higgs or kinetic mixing portal.

Dark matter and naturalness

The Standard Model of particle physics is governed by Poincaré symmetry, while all other symmetries, exact or approximate, are essentially dictated by theoretical consistency with the particle spectrum. On the other hand, many models of dark matter exist that rely upon the addition of new added global symmetries in order to stabilize the dark matter particle and/or achieve the correct abundance. In this work we begin a systematic exploration into truly natural models of dark matter, organized by only relativity and quantum mechanics, without the appeal to any additional global symmetries, no fine-tuning, and no small parameters. We begin by reviewing how singlet dark sectors based on spin 0 or spin frac{1}{2} should readily decay, while pure strongly coupled spin 1 models have an overabun-dance problem. This inevitably leads us to construct chiral models with spin frac{1}{2} particles charged under confining spin 1 particles. This leads to stable dark matter candidates that are analogs of baryons, with a confinement scale that can be naturally \U0001d4aa(100)TeV. This leads to the right freeze-out abundance by annihilating into massless unconfined dark fermions. The minimal model involves a dark copy of SU(3) × SU(2) with 1 generation of chiral dark quarks and leptons. The presence of massless dark leptons can potentially give rise to a somewhat large value of ∆Neff during BBN. In order to not upset BBN one may either appeal to a large number of heavy degrees of freedom beyond the Standard Model, or to assume the dark sector has a lower reheat temperature than the visible sector, which is also natural in this framework. This reasoning provides a robust set of dark matter models that are entirely natural. Some are concrete realizations of the nightmare scenario in which dark matter may be very difficult to detect, which may impact future search techniques.

The Higgs boson can delay reheating after inflation

The Standard Model Higgs boson, which has previously been shown to develop an effective vacuum expectation value during inflation, can give rise to large particle masses during inflation and reheating, leading to temporary blocking of the reheating process and a lower reheat temperature after inflation. We study the effects on the multiple stages of reheating: resonant particle production (preheating) as well as perturbative decays from coherent oscillations of the inflaton field. Specifically, we study both the cases of the inflaton coupling to Standard Model fermions through Yukawa interactions as well as to Abelian gauge fields through a Chern-Simons term. We find that, in the case of perturbative inflaton decay to SM fermions, reheating can be delayed due to Higgs blocking and the reheat temperature can decrease by up to an order of magnitude. In the case of gauge-reheating, Higgs-generated masses of the gauge fields can suppress preheating even for large inflaton-gauge couplings. In extreme cases, preheating can be shut down completely and must be substituted by perturbative decay as the dominant reheating channel. Finally, we discuss the distribution of reheat temperatures in different Hubble patches, arising from the stochastic nature of the Higgs VEV during inflation and its implications for the generation of both adiabatic and isocurvature fluctuations.

μ -hybrid inflation with low reheat temperature and observable gravity waves

In $\mu$-hybrid inflation a nonzero inflaton vacuum expectation value induced by supersymmetry breaking is proportional to the gravitino mass $m_{3/2}$, which can be exploited to resolve the minimal supersymmetric standard model $\mu$ problem. We show how this scenario can be successfully implemented with $m_{3/2} \sim 1-100$ TeV and reheat temperature as low as $10^6$ GeV by employing a minimal renormalizable superpotential coupled with a well defined non-minimal K\"ahler potential. The tensor-to-scalar ratio $r$, a canonical measure of primordial gravity waves in most cases is less than or of the order of $10^{-6}-10^{-3}$.

Gravitino production in a thermal Universe revisited

We study the production of spin 1/2 gravitinos in a thermal Universe. Taking into account supersymmetry breaking due to the finite thermal energy density of the Universe, there is a large enhancement in the cross section of production of these gravitino states. We consider gravitinos with zero temperature masses of 0.1 eV, 1 keV, 100 GeV and 30 TeV as representative of gauge mediated, gravity mediated and anomaly mediated supersymmetry breaking scenarios. We find that the abundance of gravitinos produced in the early Universe is very high for gravitinos of mass 1 keV and 100 GeV. The gravitino abundances can be sufficiently suppressed if the reheat temperature is less than 100 GeV and 4×104GeV respectively. However such low reheat temperatures will rule out many models of baryogenesis including those via leptogenesis.

Assessment of the potential for conversion of TP-108 boilers to firing natural gas and fuel oil

TP-108 boilers were initially designed to burn milled peat. In the 1980s, they were reconstructed for conversion to burning natural gas as well. However, operation of these boilers revealed problems due to low reheat temperature and great air inleakage in the furnace. The initial design of the boiler and its subsequent reconstruction are described in the paper. Measures are presented for further modernization of TP-108 boilers to eliminate the above-mentioned problems and enable natural gas or fuel oil only to be burned in them. Thermal design calculations made using a specially developed adapted model (AM) suggest that replacement of the existing burners with new oil/gas burners, installation of steam-to-steam heat exchangers (SSHE), and sealing of the boiler gas path to make it gas tight will allow the parameters typical of gas-and-oil fired boilers to be attained. It is demonstrated that SSHEs can yield the design secondary steam reheat temperature, although this solution is not typical for natural circulation boilers with steam reheat. The boiler equipped with SSHEs can operate on fuel oil or natural gas with flue gas recirculation or without it. Moreover, operation of the boiler with flue gas recirculation to the air duct in combination with staged combustion enables the required environmental indicators to be attained.

Natural inflation from 5D SUGRA and low reheat temperature

Motivated by recent cosmological observations of a possibly unsuppressed primordial tensor component r of inflationary perturbations, we reanalyze in detail the 5D conformal SUGRA originated natural inflation model of Ref. [1]. The model is a supersymmetric variant of 5D extranatural inflation, also based on a shift symmetry, and leads to the potential of natural inflation. Coupling the bulk fields generating the inflaton potential via a gauge coupling to the inflaton with brane SM states we necessarily obtain a very slow gauge inflaton decay rate and a very low reheating temperature Tr≲O(100) GeV. Analysis of the required number of e-foldings (from the CMB observations) leads to values of ns in the lower range of present Planck 2015 results. Some related theoretical issues of the construction, along with phenomenological and cosmological implications, are also discussed.

Study of the Energy Consumption Characteristic of a 1000MW Ultra-Supercritical Unit

A 1000MW ultra-supercritical unit was studied to gain the energy consumption characteristics by means of thermodynamic analysis. Comparing with the designed conditions, the power generation efficiency under real operation is much less; especially under 50% and 100% rated loads. The higher superheated steam temperature and lower reheat temperature were found to explain that. At the real running, the higher superheated steam temperature induced more attemperation water, while reheat temperature lower than the designed point would decrease the power output. Aiming at solving issues about temperature control in unit operation, several details could be paid extra attention to. For instance, attemperating water comes from outlet of the high-pressure heaters would have a much slighter influence on generating efficiency.

Gravitino dark matter and neutrino masses with bilinearR-parity violation

Bilinear R-parity violation provides an attractive origin for neutrino masses and mixings. In such schemes the gravitino is a viable decaying dark matter particle whose R-parity violating decays lead to monochromatic photons with rates accessible to astrophysical observations. We determine the parameter region allowed by gamma-ray line searches, dark matter relic abundance and neutrino oscillation data, obtaining a limit on the gravitino mass $m_{\tilde G} \lsim$ 1-10 GeV corresponding to a relatively low reheat temperature $T_R \lsim$ few $\times 10^7-10^8$ GeV. Neutrino mass and mixing parameters may be reconstructed at accelerator experiments like the Large Hadron Collider.

Reheating effects in the matter power spectrum and implications for substructure

The thermal and expansion history of the Universe before big bang nucleosynthesis is unknown. We investigate the evolution of cosmological perturbations through the transition from an early matter era to radiation domination. We treat reheating as the perturbative decay of an oscillating scalar field into relativistic plasma and cold dark matter. After reheating, we find that subhorizon perturbations in the decay-produced dark matter density are significantly enhanced, while subhorizon radiation perturbations are instead suppressed. If dark matter originates in the radiation bath after reheating, this suppression may be the primary cutoff in the matter power spectrum. Conversely, for dark matter produced nonthermally from scalar decay, enhanced perturbations can drive structure formation during the cosmic dark ages and dramatically increase the abundance of compact substructures. For low reheat temperatures, we find that as much as 50% of all dark matter is in microhalos with M > 0.1 Earth masses at z=100, compared to a fraction of 1e-10 in the standard case. In this scenario, ultradense substructures may constitute a large fraction of dark matter in galaxies today.

Collapse of small-scale density perturbations during preheating in single field inflation

After cosmic inflation and before the transition to radiation domination, the cosmic energy density may have been dominated during an extended period by an oscillating massive scalar condensate. We show that during this period, sub-Hubble scale perturbations are subject to a metric preheating instability in the narrow resonance regime. We analyze in detail both, quadratic and quartic potentials. The instability leads to the growth of density perturbations which in many cases become non-linear already before the beginning of a radiation dominated Universe. This is particularly the case when requiring a phenomenologically preferred low reheat temperature. These early structures may lead to the emission of gravitational waves and the production of primordial black holes.

Inflation, baryogenesis, and gravitino dark matter at ultralow 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. TR∼1–10 MeV. At such low reheat temperatures generating matter, antimatter 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 antibaryons and at the same time they can explain the longevity of dark matter with the right abundance.

Perturbative reheating and gravitino production in inflationary models

The low reheat temperature at the end of inflation from the gravitino bound constrains the creation of heavy Majorana neutrinos associated with models of leptogenesis. However, a detailed view of the reheating of the Universe at the end of inflation implies that the maximum temperature during reheating, ${T}_{\mathrm{max}}$, can be orders of magnitude higher than the final reheat temperature. This then allows for the production of the heavy Majorana neutrinos needed for leptogenesis. We carry out the complementary calculation of the gravitino production during reheating and its dependence on ${T}_{\mathrm{max}}$. We find that the gravitino abundance generated during reheating for a quartic potential is comparable to the standard estimate of the abundance generated after reheating and study its consequences for leptogenesis.

GRAVITINO PRODUCTION IN AN INFLATIONARY UNIVERSE AND IMPLICATIONS FOR LEPTOGENESIS

Models of leptogenesis are constrained by the low reheat temperature at the end of reheating associated with the gravitino bound. However, a detailed view of reheating, in which the maximum temperature during reheating, T max , can be orders of magnitude higher than the reheat temperature, allows for the production of heavy Majorana neutrinos needed for leptogenesis. But then one must also consider the possibility of enhanced gravitino production in such scenarios. In this paper we consider gravitino production during reheating, its dependence on T max , and its relevance for leptogenesis. Earlier analytical studies of the gravitino abundance have only considered gravitino production in the post-reheating radiation dominated era. We find that the gravitino abundance generated during reheating is comparable to that generated after reheating. This lowers the upper bound on the reheat temperature by a factor of 4/3.

Anatomy ofFD-term hybrid inflation

We analyze the cosmological implications of F-term hybrid inflation with a subdominant Fayet--Iliopoulos D-term whose presence explicitly breaks a D-parity in the inflaton-waterfall sector. This scenario of inflation, which is called F_D-term hybrid model for brevity, can naturally predict lepton number violation at the electroweak scale, by tying the mu-parameter of the MSSM to an SO(3)-symmetric Majorana mass m_N, via the vacuum expectation value of the inflaton field. We show how a negative Hubble-induced mass term in a next-to-minimal extension of supergravity helps to accommodate the present CMB data and considerably weaken the strict constraints on the theoretical parameters, resulting from cosmic string effects on the power spectrum P_R. The usual gravitino overabundance constraint may be significantly relaxed in this model, once the enormous entropy release from the late decays of the ultraheavy waterfall gauge particles is properly considered. As the Universe enters a second thermalization phase involving a very low reheat temperature, which might be as low as about 0.3 TeV, thermal electroweak-scale resonant leptogenesis provides a viable mechanism for successful baryogenesis, while thermal right-handed sneutrinos emerge as new possible candidates for solving the cold dark matter problem. In addition, we discuss grand unified theory realizations of F_D-term hybrid inflation devoid of cosmic strings and monopoles, based on the complete breaking of an SU(2) subgroup. The F_D-term hybrid model offers rich particle-physics phenomenology, which could be probed at high-energy colliders, as well as in low-energy experiments of lepton flavour or number violation.

Supersymmetric thermalization and quasi-thermal Universe: consequences for gravitinosand leptogenesis

Motivated by our earlier paper [Allahverdi R and Mazumdar A, Quasi-thermal universe andits implications for gravitino production, baryogenesis and dark matter, 2005 Preprinthep-ph/0505050], we discuss how the infamous gravitino problem has a natural built-insolution within supersymmetry. Supersymmetry allows a large number of flatdirections made up of gauge-invariant combinations of squarks and sleptons. Out ofmany, at least one generically obtains a large vacuum expectation value duringinflation. Gauge bosons and gauginos then obtain large masses by virtue of the Higgsmechanism. This makes the rate of thermalization after the end of inflation very smalland as a result the Universe enters a quasi-thermal phase after the inflaton hascompletely decayed. A full thermal equilibrium is generically established much later onwhen the flat direction expectation value has substantially decreased. This resultsin low reheat temperatures, i.e., , which are compatible with the stringent bounds arising from the big bangnucleosynthesis. There are two very important implications: the production ofgravitinos and generation of a baryonic asymmetry via leptogenesis during thequasi-thermal phase. In both the cases the abundances depend not only on an effectivetemperature of the quasi-thermal phase (which could be higher, i.e., ), but also on the state of equilibrium in the reheat plasma. We show that there is no‘thermal gravitino problem’ at all within supersymmetry and we stress the need for a newparadigm based on a ‘quasi-thermal leptogenesis’, because in the bulk of theparameter space the old thermal leptogenesis cannot account for the observed baryonasymmetry.

Sneutrino hybrid inflation in supergravity

We propose a hybrid inflation scenario in which the singlet sneutrino, the superpartner of the right-handed neutrino, plays the role of the inflaton. We study a minimal model of sneutrino hybrid inflation in supergravity, where we find a spectral index ${n}_{\mathrm{s}}\ensuremath{\approx}1+2\ensuremath{\gamma}$ with $|\ensuremath{\gamma}|\ensuremath{\lesssim}0.02$, and predict a running spectral index $|\mathrm{d}{n}_{\mathrm{s}}/\mathrm{d}\mathrm{ln}k|\ensuremath{\ll}|\ensuremath{\gamma}|$ and a tensor-to-scalar ratio $r\ensuremath{\ll}{\ensuremath{\gamma}}^{2}$ for field values well below the Planck scale. In our scenario, the baryon asymmetry of our universe can be explained via nonthermal leptogenesis and a low reheat temperature ${T}_{\mathrm{RH}}\ensuremath{\approx}{10}^{6}$ GeV can be realized.

Sleptogenesis

We propose that the observed baryon asymmetry of the Universe can naturally arise from a net asymmetry generated in the right-handed sneutrino sector at fairly low reheat temperatures. The initial asymmetry in the sneutrino sector is produced from the decay of the inflaton, and is subsequently transferred into the standard model (s)lepton doublet via three-body decay of the sneutrino. Our scenario relies on two main assumptions: a considerable branching ratio for the inflaton decay to the right-handed (s)neutrinos, and Majorana masses which are generated by the Higgs mechanism. The marked feature of this scenario is that the lepton asymmetry is decoupled from the neutrino Dirac Yukawa couplings. We exhibit that our scenario can be embedded within minimal models which seek the origin of a tiny mass for neutrinos.