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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
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DOE OSTI2020

Pseudosmooth tribrid inflation in SU(5)

A realistic tribrid model of sneutrino inflation is constructed in an R-symmetric SU(5) grand unified theory (GUT). To avoid the monopole problem, a pseudosmooth inflationary trajectory is generated with the help of an additional Z 5 symmetry which is broken during and after inflation. The predictions of inflationary parameters are made at the central value of the scalar spectral index, n s =0.968. The largest possible value of the tensor to scalar ratio, r ≲ 0.0027, is obtained with sub-Planckian field values (≲m P ). A successful realization of reheating and leptogenesis is achieved by avoiding the gravitino problem with a reheat temperature as low as 10 6 GeV. The predicted range of the gauge symmetry breaking scale, 5 × 10 16 ≲ M/GeV ≲ 5 × 10 17 , turns out to be somewhat larger than the typical GUT scale. Finally, with additional vector-like families, a successful gauge coupling unification is achieved by avoiding the no-go theorem related to R-symmetric SU(5) GUT.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Cosmological dependence of resonantly produced sterile neutrinos

The detection of a sterile neutrino could constitute the first observation of a particle that could have been produced before Big-Bang Nucleosynthesis (BBN), and could provide information about the yet untested pre-BBN era. The cosmological evolution in this era could be drastically different than typically assumed in what constitutes the standard cosmology, as happens in a variety of motivated particle models. In this work we assess the sensitivity to different pre-BBN cosmologies in which entropy is conserved of 0.01 eV to 1 MeV mass sterile neutrinos produced in the early Universe via resonant active-sterile oscillations, which requires a large lepton asymmetry. We identify mass ranges where it is possible to have two populations of the same sterile neutrino, one with a colder and one with a hotter momentum spectra, which is in principle an observable effect. Furthermore, we show the regions in mass and mixing where fully resonant production (i.e. simultaneously coherent and adiabatic) can occur. Here, we find that in several of the cosmologies we consider, including the standard one, for a lepton asymmetry larger than ~10 –4 fully resonantly produced sterile neutrinos in the eV-mass range can evade all cosmological constraints.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2020

Addendum: Cosmological dependence of non-resonantly produced sterile neutrinos

In this addendum to the article JCAP 12 (2019) 047 on the cosmological dependence of non-resonantly produced sterile neutrinos we discuss, using an analytic treatment, the parameter regions of large active-sterile neutrino mixing angles where sterile neutrinos can approach thermalization. We show that these additional considerations affect only large active-sterile neutrino mixing already rejected by different limits. Hence, the allowed sterile neutrino parameter regions are unaffected.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Increasing temperature toward the completion of reheating

Reheating is a process where the energy density of a dominant component of the universe other than radiation, such as a matter component, is transferred into radiation. It is usually assumed that the temperature of the universe decreases due to cosmic expansion even during the reheating process, in which case the maximal temperature of the universe is much higher than the reheat temperature. We point out that the temperature of the universe during reheating may in fact increase in well-motivated scenarios. We derive the necessary conditions for the temperature to increase during reheating and discuss concrete examples involving a scalar field. Here, we comment on implications for particle physics and cosmology due to an increasing temperature during reheating.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Common origin of warm dark matter and dark radiation

We consider a cosmological scenario where a relativistic particle and a stable massive particle are simultaneously produced from the decay of a late-decaying particle after Big-Bang Nucleosynthesis but before matter-radiation equality. The relativistic and massive particles behave as dark radiation and warm dark matter, respectively. Due to a common origin, the warmness and abundances are closely related. We refer to the models that lead to such a scenario as Common Origin of Warm and Relativistic Decay Products (COWaRD). We show that COWaRD predicts a correlation between the amount of dark radiation and suppression of the large scale structure, which can be tested in future precision cosmology observations. Furthermore, we demonstrate that COWaRD is realized, as an example, in a class of supersymmetric axion models and that future observations by the next generation Cosmic Microwave Background, Large Scale Structure, and 21-cm surveys can reveal the structure of the theory.

cosmology of theories beyond the SM↗
DOE OSTI2021

The impact of new d(p,γ)3 rates on Big Bang Nucleosynthesis

We consider the effect on Big Bang Nucleosynthesis (BBN) of new measurements of the d(p,γ) 3 He cross section by the LUNA Collaboration. These have an important effect on the primordial abundance of D/H which is also sensitive to the baryon density at the time of BBN. We have re-evaluated the thermal rate for this reaction, using a world average of cross section data, which we describe with model-independent polynomials; our results are in good agreement with a similar analysis by LUNA. We then perform a full likelihood analysis combining BBN and Planck cosmic microwave background (CMB) likelihood chains using the new rate combined with previous measurements and compare with the results using previous rates. Concordance between BBN and CMB measurements of the anisotropy spectrum using the old rates was excellent. The predicted deuterium abundance at the Planck value of the baryon density was (D/H) BBN+CMB old = (2.57 ± 0.13) × 10 –5 which can be compared with the value determined from quasar absorption systems (D/H) obs = (2.55 ± 0.03) × 10 –5 . Using the new rates we find (D/H) BBN+CMB = (2.51 ± 0.11) × 10 –5 . We thus find consistency among BBN theory, deuterium and 4He observations, and the CMB, when using reaction rates fit in our data-driven approach. We also find that the new reaction data tightens the constraints on the number of relativistic degrees of freedom during BBN, giving the effective number of light neutrino species N ν = 2.880 ± 0.144 in good agreement with the Standard Model of particle physics. Lastly, we note that the observed deuterium abundance continues to be more precise than the BBN+CMB prediction, whose error budget is now dominated by d(d,n) 3 He and d(d,p) 3 H.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Inflaton oscillations and post-inflationary reheating

We analyze in detail the perturbative decay of the inflaton oscillating about a generic form of its potential V(Φ) = Φ k , taking into account the effects of non-instantaneous reheating. We show that evolution of the temperature as a function of the cosmological scale factor depends on the spin statistics of the final state decay products when k > 2. Here, we also include the inflaton-induced mass of the final states leading to either kinematic suppression or enhancement if the final states are fermionic or bosonic respectively. We compute the maximum temperature reached after inflation, the subsequent evolution of the temperature and the final reheat temperature. We apply our results to the computation of the dark matter abundance through thermal scattering during reheating. We also provide an example based on supersymmetry for the coupling of the inflaton to matter.

supersymmetry and cosmology↗
DOE OSTI2021

Large N-ightmare dark matter

A dark QCD sector is a relatively minimal extension of the Standard Model (SM) that admits Dark Matter (DM) candidates, but requires no portal to the visible sector beyond gravitational interactions: a "nightmare scenario" for DM detection. Here, we consider a secluded dark sector containing a single flavor of light, vector-like dark quark gauged under (N). In the large-N limit, this single-flavor theory becomes highly predictive, generating two DM candidates whose masses and dynamics are described by few parameters: a light quark-antiquark bound state, the dark analog of the η' meson, and a heavy bound state of N quarks, the dark analog of the Δ ++ baryon. We show that the latter may freeze-in with an abundance independent of the confinement scale, forming DM-like relics for N ≲ 10, while the former may generate DM via cannibalization and freeze-out. We study the interplay of this two-component DM system, and determine the characteristic ranges of the confinement scale, dark-visible sector temperature ratio, and N that admit non-excluded DM, once effects of self-interaction constraints and bounds on effective degrees of freedom at the BBN and CMB epochs are included.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Possible hints of sterile neutrinos in recent measurements of the Hubble parameter

Local Universe observations find a value of the Hubble constant H 0 that is larger than the value inferred from the Cosmic Microwave Background and other early Universe measurements, assuming known physics and the ΛCDM cosmological model. We show that additional radiation in active neutrinos produced just before Big Bang Nucleosynthesis by an unstable sterile neutrino with mass m s = O(10) MeV can alleviate this discrepancy. Furthermore, the necessary masses and couplings of the sterile neutrino, assuming it mixes primarily with ν τ and/or ν μ neutrinos, are within reach of Super-Kamiokande as well as upcoming laboratory experiments such as NA62 and DUNE.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

On the realization of WIMPflation

In this work, we consider models for inflation with a stable inflation. Reheating is achieved through scattering processes such as ΦΦ → h h, where h is the Standard Model Higgs boson. We consider the reheating process in detail and show that for a relatively large coupling (needed for the late annihilations of the inflation during freeze-out), reheating is almost instantaneous leading to a relatively high reheating temperature. The process ΦΦ ↔ h h brings the inflation back into equilibrium, leading to a well studied scalar singlet dark matter candidate and Higgs portal model. We argue that such models can be derived from no-scale supergravity.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2021

Warming up cold inflation

The axion is a well-motivated candidate for the inflaton, as the radiative corrections that spoil many single-field models are avoided by virtue of its shift symmetry. However, axions generically couple to gauge sectors. As the axion slow-rolls during inflation, this coupling can cause the production of a non-diluting thermal bath, a situation known as “warm inflation”. This thermal bath can dramatically alter inflationary dynamics and observable predictions. In this paper, we demonstrate that a thermal bath can form for a wide variety of initial conditions. Furthermore, we find that axion inflation becomes warm over a large range of couplings, and explicitly map the parameter space for two axion inflation potentials. Finally, we show that in large regions of parameter space, axion inflation models once assumed to be safely “cold” are in fact warm, and must be reevaluated in this context.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Sneutrino tribrid inflation, metastable cosmic strings and gravitational waves

Here, we present a successful realization of sneutrino tribrid inflation model based on a gauged U(1)_B-L extension of Minimal Supersymmetric Standard Model (MSSM). A single interaction term involving the B-L Higgs field and the right-handed neutrinos serves multiple purposes. These include the generation of heavy Majorana masses for the right-handed neutrinos to provide an explanation for the tiny neutrino masses via the seesaw mechanism, a realistic scenario for reheating and non-thermal leptogenesis with a reheat temperature as low as 10 6 GeV, and a successful realization of inflation with right-handed sneutrino as the inflaton. The matter parity which helps avoid rapid proton decay survives as a Z 2 subgroup of a U(1) R-symmetry. Depending on the choice of model parameters yields the following predicted range of the tensor to scalar ratio, 3 x 10 -11 ≲ r≲ 7x 10 -4 (6 x 10 -7 ≲ r ≲ 0.01), and the running of the scalar spectral index, -0.00022 ≲ dn_s/dln k ≲ -0.0026 (-0.00014 ≲ dn_s/dln k ≲ 0.005), along with the B-L breaking scale, 3 x 10 14 ≲ M/ GeV≲ 5 x 10 15 (6 x 10 15 ≲ M/ GeV≲ 2 x 10 16 ), calculated at the central value of the scalar spectral index, n_s =0.966, reported by Planck 2018. The possibility of realizing metastable cosmic strings in a grand unified theory setup is briefly discussed. The metastable cosmic string network admits string tension values in the range 10 -8 ≲ Gμ s ≲ 10 -6 , and predicts a stochastic gravitational wave background lying within the 2-σ bounds of the recent NANOGrav 12.5-yr data.

supersymmetry and cosmology↗
DOE OSTI2021

Comments on axions, domain walls, and cosmic strings

Axions have for some time been considered a plausible candidate for dark matter. They can be produced through misalignment, but it has been argued that when inflation occurs before a Peccei-Quinn transition, appreciable production can result from cosmic strings. This has been the subject of extensive simulations. But there are reasons to be skeptical about the possible role of axion strings. Here, we review and elaborate on these questions, and argue that parametrically strings are already accounted for by the assumption of random misalignment angles. We review and elaborate on these questions, and provide several qualitative arguments that parametrically strings are already accounted for by the assumption of random misalignment angles. The arguments are base on considerations of the collective modes of the string solutions, on computations of axion radiation in particular models, and reviews of simulations.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Exploring the early Universe with Gaia and Theia

It has recently been pointed out that Gaia is capable of detecting a stochastic gravitational wave background in the sensitivity band between the frequency of pulsar timing arrays and LISA. Here, we argue that Gaia and Theia have great potential for early universe cosmology, since such a frequency range is ideal for probing phase transitions in asymmetric dark matter, SIMP and the cosmological QCD transition. Furthermore, there is the potential for detecting primordial black holes in the solar mass range produced during such an early universe transition and distinguish them from those expected from the QCD epoch. Finally, we discuss the potential for Gaia and Theia to probe topological defects and the ability of Gaia to potentially shed light on the recent NANOGrav results.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Preheating in Palatini Higgs inflation on the lattice

We study preheating following Higgs inflation in the Palatini formulation of gravity. We numerically evolve perturbations of the radial mode of the Higgs field and that of three scalars modeling the gauge bosons. We compare the two non-perturbative mechanisms of growth of excitations — parametric resonance and tachyonic instability — and confirm that the latter plays the dominant role. Our results provide further evidence that preheating in Palatini Higgs inflation happens within a single oscillation of the Higgs field about the bottom of its potential, consistent with the approximation of an instantaneous preheating.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Probing physics beyond the standard model: limits from BBN and the CMB independently and combined

We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number N ν of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates d + d → 3 He + n and d + d → 3 H+p. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs N ν and η prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives N ν = 2.898 ± 0.141, resulting in N ν < 3.180 at 2σ. We apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. The strength of the independent BBN and CMB constraints now opens a new window: we can search for limits on potential changes in N ν and/or the baryon-to-photon ratio η between the two epochs. The present data place strong constraints on the allowed changes in N ν between BBN and CMB decoupling; for example, we find -0.708 < N ν CMB - N ν BBN < 0.328 in the case where η and the primordial helium mass fraction Yp are unchanged between the two epochs; we also give limits on the allowed variations in η or in (η, N ν ) jointly. We discuss scenarios in which such changes could occur, and show that BBN+CMB results combine to place important constraints on some early dark energy models to explain the H 0 tension. Looking to the future, we forecast the tightened precision for N ν arising from both CMB Stage 4 measurements as well as improvements in astronomical 4 He measurements. Here, we find that CMB-S4 combined with present BBN and light element observation precision can give σ(N ν ) ≃ 0.03. Such future precision would reveal the expected effect of neutrino heating (N eff -3 = 0.044) of the CMB during BBN, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model. Improved Y p measurements can push this precision even further.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2023

MeV dark matter with MeV dark photons in Abelian kinetic mixing theories

Here we consider the cosmology and phenomenology of a dark photon portal to a simple dark sector consisting of a single, light, fermionic dark matter particle species with mass in the MeV range. We entertain three possible kinetic mixing structures of a new Abelian gauge group U(1) dark with the visible sector through U(1) e.m. , U(1) Y and T[SU(2)_L]. We assume the dark photon to be massive and around the MeV scale, thus close to the mass scale of the dark matter candidate. We compute the dark matter relic density via freeze-out and freeze-in, entertaining the additional possibility of a late inflationary period that could dilute the dark matter yield of heavy candidates, and (ii) additional production modes, for models with under-abundant thermal production. We explore the parameter space compatible with a variety of experimental and astrophysical bounds, and discuss prospects for discovery with new CMB probes and MeV gamma-ray telescopes.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Photons from dark photon solitons via parametric resonance

Wave-like dark matter made of spin-1 particles (dark photons) is expected to form ground state clumps called "vector solitons", which can have different polarizations. Here, in this work, we consider the interaction of dark photons with photons, expressed as dimension-6 operators, and study the electromagnetic radiation that arises from an isolated vector soliton due to parametric resonant amplification of the ambient electromagnetic field. We characterize the directional dependence and polarization of the outgoing radiation, which depends on the operator as well as the polarization state of the underlying vector soliton. We discuss the implications of this radiation for the stability of solitons and as a possible channel for detecting mergers of vector solitons through astrophysical observations.

79 ASTRONOMY AND ASTROPHYSICS↗