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Keith A. Olive

Publications and source records attributed to Keith A. Olive.

At least 73 records · Page 4Linked to original sources
arXiv2021

A Minimal Supersymmetric SU(5) Missing-Partner Model

We explore a missing-partner model based on the minimal SU(5) gauge group with $\bf{75}$, $\bf{50}$ and $\bf{\overline{50}}$ Higgs representations, assuming a super-GUT CMSSM scenario in which soft supersymmetry-breaking parameters are universal at some high scale $M_{\rm in}$ above the GUT scale $M_{\rm GUT}$. We identify regions of parameter space that are consistent with the cosmological dark matter density, the measured Higgs mass and the experimental lower limit on $τ(p \to K^+ ν)$. These constraints can be satisfied simultaneously along stop coannihilation strips in the super-GUT CMSSM with $\tan β\sim 3.5 - 5$ where the input gaugino mass $m_{1/2} \sim 15 - 25$~TeV, corresponding after strong renormalization by the large GUT Higgs representations between $M_{\rm in}$ and $M_{\rm GUT}$ to $m_{\rm LSP}, m_{\tilde t_1} \sim 2.5 - 5$~TeV and $m_{\tilde g} \sim 13 - 20$~TeV, with the light-flavor squarks significantly heavier. We find that $τ(p \to K^+ ν) \lesssim 3 \times 10^{34}$~yrs throughout the allowed range of parameter space, within the range of the next generation of searches with the JUNO, DUNE and Hyper-Kamiokande experiments.

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arXiv2021

Non-Oscillatory No-Scale Inflation

We propose a non-oscillatory no-scale supergravity model of inflation (NO-NO inflation) in which the inflaton does not oscillate at the end of the inflationary era. Instead, the Universe is then dominated by the inflaton kinetic energy density (kination). During the transition from inflation to kination, the Universe preheats instantly through a coupling to Higgs-like fields. These rapidly annihilate and scatter into ultra-relativistic matter particles, which subsequently dominate the energy density, and reheating occurs at a temperature far above that of Big Bang Nucleosynthesis. After the electroweak transition, the inflaton enters a tracking phase as in some models of quintessential inflation. The model predictions for cosmic microwave background observables are consistent with Planck 2018 data, and the density of gravitational waves is below the upper bound from Big Bang Nucleosynthesis. We also find that the density of supersymmetric cold dark matter produced by gravitino decay is consistent with Planck 2018 data over the expected range of supersymmetric particle masses.

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arXiv2020

The Impact of New d(p,γ)He3 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 $({\rm D/H})_{\rm BBN+CMB}^{\rm old} = (2.57 \pm 0.13) \times 10^{-5}$ which can be compared with the value determined from quasar absorption systems $({\rm D/H})_{\rm obs} = (2.55 \pm 0.03) \times 10^{-5} $. Using the new rates we find $({\rm D/H})_{\rm BBN+CMB} = (2.51 \pm 0.11) \times 10^{-5}$. We thus find consistency among BBN theory, deuterium and ${}^4$He 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 $N_ν= 2.880 \pm 0.144$ in good agreement with the Standard Model of particle physics. Finally, 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 $d(d,p){}^{3}{\rm H}$.

astro-ph.CO↗
arXiv2020

Low-Energy Probes of No-Scale SU(5) Super-GUTs

We explore the possible values of the $μ\to e γ$ branching ratio, $\text{BR}(μ\rightarrow eγ)$, and the electron dipole moment (eEDM), $d_e$, in no-scale SU(5) super-GUT models with the boundary conditions that soft supersymmetry-breaking matter scalar masses vanish at some high input scale, $M_{\rm in}$, above the GUT scale, $M_{\rm GUT}$. We take into account the constraints from the cosmological cold dark matter density, $Ω_{CDM} h^2$, the Higgs mass, $M_h$, and the experimental lower limit on the lifetime for $p \to K^+ \bar ν$, the dominant proton decay mode in these super-GUT models. Reconciling this limit with $Ω_{CDM} h^2$ and $M_h$ requires the Higgs field responsible for the charge-2/3 quark masses to be twisted, and possibly also that responsible for the charge-1/3 and charged-lepton masses, with model-dependent soft supersymmetry-breaking masses. We consider six possible models for the super-GUT initial conditions, and two possible choices for quark flavor mixing, contrasting their predictions for proton decay with versions of the models in which mixing effects are neglected. We find that $τ\left(p\rightarrow K^+ \barν\right)$ may be accessible to the upcoming Hyper-Kamiokande experiment, whereas all the models predict $\text{BR}(μ\rightarrow eγ)$ and $d_e$ below the current and prospective future experimental sensitivities or both flavor choices, when the dark matter density, Higgs mass and current proton decay constraints are taken into account. However, there are limited regions with one of the flavor choices in two of the models where $μ\to e$ conversion on a heavy nucleus may be observable in the future. Our results indicate that there is no supersymmetric flavor problem in the class of no-scale models we consider.

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arXiv2020

The case for decaying spin-3/2 dark matter

We couple a sterile neutrino sector to a spin-3/2 particle and show that with a Planck reduced coupling, we can obtain a sufficiently long lifetime making the spin-3/2 particle a good dark matter candidate. We show that this dark matter candidate can be produced during inflationary reheating through the scattering of Standard Model particles. The relic abundance as determined by Planck and other experimental measurements is attained for reasonable values of the reheating temperature $T_{\rm RH} \gtrsim 10^{8}$ GeV. We consider two possible gauge invariant couplings to the extended Standard Model. We find a large range of masses are possible which respect the experimental limits on its decay rate. We expect smoking-gun signals in the form of a monochromatic photon with a possible monochromatic neutrino, which can be probed in the near future in IceCube and other indirect detection experiments.

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arXiv2020

Improving Helium Abundance Determinations with Leo P as a Case Study

Currently, the primordial helium abundance is best estimated through spectroscopic observations of H II regions in metal-poor galaxies. However these determinations are limited by several systematic uncertainties which ultimately limit our ability to accurately ascertain the primordial abundance. In this study, we improve the methodologies for solving for the reddening, the emission contributions from collisional excitation of the H I atoms, the effects underlying absorption in the H I and He I emission lines, and the treatment of the blended H I and He I emission at $λ$3889 with the aim of lowering the systematic uncertainties in helium abundance determinations. To apply these methods, we have obtained observations of the He I $λ$10830 emission line in the brightest H II region in the extremely metal-poor (3$\%$ Z$_{\odot}$) galaxy Leo P with the LUCI1 instrument on the LBT. We combine this measurement with previous MODS/LBT observations to derive an improved helium abundance. In doing so, our present analysis results in a decrease in the uncertainty in the helium abundance of Leo P by approximately 70%. This result is combined with data from other observations to estimate the primordial helium mass fraction, Y$_{p}$ $=$ 0.2453 $\pm$ 0.0034.

astro-ph.CO↗
arXiv2020

Building Models of Inflation in No-Scale Supergravity

After reviewing the motivations for cosmological inflation formulated in the formalism of supersymmetry, we argue that the appropriate framework is that of no-scale supergravity. We then show how to construct within this framework inflationary models whose predictions for the tilt in the spectrum of scalar perturbations, $n_s$, and the ratio, $r$, of tensor and scalar perturbations coincide with those of the $R + R^2$ model of inflation proposed by Starobinsky. A more detailed study of no-scale supergravity reveals a structure that is closely related to that of $R^2$ modifications of the minimal Einstein-Hilbert action for general relativity, opening avenues for constructing no-scale de Sitter and anti-de Sitter models by combining pairs of Minkowski models, as well as generalizations of the original no-scale Starobinsky models of inflation. We then discuss the phenomenology of no-scale models of inflation, including inflaton decay and reheating, and then the construction of explicit scenarios based on SU(5), SO(10) and string-motivated flipped SU(5)$\times$U(1) GUT models. The latter provides a possible model of almost everything below the Planck scale, including neutrino masses and oscillations, the cosmological baryon asymmetry and cold dark matter, as well as $n_s$ and $r$.

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arXiv2020

Phenomenology and Cosmology of No-Scale Attractor Models of Inflation

We have recently proposed attractor models for modulus fixing, inflation, supersymmetry breaking and dark energy based on no-scale supergravity. In this paper we develop phenomenological and cosmological aspects of these no-scale attractor models that underpin their physical applications. We consider models in which inflation is driven by a modulus field ($T$-type) with supersymmetry broken by a Polonyi field, or a matter field ($ϕ$-type) with supersymmetry broken by the modulus field. We derive the possible patterns of soft supersymmetry-breaking terms, which depend in $T$-type models whether the Polonyi and/or matter fields are twisted or not, and in $ϕ$-type models on whether the inflaton and/or other matter fields are twisted or not. In $ϕ$-type models, we are able to directly relate the scale of supersymmetry breaking to the inflaton mass. We also discuss cosmological constraints from entropy considerations and the density of dark matter on the mechanism for stabilizing the modulus field via higher-order terms in the no-scale Kähler potential.

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arXiv2020

Reheating and Post-inflationary Production of Dark Matter

We perform a systematic analysis of dark matter production during post-inflationary reheating. Following the period of exponential expansion, the inflaton begins a period of damped oscillations as it decays. These oscillations and the evolution of temperature of the thermalized decay products depend on the shape of the inflaton potential $V(Φ)$. We consider potentials of the form $Φ^k$. Standard matter-dominated oscillations occur for $k=2$. In general, the production of dark matter may depend on either (or both) the maximum temperature after inflation, or the reheating temperature, where the latter is defined when the Universe becomes radiation dominated. We show that dark matter production is sensitive to the inflaton potential and depends heavily on the maximum temperature when $k>2$. We also consider the production of dark matter with masses larger than the reheating temperature.

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arXiv2020

$θ$-dependence of light nuclei and nucleosynthesis

We investigate the impact of the QCD vacuum at nonzero $θ$ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the $θ$-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the $θ$-dependence of the nucleon-nucleon interaction using a one-boson-exchange model and compute the properties of the two-nucleon system. Using the universal properties of four-component fermions at large scattering length, we then deduce the binding energies of the three-nucleon and four-nucleon systems. Based on these results, we discuss the implications for primordial abundances of light nuclei, the production of nuclei in stellar environments, and implications for an anthropic view of the universe.

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arXiv2020

Axion Kinetic Misalignment and Parametric Resonance from Inflation

Axion cold dark matter from standard misalignment typically requires a decay constant $f_a~\gtrsim~10^{11}$ GeV. Kinetic misalignment and parametric resonance easily allow lower values of $f_a$ when the radial Peccei-Quinn (PQ) symmetry breaking field takes large initial values. Here, we consider the effects of inflation on kinetic misalignment and parametric resonance. We assume that the initial PQ field value is determined by quantum fluctuations, and is set by the Hubble parameter during inflation, $H_I$, and the PQ field mass. PQ field oscillations begin before or after the completion of reheating after inflation at a temperature $T_R$. We determine the range of $f_a$ and the inflationary parameters $(H_I, T_R)$ consistent with axion dark matter for a quartic potential for the PQ field. We find that $4\times 10^8$ GeV $< f_a < 10^{11}$ GeV can consistently produce axion dark matter. A significant portion of the allowed parameter space predicts rare kaon decays, $K_L \rightarrow (π^0 + \rm{missing \; energy})$, and/or suppression of structure formation on small scales.

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arXiv2020

A Model of Metastable EeV Dark Matter

We propose a model where a long-lived pseudoscalar EeV particle can be produced with sufficient abundance so as to account for the cold dark matter density, despite having a Planck mass suppressed coupling to the thermal bath. Connecting this state to a hidden sterile neutrino sector through derivative couplings, induced by higher dimensional operators, allows one to account for light neutrino masses while having a lifetime that can be much larger than the age of the Universe. Moreover, the same derivative coupling accounts for the production of dark matter in the very first instant of the reheating. Given the sensitivity of the IceCube and ANITA collaborations, we study the possible signatures of such a model in the form of Ultra-High-Energy Cosmic Rays in the neutrino sector, and show that such signals could be detected in the near future.

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arXiv2020

Proton Decay: Flipped vs Unflipped SU(5)

We analyze nucleon decay modes in a no-scale supersymmetric flipped SU(5) GUT model, and contrast them with the predictions for proton decays via dimension-6 operators in a standard unflipped supersymmetric SU(5) GUT model. We find that these GUT models make very different predictions for the ratios $Γ(p \to π^0 μ^+)/Γ(p \to π^0 e^+)$, $Γ(p \to π^+ \barν)/Γ(p \to π^0 e^+)$, $Γ(p \to K^0 e^+)/Γ(p \to π^0 e^+)$ and $Γ(p \to K^0 μ^+)/Γ(p \to π^0 μ^+)$, and that predictions for the ratios $Γ(p \to π^0 μ^+)/Γ(p \to π^0 e^+)$ and $Γ(p \to π^+ \barν)/Γ(p \to π^0 e^+)$ also differ in variants of the flipped SU(5) model with normal- or inverse-ordered light neutrino masses. Upcoming large neutrino experiments may have interesting opportunities to explore both GUT and flavour physics in proton and neutron decays.

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arXiv2019

Supersymmetric Proton Decay Revisited

Encouraged by the advent of a new generation of underground detectors---JUNO, DUNE and Hyper-Kamiokande---that are projected to improve significantly on the present sensitivities to various baryon decay modes, we revisit baryon decay in the minimal supersymmetric SU(5) GUT. We discuss the phenomenological uncertainties associated with hadronic matrix elements and the value of the strong coupling $α_s$---which are the most important---the weak mixing angle $θ_W$, quark masses including one-loop renormalization effects, quark mixing and novel GUT phases that are not visible in electroweak interaction processes. We apply our analysis to a variety of CMSSM, super- and sub-GUT scenarios in which soft supersymmetry-breaking parameters are assumed to be universal at, above and below the GUT scale, respectively. In many cases, we find that the next generation of underground detectors should be able to probe models with sparticle masses that are ${\cal O}(10)$~TeV, beyond the reach of the LHC.

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arXiv2019

Big-Bang Nucleosynthesis After Planck

We assess the status of big-bang nucleosynthesis (BBN) in light of the final Planck data release and other recent developments, and in anticipation of future measurements. Planck data fix the cosmic baryon density to 0.9% precision, and determine the helium abundance and effective number of neutrinos with precision approaching that of astronomical and BBN determinations respectively. In addition, new high-redshift measurements give D/H to better precision than theoretical predictions, and new Li/H data reconfirm the lithium problem. We present new ${}^{7}{\rm Be}(n,p){}^{7}{\rm Li}$ rates using new neutron capture measurements; we have also examined the effect of proposed changes in the $d(p,γ){}^{3}{\rm He}$ rates. Using these results we perform a series of likelihood analyses. We assess BBN/CMB consistency, with attention to how our results depend on the choice of Planck data, as well as how the results depend on the choice of non-BBN, non-Planck data sets. Most importantly the lithium problem remains, and indeed is more acute given the very tight D/H observational constraints; new neutron capture data reveals systematics that somewhat increases uncertainty and thus slightly reduces but does not essentially change the problem. We confirm that $d(p,γ){}^{3}{\rm He}$ theoretical rates brings D/H out of agreement and slightly increases 7Li; new experimental data are needed at BBN energies. Setting the lithium problem aside, we find the effective number of neutrino species at BBN is $N_ν= 2.86 \pm 0.15$. Future CMB Stage-4 measurements promise substantial improvements in BBN parameters: helium abundance determinations will be competitive with the best astronomical determinations, and $N_{\rm eff}$ will approach sensitivities capable of detecting the effects of Standard Model neutrino heating of the primordial plasma. (Abridged)

astro-ph.CO↗
arXiv2019

Inflation and Leptogenesis in High-Scale Supersymmetry

No-scale supergravity provides a successful framework for Starobinsky-like inflation models. Two classes of models can be distinguished depending on the identification of the inflaton with the volume modulus, $T$ (C-models), or a matter-like field, $ϕ$ (WZ-models). When supersymmetry is broken, the inflationary potential may be perturbed, placing restrictions on the form and scale of the supersymmetry breaking sector. We consider both types of inflationary models in the context of high-scale supersymmetry. We further distinguish between models in which the gravitino mass is below and above the inflationary scale. We examine the mass spectra of the inflationary sector. We also consider in detail mechanisms for leptogenesis for each model when a right-handed neutrino sector, used in the seesaw mechanism to generate neutrino masses, is employed. In the case of C-models, reheating occurs via inflaton decay to two Higgs bosons. However, there is a direct decay channel to the lightest right-handed neutrino which leads to non-thermal leptogenesis. In the case of WZ-models, in order to achieve reheating, we associate the matter-like inflaton with one of the right-handed sneutrinos whose decay to the lightest right handed neutrino simultaneously reheats the Universe and generates the baryon asymmetry through leptogenesis.

hep-ph↗
arXiv2019

Superstring-Inspired Particle Cosmology: Inflation, Neutrino Masses, Leptogenesis, Dark Matter & the SUSY Scale

We develop a string-inspired model for particle cosmology, based on a flipped SU(5)$\times$U(1) gauge group formulated in a no-scale supergravity framework. The model realizes Starobinsky-like inflation, which we assume to be followed by strong reheating, with the GUT symmetry being broken subsequently by a light `flaton' field whose decay generates a second stage of reheating. We discuss the production of gravitinos and the non-thermal contribution made by their decays to the density of cold dark matter, which is assumed to be provided by the lightest neutralino. We also discuss the masses of light and heavy neutrinos and leptogenesis. As discussed previously [1], a key rôle is played by a superpotential coupling between the inflaton, matter and GUT Higgs fields, called $λ_6$. We scan over possible values of $λ_6$, exploring the correlations between the possible values of observables. We emphasize that the release of entropy during the GUT transition allows large regions of supersymmetry-breaking parameter space that would otherwise lead to severe overdensity of dark matter. Furthermore, we find that the Big Bang nucleosynthesis lower limit on the reheating temperature of $\sim 1$ MeV restricts the supersymmetry-breaking scale to a range ${\cal O}(10)$ TeV that is consistent with the absence of supersymmetric particles at the LHC.

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