arXiv subjects

K. A. Olive

Publications and source records attributed to K. A. Olive.

66 records · Page 4Linked to original sources

arXiv2000

Calculations of Neutralino-Stau Coannihilation Channels and the Cosmologically Relevant Region of MSSM Parameter Space

Assuming that the lightest supersymmetric particle (LSP) is the lightest neutralino, we present a detailed exploration of neutralino-stau coannihilation channels, including analytical expressions and numerical results. We also include neutralino coannihilations with the selectron and smuon. We evaluate the implications of coannihilations for the cosmological relic density of the LSP, which is assumed to be stable, in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which the soft supersymmetry-breaking parameters are universal at the supergravity GUT scale. We evaluate the changes due to coannihilations in the region of the MSSM parameter space that is consistent with the cosmological upper limit on the relic LSP density. In particular, we find that the upper limit on the mass of the neutralino is increased from about 200 GeV to about 600 GeV in the CMSSM, and estimate a qualitatively similar increase for gauginos in the general MSSM.

hep-ph↗

arXiv2000

Exploration of Elastic Scattering Rates for Supersymmetric Dark Matter

We explore the possible cross sections for the elastic scattering of neutralinos chi on nucleons p,n in the minimal supersymmetric extension of the standard model (MSSM). Universality of the soft supersymmetry-breaking scalar masses for the Higgs multiplets is not assumed, but the MSSM parameters are nevertheless required to lead consistently to an electroweak vacuum. We explore systematically the region of MSSM parameter space where LEP and other accelerator constraints are respected, and the relic neutralino density lies in the range 0.1 < Omega_chi h^2 < 0.3 preferred by cosmology. We also discuss models with Omega_chi h^2 < 0.1, in which case we scale the density of supersymmetric dark matter in our galactic halo by Omega_chi h^2 / 0.1, allowing for the possible existence of some complementary form of cold dark matter. We find values of the cross sections that are considerably lower than the present experimental sensitivities. At low neutralino masses, m_chi < 100 GeV, the cross sections may be somewhat higher than in the constrained MSSM with universal soft Higgs masses, though they are generally lower. In the case of large m_chi, the cross sections we find may be considerably larger than in the constrained model, but still well below the present experimental sensitivity.

hep-ph↗

arXiv2000

Single-Brane Cosmological Solutions with a Stable Compact Extra Dimension

We consider 5-dimensional cosmological solutions of a single brane. The correct cosmology on the brane, i.e., governed by the standard 4-dimensional Friedmann equation, and stable compactification of the extra dimension is guaranteed by the existence of a non-vanishing \hat{T}^5_5 which is proportional to the 4-dimensional trace of the energy-momentum tensor. We show that this component of the energy-momentum tensor arises from the backreaction of the dilaton coupling to the brane. The same positive features are exhibited in solutions found in the presence of non-vanishing cosmological constants both on the brane (Λ_{br}) and in the bulk (Λ_B). Moreover, the restoration of the Friedmann equation, with the correct sign, takes place for both signs of $Λ_B$ so long as the sign of $Λ_{br}$ is opposite $Λ_B$ in order to cancel the energy densities of the two cosmological constants. We further extend our single-brane thin-wall solution to allow a brane with finite thickness.

hep-ph↗

arXiv1999

Cosmological 3-Brane Solutions

We analyze cosmological equations in the brane world scenario with one extra space-like dimension. We demonstrate that the cosmological equations can be reduced to the usual 4D Friedmann type if the bulk energy-momentum tensor is different from zero. We then generalize these equations to the case of a brane of finite thickness. We also demonstrate that when the bulk energy-momentum tensor is different from zero, the extra space-like dimension can be compactified with a single brane and show that the stability of the radius of compactification implies standard cosmology and vice versa. For a brane of finite thickness, we provide a solution such that the 4D Planck scale is related to the fundamental scale by the thickness of the brane. In this case, compactification of the extra dimension is unnecessary.

hep-ph↗

arXiv1999

Primordial Lithium and Big Bang Nucleosynthesis

In the standard hot big bang nucleosynthesis (BBN) model the primordial abundances of H, H2, He3, He4, and Li7, fix the baryon density of the universe, $Ω_b$, via the baryon-to-photon ratio, $η$, for a given Hubble parameter. Recent observations of Li show that its intrinsic dispersion in metal-poor stars is essentially zero, and the random error in the mean Li abundance is negligible. However, a decreasing trend in the Li abundance towards lower metallicity, plus Li6 detections, indicate that its primordial abundance can be inferred only after allowing for nucleosynthesis processes in the Galaxy (Galactic chemical evolution (GCE)). We show that the Li vs Fe trend provides a tough discriminant between alternative models for GCE of light-elements. We critically assess current systematic uncertainties, and determine the primordial Li abundance within new, much tighter limits. We show that the Li constraint on $Ω_b$ is now limited principally by uncertainties in the nuclear cross-sections used in BBN {\it calculations}, not by the abundance itself. A clearer understanding of systematics allows for a much more accurate inference of the primordial Li abundance, sharpening the comparison with He4 and deuterium and the resulting test of BBN. We find that the Li data are in good agreement with He4 and with ``high'' deuterium values, but that low deuterium abundances are at best marginally within the Li range.

astro-ph↗

arXiv1996

Accelerator Constraints on Neutralino Dark Matter

The constraints on neutralino dark matter χobtained from accelerator searches at LEP, the Fermilab Tevatron and elsewhere are reviewed, with particular emphasis on results from LEP 1.5. These imply within the context of the minimal supersymmetric extension of the Standard Model that m_χ\ge 21.4 GeV if universality is assumed, and yield for large tanβa significantly stronger bound than is obtained indirectly from Tevatron limits on the gluino mass. We update this analysis with preliminary results from the first LEP 2W run, and also preview the prospects for future sparticle searches at the LHC.

hep-ph↗

arXiv1995

Axions and the Graceful Exit Problem in String Cosmology

We reexamine the graceful exit problem in the Pre-Big-Bang inflationary scenario. The dilaton-gravity action is generalized by adding the axion and a general axion/dilaton potential. We provide a phase space analysis of the dynamics which leads us to extend the previous no-go theorem and rule out the branch change necessary for graceful exit in this context.

hep-th↗

arXiv1994

Protecting the Baryon Asymmetry with Thermal Masses

We consider the evolution of baryon number $B$ in the early universe under the influence of rapid sphaleron interactions and show that $B$ will remain nonzero at all times even in the case of $B-L = 0$. This result arises due to thermal Yukawa interactions that cause nonidentical dispersion relations (thermal masses) for different lepton families. We point out the relevance of our result to the Affleck-Dine type baryogenesis.

hep-ph↗

arXiv1993

On the Erasure and Regeneration of the Primordial Baryon Asymmetry by Sphalerons

We show that a cosmological baryon asymmetry generated at the GUT scale, which would be destroyed at lower temperatures by sphalerons and possible new B- or L-violating effects, can naturally be preserved by an asymmetry in the number of right-handed electrons. This results in a significant softening of previously derived baryogenesis-based constraints on the strength of exotic B- or L-violating interactions.

hep-ph↗

arXiv1993

Physical Properties of Four Dimensional Superstring Gravity Black Hole Solutions

We consider the physical properties of four dimensional black hole solutions to the effective action describing the low energy dynamics of the gravitational sector of heterotic superstring theory. We compare the properties of the external field strengths in the perturbative solution to the full $O(α')$ string effective action equations, to those of exact solutions in a truncated action for charged black holes, and to the Kerr-Newman family of solutions of Einstein-Maxwell theory. We contrast the numerical results obtained in these approaches, and discuss limitations of the analyses. Finally we discuss how the new features of classical string gravity affect the standard tests of general relativity.

hep-th↗

arXiv1993

Supersymmetric (S)Neutrino-Mass Induced Baryogenesis

We propose a new mechanism for baryogenesis in supersymmetric extensions of the standard model, that does not depend on (super)GUT interactions. It occurs by the non-perturbative electroweak reprocessing of a lepton asymmetry. This lepton asymmetry is generated by the effects of lepton number violating induced operators, arising from "see-saw" (s)neutrino masses, which act on scalar condensate oscillations along flat directions of the supersymmetric standard model.

hep-ph↗

arXiv1993

Inflation, Neutrino Baryogenesis, and (S)Neutrino-Induced Baryogenesis

We evaluate the constraints that the COBE observations put on baryogenesis in inflationary cosmologies.We consider the supersymmetric version of the proposal of Fukugita and Yanagida, that the baryon asymmetry of the universe is created by nonperturbative electroweak reprocessing of a lepton asymmetry generated in the decay of heavy right-handed see-saw (s)neutrinos. We review our recent proposal of a mechanism for baryogenesis via sphaleron reprocessing of a lepton asymmetry generated by (s)neutrino mass effects on flat direction scalar condensate oscillations. Finally we analyze in detail the implementation of these mechanisms in the recently proposed ansatze for fermion mass matrices in supersymmetric, unified, theories.

hep-ph↗