arXiv subjects

Keith A. Olive

Publications and source records attributed to Keith A. Olive.

At least 325 records · Page 18Linked to original sources

arXiv1995

LiBeB Production by Nuclei and Neutrinos

The production of LiBeB isotopes by nuclear and neutrino spallation are compared in the framework of galactic evolutionary models. As motivated by $γ$-ray observations of Orion, different possible sources of low-energy C and O nuclei are considered, such as supernovae of various masses and WC stars. We confirm that the low energy nuclei (LEN), injected in molecular clouds by stellar winds and type II supernovae originating from the most massive progenitors, can very naturally reproduce the observed Be and B evolution in the early galaxy (halo phase). Assuming the global importance of the LEN component, we compute upper and lower bounds to the neutrino process contribution corresponding to limiting cases of LEN particle spectra. A consistent solution is found with a spectrum of the kind proposed by Ramaty \etal (1995a,b), e.g. flat up to $E_c=30$ MeV/n and decreasing abruptly above. This solution fulfills the challenge of explaining at the same time the general Be and B evolution, and their solar system abundances without overproducing \li7 at very low metallicities, and the meteoritic \b11/\b10 ratio. In this case, neutrino spallation is constrained to play a limited role in the genesis of the solar system \b11. Galactic cosmic rays (GCR) become operative late in the evolution of the disk ([Fe/H]$>$-1), but their contribution to the solar abundances of \be9, \b10 and \b11 is not dominant (35\%, 30\% and 20\% respectively). Thus, with this LEN spectrum, GCR are {\it not}\ the main source of \be9 and B in the Galaxy. The most favorable case for neutrinos, (adopting the same kind of spectrum) has $E_c=20$ MeV/n. Even in this case, the neutrino yields of Woosley and Weaver (1995) must to be reduced by a factor of 5 to avoid \b11 overproduction. Furthermore, this solution leads to a high B/Be

astro-ph↗

arXiv1995

Model-Independent Predictions of Big Bang Nucleosynthesis

We derive constraints from standard (with $N_ν= 3$) BBN arising solely from two cosmologically produced nuclides, \he4 and \li7, from which the extrapolation to primordial abundances is straightforward. The abundances of D and \he3 are at present only inferred from their solar and local interstellar medium values using models of galactic chemical evolution. However, our knowledge of chemical evolution suffers from large uncertainties, and so it is of use to take an approach which minimizes the reliance on chemical evolution in determining the consistency of BBN. Using only the data on \he4 and \li7, and reasonable estimates of possible systematic errors in their abundance determinations, concordance is found if the baryon-to-photon ratio lies in the range $1.4 < 10^{10} η< 3.8$ (95\% CL). The \he4 and \li7 abundances are also used to predict the primordial abundances D and \he3, which provides an initial condition for their chemical evolution.

hep-ph↗

arXiv1995

New Constraints on Superpartner Masses

We consider the Minimal Supersymmetric Standard Model (MSSM) without imposing relations on the superpartner masses that arise in grand unified theories. Given an arbitrary pattern of superpartner masses (consistent with experimental constraints), it may happen that the scalar potential is actually unstable, even though all scalar masses-squared are positive at the weak scale $M_W$. This is most likely to happen if the running mass-squared in a ``flat'' direction in field space becomes negative at some scale $Q_0$ which is well below the GUT scale. In this case, either this pattern of masses is ruled out, or there must be new physics (beyond the MSSM) at or below the scale $Q_0$.

hep-ph↗

arXiv1995

Phases in the MSSM

The effect of CP violating phases in the MSSM on the relic density of the lightest supersymmetric particle (LSP) is considered. In particular, the upper limits on the LSP mass are relaxed when phases in the MSSM are allowed to take non-zero values and when the LSP is predominantly a gaugino (bino). Previous limits of $\mb \la 250$ GeV for $Ωh^2 < 0.25$ can be relaxed to $\mb \la 650$ GeV. The additional constraints imposed by the neutron and electron electric dipole moments induced by these phases are also considered. Though there is some restriction on the phases, the bino mass may still be as large as $\sim$ 350 GeV and certain phases can be arbitrarily large.

hep-ph↗

arXiv1995

The Local Abundance of $^3$He: A Confrontation Between Theory and Observation

Determinations of the \he3 concentrations in Galactic matter serve to impose interesting and important constraints both on cosmological models and on models of Galactic chemical evolution. At present, observations of \he3 in the solar system and in the interstellar medium today suggest that the \he3 abundance has not increased significantly over the history of the Galaxy, while theoretical models of Galactic chemical evolution (utilizing current nucleosynthesis yields from stellar evolution and supernova models) predict a rather substantial increase in \he3. We consider the possibility that the solar \he3 abundance may have been affected by stellar processing in the solar neighborhood prior to the formation of the solar system. Such a discrepancy between solar abundances and average galactic abundances by as much as a factor of two, may be evidenced by several isotopic anomalies. Local destruction of \he3 by a similar amount could serve to help to reconcile the expected increase in the \he3 abundance predicted by models of galactic chemical evolution. We find however, that the production of heavier elements, such as oxygen, places a strong constraint on the degree of \he3 destruction. We also explore the implications of both alternative models of Galactic chemical evolution and the stellar yields for \he3 in low mass stars, which can explain the history of the \he3 concentration in the Galaxy.

astro-ph↗

arXiv1995

Big Bang Nucleosynthesis: An Update

WThe current status of big bang nucleosynthesis is reviewed with an emphasis on the comparison between the observational determination of the light element abundances of \D, \he3, \he4 and \li7 and the predictions from theory. In particular, we present new analyses for \he4 and \li7. Implications for physics beyond the standard model are also discussed. Limits on the effective number of neutrino flavors are also updated.

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arXiv1995

Towards a Singularity-Free Inflationary Universe?

We consider the problem of constructing a non-singular inflationary universe in stringy gravity via branch changing, from a previously superexponentially expanding phase to an FRW-like phase. Our approach is based on the phase space analysis of the dynamics, and we obtain a no-go theorem which rules out the efficient scenario of branch changing catalyzed by dilaton potential and stringy fluid sources. We furthermore consider the effects of string-loop corrections to the gravitational action in the form recently suggested by Damour and Polyakov. These corrections also fail to produce the desired branch change. However, focusing on the possibility that these corrections may decouple the dilaton, we deduce that they may lead to an inflationary expansion in the presence of a cosmological constant, which asymptotically approaches Einstein-deSitter solution.

hep-th↗

arXiv1995

On the Thermal Regeneration Rate for Light Gravitinos in the Early Universe

We investigate the light gravitino regeneration rate in the early Universe in models based on $N=1$ supergravity. Motivated by a recent claim by Fischler, we evaluate finite-temperature effects on the gravitino regeneration rate due to the hot primordial plasma for a wide range of the supersymmetry-breaking scale $F$. We find that thermal corrections to the gravitino pole mass and to the Goldstino coupling are negligible for a wide range of temperatures, thereby justifying the extension of the equivalence theorem for the helicity-1/2 gravitino and Goldstino to a hot primordial plasma background. Utilizing the Braaten-Pisarski resummation method, the helicity-1/2 gravitino regeneration rate is found to be $0.25 α_s(T) \log(1/α_s(T))|{m_{\rm soft}/F}|^2 T^3(1 + α_s(T) \log(1/α_s(T)) + T^2 / |F|)$ up to a calculable, model-dependent ${\cal O}(1)$ numerical factor. We review the implications of this regeneration rate for supergravity cosmology, focusing in particular on scenaria for baryogenesis.

hep-ph↗

arXiv1995

Preserving Flat Directions During Inflation

Supersymmetry is generally broken by the non-vanishing vacuum energy density present during inflation. In supergravity models, such a source of supersymmetry breaking typically makes a contribution to scalar masses of order ${\tilde m}^2 \sim H^2$, where $H^2 \sim V/M_P^2$ is the Hubble parameter during inflation. We show that in supergravity models which possess a Heisenberg symmetry, supersymmetry breaking makes no contribution to scalar masses, leaving supersymmetric flat directions flat at tree-level. One-loop corrections in general lift the flat directions, but naturally give small negative squared masses $\sim - g^2 H^2/(4π)^2$ for all flat directions that do not involve the stop. No-scale supergravity of the SU(N,1) type and the untwisted sectors from orbifold compactifications are special cases of this general set of models. We point out the importance of the preservation of flat directions for baryogenesis.

hep-ph↗

arXiv1995

Big Bang Nucleosynthesis

The current status of big bang nucleosynthesis and its implications for physics beyond the standard model is reviewed. In particular, limits on the effective number of neutrino flavors and extra Z gauge boson masses are updated.

hep-ph↗

arXiv1995

Supersymmetric "Solutions" to Cosmological Problems: Baryogenesis and Dark Matter

The possible role of supersymmetry in our understanding of big bang baryogenesis and cosmological dark matter is explored. The discussion will be limited to the out-of equilibrium decay scenario in SUSY GUTs, the decay of scalar condensates, and lepto-baryogenesis as a means for generating the observed baryon asymmetry. Attention will also be focused on neutralino dark matter.

hep-ph↗

arXiv1995

A New Look At Neutrino Limits From Big Bang Nucleosynthesis

We take a fresh look at the limits on the number of neutrino flavors derived from big bang nucleosynthesis. In particular, recent measurements of the \he4 abundance enable one to estimate the primordial \he4 mass fraction at $Y_p = 0.232 \pm .003(stat) \pm .005(syst)$. For a baryon to photon ratio, $η$, consistent with the other light elements, this leads to a best fit for the number of neutrino flavors $N_ν< 3$ (the precise number depends on $η$) indicating a very strong upper limit to $N_ν$. Here, we derive new upper limits on $N_ν$, paying special attention to the fact that the best estimate may lie in an unphysical region ($N_ν< 3$ if all three neutrino flavors are light or massless; the lower bound to $N_ν$ may even be as low as 2, if the small window for a $ν_τ$ mass is exploited.) Our resulting upper limits therefore depend on whether $N_ν\ge 2$ or 3 is assumed. We also explore the sensitivity of our results to the adopted value of $η$ and the assumed systematic errors in $Y_p$.

hep-ph↗

arXiv1994

Nucleosynthesis and the Time Dependence of Fundamental Couplings

We consider the effects of the time dependence of couplings due to their dependence on a dilaton field, as occurs in superstring theory, as well as in gravity theories of the Jordan-Brans-Dicke type. Because the scale parameters of couplings set by dimensional transmutation depend exponentially on the dilaton vev, we may obtain stringent limits on the shift of the dilaton from the requirement that the induced shift in the couplings not vitiate the successful calculations of element abundances for big-bang nucleosynthesis. These limits can be substantially stronger than those obtained directly from the dilaton-induced change in the gravitational coupling.

hep-ph↗

arXiv1994

What's The Problem With ^3He?

We consider the galactic evolutionary history of \he3 in models which deplete deuterium by as much as a factor of 2 to $\sim$ 15 from its primordial value to its present day observed value in the ISM. We show that when \he3 production in low mass stars (1 -- 3 $M_\odot$) is included over the history of the galaxy, \he3 is greatly over-produced and exceeds the inferred solar values and the abundances determined in galactic \hii regions. Furthermore, the ISM abundances show a disturbing dispersion which is difficult to understand from the point of view of standard chemical evolution models. In principle, resolution of the problem may lie in either 1) the calculated \he3 production in low mass stars; 2) the observations of the \he3 abundance; or 3) an observational bias towards regions of depleted \he3. Since \he3 observations in planetary nebula support the calculated \he3 production in low mass stars, option (1) is unlikely. We will argue for option (3) since the \he3 interstellar observations are indeed made in regions dominated by massive stars in which \he3 is destroyed. In conclusion, we note that the problem with \he3 seems to be galactic and not cosmological.

astro-ph↗

arXiv1994

Large Scale Baryon Isocurvature Inhomogeneities

Big bang nucleosynthesis constraints on baryon isocurvature perturbations are determined. A simple model ignoring the effects of the scale of the perturbations is first reviewed. This model is then extended to test the claim that large amplitude perturbations will collapse, forming compact objects and preventing their baryons from contributing to the observed baryon density. It is found that baryon isocurvature perturbations are constrained to provide only a slight increase in the density of baryons in the universe over the standard homogeneous model. In particular it is found that models which rely on power laws and the random phase approximation for the power spectrum are incompatible with big bang nucleosynthesis unless an {\em ad hoc}, small scale cutoff is included.

astro-ph↗

arXiv1994

Heavy Sneutrinos as Dark Matter

We calculate the relic density of very heavy, stable scalar neutrinos in the minimal supersymmetric standard model. We include all two-body final states, as well as the effects of co-annihilation with scalar electrons. We find that the sneutrino relic density is in the cosmologically interesting region $0.1\ltwidΩ_{\sn}h^2\ltwid 1.0$ for $550\gev\ltwid\msn\ltwid 2300\gev$. For nominal values of the parameters of our galactic halo, recent results from the Heidelberg--Moscow direct detection experiment set an upper limit on $Ω_{\sn}$ which is lower by a factor ranging from two to ten, depending on $\msn$.

hep-ph↗

arXiv1994

The Deuterium Abundance and Nucleocosmochronology

We examine galactic chemical evolution models which reproduce the present-day and pre-solar values of deuterium starting with a primordial value which is consistent with a baryon-to-photon ratio of $3 \times 10^{-10}$. We consider various galactic chemical evolution models to determine the viability of significant deuterium destruction and which provide a consistent age of the galaxy at the time of the formation of the solar system and consequently its present day age from nuclear chronometers. These models generally require some amount of infall which we take with rates proportional to the gas mass as well as exponentially decreasing rates and some initial disk enrichment which we limit to the range of 0\% to 30\%. We present those models which give the observed pre-solar value and present-day value of D/H and which lead to a present-day gas fraction of $σ= .05\quad - \quad .2$. These models result in a braod range for the age of galaxy between $9.8 - 21.6$ Gyrs.

astro-ph↗

arXiv1994

Light Stops in the MSSM: Implications for Photino Dark Matter and Top Quark Decay

We consider the viability of the minimal supersymmetric standard model with a light ($m_{\tilde t_1} < $ 45 GeV) stop. In order for its relic abundance to be cosmologically significant, the photino as dark matter must be quite close in mass to the stop, $(m_{\tilde t_1} - m_{\tilde γ}) \simeq 3 - 7 $ GeV. However, as we show, the photino despite its low mass is virtually undetectable by either direct or indirect means. We also discuss the implications of these masses on the top quark branching ratios.

hep-ph↗