41 research outputs found
Star Wreck
Electroweak models with low-energy supersymmetry breaking predict the
existence of stable non-topological solitons, Q-balls, that can be produced in
the early universe. The relic Q-balls can accumulate inside a neutron star and
gradually absorb the baryons into the scalar condensate. This causes a slow
reduction in the mass of the star. When the mass reaches a critical value, the
neutron star becomes unstable and explodes. The cataclysmic destruction of the
distant neutron stars may be the origin of the gamma-ray bursts.Comment: 9 pages; references adde
Cuts and penalties: comment on "The clustering of ultra-high energy cosmic rays and their sources"
In a series of papers we have found statistically significant correlations between arrival directions of ultra-high energy cosmic rays and BL Lacertae objects. Recently, our calculations were partly repeated by Evans, Ferrer and Sarkar with the same result but different conclusions. We demonstrate that the criticism of Evans, Ferrer and Sarkar is incorrect. We also present the details of our method
Bound states and resonances in the scalar sector of the MSSM
The trilinear couplings of squarks and sleptons to the Higgs bosons can give
rise to a spectrum of bound states with exotic quantum numbers, for example,
those of a leptoquark.Comment: 8 pages, 2 eps figures, latex, epsf; published version (minor changes
in wording and referencing
Large-amplitude isothermal fluctuations and high-density dark-matter clumps
Large-amplitude isothermal fluctuations in the dark matter energy density,
parameterized by \Phi\equiv\delta\rhodm/\rhodm, are studied within the
framework of a spherical collapse model. For \Phi \ga 1, a fluctuation
collapses in the radiation-dominated epoch and produces a dense dark-matter
object. The final density of the virialized object is found to be \rho_F
\approx 140\, \Phi^3 (\Phi+1) \rhoeq, where \rhoeq is the matter density at
equal matter and radiation energy density. This expression is valid for the
entire range of possible values of , both for and . Some astrophysical consequences of high-density dark-matter clumps are
discussed.Comment: 15 pages plus 3 figures (included at the end as a uuencoded
postscript file), LaTeX, FNAL--PUB--94/055--
Non-equilibrium symmetry restoration beyond one loop
We calculate the strength of symmetry restoration effects in highly
non-equilibrium states which can arise, for example, during preheating after
inflation. We show that in certain parameter range the one-loop results are
unstable, requiring summation of multiloop diagrams. We solve this problem for
the model in the large -limit and show that the symmetry restoration
may be less effective than what predicted by the one-loop estimate.Comment: Latex, 12 pages, 2 postscript figure
Evolution of the Order Parameter after Bubble Collisions
If a first-order phase transition is terminated by collisions of new-phase
bubbles, there will exist a period of nonequilibrium between the time bubbles
collide and the time thermal equilibrium is established. We study the behavior
of the order parameter during this phase. We find that large nonthermal
fluctuations at this stage tend to restore symmetry, i.e., the order parameter
is smaller than its eventual thermal equilibrium value. We comment on possible
consequences for electroweak baryogenesis.Comment: 11 page LaTeX file with two figures, fig1.ps and fig2.p
Standard Model Neutrinos as Warm Dark Matter
Standard Model neutrinos are not usually considered plausible dark matter
candidates because the usual treatment of their decoupling in the early
universe implies that their mass must be sufficiently small to make them
``hot'' dark matter. In this paper we show that decoupling of Standard Model
neutrinos in low reheat models may result in neutrino densities very much less
than usually assumed, and thus their mass may be in the keV range. Standard
Model neutrinos may therefore be warm dark matter candidates.Comment: 5 pages, 5 figures, LaTeX file uses revtex packag
Ultra High Energy Cosmic Rays and Inflation Relics
There are two processes of matter creation after inflation that may be
relevant to the resolution of the puzzle of cosmic rays observed with energies
beyond GZK cut-off: 1) gravitational creation of superheavy (quasi)stable
particles, and 2) non-thermal phase transitions leading to formation of
topological defects. We review both possibilities.Comment: Submitted to Physics Report
Signatures of a Graviton Mass in the Cosmic Microwave Background
There exist consistent low energy effective field theories describing gravity
in the Higgs phase that allow the coexistence of massive gravitons and the
conventional 1/r potential of gravity. In an effort to constrain the value of
the graviton mass in these theories, we study the tensor contribution to the
CMB temperature anisotropy and polarization spectra in the presence of a
non-vanishing graviton mass. We find that the observation of a B-mode signal
consistent with the spectrum predicted by inflationary models would provide the
strongest limit yet on the mass of an elementary particle -- a graviton -- at a
level of m\lesssim 10^(-30) eV\approx(10 Mpc)^(-1). We also find that a
graviton mass in the range between (10 Mpc)^(-1) and (10 kpc)^(-1) leads to
interesting modifications of the polarization spectrum. The characteristic
signature of a graviton mass in this range would be a plateau in the B-mode
spectrum up to angular multipoles of l\sim 100. For even larger values of the
graviton mass the tensor contribution to the CMB spectra becomes strongly
suppressed.Comment: 22 pages, 5 figures, v2: references added, accepted for publication
in PR