410 research outputs found
Transient domain walls and lepton asymmetry in the Left-Right symmetric model
It is shown that the dynamics of domain walls in Left-Right symmetric models,
separating respective regions of unbroken SU(2)_L and SU(2)_R in the early
universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a
spatially varying complex mass matrix due to CP-violating scalar condensates in
the domain wall. The motion of the wall through the plasma generates a flux of
lepton number across the wall which is converted to a lepton asymmetry by
helicity-flipping scatterings. Subsequent processing of the lepton excess by
sphalerons results in the observed baryon asymmetry, for a range of parameters
in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in
Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3
figure files, RevTeX4 styl
Rolling down to D-brane and tachyon matter
We investigate the spatially inhomogeneous decay of an unstable D-brane and
construct an asymptotic solution which describes a codimension one D-brane and
the tachyon matter in boundary string field theory. In this solution, the
tachyon matter exists around the lower-dimensional D-brane.Comment: 8 pages, references added, solution corrected, revised and extended
version, v4:published versio
Precise interplanetary network localization of a new soft gamma repeater, SGR 1627-41
We present Ulysses, KONUS-WIND, and BATSE observations of bursts from a new
soft gamma repeater which was active in 1998 June and July. Triangulation of
the bursts results in a ~ 1.8 degree by 16 '' error box whose area is ~ 7.6
arcminutes^2, which contains the Galactic supernova remnant G337.0-0.1. This
error box intersects the position of a BeppoSAX X-ray source which is also
consistent with the position of G337.0-0.1 (Woods et al. 1999), and is thought
to be the quiescent counterpart to the repeater. If so, the resulting error box
is ~ 2 ' by 16 '' and has an area of ~ 0.6 arcminutes^2. The error box location
within the supernova remnant suggests that the neutron star has a transverse
velocity of ~ 200 - 2000 km/s.Comment: 15 pages, 2 figures, submitted to ApJ Letter
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.Comment: 10 pp. LaTex (2 figures, included) UMN-TH-1201/9
Tachyon Dynamics and the Effective Action Approximation
Recently effective actions have been extensively used to describe tachyon
condensation in string theory. While the various effective actions which have
appeared in the literature have very similar properties for static
configurations, they differ for time-dependent tachyons. In this paper we
discuss general properties of non-linear effective Lagrangians which are first
order in derivatives. In particular we show that some observed properties, such
as asymptotically vanishing pressure, are rather generic features, although the
quantative features differ. On the other hand we argue that certain features of
marginal tachyon profiles are beyond the reach of any first order Lagrangian
description. We also point out that an effective action, proposed earlier,
captures the dynamics of tachyons well.Comment: References added and confusing reference clarifie
Aspects of Tachyonic Inflation with Exponential Potential
We consider issues related to tachyonic inflation with exponential potential.
We find exact solution of evolution equations in the slow roll limit in FRW
cosmology. We also carry out similar analysis in case of Brane assisted
tachyonic inflation. We investigate the phase space behavior of the system and
show that the dust like solution is a late time attractor. The difficulties
associated with reheating in the tachyonic model are also indicated.Comment: New References added. To appear in Phys. Rev.
Brane oscillations and the cosmic coincidence problem
We show that, under general assumptions, in six-dimensional brane-world
models with compactified large extra dimensions, the energy density of brane
oscillations scales as that of cold dark matter and its present value is
compatible with observations. Such value is obtained from the only dimensional
scale in the theory, namely, the fundamental scale of gravity in six dimensions
TeV, without any fine-tuning or the introduction of additional mass
scales apart from the large size of the extra dimensions. It has been suggested
that the same kind of models could provide also the correct magnitude of the
cosmological constant. This observation can be relevant for the resolution of
the cosmic coincidence problem in the brane-world scenario.Comment: 5 pages, RevTeX. Comments on the renormalization of the branon mass
included. Final version to appear in Phys.Rev.D (R
Model Independent Properties and Cosmological Implications of the Dilaton and Moduli Sectors of 4-d Strings
We show that if there is a realistic 4-d string, the dilaton and moduli
supermultiplets will generically acquire a small mass O(m_{3/2}), providing the
only vacuum-independent evidence of low-energy physics in string theory beyond
the supersymmetric standard model. The only assumptions behind this result are
(i) softly broken supersymmetry at low energies with zero cosmological
constant, (ii) these particles interact with gravitational strength and the
scalar components have a flat potential in perturbation theory, which are
well-known properties of string theories. (iii) They acquire a of the
order of the Planck scale (as required for the correct value of the gauge
coupling constants and the expected compactification scale) after supersymmetry
gets broken. We explore the cosmological implications of these particles.
Similar to the gravitino, the fermionic states may overclose the Universe if
they are stable or destroy nucleosynthesis if they decay unless their masses
belong to a certain range or inflation dilutes them. For the scalar states it
is known that the problem cannot be entirely solved by inflation, since
oscillations around the minimum of the potential can lead to a huge entropy
generation at late times. We discus some possible ways to alleviate this
entropy problem, that favour low-temperature baryogenesis, and also comment on
the possible role of these particles as dark matter candidates or as sources of
the baryon asymmetry through their decay.Comment: 15 pages,CERN-TH.6958/93,NEIP-93-006, IEM-FT-75/93, Late
Quantum Interference: From Kaons to Neutrinos (with Quantum Beats in between)
Using the vehicle of resolving an apparent paradox, a discussion of quantum
interference is presented. The understanding of a number of different physical
phenomena can be unified, in this context. These range from the neutral kaon
system to massive neutrinos, not to mention quantum beats, Rydberg wave
packets, and neutron gravity.Comment: 12 pages, LaTeX, 3 figure
Wess-Zumino Term in Tachyon Effective Action
We show that the source of RR field computed from the boundary state
describing the decay of a non-BPS brane is reproduced by a particular form of
the Wess-Zumino term in the tachyon effective action. We also obtain a simple
expression of the S-charge associated with rolling tachyons.Comment: 10 pages, lanlma
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