4,808 research outputs found
Tachyon Defect Formation and Reheating in Brane-Antibrane Inflation
We study analytically the dynamical formation of lower dimensional branes at
the endpoint of brane-antibrane inflation through the condensation of
topological defects of the tachyon field which describes the instability of the
initial state. We then use this information to quantify the efficiency of the
reheating which is due to the coupling of time dependent tachyon background to
massless gauge fields which will be localized on the final state branes. We
improve upon previous estimates indicating that this can be an efficient
reheating mechanism for observers on the brane.Comment: 9 pages. Talk given at the 26th annual
Montreal-Rochester-Syracuse-Toronto Conference on High-Energy Physics: MRST
200
Leptogenesis with Left-Right domain walls
The presence of domain walls separating regions of unbroken and
is shown to provide necessary conditions for leptogenesis which
converts later to the observed Baryon aymmetry. The strength of lepton number
violation is related to the majorana neutrino mass and hence related to current
bounds on light neutrino masses. Thus the observed neutrino masses and the
Baryon asymmetry can be used to constrain the scale of Left-Right symmetry
breaking.Comment: References added, To appear in Praman
Shock Deformation in Zircon, a Comparison of Results from Shock-Reverberation and Single-Shock Experiments
The utility of the mineral zircon, ZrSiO4, as a shock-metamorphic geobarometer and geochronometer, has been steadily growing within the planetary science community. Zircon is an accessory phase found in many terrestrial rock types, lunar samples, lunar meteorites, martian meteorites and various other achondrites. Because zircon is refractory and has a high closure temperature for Pb diffusion, it has been used to determine the ages of some of the oldest material on Earth and elsewhere in the Solar System. Furthermore, major (O) and trace-element (REE, Ti, Hf) abundances and isotope compositions of zircon help characterize the petrogenetic environments and sources from which they crystallized. The response of zircon to impact-induced shock deformation is predominantly crystallographic, including dislocation creep and the formation of planar and sub-planar, low-angle grain boundaries; the formation of mechanical {112} twins; transformation to the high pressure polymorph reidite; the development of polycrystalline microtextures; and dissociation to the oxide constituents SiO2 and ZrO2. Shock microstructures can also variably affect the U- Pb isotope systematics of zircon and, in some instances, be used to constrain the impact age. While numerous studies have characterized shock deformation in zircon recovered from a variety of terrestrial impact craters and ejecta deposits and Apollo samples, experimental studies of shock deformation in zircon are limited to a handful of examples in the literature. In addition, the formation conditions (e.g., P, T) of various shock microstructures, such as planar-deformation bands, twins, and reidite lamellae, remain poorly con-strained. Furthermore, previous shocked-zircon experimental charges have not been analyzed using modern analytical equipment. This study will therefore under-take an new set of zircon shock experiments, which will then be microstructurally characterized using state-of-the-art instrumentation within the Astromaterials Research and Exploration Science Division (ARES), NASA Johnson Space Center
Mimicking transPlanckian effects in the CMB with conventional physics
We investigate the possibility that fields coupled to the inflaton can
influence the primordial spectrum of density perturbations through their
coherent motion. For example, the second field in hybrid inflation might be
oscillating at the beginning of inflation rather than at the minimum of its
potential. Although this effect is washed out if inflation lasts long enough,
we note that there can be up to 30 e-foldings of inflation prior to horizon
crossing of COBE fluctuations while still giving a potentially visible
distortion. Such pumping of the inflaton fluctuations by purely conventional
physics can resemble transPlanckian effects which have been widely discussed.
The distortions which they make to the CMB could leave a distinctive signature
which differs from generic effects like tilting of the spectrum.Comment: 3 pages, 4 figures; presented at PASCOS 03, TIFR, Mumbai, Indi
Primordial Hypermagnetic Knots
Topologically non-trivial configurations of the hypermagnetic flux lines lead
to the formation of hypermagnetic knots (HK) whose decay might seed the Baryon
Asymmetry of the Universe (BAU).HK can be dynamically generated provided a
topologically trivial (i.e. stochastic) distribution of flux lines is already
present in the symmetric phase of the electroweak (EW) theory. In spite of the
mechanism generating the HK, their typical size must exceed the diffusivity
length scale. In the minimal standard model (MSM) (but not necessarily in its
supersymmetric extension) HK are washed out. A classical hypermagnetic
background in the symmetric phase of the EW theory can produce interesting
amounts of gravitational radiation.Comment: 4 pages in Revtex style, 2 figure
Black Holes and Black String-like Solutions in Codimension-2 Braneworlds
We discuss black hole solutions with a Gauss-Bonnet term in the bulk and an
induced gravity term on a thin brane of codimension-2. We show that these black
holes can be localized on the brane, and they can be extended further into the
bulk by a warp function. These solutions have regular horizons and no other
curvature singularities appear apart from the string-like ones. The projection
of the Gauss-Bonnet term on the brane imposes a constraint relation which
dictates the form of matter on the brane and in the bulk.Comment: 9 pages, no figures, plenary talk given at the 7th Friedmann
International Seminar on Gravitation and Cosmology, 29 June-5 July 2008, Joao
Pessoa, Brazil, to appear in the proceeding
No Evidence for Gamma-Ray Burst/Abell Cluster or Gamma- Ray Burst/Radio-Quiet Quasar Correlations
We examine the recent claims that cosmic gamma-ray bursts are associated with
either radio-quiet quasars or Abell clusters. These associations were based on
positional coincidences between cataloged quasars or Abell clusters, and
selected events from the BATSE 3B catalog of gamma-ray bursts. We use a larger
sample of gamma-ray bursts with more accurate positions, obtained by the 3rd
Interplanetary Network, to re-evaluate these possible associations. We find no
evidence for either.Comment: Accepted for publication in the Astrophysical Journa
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
Mixing-induced CP violating sources for electroweak baryogenesis from a semiclassical approach
The effects of flavor mixing in electroweak baryogenesis is investigated in a
generalized semiclassical WKB approach. Through calculating the nonadiabatic
corrections to the particle currents it is shown that extra CP violation
sources arise from the off-diagonal part of the equation of motion of particles
moving inside the bubble wall. This type of mixing-induced source is of the
first order in derivative expansion of the Higgs condensate, but is oscillation
suppressed. The numerical importance of the mixing-induced source is discussed
in the Minimal Supersymmetric Standard Model and compared with the source term
induced by semiclassical force. It is found that in a large parameter space
where oscillation suppression is not strong enough, the mixing-induced source
can dominate over that from the semiclassical force.Comment: 19 pp, 2 figs, 1 table, some comments added, to appear in
Eur.Phys.J.
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