54,191 research outputs found
Late time evolution of brane gas cosmology and compact internal dimensions
We study the late-time behavior of a universe in the framework of brane gas
cosmology. We investigate the evolution of a universe with a gas of
supergravity particles and a gas of branes. Considering the case when different
dimensions are anisotropically wrapped by various branes, we have derived
Friedman-like equations governing the dynamics of wrapped and unwrapped
subvolumes. We point out that the compact internal dimensions are wrapped by
three or higher dimensional branes.Comment: 16 pages, typos, references, comment on the possibility of
stabilizing the internal dimensions with fluxe
Electromagnetic production of vector mesons at low energies
We have investigated exclusive photoproduction of light vector mesons
(, and ) on the nucleon at low energies. In order to
explore the questions concerning the so-called missing nucleon resonances, we
first establish the predictions from a model based on the Pomeron and meson
exchange mechanisms. We have also explored the contributions due to the
mechanisms involving - and -channel intermediate nucleon state. Some
discrepancies found at the energies near threshold and large scattering angles
suggest a possibility of using this reaction to identify the nucleon
resonances.Comment: 9 pages, LaTeX with sprocl.sty, 5 figures (11 eps files), Talk
presented at the NSTAR2000 Workshop, The Physics of Excited Nucleons,
Jefferson Lab., Newport News, Feb. 16-19, 200
Higher and missing resonances in omega photoproduction
We study the role of the nucleon resonances () in
photoproduction by using the quark model resonance parameters predicted by
Capstick and Roberts. The employed and
amplitudes include the configuration mixing effects due to the residual
quark-quark interactions. The contributions from the nucleon resonances are
found to be important in the differential cross sections at large scattering
angles and various spin observables. In particular, the parity asymmetry and
beam-target double asymmetry at forward scattering angles are suggested for a
crucial test of our predictions. The dominant contributions are found to be
from , a missing resonance, and which is
identified as the of the Particle Data Group.Comment: 8 pages, LaTeX with ws-p8-50x6-00.cls, 4 figures (5 eps files), Talk
presented at the NSTAR2001 Workshop on the Physics of Excited Nucleons,
Mainz, Germany, Mar. 7-10, 200
The Technicolor Higgs in the Light of LHC Data
We consider scenarios in which the 125 GeV resonance observed at the Large
Hadron Collider is a Technicolor (TC) isosinglet scalar, the TC Higgs. By
comparison with quantum chromodynamics, we argue that the couplings of the TC
Higgs to the massive weak bosons are very close to the Standard Model (SM)
values. The couplings to photons and gluons are model-dependent, but close to
the SM values in several TC theories. The couplings of the TC Higgs to SM
fermions are due to interactions beyond TC, such as Extended Technicolor: if
such interactions successfully generate mass for the SM fermions, we argue that
the couplings of the latter to the TC Higgs are also SM-like.
We suggest a generic parameterization of the TC Higgs interactions with SM
particles that accommodates a large class of TC models, and we perform a fit of
these parameters to the Higgs LHC data. The fit reveals regions of parameter
space where the form factors are of order unity and consistent with data at the
95% CL, in agreement with expectations in TC theories. This indicates that the
discovered Higgs boson is consistent with the TC Higgs hypothesis for several
TC theories.Comment: 26 pages, 8 figure
Spectroscopic Binary Mass Determination using Relativity
High-precision radial-velocity techniques, which enabled the detection of
extrasolar planets are now sensitive to relativistic effects in the data of
spectroscopic binary stars (SBs). We show how these effects can be used to
derive the absolute masses of the components of eclipsing single-lined SBs and
double-lined SBs from Doppler measurements alone. High-precision stellar
spectroscopy can thus substantially increase the number of measured stellar
masses, thereby improving the mass-radius and mass-luminosity calibrations.Comment: 10 pages, 1 figure, accepted for publication by the Astrophysical
Journal Letter
Sterile neutrinos, dark matter, and the pulsar velocities in models with a Higgs singlet
We identify the range of parameters for which the sterile neutrinos can
simultaneously explain the cosmological dark matter and the observed velocities
of pulsars. To satisfy all cosmological bounds, the relic sterile neutrinos
must be produced sufficiently cold. This is possible in a class of models with
a gauge-singlet Higgs boson coupled to the neutrinos. Sterile dark matter can
be detected by the x-ray telescopes. The presence of the singlet in the Higgs
sector can be tested at the Large Hadron Collider.Comment: 4 pages, one figur
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