3,853 research outputs found
Gamma Rays from SN1987A due to Pseudoscalar Conversion
A light pseudoscalar coupled to two photons would be copiously emitted by the
core of a supernova. Part of this flux would be converted to rays by
the galactic magnetic field. Measurements on the SN1987A ray flux by
the Gamma-Ray Spectrometer on the Solar Maximum Mission satellite already imply
a bound on the coupling GeV. The improved
generation of satellite-borne detectors, like EGRET or the project GLAST, could
be able to detect a pseudoscalar-to-photon signal from a nearby supernova, for
allowed values of .Comment: 8 pages, no figure
Gauge-Higgs Dark Matter
When the anti-periodic boundary condition is imposed for a bulk field in
extradimensional theories, independently of the background metric, the lightest
component in the anti-periodic field becomes stable and hence a good candidate
for the dark matter in the effective 4D theory due to the remaining accidental
discrete symmetry. Noting that in the gauge-Higgs unification scenario,
introduction of anti-periodic fermions is well-motivated by a phenomenological
reason, we investigate dark matter physics in the scenario. As an example, we
consider a five-dimensional SO(5)\timesU(1)_X gauge-Higgs unification model
compactified on the with the warped metric. Due to the structure of
the gauge-Higgs unification, interactions between the dark matter particle and
the Standard Model particles are largely controlled by the gauge symmetry, and
hence the model has a strong predictive power for the dark matter physics.
Evaluating the dark matter relic abundance, we identify a parameter region
consistent with the current observations. Furthermore, we calculate the elastic
scattering cross section between the dark matter particle and nucleon and find
that a part of the parameter region is already excluded by the current
experimental results for the direct dark matter search and most of the region
will be explored in future experiments.Comment: 16 pages, 2 figure
Passage of Time in a Planck Scale Rooted Local Inertial Structure
It is argued that the `problem of time' in quantum gravity necessitates a
refinement of the local inertial structure of the world, demanding a
replacement of the usual Minkowski line element by a 4+2n dimensional
pseudo-Euclidean line element, with the extra 2n being the number of internal
phase space dimensions of the observed system. In the refined structure, the
inverse of the Planck time takes over the role of observer-independent
conversion factor usually played by the speed of light, which now emerges as an
invariant but derivative quantity. In the relativistic theory based on the
refined structure, energies and momenta turn out to be invariantly bounded from
above, and lengths and durations similarly bounded from below, by their
respective Planck scale values. Along the external timelike world-lines, the
theory naturally captures the `flow of time' as a genuinely structural
attribute of the world. The theory also predicts expected
deviations--suppressed quadratically by the Planck energy--from the dispersion
relations for free fields in the vacuum. The deviations from the special
relativistic Doppler shifts predicted by the theory are also suppressed
quadratically by the Planck energy. Nonetheless, in order to estimate the
precision required to distinguish the theory from special relativity, an
experiment with a binary pulsar emitting TeV range gamma-rays is considered in
the context of the predicted deviations from the second-order shifts.Comment: 17 pages; Diagram depicting "the objective flow of time" is replaced
with a much-improved diagra
QCD Sum Rules, Scattering Length and the Vector Mesons in Nuclear Medium
Critical examination is made on the relation between the mass shift of vector
mesons in nuclear medium and the vector-meson nucleon scattering length. We
give detailed comparison between the QCD sum rule approach by two of the
present authors (Phys. Rev. {\bf C46} (1992) R34) and the scattering-length
approach by Koike (Phys. Rev. {\bf C51} (1995) 1488). It is shown that the
latter approach is mortally flawed both technically and conceptually.Comment: 16 pages, latex, 4 figures appended as uu-encoded fil
Low-energy gluon contributions to the vacuum polarization of heavy quarks
We calculate a correction to the electromagnetic current induced by a heavy
quark loop. The contribution of this correction to the vacuum polarization
function appears at the O(alpha_s^3) order of perturbation theory and has a
qualitatively new feature -- its absorptive part starts at zero energy in
contrast to other contributions where the absorptive parts start at the
two-particle threshold. Our result imposes a constraint on the order n of the
moments used in the heavy-quark sum rules, n<4.Comment: 8 pages in LaTeX, 1 PostScript figure included in the tex
Supergravity for Effective Theories
Higher-derivative operators are central elements of any effective field
theory. In supersymmetric theories, these operators include terms with
derivatives in the K\"ahler potential. We develop a toolkit for coupling such
supersymmetric effective field theories to supergravity. We explain how to
write the action for minimal supergravity coupled to chiral superfields with
arbitrary numbers of derivatives and curvature couplings. We discuss two
examples in detail, showing how the component actions agree with the
expectations from the linearized description in terms of a Ferrara-Zumino
multiplet. In a companion paper, we apply the formalism to the effective theory
of inflation.Comment: 26 page
Unparticles-Higgs Interplay
We show that scalar unparticles coupled to the Standard Model Higgs at the
renormalizable level can have a dramatic impact in the breaking of the
electroweak symmetry already at tree level. In particular one can get the
proper electroweak scale without the need of a Higgs mass term in the
Lagrangian. By studying the mixed unparticle-Higgs propagator and spectral
function we also show how unparticles can shift the Higgs mass away from its
Standard Model value, \lambda v^2, and influence other Higgs boson properties.
Conversely, we study in some detail how electroweak symmetry breaking affects
the unparticle sector by breaking its conformal symmetry and generating a mass
gap. We also show that, for Higgs masses above that gap, unparticles can
increase quite significantly the Higgs width.Comment: 14 pages, 7 figures, typos correcte
Searches for Lepton Flavour Violation at a Linear Collider
We investigate the prospects for detection of lepton flavour violation in
sparticle production and decays at a Linear Collider (LC), in models guided by
neutrino oscillation data. We consider both slepton pair production and
sleptons arising from the cascade decays of non-leptonic sparticles. We study
the expected signals when lepton-flavour-violating (LFV) interactions are
induced by renormalization effects in the Constrained Minimal Supersymmetric
extension of the Standard Model (CMSSM), focusing on the subset of the
supersymmetric parameter space that also leads to cosmologically interesting
values of the relic neutralino LSP density. Emphasis is given to the
complementarity between the LC, which is sensitive to mixing in both the left
and right slepton sectors, and the LHC, which is sensitive primarily to mixing
in the right sector. We also emphasize the complementarity between searches for
rare LFV processes at the LC and in low-energy experiments.Comment: 19 pages, 10 figure
Model Building with Gauge-Yukawa Unification
In supersymmetric theories with extra dimensions, the Higgs and matter fields
can be part of the gauge multiplet, so that the Yukawa interactions can arise
from the gauge interactions. This leads to the possibility of gauge-Yukawa
coupling unification, g_i=y_f, in the effective four dimensional theory after
the initial gauge symmetry and the supersymmetry are broken upon orbifold
compactification. We consider gauge-Yukawa unified models based on a variety of
four dimensional symmetries, including SO(10), SU(5), Pati-Salam symmetry,
trinification, and the Standard Model. Only in the case of Pati-Salam and the
Standard Model symmetry, we do obtain gauge-Yukawa unification. Partial
gauge-Yukawa unification is also briefly discussed.Comment: 23 page
Cosmological Implications of Dynamical Supersymmetry Breaking
We provide a taxonomy of dynamical supersymmetry breaking theories, and
discuss the cosmological implications of the various types of models. Models in
which supersymmetry breaking is produced by chiral superfields which only have
interactions of gravitational strength (\eg\ string theory moduli) are
inconsistent with standard big bang nucleosynthesis unless the gravitino mass
is greater than \CO(3) \times 10^4 GeV. This problem cannot be solved by
inflation. Models in which supersymmetry is dynamically broken by
renormalizable interactions in flat space have no such cosmological problems.
Supersymmetry can be broken either in a hidden or the visible sector. However
hidden sector models suffer from several naturalness problems and have
difficulties in producing an acceptably large gluino mass.Comment: 24 pages (uses harvmac) UCSD/PTH 93-26, RU-3
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