1,946 research outputs found
Relativistic stars in f(R) gravity, and absence thereof
Several f(R) modified gravity models have been proposed which realize the
correct cosmological evolution and satisfy solar system and laboratory tests.
Although nonrelativistic stellar configurations can be constructed, we argue
that relativistic stars cannot be present in such f(R) theories. This problem
appears due to the dynamics of the effective scalar degree of freedom in the
strong gravity regime. Our claim thus raises doubts on the viability of f(R)
models.Comment: 9 pages, 7 figures, v2: references added, minor corrections, version
accepted for publication in PR
Compressed SUSY search at the 13 TeV LHC using kinematic correlations and structure of ISR jets
The LHC search for nearly degenerate gluinos and neutralinos, which can
occur, for example, in SUSY axion models, is limited by the reduced missing
transverse momentum and effective mass in the events. We propose the use of
kinematic correlations between jets coming from initial state radiation (ISR)
in gluino pair production events at the 13 TeV LHC. A significant improvement
in the signal to background ratio is obtained for the highly compressed
gluino-neutralino search, by using cuts on the rapidity and azimuthal angle
separation between the pair of tagged jets with the highest transverse momenta.
Furthermore, the distribution of the azimuthal angle difference between the
tagged jets in the gluino-pair+jets process is found to be distinctly different
from the dominant background process of Z+jets. We also find quark and gluon
jet tagging methods to be useful in separating the signal, which contains a
higher fraction of gluon initiated jets compared to the dominant backgrounds.Comment: 19 pages, 3 figures; v2: Standard model background estimates
improved, comments and references adde
Iteration Method to Derive Exact Rotation Curves from Position-Velocity Diagrams of Spiral Galaxies
We present an iteration method to derive exact rotation curves (RC) of spiral
galaxies from observed position-velocity diagrams (PVD), which comprises the
following procedure. An initial rotation curve, RC0, is adopted from an
observed PV diagram (PV0), obtained by any simple method such as the
peak-intensity method. Using this rotation curve and an observed radial
distribution of intensity (emissivity), we construct a simulated PV diagram
(PV1). The difference between a rotation curve obtained from this PV1 and the
original RC (e.g., difference between peak-intensity velocities) is used to
correct the initial RC to obtain a corrected rotation curve, RC1. This RC1 is
used to calculated another PVD (PV2) using the observed intensity distribution,
and to obtain the second iterated RC (RC2). This iteration is repeated until
PV converges to PV0, so that the differences between PV and PV0 becomes
minimum. Finally RC is adopted as the most reliable rotation curve. We apply
this method to some observed PVDs of nearby galaxies, and show that the
iteration successfully converges to give reliable rotation curves. We show that
the method is powerful to detect central massive objects.Comment: To appear in ApJ.Letters, 5 pages Latex with 4 figure
The Music of the Aetherwave - B-mode Polarization in Einstein-Aether Theory
We study how the dynamical vector degree of freedom in modified gravity
affects the CMB B-mode polarization in terms of the Einstein-aether theory. In
this theory, vector perturbations can be generated from inflation, which can
grow on superhorizon scales in the subsequent epochs and thereby leaves
imprints on the CMB B-mode polarization. We derive the linear perturbation
equations in a covariant formalism, and compute the CMB B-mode polarization
using the CAMB code modified so as to incorporate the effect of the aether
vector field. We find that the amplitude of the B-mode signal from the aether
field can surpass the contribution from the inflationary gravitational waves
for a viable range of model parameters. We also give an analytic argument
explaining the shape of the spectrum based on the tight coupling approximation.Comment: 12 pages, 6 figure
Affleck-Dine leptogenesis via multiscalar evolution in a supersymmetric seesaw model
A leptogenesis scenario in a supersymmetric standard model extended with
introducing right-handed neutrinos is reconsidered. Lepton asymmetry is
produced in the condensate of a right-handed sneutrino via the Affleck-Dine
mechanism. The LH_u direction develops large value due to a negative effective
mass induced by the right-handed sneutrino condensate through the Yukawa
coupling of the right-handed neutrino, even if the minimum during the inflation
is fixed at the origin. The lepton asymmetry is nonperturbatively transfered to
the LH_u direction by this Yukawa coupling.Comment: 19 pages, 3 figures. Revised version for publication. The model was
modified to fix some problem
A 125GeV Higgs Boson and Muon g-2 in More Generic Gauge Mediation
Recently, the ATLAS and CMS collaborations reported exciting hints of a
Standard Model-like Higgs boson with a mass around 125GeV. A Higgs boson this
heavy is difficult to realize in conventional models of gauge mediation. Here
we revisit the lightest Higgs boson mass in "more generic gauge mediation,"
where the Higgs doublets mix with the messenger doublets. We show that a Higgs
boson mass around 125GeV can be realized in more generic gauge mediation
models, even for a relatively light gluino mass ~1TeV. We also show that the
muon anomalous magnetic moment can be within 1sigma of the experimental value
for these models, even when the Higgs boson is relatively heavy. We also
discuss the LHC constraints and the prospects of discovery.Comment: 28 pages, 7 figures. Corrections and references are adde
Leptogenesis Scenarios via Non-Thermally Produced Right-handed Neutrino and Sneutrino in Supersymmetric Seesaw Model
We reconsidered leptogenesis scenario from right-handed (s)neutrino produced
by the decay of inflaton. Besides the well-investigated case that the neutrino
decays instantaneously after the production, leptogenesis is possible if
neutrino decays after it dominates the universe. In the latter case,
right-handed (s)neutrino can decay either while it is relativistic or after it
becomes non-relativistic. Especially, the first case has not been discussed
seriously in literatures. Resultant lepton asymmetry and constraints from the
gravitino problem are studied in broad parameter region, including all cases of
this scenario. It is also shown how this leptogenesis scenario depends on the
parameters, the inflaton decay rate (the reheating temperature), the
right-handed neutrino mass, the washout parameter, and the constraint from the
gravitino problem. Leptogenesis from relativistic neutrino decay is interesting
because both thermal and non-thermal gravitino problems can be relaxed.Comment: 17 pages, 6 figure
New Cosmological Solutions in Massive Gravity
We find new, simple cosmological solutions with flat, open, and closed
spatial geometries, contrary to the previous wisdom that only the open model is
allowed. The metric and the St\"{u}ckelberg fields are given explicitly,
showing nontrivial configurations of the St\"{u}ckelberg in the usual
Friedmann-Lema\^{i}tre-Robertson-Walker coordinates. The solutions exhibit
self-acceleration, while being free from ghost instabilities. Our solutions can
accommodate inhomogeneous dust collapse represented by the
Lema\^{i}tre-Tolman-Bondi metric as well. Thus, our results can be used not
only to describe homogeneous and isotropic cosmology but also to study
gravitational collapse in massive gravity.Comment: 5 page
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