8,509 research outputs found
Mode coupling theory in the FDR-preserving field theory of interacting Brownian particles
We develop a renormalized perturbation theory for the dynamics of interacting
Brownian particles, which preserves the fluctuation-dissipation relation order
by order. We then show that the resulting one-loop theory gives a closed
equation for the density correlation function, which is identical with that in
the standard mode coupling theory.Comment: version to be published in Fast Track Communication in Journal of
Physics A:Math. Theo
Non-Gaussianity from Baryon Asymmetry
We study a scenario that large non-Gaussianity arises from the baryon
asymmetry of the Universe. There are baryogenesis scenarios containing a light
scalar field, which may result in baryonic isocurvature perturbations with some
amount of non-Gaussianity. As an explicit example we consider the Affleck-Dine
mechanism and show that a flat direction of the supersymmeteric standard model
can generate large non-Gaussianity in the curvature perturbations, satisfying
the observational constraints on the baryonic isocurvature perturbations. The
sign of a non-linearity parameter, f_{NL}, is negative, if the Affleck-Dine
mechanism accounts for the observed baryon asymmetry; otherwise it can be
either positive or negative.Comment: 25 pages, 7 figures; minor correction, references added; version to
appear in JCA
General treatment of isocurvature perturbations and non-Gaussianities
We present a general formalism that provides a systematic computation of the
linear and non-linear perturbations for an arbitrary number of cosmological
fluids in the early Universe going through various transitions, in particular
the decay of some species (such as a curvaton or a modulus). Using this
formalism, we revisit the question of isocurvature non-Gaussianities in the
mixed inflaton-curvaton scenario and show that one can obtain significant
non-Gaussianities dominated by the isocurvature mode while satisfying the
present constraints on the isocurvature contribution in the observed power
spectrum. We also study two-curvaton scenarios, taking into account the
production of dark matter, and investigate in which cases significant
non-Gaussianities can be produced.Comment: Substantial improvements with respect to the first version. In
particular, we added a discussion on the confrontation of the models with
future observational data. This version is accepted for publication in JCA
Inhomogeneous baryogenesis, cosmic antimatter, and dark matter
A model of inhomogeneous baryogenesis based on the Affleck and Dine mechanism
is described. A simple coupling of the scalar baryon field to the inflaton
allows for formation of astronomically significant bubbles with a large baryon
(or antibaryon) asymmetry. During the farther evolution these domains form
compact stellar-like objects, or lower density clouds, or primordial black
holes of different size. According to the scenario, such high baryonic number
objects occupy relatively small fraction of space but despite that they may
significantly contribute to the cosmological mass density. For some values of
parameters the model allows the possibility the whole dark matter in the
universe to be baryonic. Furthermore, the model allows the existence of the
antibaryonic B-bubbles, i.e. a significant fraction of the mass density in the
universe can be in the form of the compact antimatter objects (e.g.
anti-stars).Comment: 31 pages, 5 figures, three references are adde
Spectrum of Background X-rays from Moduli Dark Matter
We examine the -ray spectrum from the decay of the dark-matter moduli with
mass keV, in particular, paying attention to the line
spectrum from the moduli trapped in the halo of our galaxy. It is found that
with the energy resolution of the current experiments (%) the line
intensity is about twice stronger than that of the continuum spectrum from the
moduli that spread in the whole universe. Therefore, in the future experiments
with higher energy resolutions it may be possible to detect such line photons.
We also investigate the -ray spectrum emitted from the decay of the
multi-GeV moduli. It is shown that the emitted photons may form MeV-bump in the
-ray spectrum. We also find that if the modulus mass is of the order of
10 GeV, the emitted photons at the peak of the continuum spectrum loses their
energy by the scattering and the shape of the spectrum is significantly
changed, which makes the constraint weaker than that obtained in the previous
works.Comment: 14 pages (RevTeX file) including four postscript figures, reviced
version to be published in Physical Review
Gapless Magnetic and Quasiparticle Excitations due to the Coexistence of Antiferromagnetism and Superconductivity in CeRhIn : A study of In-NQR under Pressure
We report systematic measurements of ac-susceptibility,
nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time
() on the pressure ()- induced heavy-fermion (HF) superconductor
CeRhIn. The temperature () dependence of at = 1.6 GPa has
revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist
microscopically, exhibiting the respective transition at K and
= 0.9 K. It is demonstrated that SC does not yield any trace of gap
opening in low-lying excitations below K, but K, followed by a = const law. These results point to the
unconventional characteristics of SC coexisting with AFM. We highlight that
both of the results deserve theoretical work on the gapless nature in low-lying
excitation spectrum due to the coexistence of AFM and SC and the lack of the
mean-field regime below K.Comment: 4pages,5figures,revised versio
Polarization dependent Landau level crossing in a two-dimensional electron system in MgZnO/ZnO-heterostructure
We report electrical transport measurements in a tilted magnetic field on a
high-mobility two-dimensional electron system confined at the MgZnO/ZnO
heterointerface. The observation of multiple crossing events of spin-resolved
Landau levels (LLs) enables the mapping of the sequence of electronic states.
We further measure the renormalization of electron spin susceptibility at zero
field and the susceptibility dependence on the electron spin polarization. The
latter manifests the deviation from the Pauli spin susceptibility. As the
result, the crossing of spin-resolved LLs shifts to smaller tilt angles and the
first Landau level coincidence event is absent even when the magnetic field has
only a perpendicular component to the 2DES plane.Comment: 5 pages, 4 figure
Evidence for Uniform Coexistence of Ferromagnetism and Unconventional Superconductivity in UGe_2: A ^73Ge-NQR Study under Pressure
We report on the itinerant ferromagnetic superconductor UGe_2 through
^73Ge-NQR measurements under pressure (P). The P dependence of the NQR spectrum
signals a first-order transition from the low-temperature (T) and low-P
ferromagnetic phase (FM2) to high-T and high-P one (FM1) around a critical
pressure of P_x ~ 1.2 GPa. The superconductivity exhibiting a maximum value of
T_sc=0.7 K at P_x ~ 1.2 GPa, was found to take place in connection with the
P-induced first-order transition. The nuclear spin-lattice relaxation rate
1/T_1 has probed the ferromagnetic transition, exhibiting a peak at the Curie
temperature as well as a decrease without the coherence peak below T_sc. These
results reveal the uniformly coexistent phase of ferromagnetism and
unconventional superconductivity with a line-node gap. We remark on an intimate
interplay between the onset of superconductivity and the underlying electronic
state for the ferromagnetic phases.Comment: 8 pages, 9 figures. to appear in J. Phys. Soc. JPN, 74 No.2 (2005
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