3,647 research outputs found
Single Field Baryogenesis
We propose a new variant of the Affleck-Dine baryogenesis mechanism in which
a rolling scalar field couples directly to left- and right-handed neutrinos,
generating a Dirac mass term through neutrino Yukawa interactions. In this
setup, there are no explicitly CP violating couplings in the Lagrangian. The
rolling scalar field is also taken to be uncharged under the quantum
numbers. During the phase of rolling, scalar field decays generate a
non-vanishing number density of left-handed neutrinos, which then induce a net
baryon number density via electroweak sphaleron transitions.Comment: 4 pages, LaTe
Baryon and lepton numbers in two scenarios of leptogenesis
Baryon and lepton numbers of the Universe in leptogenesis with Dirac neutrino
and leptogenesis with Majorana neutrino scenarios are considered. It is shown
that despite quite different features of Dirac and Majorana fermions both
scenarios yield the same relation among the initial lepton and the final baryon
asymmetries. Moreover right-handed neutrinos in the leptogenesis with Dirac
neutrino scenario have very little impact on the effective number of
relativistic degrees of freedom, constrained by BBN. Thus the two scenarios are
similar from the cosmological point of view. It is also pointed out that in
thermal equilibrium the 3B+L sum is zero for left-handed fermions.Comment: 9 pages, 4 figure
Gravitational waves from first order phase transitions during inflation
We study the production, spectrum and detectability of gravitational waves in
models of the early Universe where first order phase transitions occur during
inflation. We consider all relevant sources. The self-consistency of the
scenario strongly affects the features of the waves. The spectrum appears to be
mainly sourced by collisions of bubble of the new phases, while plasma dynamics
(turbulence) and the primordial gauge fields connected to the physics of the
transitions are generally subdominant. The amplitude and frequency dependence
of the spectrum for modes that exit the horizon during inflation are different
from those of the waves produced by quantum vacuum oscillations of the metric
or by first order phase transitions not occurring during inflation. A moderate
number of slow (but still successful) phase transitions can leave detectable
marks in the CMBR, but the signal weakens rapidly for faster transitions. When
the number of phase transitions is instead large, the primordial gravitational
waves can be observed both in the CMBR or with LISA (marginally) and especially
DECIGO. We also discuss the nucleosynthesis bound and the constraints it places
on the parameters of the models.Comment: minor changes in the text and the references to match the published
versio
`Thermodynamics' of Minimal Surfaces and Entropic Origin of Gravity
Deformations of minimal surfaces lying in constant time slices in static
space-times are studied. An exact and universal formula for a change of the
area of a minimal surface under shifts of nearby point-like particles is found.
It allows one to introduce a local temperature on the surface and represent
variations of its area in a thermodynamical form by assuming that the entropy
in the Planck units equals the quarter of the area. These results provide a
strong support to a recent hypothesis that gravity has an entropic origin, the
minimal surfaces being a sort of holographic screens. The gravitational entropy
also acquires a definite physical meaning related to quantum entanglement of
fundamental degrees of freedom across the screen.Comment: 12 pages, 1 figur
Friedmann Equations from Entropic Force
In this note by use of the holographic principle together with the
equipartition law of energy and the Unruh temperature, we derive the Friedmann
equations of a Friedmann-Robertson-Walker universe.Comment: latex, 8 pages, v2: minor modifications and to appear in PRD (Rapid
Communication
CPT violation and B-meson oscillations
Recent evidence for anomalous CP violation in B-meson oscillations can be
interpreted as resulting from CPT violation. This yields the first sensitivity
to CPT violation in the B_s^0 system, with the relevant coefficient for CPT
violation constrained at the level of parts in 10^{12}.Comment: 4 pages two-column REVTeX; Rapid Communications, Physical Review D,
in pres
Experimental results on mass-thickness distribution in spacecraft equipment
A technique is described for evaluating the shielding properties of spacecraft equipment with respect to cosmic radiation. A gamma-ray source is used in conjunction with a scintillation detector to determine mass-thickness distribution both in plane geometry for equipment units, and in spherical geometry for given points within the spacecraft. Equations are presented for calculating mass-thickness distribution functions, and the results are compared with experimental measurements
Information-preserving black holes still do not preserve baryon number and other effective global quantum numbers
It has been claimed recently that the black hole information-loss paradox has
been resolved: the evolution of quantum states in the presence of a black hole
is unitary and information preserving. We point out that, contrary to some
claims in literature, information-preserving black holes still violate baryon
number and any other quantum number which follows from an effective (and thus
approximate) or anomalous symmetry.Comment: Honorable Mention on Gravity Essay Competition 2005; Published in the
special Essay issue of Int.J.Mod.Phy
Dark Matter from Baryon Asymmetry
The measured densities of dark and baryonic matter are surprisingly close to
each other, even though the baryon asymmetry and the dark matter are usually
explained by unrelated mechanisms. We consider a scenario where the dark matter
S is produced non-thermally from the decay of a messenger particle X, which
carries the baryon number and compensates for the baryon asymmetry in the
Universe, thereby establishing a connection between the baryonic and dark
matter densities. We propose a simple model to realize this scenario, adding
only a light singlet fermion S and a colored particle X which has a mass in the
O(TeV) range and a lifetime to appear long-lived in collider detector.
Therefore in hadron colliders the signal is similar to that of a stable or
long-lived gluino in supersymmetric models.Comment: 12 pages; v2: bounds on the mass of the messenger particle are
relaxed; conclusions unchanged. additional minor modification
Leptonic CP violation studies at MiniBooNE in the (3+2) sterile neutrino oscillation hypothesis
We investigate the extent to which leptonic CP-violation in (3+2) sterile
neutrino models leads to different oscillation probabilities for
and oscillations at
MiniBooNE. We are using a combined analysis of short-baseline (SBL) oscillation
results, including the LSND and null SBL results, to which we impose additional
constraints from atmospheric oscillation data. We obtain the favored regions in
MiniBooNE oscillation probability space for both (3+2) CP-conserving and (3+2)
CP-violating models. We further investigate the allowed CP-violation phase
values and the MiniBooNE reach for such a CP violation measurement. The
analysis shows that the oscillation probabilities in MiniBooNE neutrino and
antineutrino running modes can differ significantly, with the latter possibly
being as much as three times larger than the first. In addition, we also show
that all possible values of the single CP-violation phase measurable at short
baselines in (3+2) models are allowed within 99% CL by existing data.Comment: Fixed a typo following PRD Erratum. 8 pages, 5 figure
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