334 research outputs found
Gravity induced neutrino-antineutrino oscillation: CPT and lepton number non-conservation under gravity
We introduce a new effect in the neutrino oscillation phase which shows the
neutrino-antineutrino oscillation is possible under gravity even if the rest
masses of the corresponding eigenstates are same. This is due to CPT violation
and possible to demonstrate if the neutrino mass eigenstates are expressed as a
combination of neutrino and antineutrino eigenstates, as of the neutral kaon
system, with the plausible breaking of lepton number conservation. For Majorana
neutrinos, this oscillation is expected to affect significantly the inner edge
of neutrino dominated accretion disks around a compact object by influencing
the neutrino sphere which controls the accretion dynamics, and then the related
type-II supernova evolution and the r-process nucleosynthesis. On the other
hand, in early universe, in presence of various lepton number violating
processes, this oscillation, we argue, might lead to neutrino asymmetry which
resulted baryogenesis from the B-L symmetry by electro-weak sphaleron
processes.Comment: 15 pages; Accepted for publication in Classical and Quantum Gravit
Predictive Power of Strong Coupling in Theories with Large Distance Modified Gravity
We consider theories that modify gravity at cosmological distances, and show
that any such theory must exhibit a strong coupling phenomenon, or else it is
either inconsistent or is already ruled out by the solar system observations.
We show that all the ghost-free theories that modify dynamics of spin-2
graviton on asymptotically flat backgrounds, automatically have this property.
Due to the strong coupling effect, modification of the gravitational force is
source-dependent, and for lighter sources sets in at shorter distances. This
universal feature makes modified gravity theories predictive and potentially
testable not only by cosmological observations, but also by precision
gravitational measurements at scales much shorter than the current cosmological
horizon. We give a simple parametrization of consistent large distance modified
gravity theories and their predicted deviations from the Einsteinian metric
near the gravitating sources.Comment: 12 pages, Latex, to be published in New Journal of Physic
Test of the Equivalence Principle Using a Rotating Torsion Balance
We used a continuously rotating torsion balance instrument to measure the
acceleration difference of beryllium and titanium test bodies towards sources
at a variety of distances. Our result Delta a=(0.6+/-3.1)x10^-15 m/s^2 improves
limits on equivalence-principle violations with ranges from 1 m to infinity by
an order of magnitude. The Eoetvoes parameter is eta=(0.3+/-1.8)x10^-13. By
analyzing our data for accelerations towards the center of the Milky Way we
find equal attractions of Be and Ti towards galactic dark matter, yielding
eta=(-4 +/- 7)x10^-5. Space-fixed differential accelerations in any direction
are limited to less than 8.8x10^-15 m/s^2 with 95% confidence.Comment: 4 pages, 4 figures; accepted for publication in PR
Anapole moment of an exotic nucleus
We demonstrate that there is no appreciable enhancement of the anapole moment
of Be. The effect of small energy intervals is compensated for by a
small overlap of the halo neutron wave function with core.Comment: 5 pages, LaTe
Solar models and electron screening
We investigate the sensitivity of the solar model to changes in the nuclear
reaction screening factors. We show that the sound speed profile as determined
by helioseismology certainly rules out changes in the screening factors
exceeding more than 10%. A slightly improved solar model could be obtained by
enhancing screening by about 5% over the Salpeter value. We also discuss how
envelope properties of the Sun depend on screening, too. We conclude that the
solar model can be used to help settling the on-going dispute about the
``correct'' screening factors.Comment: accepted for publication by Astron. Astrophy
Constrains on non-Newtonian gravity from the experiment on neutron quantum states in the Earth's gravitational field
An upper limit to non-Newtonian attracive forces is obtained from the
measurement of quantum states of neutrons in the Earth's gravitational field.
This limit improves the existing constrains in the nanometer range
Photometric Properties of Lyman-break Galaxies at z=3 in Cosmological SPH Simulations
We study the photometric properties of Lyman-break galaxies (LBGs) formed by
redshift z=3 in a set of large cosmological smoothed-particle hydrodynamics
simulations of the Lambda cold dark matter (CDM) model. Our numerical
simulations include radiative cooling and heating with a uniform UV background,
star formation, supernova feedback, and a phenomenological model for galactic
winds. Analysing a series of simulations of varying boxsize and particle number
allows us to isolate the impact of numerical resolution on our results. We
compute spectra of simulated galaxies using a population synthesis model, and
derive colours and luminosity functions of galaxies at z=3 after applying local
dust extinction and absorption by the intergalactic medium (IGM). We find that
the simulated galaxies have U-G and G-R colours consistent with observations,
provided that intervening absorption by the IGM is applied. The observed
properties of LBGs, including their number density, colours, and luminosity
functions, can be explained if LBGs are identified with the most massive
galaxies at z=3, having typical stellar mass of M_{star} ~ 1e10 Msun/h, a
conclusion broadly consistent with earlier studies based on hydrodynamic
simulations of the Lamda CDM model. We also find that most simulated LBGs were
continuously forming stars at a high rate for more than one Gyr up until z=3,
but with numerous starbursts lying on top of the continuous component.
Interestingly, our simulations suggest that more than 50% of the total stellar
mass and star formation rate in the Universe are accounted for by galaxies that
are not detected in the current generation of LBG surveys.Comment: 12 pages, 8 figures, Error in AB magnitude calculation corrected.
Figures in the original published version in MNRAS contain error except Fig.5
& 6, but the basic conclusions are unchanged. Higher resolution version
available at http://cfa-www.harvard.edu/~knagamine/lbg.ps.g
Local Starbursts in a Cosmological Context
In this contribution I introduce some of the major issues that motivate the
conference, with an emphasis on how starbursts fit into the ``big picture''. I
begin by defining starbursts in several different ways, and discuss the merits
and limitations of these definitions. I will argue that the most physically
useful definition of a starburst is its ``intensity'' (star formation rate per
unit area). This is the most natural parameter to compare local starbursts with
physically similar galaxies at high redshift, and indeed I will argue that
local starbursts are unique laboratories to study the processes at work in the
early universe. I will describe how NASA's GALEX mission has uncovered a rare
population of close analogs to Lyman Break Galaxies in the local universe. I
will then compare local starbursts to the Lyman-Break and sub-mm galaxies high
redshift populations, and speculate that the multidimensional ``manifold'' of
starbursts near and far can be understood largely in terms of the
Schmidt/Kennicutt law and galaxy mass-metallicity relation. I will briefly
summarize he properties of starburst-driven galactic superwinds and their
possible implications for the evolution of galaxies and the IGM. These complex
multiphase flows are best studied in nearby starbursts, where we can study the
the hot X-ray gas that contains the bulk of the energy and newly produced
metals.Comment: Proceedings of the Conference "Starbursts: Fropm 30 Doradus to Lyman
Break Galaxies
Constraints on Light Pseudoscalars Implied by Tests of the Gravitational Inverse-Square Law
The exchange of light pseudoscalars between fermions leads to a
spin-independent potential in order g^4, where g is the Yukawa
pseudoscalar-fermion coupling constant. This potential gives rise to detectable
violations of both the weak equivalence principle (WEP) and the gravitational
inverse-square law (ISL), even if g is quite small. We show that when
previously derived WEP constraints are combined with those arisingfrom ISL
tests, a direct experimental limit on the Yukawa coupling of light
pseudoscalars to neutrons can be inferred for the first time (g_n^2/4pi < 1.6
\times 10^-7), along with a new (and significantly improved) limit on the
coupling of light pseudoscalars to protons.Comment: 12 pages, Revtex, with 1 Postscript figure (submitted to Physical
Review Letters
Extremely Red Objects in the Field of QSO 1213-0017: A Galaxy Concentration at z=1.31
We have discovered a concentration of extremely red objects (EROs; R-K>6) in
the field of the z=2.69 quasar QSO 1213-0017 (UM 485), which is significantly
overabundant compared to the field ERO surface density. The optical/near-IR
colors of the EROs and numerous other red galaxies in this field are consistent
with elliptical galaxies at z=1-2. HST optical images for a subset of galaxies
show regular morphologies, most of them being disky or diffuse and without any
obvious evidence for interactions. Ground-based IR images show similar
morphologies, indicating any dust reddening in these objects is spatially
uniform. Optical spectroscopy with the W. M. Keck Telescope has found that four
of the red galaxies lie at =1.31, and a fifth lies in the foreground at
z=1.20. Of the =1.31 galaxies, one is a reddened AGN while the remaining
three have rest-frame UV absorption-line spectra characteristic of old (few
Gyr) stellar populations, similar to the old red galaxy LBDS 53W091 at z=1.55.
Including the MgII absorber seen in the QSO spectrum, we find five galaxies at
=1.31 spread over 1.5 h_50^{-1} Mpc on the sky. These results suggest we
have discovered a coherent structure of old galaxies at high-redshift, possibly
associated with a massive galaxy cluster.Comment: 37 pages including 11 Postscript figures. To appear in the June 2000
issue of the Astronomical Journa
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