535 research outputs found
Supernova Constraints on a Superlight Gravitino
In supergravity models with low supersymmetry breaking scale the gravitinos
can be superlight with mass in the micro-eV to keV range. In such a case,
gravitino emission provides a new cooling mechanism for protoneutron stars and
therefore can provide constraints on the mass of the superlight gravitino. This
happens because the coupling to matter of superlight gravitinos is dominated by
its goldstino component, whose coupling to matter is inversely proportional to
the scale of supersymmetry breaking and increases as the gravitino mass
decreases. Present observations therefore provide lower limits on the gravitino
mass. Using recently revised goldstino couplings, we find that the two dominant
processes in supernova cooling are and
. They lead to lower limits on the
supersymmetry breaking scale from 160 to 500 GeV for core
temperatures 30 to 60 MeV and electron chemical potentials 200 to 300 MeV. The
corresponding lower limits on the gravitino mass are eV.Comment: Latex 6 pages; one figure; UTEXAS-HEP-97-19, UMD-PP-98-07,
SMU-HEP-97-1
Supernova Bounds on the Dark Photon Using its Electromagnetic Decay
The hypothetical massive dark photon () which has kinetic mixing
with the SM photon can decay electromagnetically to pairs if its mass
exceeds and otherwise into three SM photons. These decays yield
cosmological and supernovae associated signatures. We briefly discuss these
signatures, particularly in connection with the supernova SN1987A and delineate
the extra constraints that may then arise on the mass and mixing parameter of
the dark photon. In particular, we find that for dark photon mass
in the 5-20 MeV range, arguments based on supernova 1987A observations lead to
a bound on which is about 300 times stronger than the presently
existing bounds based on energy loss arguments.Comment: 10 pages, 6 figures, minor typos corrected, version to appear in NP
Competition Between Gravitational and Scalar Field Radiation
Recent astrophysical observations have provided strong evidence that the
present expansion of the universe is accelerating, powered by the energy
density associated with a cosmological term. Assuming the latter to be not
simply a constant term but a "quintessence" field, we study the radiation of
quanta of such a "quintessence" field ("quintons") by binary systems of
different types and compare intensities to those of standard tensor
gravitational wave emission. We consider both the case in which the
quintessence field varies only over cosmological distances and the case in
which it is modified spatially by (strong) gravitational fields, a condition
that results in bounds on the gradient of the scalar field. We show that, in
both the first case and, because of a bound we derive from the Hulse-Taylor
pulsar, in the second, there is not sufficient quinton radiation to affect
expected LISA and LIGO gravity wave signals from binary systems. We show that,
in the second case, the Large Hadron Collider is capable of setting a bound
similar to that from the binary pulsar.Comment: 12 pages aastex, accepted for publication in the Astrophysical
Journal. Minor typographical errors and reference list correcte
Critical Charges on Strange Quark Nuggets and Other Extended Objects
We investigate the behavior of the critical charge for spontaneous pair
production, , defined as the charge at which the total energy of a
-shell electron is , as a function of the radius of the charge
distribution. Our approach is to solve the Dirac equation for a potential
consisting of a spherically symmetrical charge distribution of radius
and a Coulomb tail. For a spherical shell distribution of the type usually
associated with color-flavor locked strange quark nuggets, we confirm the
relation for sufficiently large obtained by Madsen,
who used an approach based on the Thomas-Fermi model. We also present results
for a uniformly charged sphere and again find that for large enough
. Also discussed is the behavior of when simple {\it ad hoc}
modifications are made to the potential for .Comment: 7 pages, 6 figure
Spitzer Observations of the z=2.73 Lensed Lyman Break Galaxy, MS1512-cB58
We present Spitzer infrared (IR) photometry and spectroscopy of the lensed
Lyman break galaxy (LBG), MS1512-cB58 at z=2.73. The large (factor ~30)
magnification allows for the most detailed infrared study of an L*_UV(z=3) LBG
to date. Broadband photometry with IRAC (3-10 micron), IRS (16 micron), and
MIPS (24, 70 & 160 micron) was obtained as well as IRS spectroscopy spanning
5.5-35 microns. A fit of stellar population models to the optical/near-IR/IRAC
photometry gives a young age (~9 Myr), forming stars at ~98 M_sun/yr, with a
total stellar mass of ~10^9 M_sun formed thus far. The existence of an old
stellar population with twice the stellar mass can not be ruled out. IR
spectral energy distribution fits to the 24 and 70 micron photometry, as well
as previously obtained submm/mm, data give an intrinsic IR luminosity L_IR =
1-2 x10^11 L_sun and a star formation rate, SFR ~20-40 M_sun/yr. The UV derived
star formation rate (SFR) is ~3-5 times higher than the SFR determined using
L_IR or L_Halpha because the red UV spectral slope is significantly over
predicting the level of dust extinction. This suggests that the assumed
Calzetti starburst obscuration law may not be valid for young LBGs. We detect
strong line emission from Polycyclic Aromatic Hydrocarbons (PAHs) at 6.2, 7.7,
and 8.6 microns. The line ratios are consistent with ratios observed in both
local and high redshift starbursts. Both the PAH and rest-frame 8 micron
luminosities predict the total L_IR based on previously measured relations in
starbursts. Finally, we do not detect the 3.3 micron PAH feature. This is
marginally inconsistent with some PAH emission models, but still consistent
with PAH ratios measured in many local star-forming galaxies.Comment: Accepted for publication in ApJ. aastex format, 18 pages, 7 figure
Strange Quarks Nuggets in Space: Charges in Seven Settings
We have computed the charge that develops on an SQN in space as a result of
balance between the rates of ionization by ambient gammas and capture of
ambient electrons. We have also computed the times for achieving that
equilibrium and binding energy of the least bound SQN electrons. We have done
this for seven different settings. We sketch the calculations here and give
their results in the Figure and Table II; details are in the Physical Review
D.79.023513 (2009).Comment: Six pages, one figure. To appear in proceedings of the 2008 UCLA
coference on dark matter and dark energ
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