1,310 research outputs found
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
Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars
(ABBREVIATED) We consider the structure of neutron star magnetospheres
threaded by large-scale electrical currents, and the effect of resonant Compton
scattering by the charge carriers (both electrons and ions) on the emergent
X-ray spectra and pulse profiles. In the magnetar model for the SGRs and AXPs,
these currents are maintained by magnetic stresses acting deep inside the star.
We construct self-similar, force-free equilibria of the current-carrying
magnetosphere with a power-law dependence of magnetic field on radius, B ~
r^(-2-p), and show that a large-scale twist softens the radial dependence to p
< 1. The spindown torque acting on the star is thereby increased in comparison
with a vacuum dipole. We comment on the strength of the surface magnetic field
in the SGR and AXP sources, and the implications of this model for the narrow
measured distribution of spin periods. A magnetosphere with a strong twist,
B_\phi/B_\theta = O(1) at the equator, has an optical depth ~ 1 to resonant
cyclotron scattering, independent of frequency (radius), surface magnetic field
strength, or charge/mass ratio of the scattering charge. When electrons and
ions supply the current, the stellar surface is also heated by the impacting
charges at a rate comparable to the observed X-ray output of the SGR and AXP
sources, if B_{dipole} ~ 10^{14} G. Redistribution of the emerging X-ray flux
at the ion and electron cyclotron resonances will significantly modify the
emerging pulse profile and, through the Doppler effect, generate a non-thermal
tail to the X-ray spectrum. The sudden change in the pulse profile of SGR
1900+14 after the 27 August 1998 giant flare is related to an enhanced optical
depth to electron cyclotron scattering, resulting from a sudden twist imparted
to the external magnetic field.Comment: 31 January 2002, minor revisions, new section 5.4.
Magnetic Photon Splitting: the S-Matrix Formulation in the Landau Representation
Calculations of reaction rates for the third-order QED process of photon
splitting in strong magnetic fields traditionally have employed either the
effective Lagrangian method or variants of Schwinger's proper-time technique.
Recently, Mentzel, Berg and Wunner (1994) presented an alternative derivation
via an S-matrix formulation in the Landau representation. Advantages of such a
formulation include the ability to compute rates near pair resonances above
pair threshold. This paper presents new developments of the Landau
representation formalism as applied to photon splitting, providing significant
advances beyond the work of Mentzel et al. by summing over the spin quantum
numbers of the electron propagators, and analytically integrating over the
component of momentum of the intermediate states that is parallel to field. The
ensuing tractable expressions for the scattering amplitudes are satisfyingly
compact, and of an appearance familiar to S-matrix theory applications. Such
developments can facilitate numerical computations of splitting considerably
both below and above pair threshold. Specializations to two regimes of interest
are obtained, namely the limit of highly supercritical fields and the domain
where photon energies are far inferior to that for the threshold of
single-photon pair creation. In particular, for the first time the
low-frequency amplitudes are simply expressed in terms of the Gamma function,
its integral and its derivatives. In addition, the equivalence of the
asymptotic forms in these two domains to extant results from effective
Lagrangian/proper-time formulations is demonstrated.Comment: 19 pages, 3 figures, REVTeX; accepted for publication in Phys. Rev.
Constraints for hypothetical interactions from a recent demonstration of the Casimir force and some possible improvements
The Casimir force is calculated in the configuration of a spherical lens and
a disc of finite radius covered by and thin layers which was used in
a recent experiment. The correction to the Casimir force due to finiteness of
the disc radius is shown to be negligible. Also the corrections are discussed
due to the finite conductivity, large-scale and short-scale deviations from the
perfect shape of the bounding surfaces and the temperature correction. They
were found to be essential when confronting the theoretical results with
experimental data. Both Yukawa-type and power-law hypothetical forces are
computed which may act in the configuration under consideration due to the
exchange of light and/or massless elementary particles between the atoms of the
lens and the disc. New constraints on the constants of these forces are
determined which follow from the fact that they were not observed within the
limits of experimental errors. For Yukawa-type forces the new constraints are
up to 30 times stronger than the best ones known up today. A possible
improvement of experimental parameters is proposed which gives the possibility
to strengthen constraints on Yukawa-type interactions up to times and on
power-law interactions up to several hundred times.Comment: 15 pages, 3 figures, subm. to Phys. Rev.
Gauge Boson - Gauge Boson Scattering in Theories with Large Extra Dimensions
We consider the scattering amplitudes of the form V_1 V_2 -> V_3 V_4, where
V_i=\gamma, Z, W or g(=gluon) are the Standard Model gauge bosons, due to
graviton exchange in Kaluza-Klein theories with large extra dimensions. This
leads to a number of experimentally viable signatures at high energy leptonic
and hadronic colliders. We discuss the observability or future limits on the
scale of the gravitational interactions (m_D), that may be obtained at an e+e-
Next Linear Collider (NLC) and at the LHC, by studying some of these type of
gauge boson scattering processes. We find that the attainable limits through
these type of processes are: m_D > 3 TeV at the NLC and m_D > 6 TeV at the LHC.Comment: 27 pages, plain latex, 7 figures embadded in the text using epsfi
Dijet Production at Hadron Colliders in Theories with Large Extra Dimensions
We consider the production of high invariant mass jet pairs at hadron
colliders as a test for TeV scale gravitational effects. We find that this
signal can probe effective Planck masses of about 10 TeV at the LHC with center
of mass energy of 14 TeV and 1.5 TeV at the Tevatron with center of mass energy
of 2 TeV. These results are compared to analogous scattering processes at
leptonic colliders.Comment: 15 pages with 3 figure
The Interplanetary Network Supplement to the Fermi GBM Catalog of Cosmic Gamma-Ray Bursts
We present Interplanetary Network (IPN) data for the gamma-ray bursts in the
first Fermi Gamma-Ray Burst Monitor (GBM) catalog. Of the 491 bursts in that
catalog, covering 2008 July 12 to 2010 July 11, 427 were observed by at least
one other instrument in the 9-spacecraft IPN. Of the 427, the localizations of
149 could be improved by arrival time analysis (or triangulation). For any
given burst observed by the GBM and one other distant spacecraft, triangulation
gives an annulus of possible arrival directions whose half-width varies between
about 0.4' and 32 degrees, depending on the intensity, time history, and
arrival direction of the burst, as well as the distance between the spacecraft.
We find that the IPN localizations intersect the 1 sigma GBM error circles in
only 52% of the cases, if no systematic uncertainty is assumed for the latter.
If a 6 degree systematic uncertainty is assumed and added in quadrature, the
two localization samples agree about 87% of the time, as would be expected. If
we then multiply the resulting error radii by a factor of 3, the two samples
agree in slightly over 98% of the cases, providing a good estimate of the GBM 3
sigma error radius. The IPN 3 sigma error boxes have areas between about 1
square arcminute and 110 square degrees, and are, on the average, a factor of
180 smaller than the corresponding GBM localizations. We identify two bursts in
the IPN/GBM sample that did not appear in the GBM catalog. In one case, the GBM
triggered on a terrestrial gamma flash, and in the other, its origin was given
as uncertain. We also discuss the sensitivity and calibration of the IPN.Comment: 52 pages, 12 figures, 4 tables. Revised version, resubmitted to the
Astrophysical Journal Supplement Series following refereeing. Figures of the
localizations in Table 3 may be found on the IPN website, at
ssl.berkeley.edu/ipn3/YYMMDD, where YY, MM, and DD are the year, month, and
day of the burst, sometimes with suffixes A or
IPN localizations of Konus short gamma-ray bursts
Between the launch of the \textit{GGS Wind} spacecraft in 1994 November and
the end of 2010, the Konus-\textit{Wind} experiment detected 296 short-duration
gamma-ray bursts (including 23 bursts which can be classified as short bursts
with extended emission). During this period, the IPN consisted of up to eleven
spacecraft, and using triangulation, the localizations of 271 bursts were
obtained. We present the most comprehensive IPN localization data on these
events. The short burst detection rate, 18 per year, exceeds that of many
individual experiments.Comment: Published versio
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