2,720 research outputs found
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
A gamma-ray testing technique for spacecraft
The simulated cosmic radiation effect on a spacecraft structure is evaluated by gamma ray testing in relation to structural thickness. A drawing of the test set-up is provided and measurement errors are discussed
Synchrotron Radiation and Quantum Gravity
Photons may evade a synchrotron radiation constraint on quantum gravity by
violating the equivalence principle.Comment: 4 pages. Comment on Jacobson et al astro-ph/0212190. Presentation
revised for brief communication to Nature with extended bibliograph
Quantum-Gravity Analysis of Gamma-Ray Bursts using Wavelets
In some models of quantum gravity, space-time is thought to have a foamy
structure with non-trivial optical properties. We probe the possibility that
photons propagating in vacuum may exhibit a non-trivial refractive index, by
analyzing the times of flight of radiation from gamma-ray bursters (GRBs) with
known redshifts. We use a wavelet shrinkage procedure for noise removal and a
wavelet `zoom' technique to define with high accuracy the timings of sharp
transitions in GRB light curves, thereby optimizing the sensitivity of
experimental probes of any energy dependence of the velocity of light. We apply
these wavelet techniques to 64 ms and TTE data from BATSE, and also to OSSE
data. A search for time lags between sharp transients in GRB light curves in
different energy bands yields the lower limit GeV on
the quantum-gravity scale in any model with a linear dependence of the velocity
of light . We also present a limit on any quadratic dependence.Comment: This version is accepted for publication in Astronomy & Astrophysics.
The discussion and introduction are extended making clear why the wavelet
analysis should be superior to straight cross-correlation analysis. More
details on compiled data are elaborated. 18 pages, 9 figures, A&A forma
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
Infinite statistics, symmetry breaking and combinatorial hierarchy
The physics of symmetry breaking in theories with strongly interacting quanta
obeying infinite (quantum Boltzmann) statistics known as quons is discussed.
The picture of Bose/Fermi particles as low energy excitations over nontrivial
quon condensate is advocated. Using induced gravity arguments it is
demonstrated that the Planck mass in such low energy effective theory can be
factorially (in number of degrees of freedom) larger than its true ultraviolet
cutoff. Thus, the assumption that statistics of relevant high energy
excitations is neither Bose nor Fermi but infinite can remove the hierarchy
problem without necessity to introduce any artificially large numbers. Quantum
mechanical model illustrating this scenario is presented.Comment: LaTeX, 11 page
The Supersymmetric Origin of Matter
The Minimal Supersymmetric extension of the Standard Model (MSSM) can provide
the correct neutralino relic abundance and baryon number asymmetry of the
universe. Both may be efficiently generated in the presence of CP violating
phases, light charginos and neutralinos, and a light top squark. Due to the
coannihilation of the neutralino with the light stop, we find a large region of
parameter space in which the neutralino relic density is consistent with WMAP
and SDSS data. We perform a detailed study of the additional constraints
induced when CP violating phases, consistent with the ones required for
baryogenesis, are included. We explore the possible tests of this scenario from
present and future electron Electric Dipole Moment (EDM) measurements, direct
neutralino detection experiments, collider searches and the b -> s gamma decay
rate. We find that the EDM constraints are quite severe and that electron EDM
experiments, together with stop searches at the Tevatron and Higgs searches at
the LHC, will provide a definite test of our scenario of electroweak
baryogenesis in the next few years.Comment: 30 pages, 14 figure
Leptogenesis with Dirac Neutrinos
We describe a "neutrinogenesis" mechanism whereby, in the presence of
right-handed neutrinos with sufficiently small pure Dirac masses,
(B+L)-violating sphaleron processes create the baryon asymmetry of the
Universe, even when B=L=0 initially. It is shown that the resulting neutrino
mass constraints are easily fulfilled by the neutrino masses suggested by
current experiments. We present a simple toy model which uses this mechanism to
produce the observed baryon asymmetry of the Universe. (PostScript Errors
corrected in latest Version).Comment: 4 pages, Latex (using amsmath,feynmp,graphicx), 4 figure
The universal viscosity to entropy density ratio from entanglement
We present evidence that the universal Kovtun-Son-Starinets shear viscosity
to entropy density ratio of 1/4\pi can be associated with a Rindler causal
horizon in flat spacetime. Since there is no known holographic (gauge/gravity)
duality for this spacetime, a natural microscopic explanation for this
viscosity is in the peculiar properties of quantum entanglement. In particular,
it is well-known that the Minkowski vacuum state is a thermal state and carries
an area entanglement entropy density in the Rindler spacetime. Based on the
fluctuation-dissipation theorem, we expect a similar notion of viscosity
arising from vacuum fluctuations. Therefore, we propose a holographic Kubo
formula in terms of a two-point function of the stress tensor of matter fields
in the bulk. We calculate this viscosity assuming a minimally coupled scalar
field theory and find that the ratio with respect to the entanglement entropy
density is exactly 1/4\pi in four dimensions. The issues that arise in
extending this result to non-minimally coupled scalar fields, higher spins, and
higher dimensions provide interesting hints about the relationship between
entanglement entropy and black hole entropy.Comment: 30 pages; v2: footnote added, minor editin
Baryon asymmetry from hypermagnetic helicity in dilaton hypercharge electromagnetism
The generation of the baryon asymmetry of the Universe (BAU) from the
hypermagnetic helicity, the physical interpretation of which is given in terms
of hypermagnetic knots, is studied in inflationary cosmology, taking into
account the breaking of the conformal invariance of hypercharge electromagnetic
fields through both a coupling with the dilaton and that with a pseudoscalar
field. It is shown that if the electroweak phase transition (EWPT) is strongly
first order and the present amplitude of the generated magnetic fields on the
horizon scale is sufficiently large, a baryon asymmetry with a sufficient
magnitude to account for the observed baryon to entropy ratio can be generated.Comment: 16 pages, 2 figures, a reference added, typos correcte
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