1,414 research outputs found
The exterior degree of a pair of finite groups
The exterior degree of a pair of finite groups , which is a
generalization of the exterior degree of finite groups, is the probability for
two elements in such that . In the present paper,
we state some relations between this concept and the relative commutatively
degree, capability and the Schur multiplier of a pair of groups.Comment: To appear in Mediterr. J. Mat
On the reheating stage after inflation
We point out that inflaton decay products acquire plasma masses during the
reheating phase following inflation. The plasma masses may render inflaton
decay kinematicaly forbidden, causing the temperature to remain frozen for a
period at a plateau value. We show that the final reheating temperature may be
uniquely determined by the inflaton mass, and may not depend on its coupling.
Our findings have important implications for the thermal production of
dangerous relics during reheating (e.g., gravitinos), for extracting bounds on
particle physics models of inflation from Cosmic Microwave Background
anisotropy data, for the production of massive dark matter candidates during
reheating, and for models of baryogenesis or leptogensis where massive
particles are produced during reheating.Comment: 8 pages, 2 figures. Submitted for publication in Phys. Rev.
Non-Critical Liouville String Escapes Constraints on Generic Models of Quantum Gravity
It has recently been pointed out that generic models of quantum gravity must
contend with severe phenomenological constraints imposed by gravitational
Cerenkov radiation, neutrino oscillations and the cosmic microwave background
radiation. We show how the non-critical Liouville-string model of quantum
gravity we have proposed escapes these constraints. It gives energetic
particles subluminal velocities, obviating the danger of gravitational Cerenkov
radiation. The effect on neutrino propagation is naturally flavour-independent,
obviating any impact on oscillation phenomenology. Deviations from the expected
black-body spectrum and the effects of time delays and stochastic fluctuations
in the propagation of cosmic microwave background photons are negligible, as
are their effects on observable spectral lines from high-redshift astrophysical
objects.Comment: 15 pages LaTeX, 2 eps figures include
Measuring the Spin of the Higgs Boson
By studying the threshold dependence of the excitation curve and the angular
distribution in Higgs-strahlung at e+e- colliders, e+e- -> HZ, the spin of the
Higgs boson in the Standard Model and related extensions can be determined
unambiguously in a model-independent way.Comment: 10 pages, 1 Postscript figure, sign typo correcte
Discovery of a redshift 6.13 quasar in the UKIRT infrared deep sky survey
Original article can be found at: http://www.aanda.org/ Copyright The European Southern Observatory (ESO) DOI: 10.1051/0004-6361/200811161Optical and near-infrared (NIR) spectra are presented for ULAS J131911.29+095051.4 (hereafter ULAS J1319+0950), a new redshift z = 6.127 0.004 quasar discovered in the Third Data Release (DR3) of the UKIRT Infrared Deep Sky Survey (UKIDSS). The source has = 19.10 0.03, corresponding to = -27.12, which is comparable to the absolute magnitudes of the z 6 quasars discovered in the Sloan Digital Sky Survey (SDSS). ULAS J1319+0950 was, in fact, registered by SDSS as a faint source with = 20.13 0.12, just below the signal-to-noise ratio limit of the SDSS high-redshift quasar survey. The faint z-band magnitude is a consequence of the weak Ly /N V emission line, which has a rest-frame equivalent width of ~20Å and provides only a small boost to the z-band flux. Nevertheless, there is no evidence of a significant new population of high-redshift quasars with weak emission lines from this UKIDSS-based search. The Ly  optical depth to ULAS J1319+0950 is consistent with that measured towards similarly distant SDSS quasars, implying that results from optical- and NIR-selected quasars may be combined in studies of cosmological reionization. Also presented is a new NIR-spectrum of the previously discovered UKIDSS quasar ULAS J020332.38+001229.2, which reveals the object to be a broad absorption line quasar. The new spectrum shows that the emission line initially identified as Ly  is actually N V, leading to a revised redshift of z = 5.72, rather than z = 5.86 as previously estimatedPeer reviewe
Fluctuation Theorems for Entropy Production and Heat Dissipation in Periodically Driven Markov Chains
Asymptotic fluctuation theorems are statements of a Gallavotti-Cohen symmetry
in the rate function of either the time-averaged entropy production or heat
dissipation of a process. Such theorems have been proved for various general
classes of continuous-time deterministic and stochastic processes, but always
under the assumption that the forces driving the system are time independent,
and often relying on the existence of a limiting ergodic distribution. In this
paper we extend the asymptotic fluctuation theorem for the first time to
inhomogeneous continuous-time processes without a stationary distribution,
considering specifically a finite state Markov chain driven by periodic
transition rates. We find that for both entropy production and heat
dissipation, the usual Gallavotti-Cohen symmetry of the rate function is
generalized to an analogous relation between the rate functions of the original
process and its corresponding backward process, in which the trajectory and the
driving protocol have been time-reversed. The effect is that spontaneous
positive fluctuations in the long time average of each quantity in the forward
process are exponentially more likely than spontaneous negative fluctuations in
the backward process, and vice-versa, revealing that the distributions of
fluctuations in universes in which time moves forward and backward are related.
As an additional result, the asymptotic time-averaged entropy production is
obtained as the integral of a periodic entropy production rate that generalizes
the constant rate pertaining to homogeneous dynamics
All-optical phase and amplitude regeneration properties of a 40 Gbit/s DPSK black-box phase sensitive amplifier
We experimentally study the pure amplitude and phase regeneration capabilities of a blackbox degenerate four wave mixing (FWM) based bit-rate-flexible phase sensitive amplifier (PSA) for a 40 Gbit/s differential phase-shift keyed (DPSK) signal
Colliders and Cosmology
Dark matter in variations of constrained minimal supersymmetric standard
models will be discussed. Particular attention will be given to the comparison
between accelerator and direct detection constraints.Comment: Submitted for the SUSY07 proceedings, 15 pages, LaTex, 26 eps figure
A tentative derivation of the main cosmological parameters
Based on the assumption that some apparent properties of the observable
universe are accurate at a reasonable level of approximation, a tentative is
made to independently derive the values of the baryon density parameter, the
Hubble constant, the cosmic microwave background temperature and the helium
mass fraction. The obtained values are in excellent agreement with those given
by the most recent observational data.Comment: 13 pages. Accepted for publication in Astrophysics & Space Scienc
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