PMC Physics A - Latest articles

Hadron multiplicity in e+e- events induced by top quark pairs at the ILC energy

Alexandre V Kisselev and Vladimir A Petrov — 2008-04-04

The average charged hadron multiplicity in the e+e- events with the primary tt¯ MathType@MTEF@5@5@+=feaafiart1ev1aaatCvAUfKttLearuWrP9MDH5MBPbIqV92AaeXatLxBI9gBaebbnrfifHhDYfgasaacH8bkY=wiFfYlOipiY=Hhbbf9v8qqaqFr0xc9vqpe0di9q8qqpG0dHiVcFbIOFHK8Feei0lXdar=Jb9qqFfeaYRXxe9vr0=vr0=LqpWqaaeaabiGaciaacaqabeaabeqacmaaaOqaaiabdsha0jqbdsha0zaaraaaaa@2DF1@-pair at the collision energy 500 GeV, as well as the average multiplicity of charged hadrons from the top quark are calculated in QCD to be 86.7 ± 1.11 and 41.0 ± 0.54, respectively.PACS Codes: 14.65.Ha, 13.66.Bc, 12.38.Bx

Effects of supersymmetric threshold corrections on high-scale flavour textures

Altan Çakir and Levent Solmaz — 2008-03-07

Integration of superpartners out of the spectrum induces potentially large contributions to Yukawa couplings. Supersymmetric threshold corrections therefore influence the CKM matrix prediction in a non-trivial way. We study the effects of threshold corrections on high-scale flavor structures specified at the gauge coupling unification scale in supersymmetry. We first consider high-scale Yukawa textures which qualify as phenomenologically viable at tree level, and find that they are disqualified after incorporating the threshold corrections. Next, we consider Yukawa couplings, such as those with five texture zeroes, which are incapable of explaining flavor-changing processes. Incorporating threshold corrections, however, makes them phenomenologically viable textures. Therefore, supersymmetric threshold corrections are found to have an observable impact on Yukawa couplings of quarks, and any confrontation of high-scale textures with experiments at the weak scale must take into account such corrections.PACS Codes: 12.60.Jv, 12.15.Hh

Supernova Ia observations in the Lemaître-Tolman model

Krzysztof Bolejko — 2008-02-12

The aim of this paper is to check if the models with realistic inhomogeneous matter distribution and without cosmological constant can explain the dimming of the supernovae in such a way that it can be interpreted as an acceleration of the Universe. Employing the simplest inhomogeneous model, i.e. Lemaître-Tolman model, this paper examines the impact of inhomogeneous matter distribution on light propagation. These analyses show that realistic matter fluctuations on small scales induce brightness fluctuations in the residual Hubble diagram of amplitude around 0.15 mag, and thus can mimic acceleration. However, it is different on large scales. All these brightness fluctuations decrease with distance and hence cannot explain the dimmining of supernovae for high redshift without without invoking the cosmological constant. This paper concludes that models with realistic matter distribution (i.e. where variation of the density contrast is similar to what is observed in the local Universe) cannot explain the observed dimming of supernovae without the cosmological constant.PACS Codes: 98.65.Dx, 98.65.-r, 98.62.Ai

The luminosity-redshift relation in brane-worlds: II. Confrontation with experimental data

Gyula M Szabó, László Á Gergely and Zoltán Keresztes — 2007-12-12

The luminosity distance – redshift relation for a wide class of generalized Randall-Sundrum type II brane-world models with Weyl fluid is compared to the presently available supernova data. We find that there is a class of spacially flat models with different amounts of matter Ωρ and Weyl fluid Ωd, which have a very similar fitting quality. The best-fit models are equally likely and can be regarded as extensions of the ΛCDM model, which is also included. We examine three models with different evolutionary history of the Weyl fluid, characterized by a parameter α = 0, 2 and 3. The first model describes a brane which had radiated energy into the bulk some time ago, but in recent times this energy exchange has ceased and only a dark radiation (α = 0) is left. In the other two models the Weyl-fluid describes a radiating brane throughout the cosmological evolution, up to our days. We find that the throughout of the fitting surface extends over a wider Ωd-range with increasing α, but the linear correlation of Ωd and Ωρ holds all over the examined Ωd range.PACS codes: 11.25-w, 98.62.Py, 98.80.Es

Interactive visualization of multidimensional coincidence spectra

Miroslav Morháč and Vladislav Matoušek — 2007-11-23

The paper presents direct visualization techniques of multidimensional nuclear spectra as well as visualization techniques based on projections of embedded subspaces. While the first group of graphical models is limited to four dimensions, the second one can be theoretically extended to any dimension. The presented algorithms of visualization have been implemented in nuclear data acquisition, processing and visualization system developed at the Institute of Physics, Slovak Academy of Sciences. The paper focuses on presentation of nuclear spectra. However the majority of algorithms can be successfully applied for visualization of scalar arrays of other data types.PACS Code: 29.85.+c, 07.05.Rm

Exclusive ρ0 production in deep inelastic scattering at HERA

ZEUS Collaboration — 2007-11-12

Exclusive ρ0 electroproduction at HERA has been studied with the ZEUS detector using 120 pb-1 of integrated luminosity collected during 1996–2000. The analysis was carried out in the kinematic range of photon virtuality 2

Semi-analytical approach to magnetized temperature autocorrelations

Massimo Giovannini — 2007-10-18

The cosmic microwave background (CMB) temperature autocorrelations, induced by a magnetized adiabatic mode of curvature inhomogeneities, are computed with semi-analytical methods. As suggested by the latest CMB data, a nearly scale-invariant spectrum for the adiabatic mode is consistently assumed. In this situation, the effects of a fully inhomogeneous magnetic field are scrutinized and constrained with particular attention to harmonics which are relevant for the region of Doppler oscillations. Depending on the parameters of the stochastic magnetic field a hump may replace the second peak of the angular power spectrum. Detectable effects on the Doppler region are then expected only if the magnetic power spectra have quasi-flat slopes and typical amplitude (smoothed over a comoving scale of Mpc size and redshifted to the epoch of gravitational collapse of the protogalaxy) exceeding 0.1 nG. If the magnetic energy spectra are bluer (i.e. steeper in frequency) the allowed value of the smoothed amplitude becomes, comparatively, larger (in the range of 20 nG). The implications of this investigation for the origin of large-scale magnetic fields in the Universe are discussed. Connections with forthcoming experimental observations of CMB temperature fluctuations are also suggested and partially explored.

The luminosity-redshift relation in brane-worlds: I. Analytical results

2007-10-02

The luminosity distance – redshift relation is analytically given for generalized Randall-Sundrum type II brane-world models containing Weyl fluid either as dark radiation or as a radiation field from the brane. The derived expressions contain both elementary functions and elliptic integrals of the first and second kind. First we derive the relation for models with the Randall-Sundrum fine-tuning. Then we generalize the method for models with cosmological constant. The most interesting models contain small amounts of Weyl fluid, expected to be in good accordance with supernova data. The derived analytical results are suitable for testing brane-world models with Weyl fluid when future supernova data at higher redshifts will be available.PACS Codes: 98.62.Py, 98.80.Jk, 11.25.-w

Ricci Flow Gravity

Wolfgang Graf — 2007-10-02

A theory of gravitation is proposed, modeled after the notion of a Ricci flow. In addition to the metric an independent volume enters as a fundamental geometric structure. Einstein gravity is included as a limiting case. Despite being a scalar-tensor theory the coupling to matter is different from Jordan-Brans-Dicke gravity. In particular there is no adjustable coupling constant. For the solar system the effects of Ricci flow gravity cannot be distinguished from Einstein gravity and therefore it passes all classical tests. However for cosmology significant deviations from standard Einstein cosmology will appear.PACS Codes: 04.50.+h, 04.20.Cv, 02.40.Hw

Dilaton and off-shell (non-critical string) effects in Boltzmann equation for species abundances

AB Lahanas, NE Mavromatos and DV Nanopoulos — 2007-10-02

In this work we derive the modifications to the Boltzmann equation governing the cosmic evolution of relic abundances induced by dilaton dissipative-source and non-critical-string terms in dilaton-driven non-equilibrium string Cosmologies. We also discuss briefly the most important phenomenological consequences, including modifications of the constraints on the available parameter space of cosmologically appealing particle physics models, imposed by recent precision data of astrophysical measurements.PACS codes: 11.25.Wx, 98.80.Ft, 95.35.+d

Welcome to PMC Physics A

Ken Peach — 2007-10-02

Welcome to the first issue of PhysMath Central (PMC) Physics A, a new peer-reviewed Open Access journal covering particle and nuclear physics, cosmology, gravity & astroparticle physics, instrumentation and data analysis.