20,881 research outputs found
Five-Dimensional QED, Muon Pair Production and Correction to the Coulomb Potential
We consider QED in five dimensions in a configuration where matter is
localized on a 3-brane while foton propagates in the bulk. The idea is to
investigate the effects of the Kaluza-Klein modes of the photon in the
relativistic regime, but in low energy, and in the nonrelativistic regime. In
the relativistic regime, we calculate the cross section for the reaction . We compare our theoretical result with a precise
measurement of this cross section at GeV. As result, we
extract a lower bound on the size of the extra dimension. In the
nonrelativistic regime, we derive the contribution for the Coulomb potential
due to the whole tower of the Kaluza-Klein excited modes of the photon. We use
the modified potential to calculate the Rutherford scattering differential
cross section.Comment: minor changes, three new refs. added, to appear in IJMP
Scaling laws and universality in the choice of election candidates
Nowadays there is an increasing interest of physicists in finding
regularities related to social phenomena. This interest is clearly motivated by
applications that a statistical mechanical description of the human behavior
may have in our society. By using this framework, we address this work to cover
an open question related to elections: the choice of elections candidates
(candidature process). Our analysis reveals that, apart from the social
motivations, this system displays features of traditional out-of-equilibrium
physical phenomena such as scale-free statistics and universality. Basically,
we found a non-linear (power law) mean correspondence between the number of
candidates and the size of the electorate (number of voters), and also that
this choice has a multiplicative underlying process (lognormal behavior). The
universality of our findings is supported by data from 16 elections from 5
countries. In addition, we show that aspects of network scale-free can be
connected to this universal behavior.Comment: Accepted for publication in EP
Group theory for structural analysis and lattice vibrations in phosphorene systems
Group theory analysis for two-dimensional elemental systems related to
phosphorene is presented, including (i) graphene, silicene, germanene and
stanene, (ii) dependence on the number of layers and (iii) two stacking
arrangements. Departing from the most symmetric graphene space
group, the structures are found to have a group-subgroup relation, and analysis
of the irreducible representations of their lattice vibrations makes it
possible to distinguish between the different allotropes. The analysis can be
used to study the effect of strain, to understand structural phase transitions,
to characterize the number of layers, crystallographic orientation and
nonlinear phenomena.Comment: 24 pages, 3 figure
Dynamical analysis of the cluster pair: A3407 + A3408
We carried out a dynamical study of the galaxy cluster pair A3407 \& A3408
based on a spectroscopic survey obtained with the 4 meter Blanco telescope at
the CTIO, plus 6dF data, and ROSAT All-Sky-Survey. The sample consists of 122
member galaxies brighter than . Our main goal is to probe the galaxy
dynamics in this field and verify if the sample constitutes a single galaxy
system or corresponds to an ongoing merging process. Statistical tests were
applied to clusters members showing that both the composite system A3407 +
A3408 as well as each individual cluster have Gaussian velocity distribution. A
velocity gradient of was identified around
the principal axis of the projected distribution of galaxies, indicating that
the global field may be rotating. Applying the KMM algorithm to the
distribution of galaxies we found that the solution with two clusters is better
than the single unit solution at the 99\% c.l. This is consistent with the
X-ray distribution around this field, which shows no common X-ray halo
involving A3407 and A3408. We also estimated virial masses and applied a
two-body model to probe the dynamics of the pair. The more likely scenario is
that in which the pair is gravitationally bound and probably experiences a
collapse phase, with the cluster cores crossing in less than 1
Gyr, a pre-merger scenario. The complex X-ray morphology, the gas temperature,
and some signs of galaxy evolution in A3408 suggests a post-merger scenario,
with cores having crossed each other Gyr ago, as an
alternative solution.Comment: 17 pages, 12 figures, submitted to MNRAS, accepted 2016 May 9.
Received 2016 May 9; in original form 2016 April 1
Matching LTB and FRW spacetimes through a null hypersurface
Matching of a LTB metric representing dust matter to a background FRW
universe across a null hypersurface is studied. In general, an unrestricted
matching is possible only if the background FRW is flat or open. There is in
general no gravitational impulsive wave present on the null hypersurface which
is shear-free and expanding. Special cases of the vanishing pressure or energy
density on the hypersurface is discussed. In the case of vanishing energy
momentum tensor of the null hypersurface, i.e. in the case of a null boundary,
it turns out that all possible definitions of the Hubble parameter on the null
hypersurface, being those of LTB or that of FRW, are equivalent, and that a
flat FRW can only be joined smoothly to a flat LTB.Comment: 9 page
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