14,108 research outputs found
Signals of new physics in global event properties in pp collisions in the TeV energy domain: rapidity intervals
The study of possible new physics signals in global event properties in pp
collisions in the TeV energy domain is extended from full phase-space to
rapidity intervals experimentally accessible at LHC. The elbow structure in the
total multiplicity distribution predicted in full phase-space is clearly
present also in restricted rapidity intervals, leading to very strong charged
particle correlations. It is also found that energy densities comparable to
those reached in heavy ion collisions at RHIC could be attained in pp
collisions at LHC.Comment: 10 pages, 4 figure
On Statistical Mechanics Developments of Clan Concept in Multiparticle Production
Clan concept has been introduced in multiparticle dynamics in order to
interpret the wide occurrence of negative binomial (NB) regularity in n-charged
particle multiplicity distributions (MDs) in various high energy collisions.
The centrality of clan concept led to the attempt to justify its occurrence
within a statistical model of clan formation and evolution. In this framework
all thermodynamical potentials have been explicitly calculated in terms of NB
parameters. Interestingly it was found that NB parameter k corresponds to the
one particle canonical partition function. The goal of this paper is to explore
a possible temperature and volume dependence of parameter k in various classes
of events in high energy hadron-hadron collisions. It is shown that the
existence of a phase transition at parton level from the ideal clan gas
associated to the semihard component with k>1 to the ideal clan gas of the hard
component with k<1 implies a discontinuity in the average number of particles
at hadron level.Comment: 20 pages, latex, no figures; v2: the description of the framework has
been considerably expanded, and the main body has been reorganized for
clarit
On signals of new physics in global event properties in pp collisions in the TeV energy domain
In the framework of the weighted superposition mechanism of different classes
of minimum bias events (or substructures), described by the negative binomial
multiplicity distribution, in possible scenarios for pp collisions in the TeV
energy domain, we explore global properties of an eventual new class of events,
characterised by high hadron and clan densities, to be added to the soft
(without minijets) and semihard (with minijets) ones. It turns out that the
main signal of the mentioned new physical expectations at 14 TeV c.m. energy
would be an ``elbow structure'' in the tail of the total charged particle
multiplicity distribution in complete disagreement with the second shoulder
structure predicted by Pythia Monte Carlo calculations: a challenging problem
for new experimental work.Comment: 14 pages, 6 ps figures include
B2 1144+35B, a giant low power radio galaxy with superluminal motion. Orientation and evidence for recurrent activity
The goal of this work is a detailed study of the nearby, low power radio
galaxy B2 1144+35B. For this purpose, we performed new Very Long Baseline Array
(VLBA) and Very Large Array (VLA) observations. This source has several
properties (bright, nearby, large range of spatial structures, visible
counterjet, etc.) that make it an excellent astrophysical laboratory for the
study of the evolution of radio jets. Here we report the detection of motion in
the counterjet at 0.23 0.07 c, which allows us to estimate the
orientation of the parsec-scale jet at 33 from the line of
sight, with an intrinsic velocity of (0.94)c. We also report
on a brightening of the core at high frequencies which we suggest could be the
result of a new component emerging from the core. High dynamic range VLBA
observations at 5 GHz reveal, for the first time, extended emission connecting
the core with the bright complex of emission that dominates the flux density of
the parsec scale structure at frequencies below 20 GHz. The evolution of this
bright complex is considered and its slow decline in flux density is
interpreted as the result of an interaction with the interstellar medium of the
host galaxy.Comment: 7 pages, 6 b&w figures. A&A in pres
Multiplicity distributions in gravitational and strong interactions
The multiplicity distributions produced by the variation of time-dependent
gravitational fields in a conformally flat background geometry belong to the
same class of infinitely divisible distributions found, for fixed centre of
mass energies and symmetric (pseudo)rapidity intervals, in charged
multiplicities produced in , and in heavy ion collisions.
Apparently unrelated multiplicity distributions are classified in terms of the
(positive) discrete representations of the group. The gravitational
analogy suggest a global high-energy asymptote for the distributions measured
in and collisions. Second-order cross correlations between
positively and negatively charged distributions represent a relevant diagnostic
for a closer scrutiny of the multiparticle final state.Comment: 11 pages, 2 included figures; to appear in Physics Letters
Stochastic GW backgrounds and Ground based detectors
The interplay between different ground based detectors and stochastic
backgrounds of relic GW is described. A simultaneous detection of GW in the kHz
and in the MHz--GHz region can point towards a cosmological nature of the
signal. The sensitivity of a pair of VIRGO detectors to string cosmological
models is presented. The implications of microwave cavities for stochastic GW
backgrounds are discussed.Comment: 4 pages in Latex style, one figur
Comment on "Accelerating cosmological expansion from shear and bulk viscosity"
In a recent Letter [Phys. Rev. Lett. 114 091301 (2105)] the cause of the
acceleration of the present Universe has been identified with the shear
viscosity of an imperfect relativistic fluid even in the absence of any bulk
viscous contribution. The gist of this comment is that the shear viscosity, if
anything, can only lead to an accelerated expansion over sufficiently small
scales well inside the Hubble radius
Magnetized birefringence and CMB polarization
The polarization plane of the cosmic microwave background radiation can be
rotated either in a magnetized plasma or in the presence of a quintessential
background with pseudoscalar coupling to electromagnetism. A unified treatment
of these two phenomena is presented for cold and warm electron-ion plasmas at
the pre-recombination epoch. The electron temperature is only relevant to the
relativistic correction of the cold plasma results. The spectrum of plasma
excitations is obtained from a generalized Appleton--Hartree equation,
describing simultaneously the high-frequency propagation of electromagnetic
waves in a magnetized plasma with a dynamical quintessence field. It is shown
that these two effects are comparable for the plausible range of parameters
allowed by present constraints. It is then argued that the generalized
expressions derived in the present study may be relevant for direct searches of
a possible rotation of the cosmic microwave background polarization.Comment: 9 pages; corrected typos, references adde
Stringy bounces and gradient instabilities
Bouncing solutions are obtained from a generally covariant action
characterized by a potential which is a nonlocal functional of the dilaton
field at two separated space-time points. Gradient instabilities are shown to
arise in this context but they are argued to be nongeneric. After performing a
gauge-invariant and frame-invariant derivation of the evolution equations of
the fluctuations, a heuristic criterion for the avoidance of pathological
instabilities is proposed and corroborated by a number of explicit examples
that turn out to be compatible with a quasi-flat spectrum of curvature
inhomogeneities for typical wavelengths larger than the Hubble radius.Comment: 25 pages; comments added and corrected typos; to appear in Phys. Rev.
Anomalous Magnetohydrodynamics
Anomalous symmetries induce currents which can be parallel rather than
orthogonal to the hypermagnetic field. Building on the analogy with charged
liquids at high magnetic Reynolds numbers, the persistence of anomalous
currents is scrutinized for parametrically large conductivities when the plasma
approximation is accurate. Different examples in globally neutral systems
suggest that the magnetic configurations minimizing the energy density with the
constraint that the helicity be conserved coincide, in the perfectly conducting
limit, with the ones obtainable in ideal magnetohydrodynamics where the
anomalous currents are neglected. It is argued that this is the rationale for
the ability of extending to anomalous magnetohydrodynamics the hydromagnetic
solutions characterized by finite gyrotropy. The generally covariant aspects of
the problem are addressed with particular attention to conformally flat
geometries which are potentially relevant for the description of the
electroweak plasma prior to the phase transition.Comment: 25 pages, no figure
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