13,882 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
Primordial magnetic fields
Large scale magnetic fields represent a triple point where cosmology,
high-energy physics and astrophysics meet for different but related purposes.
After reviewing the implications of large scale magnetic fields in these
different areas, the role of primordial magnetic fields is discussed in various
physical processes occurring prior to the decoupling epoch with particular
attention to the big bang nucleosynthesis (BBN) epoch and to the electroweak
(EW) epoch. The generation of matter--antimatter isocurvature fluctuations,
induced by hypermagnetic fields, is analyzed in light of a possible increase of
extra-relativistic species at BBN. It is argued that stochastic GW backgrounds
can be generated by hypermagnetic fields at the LISA frequency. The problem of
the origin of large scale magnetic fields is also scrutinized.Comment: 41 pages in Latex style, 5 figure
Viscous modes, isocurvature perturbations and CMB initial conditions
When the predecoupling plasma is thermodynamically reversible its
fluctuations are classified in terms of the adiabatic and entropic modes. A
different category of physical solutions, so far unexplored, arises when the
inhomogeneities of the viscosity coefficients induce computable curvature
perturbations. The viscous modes are explicitly illustrated and compared with
the conventional isocurvature solutions.Comment: 9 pages, no figures; corrected typos; to appear in Physical Review as
a Rapid Communicatio
Fluctuations of inflationary magnetogenesis
This analysis aims at exploring what can be said about the growth rate of
magnetized inhomogeneities under two concurrent hypotheses: a phase of quasi-de
Sitter dynamics driven by a single inflaton field and the simultaneous presence
of a spectator field coupled to gravity and to the gauge sector. Instead of
invoking ad hoc correlations between the various components, the system of
scalar inhomogeneities is diagonalized in terms of two gauge-invariant
quasi-normal modes whose weighted sum gives the curvature perturbations on
comoving orthogonal hypersurfaces. The predominance of the conventional
adiabatic scalar mode implies that the growth rate of magnetized
inhomogeneities must not exceed 2.2 in Hubble units if the conventional
inflationary phase is to last about 70 efolds and for a range of slow roll
parameters between 0.1 and 0.001. Longer and shorter durations of the quasi-de
Sitter stage lead, respectively, either to tighter or to looser bounds which
are anyway more constraining than the standard backreaction demands imposed on
the gauge sector. Since a critical growth rate of order 2 leads to a quasi-flat
magnetic energy spectrum, the upper bounds on the growth rate imply a lower
bound on the magnetic spectral index. The advantages of the uniform curvature
gauge are emphasized and specifically exploited throughout the treatment of the
multicomponent system characterizing this class of problems.Comment: 37 pages, 4 figure
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