132 research outputs found
TeV-scale bileptons, see-saw type II and lepton flavor violation in core-collapse supernova
Electrons and electron neutrinos in the inner core of the core-collapse
supernova are highly degenerate and therefore numerous during a few seconds of
explosion. In contrast, leptons of other flavors are non-degenerate and
therefore relatively scarce. This is due to lepton flavor conservation. If this
conservation law is broken by some non-standard interactions, electron
neutrinos are converted to muon and tau-neutrinos, and electrons - to muons.
This affects the supernova dynamics and the supernova neutrino signal. We
consider lepton flavor violating interactions mediated by scalar bileptons,
i.e. heavy scalars with lepton number 2. It is shown that in case of TeV-mass
bileptons the electron fermi gas is equilibrated with non-electron species
inside the inner supernova core at a time-scale of order of (1-100) ms. In
particular, a scalar triplet which generates neutrino masses through the
see-saw type II mechanism is considered. It is found that supernova core is
sensitive to yet unprobed values of masses and couplings of the triplet.Comment: accepted to Eur.Phys.J.
The Supernova Relic Neutrino Background
An upper bound to the supernova relic neutrino background from all past Type
II supernovae is obtained using observations of the Universal metal enrichment
history. We show that an unambiguous detection of these relic neutrinos by the
Super-Kamiokande detector is unlikely. We also analyze the event rate in the
Sudbury Neutrino Observatory (where coincident neutrons from anti-nu_e + D -->
n + n + e+ might enhance background rejection), and arrive at the same
conclusion. If the relic neutrino flux should be observed to exceed our upper
bound and if the observations of the metal enrichment history (for z<1) are not
in considerable error, then either the Type II supernova rate does not track
the metal enrichment history or some mechanism may be responsible for
transforming anti-nu_{mu,tau} --> anti-nu_e.Comment: Matches version accepted for publication in Phys. Rev.
Quantum Mechanics of the Vacuum State in Two-Dimensional QCD with Adjoint Fermions
A study of two-dimensional QCD on a spatial circle with Majorana fermions in
the adjoint representation of the gauge groups SU(2) and SU(3) has been
performed. The main emphasis is put on the symmetry properties related to the
homotopically non-trivial gauge transformations and the discrete axial symmetry
of this model. Within a gauge fixed canonical framework, the delicate interplay
of topology on the one hand and Jacobians and boundary conditions arising in
the course of resolving Gauss's law on the other hand is exhibited. As a
result, a consistent description of the residual gauge symmetry (for
SU(N)) and the ``axial anomaly" emerges. For illustrative purposes, the vacuum
of the model is determined analytically in the limit of a small circle. There,
the Born-Oppenheimer approximation is justified and reduces the vacuum problem
to simple quantum mechanics. The issue of fermion condensates is addressed and
residual discrepancies with other approaches are pointed out.Comment: 44 pages; for hardcopies of figures, contact
[email protected]
Quantum Black Holes from Quantum Collapse
The Schwarzschild black hole can be viewed as the special case of the
marginally bound Lema\^\i tre-Tolman-Bondi models of dust collapse which
corresponds to a constant mass function. We have presented a midi-superspace
quantization of this model for an arbitrary mass-function in a separate
publication. In this communication we show that our solution leads both to
Bekenstein's area spectrum for black holes as well as to the black hole
entropy, which, in this context, is naturally interpreted as the loss of
information of the original matter distribution within the collapsing dust
cloud.Comment: LaTeX file, 6 pages, 1 figure, Paper re-written into sections, some
references added, some elaborations, conclusions unchanged, to appear in
Physical Review
A Phenomenological Analysis of Gluon Mass Effects in Inclusive Radiative Decays of the and $\Upsilon
The shapes of the inclusive photon spectra in the processes \Jp \to \gamma
X and \Up \to \gamma X have been analysed using all available experimental
data.
Relativistic, higher order QCD and gluon mass corrections were taken into
account in the fitted functions. Only on including the gluon mass corrections,
were consistent and acceptable fits obtained. Values of
GeV and GeV were found for the
effective gluon masses (corresponding to Born level diagrams) for the \Jp and
\Up respectively. The width ratios \Gamma(V \to {\rm hadrons})/\Gamma(V \to
\gamma+ {\rm hadrons}) V=\Jp, \Up were used to determine and . Values consistent with the current world
average were obtained only when gluon mass correction factors,
calculated using the fitted values of the effective gluon mass, were applied. A
gluon mass GeV, as suggested with these results, is consistent with
previous analytical theoretical calculations and independent phenomenological
estimates, as well as with a recent, more accurate, lattice calculation of the
gluon propagator in the infra-red region.Comment: 50 pages, 11 figures, 15 table
Accretion, Outflows, and Winds of Magnetized Stars
Many types of stars have strong magnetic fields that can dynamically
influence the flow of circumstellar matter. In stars with accretion disks, the
stellar magnetic field can truncate the inner disk and determine the paths that
matter can take to flow onto the star. These paths are different in stars with
different magnetospheres and periods of rotation. External field lines of the
magnetosphere may inflate and produce favorable conditions for outflows from
the disk-magnetosphere boundary. Outflows can be particularly strong in the
propeller regime, wherein a star rotates more rapidly than the inner disk.
Outflows may also form at the disk-magnetosphere boundary of slowly rotating
stars, if the magnetosphere is compressed by the accreting matter. In isolated,
strongly magnetized stars, the magnetic field can influence formation and/or
propagation of stellar wind outflows. Winds from low-mass, solar-type stars may
be either thermally or magnetically driven, while winds from massive, luminous
O and B type stars are radiatively driven. In all of these cases, the magnetic
field influences matter flow from the stars and determines many observational
properties. In this chapter we review recent studies of accretion, outflows,
and winds of magnetized stars with a focus on three main topics: (1) accretion
onto magnetized stars; (2) outflows from the disk-magnetosphere boundary; and
(3) winds from isolated massive magnetized stars. We show results obtained from
global magnetohydrodynamic simulations and, in a number of cases compare global
simulations with observations.Comment: 60 pages, 44 figure
Atomic X-ray Spectroscopy of Accreting Black Holes
Current astrophysical research suggests that the most persistently luminous
objects in the Universe are powered by the flow of matter through accretion
disks onto black holes. Accretion disk systems are observed to emit copious
radiation across the electromagnetic spectrum, each energy band providing
access to rather distinct regimes of physical conditions and geometric scale.
X-ray emission probes the innermost regions of the accretion disk, where
relativistic effects prevail. While this has been known for decades, it also
has been acknowledged that inferring physical conditions in the relativistic
regime from the behavior of the X-ray continuum is problematic and not
satisfactorily constraining. With the discovery in the 1990s of iron X-ray
lines bearing signatures of relativistic distortion came the hope that such
emission would more firmly constrain models of disk accretion near black holes,
as well as provide observational criteria by which to test general relativity
in the strong field limit. Here we provide an introduction to this phenomenon.
While the presentation is intended to be primarily tutorial in nature, we aim
also to acquaint the reader with trends in current research. To achieve these
ends, we present the basic applications of general relativity that pertain to
X-ray spectroscopic observations of black hole accretion disk systems, focusing
on the Schwarzschild and Kerr solutions to the Einstein field equations. To
this we add treatments of the fundamental concepts associated with the
theoretical and modeling aspects of accretion disks, as well as relevant topics
from observational and theoretical X-ray spectroscopy.Comment: 63 pages, 21 figures, Einstein Centennial Review Article, Canadian
Journal of Physics, in pres
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in √s = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fb−1 of proton–proton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
Measurement of the top pair production cross section in 8 TeV proton-proton collisions using kinematic information in the lepton plus jets final state with ATLAS
A measurement is presented of the inclusive production
cross-section in collisions at a center-of-mass energy of TeV
using data collected by the ATLAS detector at the CERN Large Hadron Collider.
The measurement was performed in the lepton+jets final state using a data set
corresponding to an integrated luminosity of 20.3 fb. The cross-section
was obtained using a likelihood discriminant fit and -jet identification was
used to improve the signal-to-background ratio. The inclusive
production cross-section was measured to be
pb assuming a top-quark mass of 172.5 GeV, in good agreement with the
theoretical prediction of pb. The production cross-section in the fiducial region
determined by the detector acceptance is also reported.Comment: Published version, 19 pages plus author list (35 pages total), 3
figures, 2 tables, all figures including auxiliary figures are available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2013-06
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