12,066 research outputs found
On the Decoupling of the Homogeneous and Inhomogeneous Parts in Inhomogeneous Quantum Groups
We show that, if there exists a realization of a Hopf algebra in a
-module algebra , then one can split their cross-product into the tensor
product algebra of itself with a subalgebra isomorphic to and commuting
with . This result applies in particular to the algebra underlying
inhomogeneous quantum groups like the Euclidean ones, which are obtained as
cross-products of the quantum Euclidean spaces with the quantum groups
of rotation of , for which it has no classical analog.Comment: Latex file, 27 pages. Final version to appear in J. Phys.
Iron line emission in X-ray afterglows
Recent observations of X-ray afterglows reveal the presence of a redshifted
Kalpha iron line in emission in four bursts. In GRB 991216, the line was
detected by the low energy grating of Chandra, which showed the line to be
broad, with a full width of ~15,000 km/s. These observations indicate the
presence of a >1 solar mass of iron rich material in the close vicinity of the
burst, most likely a supernova remnant. The fact that such strong lines are
observed less than a day after the trigger strongly limits the size of the
remnant, which must be very compact. If the remnant had the observed velocity
since the supernova explosion, its age would be less than a month. In this case
nickel and cobalt have not yet decayed into iron. We show how to solve this
paradox.Comment: 3 pages, to appear in the proceedings of the the 2nd Workshop on
Gamma-Ray Bursts in the Afterglow Era, Rome, Oct. 200
Analysis of X-ray flares in GRBs
We present a detailed study of the spectral and temporal properties of the
X-ray flares emission of several GRBs. We select a sample of GRBs which X-ray
light curve exhibits large amplitude variations with several rebrightenings
superposed on the underlying three-segment broken powerlaw that is often seen
in Swift GRBs. We try to understand the origin of these fluctuations giving
some diagnostic in order to discriminate between refreshed shocks and late
internal shocks. For some bursts our time-resolved spectral analysis supports
the interpretation of a long-lived central engine, with rebrightenings
consistent with energy injection in refreshed shocks as slower shells generated
in the central engine prompt phase catch up with the afterglow shock at later
times.Comment: 9 pages, 3 figures. Invited talk at the Swift-Venice 2006 meeting to
be published by "Il Nuovo Cimento
Extinction properties of the X-ray bright/optically faint afterglow of GRB 020405
We present an optical-to-X-ray spectral analysis of the afterglow of GRB
020405. The optical spectral energy distribution not corrected for the
extragalactic extinction is significantly below the X-ray extrapolation of the
single powerlaw spectral model suggested by multiwavelength studies. We
investigate whether considerable extinction could explain the observed spectral
``mismatch'' by testing several types of extinction curves. For the first time
we test extinction curves computed with time-dependent numerical simulations of
dust grains destruction by the burst radiation. We find that an extinction law
weakly depen dent on wavelength can reconcile the unabsorbed optical and X-ray
data with the expected synchrotron spectrum. A gray extinction law can be
provided by a dust grain size distribution biased toward large grains.Comment: 6 pages, 5 figures, accepted for publication on A&
Deforming Maps for Lie Group Covariant Creation and Annihilation Operators
Any deformation of a Weyl or Clifford algebra A can be realized through a
`deforming map', i.e. a formal change of generators in A. This is true in
particular if A is covariant under a Lie algebra g and its deformation is
induced by some triangular deformation of the Hopf algebra . We
propose a systematic method to construct all the corresponding deforming maps,
together with the corresponding realizations of the action of . The
method is then generalized and explicitly applied to the case that is
the quantum group . A preliminary study of the status of deforming
maps at the representation level shows in particular that `deformed' Fock
representations induced by a compact can be interpreted as standard
`undeformed' Fock representations describing particles with ordinary Bose or
Fermi statistics.Comment: Latex file, 26 pages, no figures. Extended changes. Final Version to
appear in J. Math. Phy
Frame formalism for the N-dimensional quantum Euclidean spaces
We sketch our recent application of a non-commutative version of the Cartan
`moving-frame' formalism to the quantum Euclidean space , the space
which is covariant under the action of the quantum group . For each of
the two covariant differential calculi over based on the -matrix
formalism, we summarize our construction of a frame, the dual inner
derivations, a metric and two torsion-free almost metric compatible covariant
derivatives with a vanishing curvature. To obtain these results we have
developed a technique which fully exploits the quantum group covariance of
. We first find a frame in the larger algebra \Omega^*(R^N_q) \cocross
\uqs. Then we define homomorphisms from R^N_q \cocross U_q^{\pm}{so(N)} to
which we use to project this frame in .Comment: Latex file, 11 pages. Talks given at the Euroconference
``Non-commutative Geometry and Hopf Algebras in Field Theory and Particle
Physics'', Villa Gualino (Torino), Sept. 199
Extragalactic gamma-ray background from AGN winds and star-forming galaxies in cosmological galaxy formation models
We derive the contribution to the extragalactic gamma-ray background (EGB)
from AGN winds and star-forming galaxies by including a physical model for the
gamma-ray emission produced by relativistic protons accelerated by AGN-driven
and supernova-driven shocks into a state-of-the-art semi-analytic model of
galaxy formation. This is based on galaxy interactions as triggers of AGN
accretion and starburst activity and on expanding blast wave as the mechanism
to communicate outwards the energy injected into the interstellar medium by the
active nucleus. We compare the model predictions with the latest measurement of
the EGB spectrum performed by the Fermi-LAT in the range between 100 MeV and
820 GeV. We find that AGN winds can provide ~3515% of the observed EGB in
the energy interval E_{\gamma}=0.1-1 GeV, for ~7315% at E_{\gamma}=1-10
GeV, and for ~6020% at E_{\gamma}>10 GeV. The AGN wind contribution to the
EGB is predicted to be larger by a factor of 3-5 than that provided by
star-forming galaxies (quiescent plus starburst) in the hierarchical clustering
scenario. The cumulative gamma-ray emission from AGN winds and blazars can
account for the amplitude and spectral shape of the EGB, assuming the standard
acceleration theory, and AGN wind parameters that agree with observations. We
also compare the model prediction for the cumulative neutrino background from
AGN winds with the most recent IceCube data. We find that for AGN winds with
accelerated proton spectral index p=2.2-2.3, and taking into account internal
absorption of gamma-rays, the Fermi-LAT and IceCube data could be reproduced
simultaneously.Comment: 12 pages, 8 figures, accepted for publication in A&
q-Deformed quaternions and su(2) instantons
We have recently introduced the notion of a q-quaternion bialgebra and shown
its strict link with the SO_q(4)-covariant quantum Euclidean space R_q^4.
Adopting the available differential geometric tools on the latter and the
quaternion language we have formulated and found solutions of the
(anti)selfduality equation [instantons and multi-instantons] of a would-be
deformed su(2) Yang-Mills theory on this quantum space. The solutions depend on
some noncommuting parameters, indicating that the moduli space of a complete
theory should be a noncommutative manifold. We summarize these results and add
an explicit comparison between the two SO_q(4)-covariant differential calculi
on R_q^4 and the two 4-dimensional bicovariant differential calculi on the bi-
(resp. Hopf) algebras M_q(2),GL_q(2),SU_q(2), showing that they essentially
coincide.Comment: Latex file, 18 page
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