6,866 research outputs found
Fermion induced SU Yang-Mills Theory
We investigate the gauge interaction induced by heavy fermions using both
dimensional and lattice regularization. We study the condition under which
heavy fermions induce a continuum gauge theory.Comment: 4 pages; talk at Lattice '92, Amsterdam, requires , espcrc2.st
Gamma Ray Bursts Spectral--Energy correlations: recent results
The correlations between the rest frame peak of the EF_E spectrum of GRBs
Epeak and their isotropic energy (E_iso) or luminosity (L_iso) could have
several implications for the understanding of the GRB prompt emission. These
correlations are presently founded on the time-averaged spectral properties of
a sample of 95 bursts, with measured redshifts, collected by different
instruments in the last 13 years (pre-Fermi). One still open issue is wether
these correlations have a physical origin or are due to instrumental selection
effects. By studying 10 long and 14 short GRBs detected by Fermi we find that a
strong time-resolved correlation between E_peak and the luminosity L_iso is
present within individual GRBs and that it is consistent with the
time-integrated correlation. This result is a direct proof of the existence in
both short and long GRBs of a similar physical link between the hardness and
the luminosity which is not due to instrumental selection effects. The origin
of the E_peak-L_iso correlation should be searched in the radiation mechanism
of the prompt emission.Comment: 5 pages, 3 figures, to appear in the proceedings of the 275 IAU Symp:
"Jets at all scales", Buenos Aires, Sept. 201
A Generalized Uncertainty Principle in Quantum Gravity
We discuss a Gedanken experiment for the measurement of the area of the
apparent horizon of a black hole in quantum gravity. Using rather general and
model-independent considerations we find a generalized uncertainty principle
which agrees with a similar result obtained in the framework of string
theories. The result indicates that a minimum length of the order of the Planck
length emerges naturally from any quantum theory of gravity, and that the
concept of black hole is not operationally defined if the mass is smaller than
the Planck mass.Comment: 10 pages, 1 figure (not included), IFUP-TH 3/9
Black holes, string theory and quantum coherence
On the basis of recently discovered connections between D-branes and black
holes, I show how the information puzzle is solved by superstring theory as the
fundamental theory of quantum gravity. The picture that emerges is that a
well-defined quantum state does not give rise to a black hole even if the
apparent distribution of energy, momenta, charges, etc. would predict one on
classical grounds. Indeed, geometry - general relativistic space time
description - is unwarranted at the quantum microstate level. It is the
decoherence leading to macrostates (average over degenerate microstates) that
provides - on the same token - the loss of quantum coherence, the emergence of
a space time description with causal properties and, thus, the formation of a
black hole and its Hawking evaporatio
The Ep,i - Eiso correlation in GRBs: updated observational status, re-analysis and main implications
The correlation between the cosmological rest-frame nuFnu spectrum peak
energy, Ep,i, and the isotropic equivalent radiated energy, Eiso, discovered by
Amati et al. in 2002 and confirmed/extended by subsequent osbervations, is one
of the most intriguing and debated observational evidences in Gamma-Ray Bursts
(GRB) astrophysics. In this paper I provide an update and a re-analysis of the
Ep,i - Eiso correlation basing on an updated sample consisting of 41 long
GRBs/XRFs with firm estimates of z and observed peak energy, Ep,obs, 12 GRBs
with uncertain valeus of z and/or Ep,obs, 2 short GRBs with firm estimates of z
and Ep,obs and the peculiar sub-energetic events GRB980425/SN1998bw and
GRB031203/SN2003lw. In addition to standard correlation analysis and power-law
fitting, the data analysis here reported includes a modelization which accounts
for sample variance. All 53 classical long GRBs and XRFs, including 11 Swift
events with published spectral parameters and fluences, have Ep,i and Eiso
values, or upper/lower limits, consistent with the correlation, which shows a
chance probability as low as ~7x10{-15}, a slope of ~0.57 (~0.5 when fitting by
accounting for sample variance) and an extra-Poissonian logarithmic dispersion
of ~0.15, it extends over ~5 orders of magnitude in Eiso and ~3 orders of
magnitude in Ep,i and holds from the closer to the higher z GRBs. I also
discuss the main implications of the updated Ep,i - Eiso correlation for the
models of the physics and geometry of GRB emission, its use for discriminating
different classes and as a pseudo-z estimator, and the tests of possible
selection effects with GRBs of unknown redshift.Comment: 15 pages, 5 figures, accepted for publication in MNRAS, main journa
Extremely energetic Fermi Gamma-Ray Bursts obey spectral energy correlations
The extremely energetic Fermi GRBs 080916C, with its Eiso of ~ 10^{55} erg in
1 keV - 10 GeV and intense GeV emission, and 090323 give us a unique
opportunity to test the reliability and extension of spectral energy
correlations. Based on Konus/WIND and Fermi spectral measurements, we find that
both events are fully consistent with the updated (95 events as of April 2009)
Ep,i - Eiso correlation, thus further confirming and extending it and pointing
against a possible flattening or increased dispersion at very high energies.
This also suggests that the physics behind the emission of peculiarly bright
and hard GRBs is the same as for softer and weaker ones. In addition, we find
that the normalization of the correlation obtained by considering these two
GRBs and the other long ones for which Ep,i was measured with high accuracy by
the Fermi/GBM are fully consistent with those obtained by other instruments
(e.g., BeppoSAX, Swift, Konus-WIND), thus indicating that the correlation is
not affected significantly by detectors limited thresholds and energy bands.
Prompted by the extension of the spectrum of GRB 080916C up to several GeVs
without any excess or cut-off, we also investigated if the evaluation of Eiso
in the commonly adopted 1 keV - 10 MeV energy band may bias the Ep,i - Eiso
correlation contributing to its scatter. By computing Eiso from 1 keV to 10
GeV, the slope of the correlation becomes slightly flatter, while its
dispersion does not change significantly. Finally, we find that GRB 080916C is
also consistent with most of the other spectral energy correlations derived
from it, with the possible exception of the Ep,i - Eiso - tb correlation.Comment: 9 pages, 5 figures, final revised version accepted for pubblication
in Astronomy & Astrophysics (main Journal
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