11,926 research outputs found
Generalized definition of time delay in scattering theory
We advocate for the systematic use of a symmetrized definition of time delay
in scattering theory. In two-body scattering processes, we show that the
symmetrized time delay exists for arbitrary dilated spatial regions symmetric
with respect to the origin. It is equal to the usual time delay plus a new
contribution, which vanishes in the case of spherical spatial regions. We also
prove that the symmetrized time delay is invariant under an appropriate mapping
of time reversal. These results are also discussed in the context of classical
scattering theory.Comment: 18 page
Remarks on Resonant Scalars in the AdS/CFT Correspondence
The special properties of scalars having a mass such that the two possible
dimensions of the dual scalar respect the unitarity and the
Breitenlohner-Freedman bounds and their ratio is integral (``resonant
scalars'') are studied in the AdS/CFT correspondence. The role of logarithmic
branches in the gravity theory is related to the existence of a trace anomaly
and to a marginal deformation in the Conformal Field Theory. The existence of
asymptotic charges for the conformal group in the gravity theory is interpreted
in terms of the properties of the corresponding CFT.Comment: 16 pages, 1 figur
New Results on Holographic Three-Point Functions
We exploit a gauge invariant approach for the analysis of the equations
governing the dynamics of active scalar fluctuations coupled to the
fluctuations of the metric along holographic RG flows. In the present approach,
a second order ODE for the active scalar emerges rather simply and makes it
possible to use the Green's function method to deal with (quadratic)
interaction terms. We thus fill a gap for active scalar operators, whose
three-point functions have been inaccessible so far, and derive a general,
explicitly Bose symmetric formula thereof. As an application we compute the
relevant three-point function along the GPPZ flow and extract the irreducible
trilinear couplings of the corresponding superglueballs by amputating the
external legs on-shell.Comment: v2: reference added, typos corrected v3: sign convention for
background changed, agrees with version published in JHE
Universal Features of Holographic Anomalies
We study the mechanism by which gravitational actions reproduce the trace
anomalies of the holographically related conformal field theories. Two
universal features emerge: a) the ratios of type B trace anomalies in any even
dimension are independent of the gravitational action, being uniquely
determined by the underlying algebraic structure b) the normalization of the
type A and the overall normalization of the type B anomalies are given by
action dependent expressions with the dimension dependence completely fixed.Comment: 17 pages, harvma
Chandra observations of the planetary nebula IC 4593
The ACIS-S camera on board the Chandra X-ray Observatory has been used to
discover a hot bubble in the planetary nebula (PN) IC4593, the most distant PN
detected by Chandra so far. The data are used to study the distribution of the
X-ray-emitting gas in IC 4593 and to estimate its physical properties. The hot
bubble has a radius of ~2 and is found to be confined inside
the optically-bright innermost cavity of IC 4593. The X-ray emission is mostly
consistent with that of an optically-thin plasma with temperature
keV (or K), electron
density cm, and intrinsic X-ray luminosity in
the 0.3-1.5 keV energy range erg s. A
careful analysis of the distribution of hard (0.8 keV) photons in IC 4593
suggests the presence of X-ray emission from a point source likely associated
with its central star (CSPN). If this were the case, its estimated X-ray
luminosity would be erg s, fulfilling
the log relation for self-shocking
winds in hot stars. The X-ray detection of the CSPN helps explain the presence
of high-ionisation species detected in the UV spectra as predicted by stellar
atmosphere models.Comment: 6 pages, 4 figures; Accepted to MNRA
Extreme Warm Absorber variability in the Seyfert Galaxy Mrk 704
In about half of Seyfert galaxies, the X-ray emission is absorbed by an
optically thin, ionized medium, the so-called "Warm Absorber", whose origin and
location is still a matter of debate. The aims of this paper is to put more
constraints on the warm absorber by studying its variability. We analyzed the
X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three
years apart, by XMM-Newton. The spectra were well fitted with a two zones
absorber, possibly covering only partially the source. The parameters of the
absorbing matter - column density, ionization state, covering factor - changed
significantly between the two observations. Possible explanations for the more
ionized absorber are a torus wind (the source is a polar scattering one) or, in
the partial covering scenario, an accretion disk wind. The less ionized
absorber may be composed of orbiting clouds in the surroundings of the nucleus,
similarly to what already found in other sources, most notably NGC 1365.Comment: 10 pages. Accepted for publication in Astronomy & Astrophysic
Transmission resonances and supercritical states in a one dimensional cusp potential
We solve the two-component Dirac equation in the presence of a spatially one
dimensional symmetric cusp potential. We compute the scattering and bound
states solutions and we derive the conditions for transmission resonances as
well as for supercriticality.Comment: 10 pages. Revtex 4. To appear in Phys Rev.
Time delay for one-dimensional quantum systems with steplike potentials
This paper concerns time-dependent scattering theory and in particular the
concept of time delay for a class of one-dimensional anisotropic quantum
systems. These systems are described by a Schr\"{o}dinger Hamiltonian with a potential converging to different limits
and as and respectively. Due to the
anisotropy they exhibit a two-channel structure. We first establish the
existence and properties of the channel wave and scattering operators by using
the modern Mourre approach. We then use scattering theory to show the identity
of two apparently different representations of time delay. The first one is
defined in terms of sojourn times while the second one is given by the
Eisenbud-Wigner operator. The identity of these representations is well known
for systems where vanishes as (). We show
that it remains true in the anisotropic case , i.e. we prove
the existence of the time-dependent representation of time delay and its
equality with the time-independent Eisenbud-Wigner representation. Finally we
use this identity to give a time-dependent interpretation of the
Eisenbud-Wigner expression which is commonly used for time delay in the
literature.Comment: 48 pages, 1 figur
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