1,323 research outputs found
Eikonal Amplitude in the Gravireggeon Model at Superplanckian Energies
The gravity effects in high-energy scattering, described by a
four-dimensional eikonal amplitude related to gravireggeons induced by compact
extra dimensions are studied. It is demonstrated that the real part of the
eikonal (with a massless mode subtracted) dominates its imaginary part at both
small and large impact parameters, in contrast to the usual case of hadronic
high-energy behavior. The real part of the scattering amplitude exhibits an
exponential falloff at large momentum transfer, similar to that of the
imaginary part of the amplitude.Comment: 21 pages, LaTeX2e, no figure
Intermittency and structure functions in channel flow turbulence
We present a study of intermittency in a turbulent channel flow. Scaling
exponents of longitudinal streamwise structure functions, ,
are used as quantitative indicators of intermittency.
We find that, near the center of the channel the values of
up to are consistent with the assumption of homogeneous/isotropic
turbulence. Moving towards the boundaries, we observe a growth of intermittency
which appears to be related to an intensified presence of ordered vortical
structures. In fact, the behaviour along the normal-to-wall direction of
suitably normalized scaling exponents shows a remarkable correlation with the
local strength of the Reynolds stress and with the \rms value of helicity
density fluctuations. We argue that the clear transition in the nature of
intermittency appearing in the region close to the wall, is related to a new
length scale which becomes the relevant one for scaling in high shear flows.Comment: 4 pages, 6 eps figure
Symmetry Properties of the Effective Action for High-Energy Scattering in QCD
We study the effective action describing high-energy scattering processes in
the multi-Regge limit of QCD, which should provide the starting point for a new
attempt to overcome the limitations of the leading logarithmic and the eikonal
approximations. The action can be obtained via simple graphical rules or by
integrating in the QCD functional integral over momentum modes of gluon and
quark fields that do not appear explicitely as scattering or exchanged
particles in the considered processes. The supersymmetry is used to obtain the
terms in the action involving quarks fields from the pure gluonic ones. We
observe a Weizs\"acker - Williams type relations between terms describing
scattering and production of particles.Comment: 37 pages LATEX, 1 Table and 7 figures using package FEYNMA
Mass Spectrum in SQCD and Problems with the Seiberg Duality. Another Scenario
N=1 SQCD with SU(N_c) colors and N_F flavors of light quarks is considered
within the dynamical scenario which assumes that quarks can be in two different
phases only. These are: a) either the HQ (heavy quark) phase where they are
confined, b) or they are higgsed, at the appropriate values of parameters of
the Lagrangian.
The mass spectra of this (direct) theory and its Seiberg's dual are obtained
and compared, for quarks of equal or unequal masses. It is shown that in all
cases when there is the additional small parameter at hand (it is
0<(3N_c-N_F)/N_F << 1 for the direct theory, or its analog 0<(2N_F-3N_c)/N_F <<
1 for the dual one), the mass spectra of the direct and dual theories are
parametrically different. A number of other regimes are also considered.Comment: 30 pages, purely technical improvements for readers convenienc
On Superplanckian Scattering on the Brane
The multidimensional space-time with compact extra space dimensions
and SM fields confined on four-dimensional brane is considered. The elastic
scattering amplitude of two particles interacting by gravitational forces is
calculated at superplanckian energies. A particular attention is paid to a
proper account of zero (massless) graviton mode. The renormalized Born pole is
reproduced in the eikonal amplitude which makes a leading contribution at small
momentum transfers. This singular part of the amplitude coincides with
well-known -dimensional amplitude taken at . The expression for a
contribution from massive graviton modes to the eikonal is derived, and it
asymptotics in the impact parameter are calculated. Our formula gives correct
four-dimensional result at , where is the radius of the higher
dimensions, contrary to formulae obtained in recent papers on collisions of
particles living on the brane. The results are also compared with those
obtained previously for the scattering of the bulk fields in flat higher
dimensions.Comment: 22 pages, LaTeX2
Transplanckian bremsstrahlung and black hole production
Classical gravitational bremsstrahlung in particle collisions at
transplanckian energies is studied in .
The radiation efficiency is
computed in terms of the Schwarzschild radius , the impact
parameter and the Lorentz factor and found to be
, larger than previous
estimates by many powers of . The result is reliable for
impact parameters in the overlap of , with
marking (for ) the loss of the notion of classical trajectories
and the Compton length of the scattered particles.
The condition on and for extreme radiation damping and (presumably) no
black hole production is also derived.Comment: 4 pages, revtex 4. The discussion section is changed to better
clarify the region of validity of our calculation. The physical conclusions
and the abstract are modified accordingly. A few more references added. We
just added the preprint number CCTP-2010-1
Towards Collinear Evolution Equations in Electroweak Theory
We consider electroweak radiative corrections to hard inclusive processes at
the TeV scale, and we investigate how collinear logarithms factorize in a
spontaneously broken gauge theory, similarly to the DGLAP analysis in QCD.
Due to the uncancelled double logs noticed previously, we find a
factorization pattern which is qualitatively different from the analogous one
in QCD. New types of splitting functions emerge which are needed to describe
the initial beam charges and are infrared-sensitive, that is dependent on an
infrared cutoff provided, ultimately, by the symmetry breaking scale. We derive
such splitting functions at one-loop level in the example of SU(2) gauge
theory, and we also discuss the structure functions' evolution equations, under
the assumption that isospin breaking terms present in the Ward identities of
the theory are sufficiently subleading at higher orders.Comment: 5 pages, 3 figure
Discovery of a tight correlation among the prompt emission properties of long Gamma Ray Bursts
We report the discovery of a correlation among three prompt emission
properties of GRBs. These are the isotropic peak luminosity L_iso, the peak
energy of the time-integrated prompt emission spectrum E_pk, and the ``high
signal" timescale T_0.45, previously used to characterize the variability
behavior of bursts. In the rest frame of the source the found correlation reads
L_iso\propto E_pk^1.62 T_0.45^-0.49. We find other strong correlations, but at
the cost of increasing the number of variables, involving the variability and
the isotropic energy of the prompt emission. With respect to the previous tight
correlations found in GRBs the newly found correlation does not require any
information from the afterglow phase of the bursts, nor any model-dependent
assumption. In the popular scenario in which we are receiving beamed radiation
originating in a fireball pointing at us, the found correlation preserves its
form in the comoving frame. This helps to explain the small scatter of the
correlation, and underlines the role of the local brightness (i.e. the
brightness of the visible fraction of the fireball surface). This correlation
has been found for 19 objects, and it is hard to establish if any selection
bias affects it. Its connection with the prompt local brightness is promising,
but a solid physical understanding is still to be found. Despite all that, we
find that some properties of the correlation, which we discuss, support its
true existence, and this has important implications for the GRB physics.
Furthermore, it is possible to use such correlation as an accurate redshift
estimator, and its tightness will allow us to use it as a tool to constrain the
cosmological parameters (abridged)Comment: 15 pages, 8 figures included. To appear in MNRA
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