3,763 research outputs found
The dual parameterization of the proton generalized parton distribution functions H and E and description of the DVCS cross sections and asymmetries
We develop the minimal model of a new leading order parameterization of GPDs
introduced by Shuvaev and Polyakov. The model for GPDs H and E is formulated in
terms of the forward quark distributions, the Gegenbauer moments of the D-term
and the forward limit of the GPD E. The model is designed primarely for small
and medium-size values of x_B, x_B \leq 0.2.
We examined two different models of the t-dependence of the GPDs: The
factorized exponential model and the non-factorized Regge-motivated model.
Using our model, we successfully described the DVCS cross section measured by
H1 and ZEUS, the moments of the beam-spin A_{LU}^{\sin \phi}, beam-charge
A_{C}^{\cos \phi} and transversely-polarized target A_{UT}^{\sin \phi \cos
\phi} DVCS asymmetries measured by HERMES and A_{LU}^{\sin \phi} measured by
CLAS. The data on A_{C}^{\cos \phi} prefers the Regge-motivated model of the
t-dependence of the GPDs. The data on A_{UT}^{\sin \phi \cos \phi} indicates
that the u and d quarks carry only a small fraction of the proton total angular
momentum.Comment: 33 pages, 11 figure
Quantum Cosmology and Conformal Invariance
According to Belinsky, Khalatnikov and Lifshitz, gravity near a space-like
singularity reduces to a set of decoupled one-dimensional mechanical models at
each point in space. We point out that these models fall into a class of
conformal mechanical models first introduced by de Alfaro, Fubini and Furlan
(DFF). The deformation used by DFF to render the spectrum discrete corresponds
to a negative cosmological constant. The wave function of the universe is the
zero-energy eigenmode of the Hamiltonian, also known as the spherical vector of
the representation of the conformal group SO(1,2). A new class of conformal
quantum mechanical models is constructed, based on the quantization of
nilpotent coadjoint orbits, where the conformal group is enhanced to an ADE
non-compact group for which the spherical vector is known.Comment: 4 pages, latex2e, uses revtex
Solutions of the Klein-Gordon equation on manifolds with variable geometry including dimensional reduction
We develop the recent proposal to use dimensional reduction from the
four-dimensional space-time D=(1+3) to the variant with a smaller number of
space dimensions D=(1+d), d < 3, at sufficiently small distances to construct a
renormalizable quantum field theory. We study the Klein-Gordon equation on a
few toy examples ("educational toys") of a space-time with variable special
geometry, including a transition to a dimensional reduction. The examples
considered contain a combination of two regions with a simple geometry
(two-dimensional cylindrical surfaces with different radii) connected by a
transition region. The new technique of transforming the study of solutions of
the Klein-Gordon problem on a space with variable geometry into solution of a
one-dimensional stationary Schr\"odinger-type equation with potential generated
by this variation is useful. We draw the following conclusions: (1) The signal
related to the degree of freedom specific to the higher-dimensional part does
not penetrate into the smaller-dimensional part because of an inertial force
inevitably arising in the transition region (this is the centrifugal force in
our models). (2) The specific spectrum of scalar excitations resembles the
spectrum of the real particles; it reflects the geometry of the transition
region and represents its "fingerprints". (3) The parity violation due to the
asymmetric character of the construction of our models could be related to
violation of the CP symmetry.Comment: laTeX file, 9 pages, 8 figures. Significant corrections in the title,
abstract, text. Corrected formulas and figures. Added new references,
amendments in English. Acceptred for publication in Theoretical and
Mathematical Physics. To appear in vol. 167, may 201
Canonical quantization of a particle near a black hole
We discuss the quantization of a particle near an extreme Reissner-Nordstrom
black hole in the canonical formalism. This model appears to be described by a
Hamiltonian with no well-defined ground state. This problem can be circumvented
by a redefinition of the Hamiltonian due to de Alfaro, Fubini and Furlan (DFF).
We show that the Hamiltonian with no ground state corresponds to a gauge in
which there is an obstruction at the boundary of spacetime requiring a
modification of the quantization rules. The redefinition of the Hamiltonian a
la DFF corresponds to a different choice of gauge. The latter is a good gauge
leading to standard quantization rules. Thus, the DFF trick is a consequence of
a standard gauge-fixing procedure in the case of black hole scattering.Comment: 13 pages, ReVTeX, no figure
Electric Dipole Moments and Polarizability in the Quark-Diquark Model of the Neutron
For a bound state internal wave function respecting parity symmetry, it can
be rigorously argued that the mean electric dipole moment must be strictly
zero. Thus, both the neutron, viewed as a bound state of three quarks, and the
water molecule, viewed as a bound state of ten electrons two protons and an
oxygen nucleus, both have zero mean electric dipole moments. Yet, the water
molecule is said to have a nonzero dipole moment strength with
. The neutron may also be said to have
an electric dipole moment strength with .
The neutron analysis can be made experimentally consistent, if one employs a
quark-diquark model of neutron structure.Comment: four pages, two figure
Fermion propagators in space-time
The one- and the two-particle propagators for an infinite non-interacting
Fermi system are studied as functions of space-time coordinates. Their
behaviour at the origin and in the asymptotic region is discussed, as is their
scaling in the Fermi momentum. Both propagators are shown to have a divergence
at equal times. The impact of the interaction among the fermions on their
momentum distribution, on their pair correlation function and, hence, on the
Coulomb sum rule is explored using a phenomenological model. Finally the
problem of how the confinement is reflected in the momentum distribution of the
system's constituents is briefly addressed.Comment: 26 pages, 9 figures, accepted for publication on Phys. Rev.
Environmental effects on galaxy evolution. II: quantifying the tidal features in NIR-images of the cluster Abell 85
This work is part of a series of papers devoted to investigate the evolution
of cluster galaxies during their infall. In the present article we imaged in
NIR a selected sample of galaxies through- out the massive cluster Abell 85 (z
= 0.055). We obtained (JHK) photometry for 68 objects, reaching 1 mag/arcsec^2
deeper than 2MASS. We use these images to unveil asymmetries in the outskirts
of a sample of bright galaxies and develop a new asymmetry index, alpha_An,
which allows to quantify the degree of disruption by the relative area occupied
by the tidal features on the plane of the sky. We measure the asymmetries for a
subsample of 41 large area objects finding clear asymmetries in ten galaxies,
most of them being in groups and pairs projected at different clustercentric
distances, some of them located beyond R500 . Combining information on the
Hi-gas content of blue galaxies and the distribution of sub-structures across
Abell 85, with the present NIR asymmetry analysis, we obtain a very powerful
tool to confirm that tidal mechanisms are indeed present and are currently
affecting a fraction of galaxies in Abell 85. However, when comparing our deep
NIR images with UV-blue images of two very disrupted (jellyfish) galaxies in
this cluster, we discard the presence of tidal 1 interactions down to our
detection limit. Our results suggest that ram-pressure stripping is at the
origin of such spectacular disruptions. We conclude that across a complex
cluster like Abell 85, environment mechanisms, both gravitational and
hydrodynamical, are playing an active role in driving galaxy evolution.Comment: 30 pages, 13 figures, Accepted for Publication in A
New Observational Bounds to Quantum Gravity Signals
We consider a new set of effects arising from the quantum gravity corrections
to the propagation of fields, associated with fluctuations of the spacetime
geometry. Using already existing experimental data, we can put bounds on these
effects that are more stringent by several orders of magnitude than those
expected to be obtained in astrophysical observations. In fact these results
can be already interpreted as questioning the whole scenario of linear (in
) corrections to the dispersion relations for free fields in Lorentz
violating theories.Comment: Latex, to be published in PR
Imitation in Large Games
In games with a large number of players where players may have overlapping
objectives, the analysis of stable outcomes typically depends on player types.
A special case is when a large part of the player population consists of
imitation types: that of players who imitate choice of other (optimizing)
types. Game theorists typically study the evolution of such games in dynamical
systems with imitation rules. In the setting of games of infinite duration on
finite graphs with preference orderings on outcomes for player types, we
explore the possibility of imitation as a viable strategy. In our setup, the
optimising players play bounded memory strategies and the imitators play
according to specifications given by automata. We present algorithmic results
on the eventual survival of types
Quantization of maximally-charged slowly-moving black holes
We discuss the quantization of a system of slowly-moving extreme
Reissner-Nordstrom black holes. In the near-horizon limit, this system has been
shown to possess an SL(2,R) conformal symmetry. However, the Hamiltonian
appears to have no well-defined ground state. This problem can be circumvented
by a redefinition of the Hamiltonian due to de Alfaro, Fubini and Furlan (DFF).
We apply the Faddeev-Popov quantization procedure to show that the Hamiltonian
with no ground state corresponds to a gauge in which there is an obstruction at
the singularities of moduli space requiring a modification of the quantization
rules. The redefinition of the Hamiltonian a la DFF corresponds to a different
choice of gauge. The latter is a good gauge leading to standard quantization
rules. Thus, the DFF trick is a consequence of a standard gauge-fixing
procedure in the case of black hole scattering.Comment: Corrected errors in the gauge-fixing procedur
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