5,656 research outputs found
Polarization phenomena in elastic scattering, for axial parametrization of two-photon exchange
We analyze polarization phenomena for elastic lepton-nucleon scattering,
parametrizing the -exchange contribution, as the product of lepton and
nucleon axial vector currents, that correspond to exchange in the
annihilation channel. We found two combinations of polarization observables
(one for three T-odd observables and another one - for five T-even
observables), which allow to measure the ratio of nucleon
electromagnetic form factors in model independent way, without any specific
assumption about the -exchange mechanism. Both these combinations have
a general character and do not depend on the choice of the spin structure for
the -exchange. We show the inconsistency of other approximations
recently used in the literature.Comment: Eight pages, no figure
Radiative corrections to polarization observables for elastic -scattering. Part I: Virtual Compton Scattering
We calculate polarization phenomena for virtual Compton scattering on
protons, at relatively large momentum transfer 1 GeV 5
GeV on the basis of a model for with two main
contributions: -exchange in channel and -excitation in
-channel. This model applies from threshold to region. The
parameters entering in this model, such as coupling constants and
electromagnetic form factors are well known. The analyzing powers for
and the components of the final proton
polarization in are large in absolute value and
show strong sensitivity to interference. These results
can be applied to the calculation of radiative corrections to polarization
phenomena in elastic -scattering.Comment: 18 pages, 9 figure
Multifractality meets entanglement: relation for non-ergodic extended states
In this work we establish a relation between entanglement entropy and fractal
dimension of generic many-body wave functions, by generalizing the result
of Don N. Page [Phys. Rev. Lett. 71, 1291] to the case of {\it sparse} random
pure states (S-RPS). These S-RPS living in a Hilbert space of size are
defined as normalized vectors with only () random non-zero
elements. For these states used by Page represent ergodic states at
infinite temperature. However, for the S-RPS are non-ergodic and
fractal as they are confined in a vanishing ratio of the full Hilbert
space. Both analytically and numerically, we show that the mean entanglement
entropy of a subsystem , with Hilbert space dimension
, scales as for small fractal
dimensions , . Remarkably, saturates
at its thermal (Page) value at infinite temperature,
at larger . Consequently, we
provide an example when the entanglement entropy takes an ergodic value even
though the wave function is highly non-ergodic. Finally, we generalize our
results to Renyi entropies with and to genuine
multifractal states and also show that their fluctuations have ergodic behavior
in narrower vicinity of the ergodic state, .Comment: 7 pages, 4 figures, 92 references + 9 pages, 9 figures in appendice
Measuring the deviation from the Rutherford formula
Modern experiments with heavy ion-leptons collisions open the possibility to
measure the deviation of cross section of small angles electron(positron)-ion
elastic scattering from the Rutherford formula due to multiple virtual photons
exchange. The charge asymmetry and the polarization of the scattered leptons
are calculated and numerical predictions are given. A generalization to elastic
proton-nucleus scattering is discussed.Comment: 4 pages, 4 figures, Brief Repor
Compilation and analysis of charge asymmetry measurements from electron and positron scattering on nucleon and nuclei
World data on the lepton-charge asymmetry in the elastic and inelastic lepton
scattering off the proton and nuclei are compiled and discussed. After
reviewing the published results, we compare the elastic data to a model
calculation of the two-photon exchange mechanism. We show that the existing
data do not provide any evidence for the two-photon contribution. At
significance level 0.05 the data allow to exclude the two-photon exchange as an
explanation for the difference between Rosenbluth and polarization measurements
of proton electromagnetic form factors.Comment: 20 pages, 7 figures 2 table
Model independent study of massive lepton elastic scattering on the proton, beyond the Born approximation
Model independent expressions for all polarization observables in elastic scattering are obtained, taking into account the lepton mass and
including the two-photon exchange contribution. The spin structure of the
matrix element is parametrized in terms of six independent complex amplitudes,
functions of two independent kinematical variables. General statements about
the influence of the two--photon--exchange terms on the differential cross
section and on polarization observables are given. Polarization effects have
been investigated for the case of a longitudinally polarized lepton beam and
polarized nucleon in the final state.Comment: 28 pages, 3 figure
Neutron electric form factor at large momentum transfer
Based on the recent, high precision data for elastic electron scattering from
protons and deuterons, at relatively large momentum transfer , we
determine the neutron electric form factor up to GeV. The values
obtained from the data (in the framework of the nonrelativistic impulse
approximation) are larger than commonly assumed and are in good agreement with
the Gari-Kr\"umpelmann parametrization of the nucleon electromagnetic form
factors.Comment: 11 pages 2 figure
Survival probability in Generalized Rosenzweig-Porter random matrix ensemble
We study analytically and numerically the dynamics of the generalized
Rosenzweig-Porter model, which is known to possess three distinct phases:
ergodic, multifractal and localized phases. Our focus is on the survival
probability , the probability of finding the initial state after time
. In particular, if the system is initially prepared in a highly-excited
non-stationary state (wave packet) confined in space and containing a fixed
fraction of all eigenstates, we show that can be used as a dynamical
indicator to distinguish these three phases. Three main aspects are identified
in different phases. The ergodic phase is characterized by the standard
power-law decay of with periodic oscillations in time, surviving in the
thermodynamic limit, with frequency equals to the energy bandwidth of the wave
packet. In multifractal extended phase the survival probability shows an
exponential decay but the decay rate vanishes in the thermodynamic limit in a
non-trivial manner determined by the fractal dimension of wave functions.
Localized phase is characterized by the saturation value of ,
finite in the thermodynamic limit , which approaches
in this limit.Comment: 21 pages, 12 figures, 61 reference
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