123 research outputs found
Asymptotic Expansions for Stationary Distributions of Perturbed Semi-Markov Processes
New algorithms for computing of asymptotic expansions for stationary
distributions of nonlinearly perturbed semi-Markov processes are presented. The
algorithms are based on special techniques of sequential phase space reduction,
which can be applied to processes with asymptotically coupled and uncoupled
finite phase spaces.Comment: 83 page
Azimuthal asymmetries at CLAS: Extraction of e^a(x) and prediction of A_{UL}
First information on the chirally odd twist-3 proton distribution function
e(x) is extracted from the azimuthal asymmetry, A_{LU}, in the
electro-production of pions from deeply inelastic scattering of longitudinally
polarized electrons off unpolarized protons, which has been recently measured
by CLAS collaboration. Furthermore parameter-free predictions are made for
azimuthal asymmetries, A_{UL}, from scattering of an unpolarized beam on a
polarized proton target for CLAS kinematics.Comment: 9 pages, 5 figures, late
New observables in longitudinal single-spin asymmetries in semi-inclusive DIS
We analyze longitudinal beam and target single-spin asymmetries in
semi-inclusive deep inelastic scattering and in jet deep inelastic scattering,
including all possible twist-3 contributions as well as quark mass corrections.
We take into account the path-ordered exponential in the soft correlators and
show that it leads to the introduction of a new distribution and a new
fragmentation function contributing to the asymmetries.Comment: 8 page
The chirally-odd twist-3 distribution function e(x) in the chiral quark-soliton model
The chirally-odd twist-3 nucleon distribution e(x) is studied in the large-Nc
limit in the framework of the chiral quark-soliton model at a low normalization
point of about 0.6 GeV. The remarkable result is that in the model e(x)
contains a delta-function-type singularity at x=0. The regular part of e(x) is
found to be sizeable at the low scale of the model and in qualitative agreement
with bag model calculations.Comment: 16 pages, 6 figures, revtex, Ref.[50] and footnote 3 adde
Universality of T-odd effects in single spin and azimuthal asymmetries
We analyze the transverse momentum dependent distribution and fragmentation
functions in space-like and time-like hard processes involving at least two
hadrons, in particular 1-particle inclusive leptoproduction, the Drell-Yan
process and two-particle inclusive hadron production in electron-positron
annihilation. As is well-known, transverse momentum dependence allows for the
appearance of unsuppressed single spin azimuthal asymmetries, such as Sivers
and Collins asymmetries. Recently, Belitsky, Ji and Yuan obtained fully color
gauge invariant expressions for the relevant matrix elements appearing in these
asymmetries at leading order in an expansion in the inverse hard scale. We
rederive these results and extend them to observables at the next order in this
expansion. We observe that at leading order one retains a probability
interpretation, contrary to a claim in the literature and show the direct
relation between the Sivers effect in single spin asymmetries and the
Qiu-Sterman mechanism. We also study fragmentation functions, where the process
dependent gauge link structure of the correlators is not the only source of
T-odd observables and discuss the implications for universality.Comment: 29 pages, Revtex, 26 Postscript figures; abstract, introduction and
section VIIC significantly modified and appendix B replace
Level statistics and eigenfunctions of pseudointegrable systems: dependence on energy and genus number
We study the level statistics (second half moment and rigidity
) and the eigenfunctions of pseudointegrable systems with rough
boundaries of different genus numbers . We find that the levels form energy
intervals with a characteristic behavior of the level statistics and the
eigenfunctions in each interval. At low enough energies, the boundary roughness
is not resolved and accordingly, the eigenfunctions are quite regular functions
and the level statistics shows Poisson-like behavior. At higher energies, the
level statistics of most systems moves from Poisson-like towards Wigner-like
behavior with increasing . Investigating the wavefunctions, we find many
chaotic functions that can be described as a random superposition of regular
wavefunctions. The amplitude distribution of these chaotic functions
was found to be Gaussian with the typical value of the localization volume
. For systems with periodic boundaries we find
several additional energy regimes, where is relatively close to the
Poisson-limit. In these regimes, the eigenfunctions are either regular or
localized functions, where is close to the distribution of a sine or
cosine function in the first case and strongly peaked in the second case. Also
an interesting intermediate case between chaotic and localized eigenfunctions
appears
The problem of equilibration and the computation of correlation functions on a quantum computer
We address the question of how a quantum computer can be used to simulate
experiments on quantum systems in thermal equilibrium. We present two
approaches for the preparation of the equilibrium state on a quantum computer.
For both approaches, we show that the output state of the algorithm, after long
enough time, is the desired equilibrium. We present a numerical analysis of one
of these approaches for small systems. We show how equilibrium
(time)-correlation functions can be efficiently estimated on a quantum
computer, given a preparation of the equilibrium state. The quantum algorithms
that we present are hard to simulate on a classical computer. This indicates
that they could provide an exponential speedup over what can be achieved with a
classical device.Comment: 25 pages LaTex + 8 figures; various additional comments, results and
correction
- …