4,910 research outputs found
Breakdown of chiral expansion for parton distributions
In the framework of the chiral perturbation theory we computed two- and
three-loop corrections to the pion parton distributions which posses
-function singularities at x->0. This calculation explicitly
demonstrates that in the region of small x ~ mpi^2/(4 pi F)^2 standard ChPT
breaks down and one needs resummation of all orders. We give an example of such
resummation.Comment: 10 pages, 7 figure
One Loop Chiral Corrections to Hard Exclusive Processes:I. Pion Case
We computed the leading non-analytic chiral corrections to the generalized
parton distributions (GPDs) of the pion and to the two-pion distribution
amplitudes. This allows us to obtain the corresponding corrections for the hard
exclusive processes, such as gamma^* gamma -> pi pi, gamma^* N -> 2pi N' and
deeply virtual Compton scattering on the pion target.Comment: 17 pages, 3 figure
Stochastic Wave-Function Simulation of Irreversible Emission Processes for Open Quantum Systems in a Non-Markovian Environment
When conducting the numerical simulation of quantum transport, the main
obstacle is a rapid growth of the dimension of entangled Hilbert subspace. The
Quantum Monte Carlo simulation techniques, while being capable of treating the
problems of high dimension, are hindered by the so-called "sign problem". In
the quantum transport, we have fundamental asymmetry between the processes of
emission and absorption of environment excitations: the emitted excitations are
rapidly and irreversibly scattered away. Whereas only a small part of these
excitations is absorbed back by the open subsystem, thus exercising the
non-Markovian self-action of the subsystem onto itself. We were able to devise
a method for the exact simulation of the dominant quantum emission processes,
while taking into account the small backaction effects in an approximate
self-consistent way. Such an approach allows us to efficiently conduct
simulations of real-time dynamics of small quantum subsystems immersed in
non-Markovian bath for large times, reaching the quasistationary regime. As an
example we calculate the spatial quench dynamics of Kondo cloud for a bozonized
Kodno impurity model.Comment: 7 pages, 3 figures, ICQT2017 Conference Proceedings; corrected a few
typos; accepted for publication in the AIP Conference Proceedings journa
New Discrete States in Two-Dimensional Supergravity
Two-dimensional string theory is known to contain the set of discrete states
that are the SU(2) multiplets generated by the lowering operator of the SU(2)
current algebra.Their structure constants are defined by the area preserving
diffeomorphisms in two dimensions. We show that the interaction of
superstrings with the superconformal ghosts enlarges the algebra of dimension 1
currents and hence the new discrete states appear. These new states are the
SU(N) multiplets, if the algebra includes the currents of ghost numbers from -N
to N-2, not related by the picture-changing. We compute the structure constants
of these new discrete states for N=3 and express them in terms of SU(3)
Clebsch-Gordan coefficients,relating their operator algebra to the volume
preserving diffeomorphisms in d=3. For general N, the algebra is conjectured to
be isomorphic to SDiff(N). This points at possible holographic relations
between 2d superstrings and field theories in higher dimensions.Comment: 22 pages; typos corrected, 2 references adde
Gravitational Couplings of Higher Spins from String Theory
We calculate the interaction 3-vertex of two massless spin 3 particles with a
graviton using vertex operators for spin 3 fields in open string theory,
constructed in our previous work. The massless spin 3 fields are shown to
interact with the graviton through the linearized Weyl tensor, reproducing the
result by Boulanger, Leclercq and Sundell. This is consistent with the general
structure of the non-Abelian couplings, implying that the minimal
number of space-time derivatives in the interaction vertices of two spin s and
one spin 2 particle is equal to .Comment: 19 page
Conformal Moduli and b-c Pictures for NSR Strings
We explore the geometry of the superconformal moduli of the NSR superstring
theory in order to construct the consistent sigma-model for the NSR strings,
free of picture-changing ambiguities. The sigma-model generating functional is
constructed by the integration over the bosonic and anticommuting moduli,
corresponding to insertions of the vertex operators in scattering amplitudes.
In particular, the integration over the bosonic moduli results in the
appearance of picture-changing operators for the b-c system. Important example
of the b-c pictures involves the unintegrated and integrated forms of the
vertex operators. We derive the BRST-invariant expressions for the b-c
picture-changing operators for open and closed strings and study some of their
properties. We also show that the superconformal moduli spaces of the NSR
superstring theory contain the global singularities, leading to the appearance
of non-perturbative solitonic D-brane creation operators.Comment: 22 pages, references adde
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