1,063 research outputs found
Analyticity of the Scattering Amplitude, Causality and High-Energy Bounds in Quantum Field Theory on Noncommutative Space-Time
In the framework of quantum field theory (QFT) on noncommutative (NC)
space-time with the symmetry group , we prove that the
Jost-Lehmann-Dyson representation, based on the causality condition taken in
connection with this symmetry, leads to the mere impossibility of drawing any
conclusion on the analyticity of the -scattering amplitude in
, being the scattering angle. Discussions on the possible
ways of obtaining high-energy bounds analogous to the Froissart-Martin bound on
the total cross-section are also presented.Comment: 25 page
Kinetic simulations of turbulent magnetic-field growth by streaming cosmic rays
Efficient acceleration of cosmic rays (via the mechanism of diffusive shock
acceleration) requires turbulent, amplified magnetic fields in the shock's
upstream region. We present results of multidimensional particle-in-cell
simulations aimed at observing the magnetic field amplification that is
expected to arise from the cosmic-ray current ahead of the shock, and the
impact on the properties of the upstream interstellar medium. We find that the
initial structure and peak strength of the amplified field is somewhat
sensitive to the choice of parameters, but that the field growth saturates in a
similar manner in all cases: the back-reaction on the cosmic rays leads to
modification of their rest-frame distribution and also a net transfer of
momentum to the interstellar medium, substantially weakening their relative
drift while also implying the development of a modified shock. The upstream
medium becomes turbulent, with significant spatial fluctuations in density and
velocity, the latter in particular leading to moderate upstream heating; such
fluctuations will also have a strong influence on the shock structure.Comment: 8 pages, 6 figures, accepted by Ap
Parametric instability in dark molecular clouds
The present work investigates the parametric instability of parallel
propagating circularly polarized Alfven(pump) waves in a weakly ionized
molecular cloud. It is shown that the relative drift between the plasma
particles gives rise to the Hall effect resulting in the modified pump wave
characteristics. Although the linearized fluid equations with periodic
coefficients are difficult to solve analytically, it is shown that a linear
transformation can remove the periodic dependence. The resulting linearized
equations with constant coefficients are used to derive an algebraic dispersion
relation. The growth rate of the parametric instability is a sensitive function
of the amplitude of the pump wave as well as to the ratio of the pump and the
modified dust-cyclotron frequencies. The instability is insensitive to the
plasma-beta The results are applied to the molecular clouds.Comment: 27 page, 5 figures, accepted in Ap
Completeness of ``Good'' Bethe Ansatz Solutions of a Quantum Group Invariant Heisenberg Model
The -quantum group invariant spin 1/2 XXZ-Heisenberg model with open
boundary conditions is investigated by means of the Bethe ansatz. As is well
known, quantum groups for equal to a root of unity possess a finite number
of ``good'' representations with non-zero q-dimension and ``bad'' ones with
vanishing q-dimension. Correspondingly, the state space of an invariant
Heisenberg chain decomposes into ``good'' and ``bad'' states. A ``good'' state
may be described by a path of only ``good'' representations. It is shown that
the ``good'' states are given by all ``good'' Bethe ansatz solutions with roots
restricted to the first periodicity strip, i.e. only positive parity strings
(in the language of Takahashi) are allowed. Applying Bethe's string counting
technique completeness of the ``good'' Bethe states is proven, i.e. the same
number of states is found as the number of all restricted path's on the
-Bratteli diagram. It is the first time that a ``completeness" proof
for an anisotropic quantum invariant reduced Heisenberg model is performed.Comment: LaTeX file with LaTeX figures, 24 pages, 1 PiCTeX figur
Applications of QCD
Talk given at XIXth International Symposium on Lepton and Photon Interactions
at High Energies (LP 99), Stanford, California, 9-14 August 1999.Comment: latex, 26 page
Jost-Lehmann-Dyson Representation, Analyticity in Angle Variable and Upper Bounds in Noncommutative Quantum Field Theory
The existence of Jost-Lehmann-Dyson representation analogue has been proved
in framework of space-space noncommutative quantum field theory. On the basis
of this representation it has been found that some class of elastic amplitudes
admits an analytical continuation into complex \cos\vartheta plane and
corresponding domain of analyticity is Martin ellipse. This analyticity
combined with unitarity leads to Froissart-Martin upper bound on total cross
section.Comment: LaTeX, 15 pages, improved version, misprints corrected, the
references added, to appear in Theor. Math. Phy
The monomer-dimer problem and moment Lyapunov exponents of homogeneous Gaussian random fields
We consider an "elastic" version of the statistical mechanical monomer-dimer
problem on the n-dimensional integer lattice. Our setting includes the
classical "rigid" formulation as a special case and extends it by allowing each
dimer to consist of particles at arbitrarily distant sites of the lattice, with
the energy of interaction between the particles in a dimer depending on their
relative position. We reduce the free energy of the elastic dimer-monomer (EDM)
system per lattice site in the thermodynamic limit to the moment Lyapunov
exponent (MLE) of a homogeneous Gaussian random field (GRF) whose mean value
and covariance function are the Boltzmann factors associated with the monomer
energy and dimer potential. In particular, the classical monomer-dimer problem
becomes related to the MLE of a moving average GRF. We outline an approach to
recursive computation of the partition function for "Manhattan" EDM systems
where the dimer potential is a weighted l1-distance and the auxiliary GRF is a
Markov random field of Pickard type which behaves in space like autoregressive
processes do in time. For one-dimensional Manhattan EDM systems, we compute the
MLE of the resulting Gaussian Markov chain as the largest eigenvalue of a
compact transfer operator on a Hilbert space which is related to the
annihilation and creation operators of the quantum harmonic oscillator and also
recast it as the eigenvalue problem for a pantograph functional-differential
equation.Comment: 24 pages, 4 figures, submitted on 14 October 2011 to a special issue
of DCDS-
Emulating the impact of additional proton–proton interactions in the ATLAS simulation by presampling sets of inelastic Monte Carlo events
The accurate simulation of additional interactions at the ATLAS experiment for the analysis of proton–proton collisions delivered by the Large Hadron Collider presents a significant challenge to the computing resources. During the LHC Run 2 (2015–2018), there were up to 70 inelastic interactions per bunch crossing, which need to be accounted for in Monte Carlo (MC) production. In this document, a new method to account for these additional interactions in the simulation chain is described. Instead of sampling the inelastic interactions and adding their energy deposits to a hard-scatter interaction one-by-one, the inelastic interactions are presampled, independent of the hard scatter, and stored as combined events. Consequently, for each hard-scatter interaction, only one such presampled event needs to be added as part of the simulation chain. For the Run 2 simulation chain, with an average of 35 interactions per bunch crossing, this new method provides a substantial reduction in MC production CPU needs of around 20%, while reproducing the properties of the reconstructed quantities relevant for physics analyses with good accuracy
The Fayet-Iliopoulos D-term and its renormalisation in softly-broken supersymmetric theories
We consider the renormalisation of the Fayet-Iliopoulos D-term in a
softly-broken abelian supersymmetric theory, and calculate the associated
beta-function through three loops. We show that there exists (at least through
three loops) a renormalisation group invariant trajectory for the coefficient
of the D-term, corresponding to the conformal anomaly solution for the soft
masses and couplings.Comment: 30 pages, Revtex, 15 Figures. Minor changes, and inadvertent omission
of author from this abstract correcte
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