426 research outputs found
Relativistic ponderomotive force, uphill acceleration, and transition to chaos
Starting from a covariant cycle-averaged Lagrangian the relativistic
oscillation center equation of motion of a point charge is deduced and
analytical formulae for the ponderomotive force in a travelling wave of
arbitrary strength are presented. It is further shown that the ponderomotive
forces for transverse and longitudinal waves are different; in the latter,
uphill acceleration can occur. In a standing wave there exists a threshold
intensity above which, owing to transition to chaos, the secular motion can no
longer be described by a regular ponderomotive force.
PACS number(s): 52.20.Dq,05.45.+b,52.35.Mw,52.60.+hComment: 8 pages, RevTeX, 3 figures in PostScript, see also
http://www.physik.th-darmstadt.de/tqe
Hard-Loop Effective Action for Anisotropic Plasmas
We generalize the hard-thermal-loop effective action of the equilibrium
quark-gluon plasma to a non-equilibrium system which is space-time homogeneous
but for which the parton momentum distribution is anisotropic. We show that the
manifestly gauge-invariant Braaten-Pisarski form of the effective action can be
straightforwardly generalized and we verify that it then generates all n-point
functions following from collisionless gauge-covariant transport theory for a
homogeneous anisotropic plasma. On the other hand, the Taylor-Wong form of the
hard-thermal-loop effective action has a more complicated generalization to the
anisotropic case. Already in the simplest case of anisotropic distribution
functions, it involves an additional term that is gauge invariant by itself,
but nontrivial also in the static limit.Comment: 12 pages. Version 3: typo in (15) corrected, note added discussing
metric conventions use
A Raman spectroscopic and computational study of new aromatic pyrimidine-based halogen bond acceptors
© 2019 by the authors. Two new aromatic pyrimidine-based derivatives designed specifically for halogen bond directed self-assembly are investigated through a combination of high-resolution Raman spectroscopy, X-ray crystallography, and computational quantum chemistry. The vibrational frequencies of these new molecular building blocks, pyrimidine capped with furan (PrmF) and thiophene (PrmT), are compared to those previously assigned for pyrimidine (Prm). The modifications affect only a select few of the normal modes of Prm, most noticeably its signature ring breathing mode, ν1. Structural analyses afforded by X-ray crystallography, and computed interaction energies from density functional theory computations indicate that, although weak hydrogen bonding (C-H...O or C-H...N interactions) is present in these pyrimidine-based solid-state co-crystals, halogen bonding and π-stacking interactions play more dominant roles in driving their molecular-assembly
The Equation of State for Dense QCD and Quark Stars
We calculate the equation of state for degenerate quark matter to leading
order in hard-dense-loop (HDL) perturbation theory. We solve the
Tolman-Oppenheimer-Volkov equations to obtain the mass-radius relation for
dense quark stars. Both the perturbative QCD and the HDL equations of state
have a large variation with respect to the renormalization scale for quark
chemical potential below 1 GeV which leads to large theoretical uncertainties
in the quark star mass-radius relation.Comment: 7 pages, 3 figure
Energy Loss of a Heavy Fermion in an Anisotropic QED Plasma
We compute the leading-order collisional energy loss of a heavy fermion
propagating in a QED plasma with an electron distribution function which is
anisotropic in momentum space. We show that in the presence of such
anisotropies there can be a significant directional dependence of the heavy
fermion energy loss with the effect being quite large for highly-relativistic
velocities. We also repeat the analysis of the isotropic case more carefully
and show that the final result depends on the intermediate scale used to
separate hard and soft contributions to the energy loss. We then show that the
canonical isotropic result is obtained in the weak-coupling limit. For
intermediate-coupling we use the residual scale dependence as a measure of our
theoretical uncertainty. We also discuss complications which could arise due to
the presence of unstable soft photonic modes and demonstrate that the
calculation of the energy loss is safe.Comment: 19 pages, 18 figures. v2 - Correction to normalization of numerical
results; some figures modified as a result; discussion of role of unstable
modes added along with two new figure
Numerical convergence of the block-maxima approach to the Generalized Extreme Value distribution
In this paper we perform an analytical and numerical study of Extreme Value
distributions in discrete dynamical systems. In this setting, recent works have
shown how to get a statistics of extremes in agreement with the classical
Extreme Value Theory. We pursue these investigations by giving analytical
expressions of Extreme Value distribution parameters for maps that have an
absolutely continuous invariant measure. We compare these analytical results
with numerical experiments in which we study the convergence to limiting
distributions using the so called block-maxima approach, pointing out in which
cases we obtain robust estimation of parameters. In regular maps for which
mixing properties do not hold, we show that the fitting procedure to the
classical Extreme Value Distribution fails, as expected. However, we obtain an
empirical distribution that can be explained starting from a different
observable function for which Nicolis et al. [2006] have found analytical
results.Comment: 34 pages, 7 figures; Journal of Statistical Physics 201
Azimuthal asymmetries in lepton-pair production at a fixed-target experiment using the LHC beams (AFTER)
A multi-purpose fixed-target experiment using the proton and lead-ion beams
of the LHC was recently proposed by Brodsky, Fleuret, Hadjidakis and Lansberg,
and here we concentrate our study on some issues related to the spin physics
part of this project (referred to as AFTER). We study the nucleon spin
structure through and processes with a fixed-target experiment using
the LHC proton beams, for the kinematical region with 7 TeV proton beams at the
energy in center-of-mass frame of two nucleons GeV. We calculate
and estimate the azimuthal asymmetries of unpolarized and
dilepton production processes in the Drell--Yan continuum region and at the
-pole. We also calculate the , and
azimuthal asymmetries of and dilepton production
processes with the target proton and deuteron longitudinally or transversally
polarized in the Drell--Yan continuum region and around resonances region.
We conclude that it is feasible to measure these azimuthal asymmetries,
consequently the three-dimensional or transverse momentum dependent parton
distribution functions (3dPDFs or TMDs), at this new AFTER facility.Comment: 15 pages, 40 figures. Version accepted for publication in EPJ
Langevin Simulation of Scalar Fields: Additive and Multiplicative Noises and Lattice Renormalization
We consider the Langevin lattice dynamics for a spontaneously broken lambda
phi^4 scalar field theory where both additive and multiplicative noise terms
are incorporated. The lattice renormalization for the corresponding stochastic
Ginzburg-Landau-Langevin and the subtleties related to the multiplicative noise
are investigated.Comment: 26 pages, 4 eps figures (Elsevier latex style
Hamilton's Formalism for Systems with Constraints
The main goal of these lectures is to introduce and review the Hamiltonian
formalism for classical constrained systems and in particular gauge theories.
Emphasis is put on the relation between local symmetries and constraints and on
the relation between Lagrangean and Hamiltonian symmetries.Comment: 52 pages, revised LATEX version, ETH-TH/93-48, Lectures given at the
Seminar "The Canonical Formalism in Classical and Quantum General
Relativity", Bad Honnef, September 9
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