1,303 research outputs found
Fermions in spherical field theory
We derive the spherical field formalism for fermions. We find that the
spherical field method is free from certain difficulties which complicate
lattice calculations, such as fermion doubling, missing axial anomalies, and
computational problems regarding internal fermion loops.Comment: corrected journal inf
On the Matrix Element of the Transverse Component of Bilocal Vector Current and its Parton Interpretation
In this paper we study the matrix element of the transverse component of the
bilocal vector current in the context of deep inelastic scattering. BJL limit
of high energy amplitudes together with light-front current algebra imply the
same parton interpretation for its matrix element as that of the plus
component. On the other hand, the transverse component depends explicitly on
the gluon field operator in QCD, appears as "twist three" and hence its matrix
element has no manifest parton interpretation. In this paper we perform
calculations in light-front time-ordering perturbative QCD for a dressed quark
target to order and demonstrate that the matrix element of the
transverse component of the bilocal vector current has the same parton
interpretation as that of the plus component.Comment: 7 pages, REVTE
A Tree-Loop Duality Relation at Two Loops and Beyond
The duality relation between one-loop integrals and phase-space integrals,
developed in a previous work, is extended to higher-order loops. The duality
relation is realized by a modification of the customary +i0 prescription of the
Feynman propagators, which compensates for the absence of the multiple-cut
contributions that appear in the Feynman tree theorem. We rederive the duality
theorem at one-loop order in a form that is more suitable for its iterative
extension to higher-loop orders. We explicitly show its application to two- and
three-loop scalar master integrals, and we discuss the structure of the
occurring cuts and the ensuing results in detail.Comment: 20 pages. Few typos corrected, some additional comments included,
Appendix B and one reference added. Final version as published in JHE
Liquid-liquid coexistence in the phase diagram of a fluid confined in fractal porous materials
Multicanonical ensemble sampling simulations have been performed to calculate
the phase diagram of a Lennard-Jones fluid embedded in a fractal random matrix
generated through diffusion limited cluster aggregation. The study of the
system at increasing size and constant porosity shows that the results are
independent from the matrix realization but not from the size effects. A
gas-liquid transition shifted with respect to bulk is found. On growing the
size of the system on the high density side of the gas-liquid coexistence curve
it appears a second coexistence region between two liquid phases. These two
phases are characterized by a different behaviour of the local density inside
the interconnected porous structure at the same temperature and chemical
potential.Comment: 5 pages, 4 figures. To be published in Europhys. Letter
Efficiency improvements for the numerical computation of NLO corrections
In this paper we discuss techniques, which lead to a significant improvement
of the efficiency of the Monte Carlo integration, when one-loop QCD amplitudes
are calculated numerically with the help of the subtraction method and contour
deformation. The techniques discussed are: holomorphic and non-holomorphic
division into sub-channels, optimisation of the integration contour,
improvement of the ultraviolet subtraction terms, importance sampling and
antithetic variates in loop momentum space, recurrence relations.Comment: 34 pages, version to be publishe
Tree-based Coarsening and Partitioning of Complex Networks
Many applications produce massive complex networks whose analysis would
benefit from parallel processing. Parallel algorithms, in turn, often require a
suitable network partition. For solving optimization tasks such as graph
partitioning on large networks, multilevel methods are preferred in practice.
Yet, complex networks pose challenges to established multilevel algorithms, in
particular to their coarsening phase.
One way to specify a (recursive) coarsening of a graph is to rate its edges
and then contract the edges as prioritized by the rating. In this paper we (i)
define weights for the edges of a network that express the edges' importance
for connectivity, (ii) compute a minimum weight spanning tree with
respect to these weights, and (iii) rate the network edges based on the
conductance values of 's fundamental cuts. To this end, we also (iv)
develop the first optimal linear-time algorithm to compute the conductance
values of \emph{all} fundamental cuts of a given spanning tree. We integrate
the new edge rating into a leading multilevel graph partitioner and equip the
latter with a new greedy postprocessing for optimizing the maximum
communication volume (MCV). Experiments on bipartitioning frequently used
benchmark networks show that the postprocessing already reduces MCV by 11.3%.
Our new edge rating further reduces MCV by 10.3% compared to the previously
best rating with the postprocessing in place for both ratings. In total, with a
modest increase in running time, our new approach reduces the MCV of complex
network partitions by 20.4%
Asymmetries in polarized hadron production in e^+e^- annihilation up to order 1/Q
We present the results of the tree-level calculation of inclusive two-hadron
production in electron-positron annihilation via one photon up to subleading
order in 1/Q. We consider the situation where the two hadrons belong to
different, back-to-back jets. We include polarization of the produced hadrons
and discuss azimuthal dependences of asymmetries. New asymmetries are found, in
particular there is a leading cos(2 phi) asymmetry, which is even present when
hadron polarization is absent, since it arises solely due to the intrinsic
transverse momenta of the quarks.Comment: 26 pages, Revtex, 4 Postscript figures, uses epsfig.sty. Version to
appear in Nuclear Physics B: abstract, introduction and summary slightly
modified, references added and some typos correcte
Weak-field approximation of effective gravitational theory with local Galilean invariance
We examine the weak-field approximation of locally Galilean invariant
gravitational theories with general covariance in a -dimensional
Galilean framework. The additional degrees of freedom allow us to obtain
Poisson, diffusion, and Schr\"odinger equations for the fluctuation field. An
advantage of this approach over the usual -dimensional General
Relativity is that it allows us to choose an ansatz for the fluctuation field
that can accommodate the field equations of the Lagrangian approach to MOdified
Newtonian Dynamics (MOND) known as AQUAdratic Lagrangian (AQUAL). We
investigate a wave solution for the Schr\"odinger equations.Comment: 15 page
CPT theorem in a (5+1) Galilean space-time
We extend the 5-dimensional Galilean space-time to a (5+1) Galilean
space-time in order to define a parity transformation in a covariant manner.
This allows us to discuss the discrete symmetries in the Galilean space-time,
which is embedded in the (5+1) Minkowski space-time. We discuss the Dirac-type
field, for which we give the 8\times 8 gamma matrices explicitly. We
demonstrate that the CPT theorem holds in the (5+1) Galilean space-time.Comment: 11 pages, 0 figur
Spin operator and spin states in Galilean covariant Fermi field theories
Spin degrees of freedom of the Galilean covariant Dirac field in (4+1)
dimensions and its nonrelativistic counterpart in (3+1) dimensions are
examined. Two standard choices of spin operator, the Galilean covariant and
Dirac spin operators, are considered. It is shown that the Dirac spin of the
Galilean covariant Dirac field in (4+1) dimensions is not conserved, and the
role of non-Galilean boosts in its nonconservation is stressed out. After
reduction to (3+1) dimensions the Dirac field turns into a nonrelativistic
Fermi field with a conserved Dirac spin. A generalized form of the Levy-Leblond
equations for the Fermi field is given. One-particle spin states are
constructed. A particle-antiparticle system is discussed.Comment: Minor corrections in the text; journal versio
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