28,538 research outputs found
Infrared regulators and SCETII
We consider matching from SCETI, which includes ultrasoft and collinear
particles, onto SCETII with soft and collinear particles at one loop. Keeping
the external fermions off their mass shell does not regulate all IR divergences
in both theories. We give a new prescription to regulate infrared divergences
in SCET. Using this regulator, we show that soft and collinear modes in SCETII
are sufficient to reproduce all the infrared divergences of SCETI. We explain
the relationship between IR regulators and an additional mode proposed for
SCETII.Comment: 9 pages. Added discussion about relationship between IR regulators
and messenger mode
Spin-Hall and Anisotropic Magnetoresistance in Ferrimagnetic Co-Gd / Pt layers
We present the Co-Gd composition dependence of the spin-Hall
magnetoresistance (SMR) and anisotropic magnetoresistance (AMR) for
ferrimagnetic Co100-xGdx / Pt bilayers. With Gd concentration x, its magnetic
moment increasingly competes with the Co moment in the net magnetization. We
find a nearly compensated ferrimagnetic state at x = 24. The AMR changes sign
from positive to negative with increasing x, vanishing near the magnetization
compensation. On the other hand, the SMR does not vary significantly even where
the AMR vanishes. These experimental results indicate that very different
scattering mechanisms are responsible for AMR and SMR. We discuss a possible
origin for the alloy composition dependence.Comment: 31 Pages, 9 figure
Spin heat accumulation and its relaxation in spin valves
We study the concept of spin heat accumulation in excited spin valves, more
precisely the effective electron temperature that may become spin dependent,
both in linear response and far from equilibrium. A temperature or voltage
gradient create non-equilibrium energy distributions of the two spin ensembles
in the normal metal spacer, which approach Fermi-Dirac functions through energy
relaxation mediated by electron-electron and electron-phonon coupling. Both
mechanisms also exchange energy between the spin subsystems. This inter-spin
energy exchange may strongly affect thermoelectric properties spin valves,
leading, e.g., to violations of the Wiedemann-Franz law.Comment: 4 pages, 4 figures, close to published versio
Improving jet distributions with effective field theory
We obtain perturbative expressions for jet distributions using soft-collinear
effective theory (SCET). By matching SCET onto QCD at high energy, tree level
matrix elements and higher order virtual corrections can be reproduced in SCET.
The resulting operators are then evolved to lower scales, with additional
operators being populated by required threshold matchings in the effective
theory. We show that the renormalization group evolution and threshold
matchings reproduce the Sudakov factors and splitting functions of QCD, and
that the effective theory naturally combines QCD matrix elements and parton
showers. The effective theory calculation is systematically improvable and any
higher order perturbative effects can be included by a well defined procedure.Comment: 4 pages, 1 figure; typos corrected and notation updated to match
hep-ph/060729
Phase Transitions in a Two-Component Site-Bond Percolation Model
A method to treat a N-component percolation model as effective one component
model is presented by introducing a scaled control variable . In Monte
Carlo simulations on , , and simple cubic
lattices the percolation threshold in terms of is determined for N=2.
Phase transitions are reported in two limits for the bond existence
probabilities and . In the same limits, empirical formulas
for the percolation threshold as function of one
component-concentration, , are proposed. In the limit a new
site percolation threshold, , is reported.Comment: RevTeX, 5 pages, 5 eps-figure
Size Matters: Origin of Binomial Scaling in Nuclear Fragmentation Experiments
The relationship between measured transverse energy, total charge recovered
in the detector, and size of the emitting system is investigated. Using only
very simple assumptions, we are able to reproduce the observed binomial
emission probabilities and their dependences on the transverse energy.Comment: 14 pages, including 4 figure
Factorization and Endpoint Singularities in Heavy-to-Light decays
We prove a factorization theorem for heavy-to-light form factors. Our result
differs in several important ways from previous proposals. A proper separation
of scales gives hard kernels that are free of endpoint singularities. A general
procedure is described for including soft effects usually associated with the
tail of wavefunctions in hard exclusive processes. We give an operator
formulation of these soft effects using the soft-collinear effective theory,
and show that they appear at the same order in the power counting as the hard
spectator contribution.Comment: 5 pages, Added details on comparison with the literatur
Information entropy in fragmenting systems
The possibility of facing critical phenomena in nuclear fragmentation is a
topic of great interest. Different observables have been proposed to identify
such a behavior, in particular, some related to the use of information entropy
as a possible signal of critical behavior. In this work we critically examine
some of the most widespread used ones comparing its performance in bond
percolation and in the analysis of fragmenting Lennard Jones Drops.Comment: 3 pages, 3 figure
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