691 research outputs found
Ultrasoft Renormalization in Non-Relativistic QCD
For Non-Relativistic QCD the velocity renormalization group correlates the
renormalization scales for ultrasoft, potential and soft degrees of freedom.
Here we discuss the renormalization of operators by ultrasoft gluons. We show
that renormalization of soft vertices can induce new operators, and also
present a procedure for correctly subtracting divergences in mixed
potential-ultrasoft graphs. Our results affect the running of the
spin-independent potentials in QCD. The change for the NNLL t-tbar cross
section near threshold is very small, being at the 1% level and essentially
independent of the energy. We also discuss implications for analyzing
situations where mv^2 ~ Lambda_QCD.Comment: 31 pages, 11 fig
Power Counting in the Soft-Collinear Effective Theory
We describe in some detail the derivation of a power counting formula for the
soft-collinear effective theory (SCET). This formula constrains which operators
are required to correctly describe the infrared at any order in the
Lambda_QCD/Q expansion (lambda expansion). The result assigns a unique
lambda-dimension to graphs in SCET solely from vertices, is gauge independent,
and can be applied independent of the process. For processes with an OPE the
lambda-dimension has a correspondence with dynamical twist.Comment: 12 pages, 1 fig, journal versio
On Power Suppressed Operators and Gauge Invariance in SCET
The form of collinear gauge invariance for power suppressed operators in the
soft-collinear effective theory is discussed. Using a field redefinition we
show that it is possible to make any power suppressed ultrasoft-collinear
operators invariant under the original leading order gauge transformations. Our
manipulations avoid gauge fixing. The Lagrangians to O(lambda^2) are given in
terms of these new fields. We then give a simple procedure for constructing
power suppressed soft-collinear operators in SCET_II by using an intermediate
theory SCET_I.Comment: 15 pages, journal versio
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
Hard Scattering Factorization from Effective Field Theory
In this paper we show how gauge symmetries in an effective theory can be used
to simplify proofs of factorization formulae in highly energetic hadronic
processes. We use the soft-collinear effective theory, generalized to deal with
back-to-back jets of collinear particles. Our proofs do not depend on the
choice of a particular gauge, and the formalism is applicable to both exclusive
and inclusive factorization. As examples we treat the pi-gamma form factor
(gamma gamma* -> pi^0), light meson form factors (gamma* M -> M), as well as
deep inelastic scattering (e- p -> e- X), Drell-Yan (p pbar -> X l+ l-), and
deeply virtual Compton scattering (gamma* p -> gamma(*) p).Comment: 35 pages, 4 figures, typos corrected, journal versio
Gauge-ready formulation of the cosmological kinetic theory in generalized gravity theories
We present cosmological perturbations of kinetic components based on
relativistic Boltzmann equations in the context of generalized gravity
theories. Our general theory considers an arbitrary number of scalar fields
generally coupled with the gravity, an arbitrary number of mutually interacting
hydrodynamic fluids, and components described by the relativistic Boltzmann
equations like massive/massless collisionless particles and the photon with the
accompanying polarizations. We also include direct interactions among fluids
and fields. The background FLRW model includes the general spatial curvature
and the cosmological constant. We consider three different types of
perturbations, and all the scalar-type perturbation equations are arranged in a
gauge-ready form so that one can implement easily the convenient gauge
conditions depending on the situation. In the numerical calculation of the
Boltzmann equations we have implemented four different gauge conditions in a
gauge-ready manner where two of them are new. By comparing solutions solved
separately in different gauge conditions we can naturally check the numerical
accuracy.Comment: 26 pages, 9 figures, revised thoroughly, to appear in Phys. Rev.
Order alpha_s^2 beta_0 Correction to the Charged Lepton Spectrum in b \to c \ell \bar\nu_\ell decays
We compute the \alpha_s^2\beta_0 part of the two-loop QCD corrections to the
charged lepton spectrum in b \to c \ell \bar\nu_\ell decays and find them to be
about 50\% of the first order corrections at all lepton energies, except those
close to the end point. Including these corrections we extract the central
values \bar\Lambda=0.33 GeV and \lambda_1=-0.17 GeV^2 for the HQET matrix
elements and use them to determine the b and c quark
masses, and |V_{cb}|.Comment: 15 pages, 1 Postscript figur
Strong Phases and Factorization for Color Suppressed Decays
We prove a factorization theorem in QCD for the color suppressed decays B0->
D0 M0 and B0-> D*0 M0 where M is a light meson. Both the color-suppressed and
W-exchange/annihilation amplitudes contribute at lowest order in LambdaQCD/Q
where Q={mb, mc, Epi}, so no power suppression of annihilation contributions is
found. A new mechanism is given for generating non-perturbative strong phases
in the factorization framework. Model independent predictions that follow from
our results include the equality of the B0 -> D0 M0 and B0 -> D*0 M0 rates, and
equality of non-perturbative strong phases between isospin amplitudes,
delta(DM) = delta(D*M). Relations between amplitudes and phases for M=pi,rho
are also derived. These results do not follow from large Nc factorization with
heavy quark symmetry.Comment: 38 pages, 6 figs, typos correcte
Physical interpretation of gauge invariant perturbations of spherically symmetric space-times
By calculating the Newman-Penrose Weyl tensor components of a perturbed
spherically symmetric space-time with respect to invariantly defined classes of
null tetrads, we give a physical interpretation, in terms of gravitational
radiation, of odd parity gauge invariant metric perturbations. We point out how
these gauge invariants may be used in setting boundary and/or initial
conditions in perturbation theory.Comment: 6 pages. To appear in PR
Electronic Structure and Heavy Fermion Behavior in LiV_2O_4
First principles density functional calculations of the electronic and
magnetic properties of spinel-structure LiVO have been performed
using the full potential linearized augmented planewave method. The
calculations show that the electronic structure near the Fermi energy consists
of a manifold of 12 bands derived from V states, weakly hybridized
with O p states. While the total width of this active manifold is approximately
2 eV, it may be roughly decomposed into two groups: high velocity bands and
flatter bands, although these mix in density functional calculations. The flat
bands, which are the more atomic-like lead to a high density of states and
magnetic instability of local moment character. The value of the on-site
exchange energy is sensitive to the exact exchange correlation parameterization
used in the calculations, but is much larger than the interaction between
neighboring spins, reflecting the weak coupling of the magnetic system with the
high velocity bands. A scenario for the observed heavy fermion behavior is
discussed in which conduction electrons in the dispersive bands are weakly
scattered by local moments associated with strongly correlated electrons in the
heavy bands.This is analogous to that in conventional Kondo type heavy
fermions, but is unusual in that both the local moments and conduction
electrons come from the same d-manifold.Comment: 6 Revtex pages, Postscript figs embedded. Revision: figure 4 replaced
with a better version, showing the band character explicitel
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