1,390 research outputs found
Factorization and NNLL Resummation for Higgs Production with a Jet Veto
Using methods of effective field theory, we derive the first all-order
factorization theorem for the Higgs-boson production cross section with a jet
veto, imposed by means of a standard sequential recombination jet algorithm.
Like in the case of small-q_T resummation in Drell-Yan and Higgs production,
the factorization is affected by a collinear anomaly. Our analysis provides the
basis for a systematic resummation of large logarithms log(m_H/p_T^veto) beyond
leading-logarithmic order. Specifically, we present predictions for the
resummed jet-veto cross section and efficiency at next-to-next-to-leading
logarithmic order. Our results have important implications for Higgs-boson
searches at the LHC, where a jet veto is required to suppress background
events.Comment: 28 pages, 5 figures; v2: published version; note added in proo
Two-Hole Bound States from a Systematic Low-Energy Effective Field Theory for Magnons and Holes in an Antiferromagnet
Identifying the correct low-energy effective theory for magnons and holes in
an antiferromagnet has remained an open problem for a long time. In analogy to
the effective theory for pions and nucleons in QCD, based on a symmetry
analysis of Hubbard and t-J-type models, we construct a systematic low-energy
effective field theory for magnons and holes located inside pockets centered at
lattice momenta (\pm pi/2a,\pm pi/2a). The effective theory is based on a
nonlinear realization of the spontaneously broken spin symmetry and makes
model-independent universal predictions for the entire class of lightly doped
antiferromagnetic precursors of high-temperature superconductors. The
predictions of the effective theory are exact, order by order in a systematic
low-energy expansion. We derive the one-magnon exchange potentials between two
holes in an otherwise undoped system. Remarkably, in some cases the
corresponding two-hole Schr\"odinger equations can even be solved analytically.
The resulting bound states have d-wave characteristics. The ground state wave
function of two holes residing in different hole pockets has a d_{x^2-y^2}-like
symmetry, while for two holes in the same pocket the symmetry resembles d_{xy}.Comment: 35 pages, 11 figure
Factorization and resummation of s-channel single top quark production
In this paper we study the factorization and resummation of s-channel single
top quark production in the Standard Model at both the Tevatron and the LHC. We
show that the production cross section in the threshold limit can be factorized
into a convolution of hard function, soft function and jet function via
soft-collinear-effective-theory (SCET), and resummation can be performed using
renormalization group equation in the momentum space resummation formalism. We
find that in general, the resummation effects enhance the Next-to-Leading-Order
(NLO) cross sections by about at both the Tevatron and the LHC, and
significantly reduce the factorization scale dependence of the total cross
section at the Tevatron, while at the LHC we find that the factorization scale
dependence has not been improved, compared with the NLO results.Comment: 29 pages, 7 figures; version published in JHE
Is Heavy Baryon Approach Necessary?
It is demonstrated that using an appropriately chosen renormalization
condition one can respect power counting within the relativistic baryon chiral
perturbation theory without appealing to the technique of the heavy baryon
approach. Explicit calculations are performed for diagrams including two-loops.
It is argued that the introduction of the heavy baryon chiral perturbation
theory was useful but not necessary.Comment: 9 pages, 2 figures, minor changes, references adde
On the breaking of collinear factorization in QCD
We investigate the breakdown of collinear factorization for non-inclusive
observables in hadron-hadron collisions. For pure QCD processes, factorization
is violated at the three-loop level and it has a structure identical to that
encountered previously in the case of super-leading logarithms. In particular,
it is driven by the non-commutation of Coulomb/Glauber gluon exchanges with
other soft exchanges. Beyond QCD, factorization may be violated at the two-loop
level provided that the hard subprocess contains matrix element contributions
with phase differences between different colour topologies.Comment: Version 2: minor improvements for journal publicatio
Feedback cooling of a single trapped ion
Based on a real-time measurement of the motion of a single ion in a Paul
trap, we demonstrate its electro-mechanical cooling below the Doppler limit by
homodyne feedback control (cold damping). The feedback cooling results are well
described by a model based on a quantum mechanical Master Equation.Comment: 4 pages, 3 figure
Effective Field Theory Dimensional Regularization
A Lorentz-covariant regularization scheme for effective field theories with
an arbitrary number of propagating heavy and light particles is given. This
regularization scheme leaves the low-energy analytic structure of Greens
functions intact and preserves all the symmetries of the underlying Lagrangian.
The power divergences of regularized loop integrals are controlled by the
low-energy kinematic variables. Simple diagrammatic rules are derived for the
regularization of arbitrary one-loop graphs and the generalization to higher
loops is discussed.Comment: 22 pages, 11 figures and 1 tabl
Baryon masses and nucleon sigma terms in manifestly Lorentz-invariant baryon chiral perturbation theory
We discuss the masses of the ground state baryon octet and the nucleon sigma
terms in the framework of manifestly Lorentz-invariant baryon chiral
perturbation theory. In order to obtain a consistent power counting for
renormalized diagrams the extended on-mass-shell renormalization scheme is
applied.Comment: 18 pages, 3 figures, accepted for publication in J. Phys.
U(3) chiral perturbation theory with infrared regularization
We include the eta-prime in chiral perturbation theory without employing
1/N_c counting rules. The method is illustrated by calculating the masses and
decay constants of the Goldstone boson octet (pions, kaons, eta) and the
singlet eta-prime up to one-loop order. The effective Lagrangian describing the
interactions of the eta-prime with the Goldstone boson octet is presented up to
fourth chiral order and the loop integrals are evaluated using infrared
regularization, which preserves Lorentz and chiral symmetry.Comment: 29 page
Proteomic analysis of the Simkania-containing vacuole: the central role of retrograde transport
- …