4,849 research outputs found
Analyzing the Fierz Rearrangement Freedom for Local Chiral Two-Nucleon Potentials
Chiral effective field theory is a framework to derive systematic nuclear
interactions. It is based on the symmetries of quantum chromodynamics and
includes long-range pion physics explicitly, while shorter-range physics is
expanded in a general operator basis. The number of low-energy couplings at a
particular order in the expansion can be reduced by exploiting the fact that
nucleons are fermions and therefore obey the Pauli exclusion principle. The
antisymmetry permits the selection of a subset of the allowed contact operators
at a given order. When local regulators are used for these short-range
interactions, however, this "Fierz rearrangement freedom" is violated. In this
paper, we investigate the impact of this violation at leading order (LO) in the
chiral expansion. We construct LO and next-to-leading order (NLO) potentials
for all possible LO-operator pairs and study their reproduction of phase
shifts, the He ground-state energy, and the neutron-matter energy at
different densities. We demonstrate that the Fierz rearrangement freedom is
partially restored at NLO where subleading contact interactions enter. We also
discuss implications for local chiral three-nucleon interactions.Comment: 11 pages, 5 figure
Searching for t-bar t Resonances at the Large Hadron Collider
Many new physics models predict resonances with masses in the TeV range which
decay into a pair of top quarks. With its large cross section, t-bar t
production at the Large Hadron Collider (LHC) offers an excellent opportunity
to search for such particles. We present a detailed study of the discovery
potential of the CERN Large Hadron Collider for Kaluza-Klein (KK) excitations
of the gluon in bulk Randall-Sundrum (RS) models in the t-bar t -> ell^+/- nu
b-bar bq-bar q' (ell=e, mu) final state. We utilize final states with one or
two tagged b-quarks, and two, three or four jets (including b-jets). Our
calculations take into account the finite resolution of detectors, the energy
loss due to b-quark decays, the expected reduced b-tagging efficiency at large
t-bar t invariant masses, and include the background originating from Wb-bar
b+jets, (Wb+W-bar b)+jets, W+jets, and single top + jets production. We derive
semi-realistic 5 sigma discovery limits for nine different KK gluon scenarios,
and compare them with those for KK gravitons, and a Z_H boson in the Littlest
Higgs model. We also analyze the capabilities of the LHC experiments to
differentiate between individual KK gluon models and measure the couplings of
KK gluons to quarks. We find that, for the parameters and models chosen, KK
gluons with masses up to about 4 TeV can be discovered at the LHC. The ability
of the LHC to discriminate between different bulk RS models, and to measure the
couplings of the KK gluons is found to be highly model dependent.Comment: revtex3, 27 pages, 5 tables, 6 figure
Warped Gravitons at the LHC and Beyond
We study the production and decay of Kaluza-Klein (KK) gravitons at the Large
Hadron Collider (LHC), in the framework of a warped extra dimension in which
the Standard Model (SM) fields propagate. Such a scenario can provide solutions
to both the Planck-weak hierarchy problem and the flavor puzzle of the SM. In
this scenario, the production via annihilation and decays to the
conventional photon and lepton channels are highly suppressed. However, we show
that graviton production via gluon fusion followed by decay to longitudinal
can be significant; vector boson fusion is found to be a sub-dominant
production mode. In particular, the ``golden'' decay mode offers a
distinctive 4-lepton signal that could lead to the observation at the LHC with
300 fb (SLHC with 3 ab) of a KK graviton with a mass up to () TeV for the ratio of the AdS curvature to the Planck scale
modestly above unity. We argue that (contrary to the lore) such a size of the
curvature scale can still be within the regime of validity of the framework.
Upgrades beyond the SLHC luminosity are required to discover gravitons heavier
than TeV, as favored by the electroweak and flavor precision tests in
the simplest such models.Comment: 9 pages, 5 figures. Minor modifications, reference adde
Factorization for generic jet production
Factorization is the central ingredient in any theoretical prediction for
collider experiments. We introduce a factorization formalism that can be
applied to any desired observable, like event shapes or jet observables, for
any number of jets and a wide range of jet algorithms in leptonic or hadronic
collisions. This is achieved by using soft-collinear effective theory to prove
the formal factorization of a generic fully-differential cross section in terms
of a hard coefficient, and generic jet and soft functions. In this formalism,
whether a given observable factorizes in the usual sense, depends on whether it
is inclusive enough, so the jet functions can be calculated perturbatively. The
factorization formula for any such observable immediately follows from our
general result, including the precise definition of the jet and soft functions
appropriate for the observable in question. As examples of our formalism, we
work out several results in two-jet production for both e+e- and pp collisions.
For the latter, we also comment on how our formalism allows one to treat
underlying events and beam remnants.Comment: 33 pages, v2: minor typos corrected, journal versio
Probing jet properties via two particle correlation method
The formulae for calculating jet fragmentation momentum, , and conditional yield are discussed in
two particle correlation framework. Additional corrections are derived to
account for the limited detector acceptance and inefficiency, for cases when
the event mixing technique is used. The validity of our approach is confirmed
with Monte-carlo simulation.Comment: Proceeding for HotQuarks2004 conference. 11 pages, 8 figures,
corrected for typo
Mechanisms of Aminoglycoside Ototoxicity and Targets of Hair Cell Protection
Aminoglycosides are commonly prescribed antibiotics with deleterious side effects to the inner ear. Due to their popular application as a result of their potent antimicrobial activities, many efforts have been undertaken to prevent aminoglycoside ototoxicity. Over the years, understanding of the antimicrobial as well as ototoxic mechanisms of aminoglycosides has increased. These mechanisms are reviewed in regard to established and potential future targets of hair cell protection
Quantum Number Density Asymmetries Within QCD Jets Correlated With Lambda Polarization
The observation of jets in a variety of hard-scattering processes has allowed
the quantitative study of perturbative quantum chromodynamics (PQCD) by
comparing detailed theoretical predictions with a wide range of experimental
data. This paper examines how some important, nonperturbative, facets of QCD
involving the internal dynamical structure of jets can be studied by measuring
the spin orientation of Lambda particles produced in these jets. The
measurement of the transverse polarization for an individual Lambda within a
QCD jet permits the definition of spin-directed asymmetries in local quantum
number densities in rapidity space (such as charge, strangeness and baryon
number densities) involving neighboring hadrons in the jet. These asymmetries
can only be generated by soft, nonperturbative dynamical mechanisms and such
measurements can provide insight not otherwise accessible into the color
rearrangement that occurs during the hadronization stage of the fragmentation
process.Comment: The replacement manuscript contains a new abstract, five pages of
additional material and a revised version of Fig.
A puzzle of proportions: Two popular Bayesian tests can yield dramatically different conclusions
A puzzle of proportions: Two popular Bayesian tests can yield dramatically different conclusions
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