800 research outputs found
Neutrino Dimuon Production and the Strangeness Asymmetry of the Nucleon
We have performed the first global QCD analysis to include the CCFR and NuTeV
dimuon data, which provide direct constraints on the strange and anti-strange
parton distributions, and . To explore the strangeness
sector, we adopt a general parametrization of the non-perturbative functions satisfying basic QCD requirements. We find that the
strangeness asymmetry, as represented by the momentum integral , is sensitive to the dimuon data provided the
theoretical QCD constraints are enforced. We use the Lagrange Multiplier method
to probe the quality of the global fit as a function of and find
. Representative parton distribution sets spanning this
range are given. Comparisons with previous work are made.Comment: 23 pages, 4 figures; expanded version for publicatio
Termination Casts: A Flexible Approach to Termination with General Recursion
This paper proposes a type-and-effect system called Teqt, which distinguishes
terminating terms and total functions from possibly diverging terms and partial
functions, for a lambda calculus with general recursion and equality types. The
central idea is to include a primitive type-form "Terminates t", expressing
that term t is terminating; and then allow terms t to be coerced from possibly
diverging to total, using a proof of Terminates t. We call such coercions
termination casts, and show how to implement terminating recursion using them.
For the meta-theory of the system, we describe a translation from Teqt to a
logical theory of termination for general recursive, simply typed functions.
Every typing judgment of Teqt is translated to a theorem expressing the
appropriate termination property of the computational part of the Teqt term.Comment: In Proceedings PAR 2010, arXiv:1012.455
Higgs boson production with one bottom quark jet at hadron colliders
We present total rates and kinematic distributions for the associated
production of a single bottom quark and a Higgs boson at the Tevatron and the
LHC. We include next-to-leading order QCD corrections and compare the results
obtained in the four and five flavor number schemes for parton distribution
functions.Comment: 4 pages, 8 figures, RevTeX
Supersymmetric photonic signals at LEP
We explore and contrast the single-photon and diphoton signals expected at
LEP 2, that arise from neutralino-gravitino (e^+ e^- -> chi + gravitino ->
gamma + E_miss) and neutralino-neutralino (e^+ e^- -> chi + chi -> gamma +
gamma + E_miss) production in supersymmetric models with a light gravitino. LEP
1 limits imply that one may observe either one, but not both, of these signals
at LEP 2, depending on the values of the neutralino and gravitino masses:
single-photons for m_chi > Mz and m_gravitino < 3 x 10^-5 eV; diphotons for
m_chi < Mz and all allowed values of m_gravitino.Comment: 11 pages, LaTeX, 4 figures (included). Shortened version to appear in
Physical Review Letter
Single-photon signals at LEP in supersymmetric models with a light gravitino
We study the single-photon signals expected at LEP in models with a very
light gravitino. The dominant process is neutralino-gravitino production (e+e-
-> chi+ G) with subsequent neutralino decay via chi->gamma+G, giving a
gamma+E_miss signal. We first calculate the cross section at arbitrary
center-of-mass energies and provide new analytic expressions for the
differential cross section valid for general neutralino compositions. We then
consider the constraints on the gravitino mass from LEP 1 and LEP161
single-photon searches, and possible such searches at the Tevatron. We show
that it is possible to evade the stringent LEP 1 limits and still obtain an
observable rate at LEP 2, in particular in the region of parameter space that
may explain the CDF e+e+gamma+gamma+E_T,miss event. As diphoton events from
neutralino pair-production would not be kinematically accessible in this
scenario, the observation of whichever photonic signal will discriminate among
the various light-gravitino scenarios in the literature. We also perform a
Monte Carlo simulation of the expected energy and angular distributions of the
emitted photon, and of the missing invariant mass expected in the events.
Finally we specialize the results to the case of a recently proposed
one-parameter no-scale supergravity model.Comment: 31 pages, LaTeX, 14 figures (included
New results on rewrite-based satisfiability procedures
Program analysis and verification require decision procedures to reason on
theories of data structures. Many problems can be reduced to the satisfiability
of sets of ground literals in theory T. If a sound and complete inference
system for first-order logic is guaranteed to terminate on T-satisfiability
problems, any theorem-proving strategy with that system and a fair search plan
is a T-satisfiability procedure. We prove termination of a rewrite-based
first-order engine on the theories of records, integer offsets, integer offsets
modulo and lists. We give a modularity theorem stating sufficient conditions
for termination on a combinations of theories, given termination on each. The
above theories, as well as others, satisfy these conditions. We introduce
several sets of benchmarks on these theories and their combinations, including
both parametric synthetic benchmarks to test scalability, and real-world
problems to test performances on huge sets of literals. We compare the
rewrite-based theorem prover E with the validity checkers CVC and CVC Lite.
Contrary to the folklore that a general-purpose prover cannot compete with
reasoners with built-in theories, the experiments are overall favorable to the
theorem prover, showing that not only the rewriting approach is elegant and
conceptually simple, but has important practical implications.Comment: To appear in the ACM Transactions on Computational Logic, 49 page
New Collider Bound on Light Gravitino Mass
In supergravity theories with a very light gravitino, the gluino decays
dominantly to a gluon and a gravitino. This results in a much larger missing
for the multijet final states in hadronic colliders. We use the latest
Tevatron data for the multijet final states to set a new absolute lower bound
of 3.0 x 10^{-13} GeV for the light gravitino mass.Comment: 9 pages, Latex, macros and 2 figures not include
Combining Static and Dynamic Contract Checking for Curry
Static type systems are usually not sufficient to express all requirements on
function calls. Hence, contracts with pre- and postconditions can be used to
express more complex constraints on operations. Contracts can be checked at run
time to ensure that operations are only invoked with reasonable arguments and
return intended results. Although such dynamic contract checking provides more
reliable program execution, it requires execution time and could lead to
program crashes that might be detected with more advanced methods at compile
time. To improve this situation for declarative languages, we present an
approach to combine static and dynamic contract checking for the functional
logic language Curry. Based on a formal model of contract checking for
functional logic programming, we propose an automatic method to verify
contracts at compile time. If a contract is successfully verified, dynamic
checking of it can be omitted. This method decreases execution time without
degrading reliable program execution. In the best case, when all contracts are
statically verified, it provides trust in the software since crashes due to
contract violations cannot occur during program execution.Comment: Pre-proceedings paper presented at the 27th International Symposium
on Logic-Based Program Synthesis and Transformation (LOPSTR 2017), Namur,
Belgium, 10-12 October 2017 (arXiv:1708.07854
Probing Gauge-Mediated Supersymmetry Breaking Through Polarized Electron Beams in an Collider
Using the facts that in Gauge-Mediated Supersymmetry Breaking schemes, masses
of the right and the left sfermions can differ widely, and the gravitino is the
Lightest Supersymmetric Particle, we show that it is possible to obtain
unambiguous signatures of such schemes in a high energy collider if
one looks at the asymmetries in the cross-sections for certain final states
with left-and right-polarized beams.Comment: Plain LaTeX file, with four postscript figures adde
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