4,991 research outputs found
A comparison of analysis techniques for extracting resonance parameters from lattice Monte Carlo data
Different methods for extracting resonance parameters from Euclidean lattice
field theory are tested. Monte Carlo simulations of the O(4) non-linear sigma
model are used to generate energy spectra in a range of different volumes both
below and above the inelastic threshold. The applicability of the analysis
methods in the elastic region is compared. Problems which arise in the
inelastic region are also emphasised.Comment: 17 pages, 20 figures; clarification and minor corrections added, to
appear in PR
B -> X_s gamma in supersymmetry: large contributions beyond the leading order
We discuss possible large contributions to B -> X_s gamma, which can occur at
the next-to-leading order in supersymmetric models. They can originate from
terms enhanced by tan(beta) factors, when the ratio between the two Higgs
vacuum expectation values is large, or by logarithm of M_{susy}/M_W, when the
supersymmetric particles are considerably heavier than the W boson. We give
compact formulae which include all potentially large higher-order
contributions. We find that tan(beta) terms at the next-to-leading order do not
only appear from the Hall-Rattazzi-Sarid effect (the modified relation between
the bottom mass and Yukawa coupling), but also from an analogous effect in the
top-quark Yukawa coupling. Finally, we show how next-to-leading order
corrections, in the large tan(beta) region, can significantly reduce the limit
on the charged-Higgs mass, even if supersymmetric particles are very heavy.Comment: 18 pages, 5 figs, extended discussion of light stop case, notational
improvement
Witten index and phase diagram of compactified N=1 supersymmetric Yang-Mills theory on the lattice
Owing to confinement, the fundamental particles of N=1 Supersymmetric
Yang-Mills (SYM) theory, gluons and gluinos, appear only in colourless bound
states at zero temperature. Compactifying the Euclidean time dimension with
periodic boundary conditions for fermions preserves supersymmetry, and
confinement is predicted to persist independently of the length of the
compactified dimension. This scenario can be tested non-perturbatively with
Monte-Carlo simulations on a lattice. SUSY is, however, broken on the lattice
and can be recovered only in the continuum limit. The partition function of
compactified N=1 SYM theory with periodic fermion boundary conditions
corresponds to the Witten index. Therefore it can be used to test whether
supersymmetry is realized on the lattice. Results of our recent numerical
simulations are presented, supporting the disappearance of the deconfinement
transition in the supersymmetric limit and the restoration of SUSY at low
energies.Comment: 7 pages, 3 figures, Proceedings of the 33rd International Symposium
on Lattice Field Theory (Lattice 2015), 14-18 July 2015, Kobe International
Conference Center, Kobe, Japa
Progress in weakly coupled string phenomenology
The weakly coupled vacuum of heterotic string theory remains
an attractive scenario for particle physics. The particle spectrum and the
issue of dilaton stabilization are reviewed. A specific model for hidden sector
condensation and supersymmetry breaking, that respects known constraints from
string theory, is described, and its phenomenological and cosmological
implications are discussed.Comment: 15 pages, full postscript also available from
http://phyweb.lbl.gov/theorygroup/papers/48640.p
Gluino Decays in Split Supersymmetry
We compute the gluino lifetime and branching ratios in Split Supersymmetry.
Using an effective-theory approach, we resum the large logarithmic corrections
controlled by the strong gauge coupling and the top Yukawa coupling. We find
that the resummation of the radiative corrections has a sizeable numerical
impact on the gluino decay width and branching ratios. Finally, we discuss the
gluino decays into gravitino, relevant in models with direct mediation of
supersymmetry breaking.Comment: 21 pages, 6 figure
Phase structure of the N=1 supersymmetric Yang-Mills theory at finite temperature
Supersymmetry (SUSY) has been proposed to be a central concept for the
physics beyond the standard model and for a description of the strong
interactions in the context of the AdS/CFT correspondence. A deeper
understanding of these developments requires the knowledge of the properties of
supersymmetric models at finite temperatures. We present a Monte Carlo
investigation of the finite temperature phase diagram of the N=1 supersymmetric
Yang-Mills theory (SYM) regularised on a space-time lattice. The model is in
many aspects similar to QCD: quark confinement and fermion condensation occur
in the low temperature regime of both theories. A comparison to QCD is
therefore possible. The simulations show that for N=1 SYM the deconfinement
temperature has a mild dependence on the fermion mass. The analysis of the
chiral condensate susceptibility supports the possibility that chiral symmetry
is restored near the deconfinement phase transition.Comment: 26 pages, 12 figure
PeV-Scale Supersymmetry
Although supersymmetry has not been seen directly by experiment, there are
powerful physics reasons to suspect that it should be an ingredient of nature
and that superpartner masses should be somewhat near the weak scale. I present
an argument that if we dismiss our ordinary intuition of finetuning, and focus
entirely on more concrete physics issues, the PeV scale might be the best place
for supersymmetry. PeV-scale supersymmetry admits gauge coupling unification,
predicts a Higgs mass between 125 GeV and 155 GeV, and generally disallows
flavor changing neutral currents and CP violating effects in conflict with
current experiment. The PeV scale is motivated independently by dark matter and
neutrino mass considerations.Comment: 5 RevTex page
Complejidad y dimensiones en los estudios sobre Babbage: la máquina analítica. Un análisis del fracaso cultural del primer proyecto de calculadora digital programable secuencialmente.
En este artículo se analiza el caso histórico de la máquina analítica de Babbage junto con algunos otros ejemplos relacionados, con la intención de comprender qué tipo de condiciones retrasaron el advenimiento de la > hasta un siglo después de los primeros diseños de calculadoras programables multi-propósito. La respuesta a este interrogante proviene de una hibridación entre el enfoque socioeconómico de los estudios de ciencia, tecnología y sociedad y la teoría de la complejidad aplicada a los fenómenos sociales en la historia de la técnica. Como conclusión se prueba que el propio Babbage pudo ser consciente de estas constricciones en la estructura social de los medios de producción que retrasarían la emergencia del cálculo automático durante un siglo.This article analyses the historical case of the Babbage's machine
and other related examples in order to understand the conditions delaying the
coming of the •computer revolution· during one century since the first designs
of programmable calculators. The response derives from the joining of both
che STS socioeconomic approach and the complexity theory applied to social
phenomena in the history of technology. As a result, it is showed that Babbage
could be conscious of these constrictions in the social structure, which would
be responsible for the delay of the emergence of automatic calculus during
one century
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