27,448 research outputs found
Supergravity on R4 x S1/Z2 and singular Calabi-Yaus
We discuss the moduli space singularities that are generally present in
five-dimensional vector-coupled supergravity on a spactime of the form R4 x
S1/Z2, with vector fields surviving on the Z2 fixed planes. The framework of
supergravity is necessarily ambiguous when it comes to the non-singular
embedding theory, so we focus on those models coming from Calabi-Yau
three-folds with wrapped membranes.Comment: 13 p
Inspecting absorption in the spectra of extra-galactic gamma-ray sources for insight into Lorentz invariance violation
We examine what the absorbed spectra of extra-galactic TeV gamma-ray sources,
such as blazars, would look like in the presence of Lorentz invariance
violation (LIV). Pair-production with the extra-galactic background light
modifies the observed spectra of such sources, and we show that a violation of
Lorentz invariance would generically have a dramatic effect on this absorption
feature. Inspecting this effect, an experimental task likely practical in the
near future, can provide unique insight on the possibility of LIV.Comment: Published in Phys. Rev.
Baryon Magnetic Moments and Proton Spin: A Model with Collective Quark Rotation
We analyse the baryon magnetic moments in a model that relates them to the
parton spins , , , and includes a contribution
from orbital angular momentum. The specific assumption is the existence of a
3-quark correlation (such as a flux string) that rotates with angular momentum
around the proton spin axis. A fit to the baryon magnetic
moments, constrained by the measured values of the axial vector coupling
constants , , yields , , where the error is a theoretical
estimate. A second fit, under slightly different assumptions, gives , with no constraint on . The
model provides a consistent description of axial vector couplings, magnetic
moments and the quark polarization measured in deep
inelastic scattering. The fits suggest that a significant part of the angular
momentum of the proton may reside in a collective rotation of the constituent
quarks.Comment: 16 pages, 3 ps-figures, uses RevTeX. Abstract, Sec. II, III and IV
have been expande
Jet Investigations Using the Radial Moment
We define the radial moment, , for jets produced in hadron-hadron
collisions. It can be used as a tool for studying, as a function of the jet
transverse energy and pseudorapidity, radiation within the jet and the quality
of a perturbative description of the jet shape. We also discuss how
non-perturbative corrections to the jet transverse energy affect .Comment: 14 pages, LaTeX, 6 figure
Prospects for Detecting Supersymmetric Dark Matter at Post-LEP Benchmark Points
A new set of supersymmetric benchmark scenarios has recently been proposed in
the context of the constrained MSSM (CMSSM) with universal soft
supersymmetry-breaking masses, taking into account the constraints from LEP, and . These points have previously been used to
discuss the physics reaches of different accelerators. In this paper, we
discuss the prospects for discovering supersymmetric dark matter in these
scenarios. We consider direct detection through spin-independent and
spin-dependent nuclear scattering, as well as indirect detection through relic
annihilations to neutrinos, photons, and positrons. We find that several of the
benchmark scenarios offer good prospects for direct detection via
spin-independent nuclear scattering and indirect detection via muons produced
by neutrinos from relic annihilations inside the Sun, and some models offer
good prospects for detecting photons from relic annihilations in the galactic
centre.Comment: 24 pages, 14 figure
Supersymmetric Dark Matter Detection at Post-LEP Benchmark Points
We review the prospects for discovering supersymmetric dark matter in a
recently proposed set of post-LEP supersymmetric benchmark scenarios. We
consider direct detection through spin-independent nuclear scattering, as well
as indirect detection through relic annihilations to neutrinos, photons, and
positrons. We find that several of the benchmark scenarios offer good prospects
for direct detection through spin-independent nuclear scattering, as well as
indirect detection through muons produced by neutrinos from relic annihilations
in the Sun, and photons from annihilations in the galactic center.Comment: 4 pages, 3 figures, uses RevTeX4, contribution to Snowmass 200
Supersymmetric Dark Matter and the Reheating Temperature of the Universe
Since the thermal history of the Universe is unknown before the epoch of
primordial nucleosynthesis, the largest temperature of the radiation dominated
phase (the reheating temperature) might have been as low as 1 MeV. We perform a
quantitative study of supersymmetric dark matter relic abundance in
cosmological scenarios with low reheating temperature. We show that, for values
of the reheating temperature smaller than about 30 GeV, the domains of the
supergravity parameter space which are compatible with the hypothesis that dark
matter is composed by neutralinos are largely enhanced. We also find a lower
bound on the reheating temperature: if the latter is smaller than about 1 GeV
neutralinos cannot be efficiently produced in the early Universe and then they
are not able to explain the present amount of dark matter.Comment: 21 pages, 5 figures, typeset with ReVTeX4. The paper may also be
found at http://www.to.infn.it/~fornengo/papers/reheating.ps.g
B-Meson Observables in the Maximally CP-Violating MSSM with Minimal Flavour Violation
Additional sources of CP violation in the MSSM may affect B-meson mixings and
decays, even in scenarios with minimal flavour violation (MFV). We formulate
the maximally CP-violating and minimally flavour-violating (MCPMFV) variant of
the MSSM, which has 19 parameters, including 6 phases that violate CP. We then
develop a manifestly flavour-covariant effective Lagrangian formalism for
calculating Higgs-mediated FCNC observables in the MSSM at large tan(beta), and
analyze within the MCPMFV framework FCNC and other processes involving B
mesons. We include a new class of dominant subleading contributions due to
non-decoupling effects of the third-generation quarks. We present illustrative
numerical results that include effects of the CP-odd MCPMFV parameters on Higgs
and sparticle masses, the B_s and B_d mass differences, and on the decays B_s
--> mu+ mu-, B_u --> tau nu and b --> s gamma. We use these results to derive
illustrative constraints on the MCPMFV parameters imposed by D0, CDF, BELLE and
BABAR measurements of B mesons, demonstrating how a potentially observable
contribution to the CP asymmetry in the b --> s gamma decay may arise in the
MSSM with MCPMFV.Comment: 47 pages, 8 eps figures, comments and references added, accepted for
publication in Physical Review D, Eq.(3.2) correcte
Neutralino Dark Matter in Focus Point Supersymmetry
In recent work, it has been argued that multi-TeV masses for scalar
superpartners are not unnatural. Indeed, they appear to have significant
phenomenological virtues. Here we explore the implications of such `focus
point' supersymmetry for the dark matter problem. We find that constraints on
relic densities do not place upper bounds on neutralino or scalar masses. We
demonstrate that, in the specific context of minimal supergravity, a
cosmologically stable mixed gaugino-Higgsino state emerges as an excellent,
robust dark matter candidate. We estimate that, over a wide range of the
unknown parameters, the spin-independent proton-neutralino cross sections fall
in the range accessible to planned search experiments.Comment: 15 pages, 6 figures, version to appear in Phys. Lett. B. References
added, minor modifications of Figs. 2 and 4 due to a bug (sign error) in
neutdrive
Standard Model Top Quark Asymmetry at the Fermilab Tevatron
Top quark pair production at proton-antiproton colliders is known to exhibit
a forward-backward asymmetry due to higher-order QCD effects. We explore how
this asymmetry might be studied at the Fermilab Tevatron, including how the
asymmetry depends on the kinematics of extra hard partons. We consider results
for top quark pair events with one and two additional hard jets. We further
note that a similar asymmetry, correlated with the presence of jets, arises in
specific models for parton showers in Monte Carlo simulations. We conclude that
the measurement of this asymmetry at the Tevatron will be challenging, but
important both for our understanding of QCD and for our efforts to model it.Comment: 26 p., 10 embedded figs., comment added, version to appear in PR
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