1,471 research outputs found
Three-body Supersymmetric Top Decays
We discuss three-body supersymmetric top decays, in schemes both with and
without R-parity conservation, assuming that sfermion masses are larger than
m_t. We find that MSSM top decays into chargino/neutralino pairs have a strong
kinematic suppression in the region of the supersymmetric parameter space
consistent with the LEP limits, with a decay width =< 10^{-5} GeV. MSSM top
decays into neutralino pairs have less kinematical suppression, but require a
flavour-changing vertex, and are likely to have a smaller rate. On the other
hand, R-violating decays to single charginos, neutralinos and conventional
fermions can be larger for values of the R-violating couplings still permitted
by other upper limits. The cascade decays of the charginos and neutralinos may
lead to spectacular signals with explicit lepton-number violation, such as
like-sign lepton events.Comment: CERN-TH/2000-60, 13 pages, LaTex, 10 figure
Exploration of Possible Quantum Gravity Effects with Neutrinos II: Lorentz Violation in Neutrino Propagation
It has been suggested that the interactions of energetic particles with the
foamy structure of space-time thought to be generated by quantum-gravitational
(QG) effects might violate Lorentz invariance, so that they do not propagate at
a universal speed of light. We consider the limits that may be set on a linear
or quadratic violation of Lorentz invariance in the propagation of energetic
neutrinos, v/c=[1 +- (E/M_\nuQG1)] or [1 +- (E/M_\nu QG2}^2], using data from
supernova explosions and the OPERA long-baseline neutrino experiment.Comment: 8 pages, 6 figures, proceedings for invited talk by A.Sakharov at
DISCRETE'08, Valencia, Spain; December 200
Probes of Lorentz Violation in Neutrino Propagation
It has been suggested that the interactions of energetic particles with the
foamy structure of space-time thought to be generated by quantum-gravitational
(QG) effects might violate Lorentz invariance, so that they do not propagate at
a universal speed of light. We consider the limits that may be set on a linear
or quadratic violation of Lorentz invariance in the propagation of energetic
neutrinos, v/c=[1 +- (E/M_\nuQG1)] or [1 +- (E/M_\nu QG2}^2], using data from
supernova explosions and the OPERA long-baseline neutrino experiment. Using the
SN1987a neutrino data from the Kamioka II, IMB and Baksan experiments, we set
the limits M_\nuQG1 > 2.7(2.5)x10^10 GeV for subluminal (superluminal)
propagation, respectively, and M_\nuQG2 >4.6(4.1)x10^4 GeV at the 95%
confidence level. A future galactic supernova at a distance of 10 kpc would
have sensitivity to M_\nuQG1 > 2(4)x10^11 GeV for subluminal (superluminal)
propagation, respectively, and M_\nuQG2 > 2(4)x10^5 GeV. With the current CNGS
extraction spill length of 10.5 micro seconds and with standard clock
synchronization techniques, the sensitivity of the OPERA experiment would reach
M_\nuQG1 ~ 7x10^5 GeV (M_\nuQG2 ~ 8x10^3 GeV) after 5 years of nominal running.
If the time structure of the SPS RF bunches within the extracted CNGS spills
could be exploited, these figures would be significantly improved to M_\nuQG1 ~
5x10^7 GeV (M_\nuQG2 ~ 4x10^4 GeV). These results can be improved further if
similar time resolution can be achieved with neutrino events occurring in the
rock upstream of the OPERA detector: we find potential sensitivities to
M_\nuQG1 ~ 4x10^8 GeV and M_\nuQG2 ~ 7x10^5 GeV.Comment: 33 pages, 22 figures, version accepted for publication in Physical
Review
Space-Time Foam may Violate the Principle of Equivalence
The interactions of different particle species with the foamy space-time
fluctuations expected in quantum gravity theories may not be universal, in
which case different types of energetic particles may violate Lorentz
invariance by varying amounts, violating the equivalence principle. We
illustrate this possibility in two different models of space-time foam based on
D-particle fluctuations in either flat Minkowski space or a stack of
intersecting D-branes. Both models suggest that Lorentz invariance could be
violated for energetic particles that do not carry conserved charges, such as
photons, whereas charged particles such electrons would propagate in a
Lorentz-inavariant way. The D-brane model further suggests that gluon
propagation might violate Lorentz invariance, but not neutrinos. We argue that
these conclusions hold at both the tree (lowest-genus) and loop (higher-genus)
levels, and discuss their implications for the phenomenology of quantum
gravity.Comment: 20 pages, 4 figures, the version accepted for publication in the
International Journal of Modern Physics
Opening Pandoraâs Box:Peeking inside psychologyâs data sharing practices, and seven recommendations for change
Open data-sharing is a valuable practice that ought to enhance the impact, reach and transparency of a research project. While widely advocated by many researchers and mandated by some journals and funding agencies, little is known about detailed practices across psychological science. In a pre-registered study, we show that overall, few research papers directly link to available data in many, though not all, journals. Most importantly, even where open data can be identified, the majority of these lacked completeness and reusability - conclusions that closely mirror those reported outside of Psychology. Exploring the reasons behind these findings, we offer seven specific recommendations for engineering and incentivizing improved practices, so that the potential of open data can be better realized across psychology and social science more generally
Supersymmetric Dark Matter in the Light of LEP 1.5
We discuss the lower limit on the mass of the neutralino that can be
obtained by combining data from annihilation at LEP and elsewhere with
astrophysical and theoretical considerations. Loopholes in the purely
experimental analysis of ALEPH data from the Z peak and LEP 1.5, which appear
when for certain values of the sneutrino mass and the
ratio of supersymmetric Higgs vacuum expectation values, may be
largely or totally excluded by data from lower-energy data, the
hypothesis that most of the cosmological dark matter consists of
particles, and the assumption that electroweak symmetry breaking is triggered
by radiative corrections due to a heavy top quark. The combination of these
inputs imposes m_{\chi} \ge 21.4~\gev, if soft supersymmetry-breaking masses
are assumed to be universal at the grand-unification scale.Comment: 22 pages. one Latex file + nine eps figure
Photon mass limits from fast radio bursts
International audienceThe frequency-dependent time delays in fast radio bursts (FRBs) can be used to constrain the photon mass, if the FRB redshifts are known, but the similarity between the frequency dependences of dispersion due to plasma effects and a photon mass complicates the derivation of a limit on mÎł. The dispersion measure (DM) of FRB 150418 is known to âŒ0.1%, and there is a claim to have measured its redshift with an accuracy of âŒ2%, but the strength of the constraint on mÎł is limited by uncertainties in the modelling of the host galaxy and the Milky Way, as well as possible inhomogeneities in the intergalactic medium (IGM). Allowing for these uncertainties, the recent data on FRB 150418 indicate that mÎłâČ1.8Ă10â14 eVcâ2 (3.2Ă10â50 kg), if FRB 150418 indeed has a redshift z=0.492 as initially reported. In the future, the different redshift dependences of the plasma and photon mass contributions to DM can be used to improve the sensitivity to mÎł if more FRB redshifts are measured. For a fixed fractional uncertainty in the extra-galactic contribution to the DM of an FRB, one with a lower redshift would provide greater sensitivity to mÎł
Brany Liouville Inflation
We present a specific model for cosmological inflation driven by the
Liouville field in a non-critical supersymmetric string framework, in which the
departure from criticality is due to open strings stretched between the two
moving Type-II 5-branes. We use WMAP and other data on fluctuations in the
cosmic microwave background to fix parameters of the model, such as the
relative separation and velocity of the 5-branes, respecting also the
constraints imposed by data on light propagation from distant gamma-ray
bursters. The model also suggests a small, relaxing component in the present
vacuum energy that may accommodate the breaking of supersymmetry.Comment: 23 pages LATEX, two eps figures incorporated; version accepted for
publication in NJ
Constraints on Neutralino Dark Matter from LEP 2 and Cosmology
A significant lower limit on the mass of the lightest neutralino \chi can be
obtained by combining the results from sparticle searches at LEP at
centre-of-mass energies up to 172 GeV with cosmological considerations, if it
is assumed that the \chi is stable. Exclusion domains from slepton searches
close m_\chi \sim 0 loopholes that were left open by previous lower-energy LEP
searches for charginos and neutralinos, leading to the lower limit m_\chi \ga
17 GeV. The constraints on supersymmetric parameter space are strengthened
significantly if LEP constraints on supersymmetric Higgs bosons are taken into
account, and further if the relic neutralino density is required to fall within
the range favoured by astrophysics and cosmology. These bounds are considerably
strengthened if universality at the GUT scale is assumed for soft
supersymmetry-breaking scalar masses, including those of the Higgs bosons. In
this case, the Higgs searches play a dramatic role, and we find that m_\chi \ga
40 GeV. Furthermore, we find that if tan\beta \la 1.7 for \mu<0, or tan\beta
\la 1.4 for \mu >0, the cosmological relic density is too large for all values
of m_\chi.Comment: Latex, 17 pages incling 3 eps figure
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