31,616 research outputs found
On the Higgs Mass in the CMSSM
We estimate the mass of the lightest neutral Higgs boson h in the minimal
supersymmetric extension of the Standard Model with universal soft
supersymmetry-breaking masses (CMSSM), subject to the available accelerator and
astrophysical constraints. For m_t = 174.3 GeV, we find that 114 GeV < m_h <
127 GeV and a peak in the tan beta distribution simeq 55. We observe two
distinct peaks in the distribution of m_h values, corresponding to two
different regions of the CMSSM parameter space. Values of m_h < 119 GeV
correspond to small values of the gaugino mass m_{1/2} and the soft trilinear
supersymmetry-breaking parameter A_0, lying along coannihilation strips, and
most of the allowed parameter sets are consistent with a supersymmetric
interpretation of the possibly discrepancy in g_mu - 2. On the other hand,
values of m_h > 119 GeV may correspond to much larger values of m_{1/2} and
A_0, lying in rapid-annihilation funnels. The favoured ranges of m_h vary with
m_t, the two peaks being more clearly separated for m_t = 178 GeV and merging
for m_t = 172.7 GeV. If the g_mu - 2 constraint is imposed, the mode of the m_h
distribution is quite stable, being sim 117 GeV for all the studied values of
m_t.Comment: 14 pages, 12 figure
Constraints from Accelerator Experiments on the Elastic Scattering of CMSSM Dark Matter
We explore the allowed ranges of cross sections for the elastic scattering of
neutralinos \chi on nucleons in the constrained minimal supersymmetric
extension of the Standard Model (CMSSM), in which scalar and gaugino masses are
each assumed to be universal at some input grand unification scale. We extend
previous calculations to larger \tan \beta and investigate the limits imposed
by the recent LEP lower limit on the mass of the Higgs boson and by b \to s
\gamma, and those suggested by g_\mu - 2. The Higgs limit and b \to s \gamma
provide upper limits on the cross section, particularly at small and large \tan
\beta, respectively, and the value of g_\mu - 2 suggests a lower limit on the
cross section for \mu > 0. The spin-independent nucleon cross section is
restricted to the range 6 \times 10^{-8} pb > \sigma_{SI} > 2 \times 10^{-10}
pb for \mu > 0, and the spin-dependent nucleon cross section to the range
10^{-5} pb > \sigma_{SD} > 2 \times 10^{-7} pb. Lower values are allowed if \mu
<0.Comment: 15 pages, latex, 18 eps figure
Time-dependent perturbations in two-dimensional String Black Holes
We discuss time-dependent perturbations (induced by matter fields) of a
black-hole background in tree-level two-dimensional string theory. We analyse
the linearized case and show the possibility of having black-hole solutions
with time-dependent horizons. The latter exist only in the presence of
time-dependent `tachyon' matter fields, which constitute the only propagating
degrees of freedom in two-dimensional string theory. For real tachyon field
configurations it is not possible to obtain solutions with horizons shrinking
to a point. On the other hand, such a possibility seems to be realized in the
case of string black-hole models formulated on higher world-sheet genera. We
connect this latter result with black hole evaporation/decay at a quantum
level.}Comment: 11 pages, two figures,UA-NPPS.9/92; CERN-TH.6671/9
Polarized lepton nucleon scattering - summary of the experimental spin sessions at DIS 99
This paper summarizes the contributions to the experimental sessions on
polarized lepton nucleon scattering at the DIS 99 workshop. Results are
reported about the flavor decomposition of the quark polarization, a first
direct measurement of a positive gluon polarization, the observation of a
double-spin asymmetry in diffractive rho production, the polarization of lambda
hyperons, the observation of transverse single-spin asymmetries and the
measurement of the Gerasimov-Drell-Hearn sum rule. Prospects of future fixed
target and collider facilities are discussed.Comment: 8 pages, 5 figures, Proc. of the 7th Int. Workshop on Deep Inelastic
Scattering and QCD (DIS99), Zeuthen, Germany, April 19-23, 1999, to appear in
Nucl. Phys. B (Proc. Suppl.
Elements of F-ast Proton Decay
Gauge coupling unification in the Minimal Supersymmetric Standard Model
(MSSM) strongly suggests the existence of a Grand Unified Theory (GUT), which
could be probed by the observation of proton decay. Proton lifetime in the p
\to (e+|mu+) pi0 dimension six mode is proportional in the fourth power to the
GUT mass scale, and inversely proportional in the fourth power to the GUT
coupling. We provide an updated dictionary of solutions for the relevant
unification parameters with generic beta-function coefficients, significantly
upgrading the level of detail with which second order effects are treated, and
correcting subtle published errors. F-lipped SU(5) with strict MSSM field
content is known to survive existing null detection limits for proton decay
approaching 10^34 years, and indeed, the lifetime predicted by prior studies
can be so long that successful detection is not currently plausible. Recently
studied classes of F-theory derived GUT models postulate additional vector-like
multiplets at the TeV scale which modify the renormalization group to yield a
substantial increase in the SU(3)_C X SU(2)_L unified coupling. We find the
conjunction of these models with the F-resh analysis employed to be
comparatively F-ast proton decay, only narrowly evading existing detection
limits, and likely falling within the observable range of proposed next
generation detectors such as DUSEL and Hyper-Kamiokande. The TeV-scale vector
multiplets are themselves suitable for cross correlation by the Large Hadron
Collider. Their presence moreover magnifies the gap between the dual mass
scales of Flipped SU(5), allowing for an elongated second stage
renormalization, pushing grand unification to the doorstep of the reduced
Planck mass.Comment: V2, As published in Nuclear Physics B; 57 pages, 7 figures, 12 table
On the Solution to the Polonyi Problem with (10~TeV) Gravitino Mass in Supergravity
We study the solution to the Polonyi problem where the Polonyi field weighs
as and decays just before the primordial nucleosynthesis. It
is shown that in spite of a large entropy production by the Polonyi field
decay, one can naturally explain the present value of the baryon-to-entropy
ratio, if the Affleck-Dine mechanism for
baryogenesis works. It is pointed out, however, that there is another
cosmological problem related to the abundance of the lightest superparticles
produced by the Polonyi decay
First-Principles Thermodynamics of Coherent Interfaces in Samarium-Doped Ceria Nanoscale Superlattices
Nanoscale superlattices of samarium-doped ceria layers with varying doping levels have been recently proposed as a novel fuel cell electrolyte. We calculate the equilibrium composition profile across the coherent {100} interfaces present in this system using lattice-gas Monte Carlo simulations with long-range interactions determined from electrostatics and short-range interactions obtained from ab initio calculations. These simulations reveal the formation of a diffuse, nonmonotonic, and surprisingly wide (11 nm at 400 K) interface composition profile, despite the absence of space charge regions
Physics Motivations for Future CERN Accelerators
We summarize the physics motivations for future accelerators at CERN. We
argue that (a) a luminosity upgrade for the LHC could provide good physics
return for a relatively modest capital investment, (b) CLIC would provide
excellent long-term perspectives within many speculative scenarios for physics
beyond the Standard Model, (c) a Very Large Hadron Collider could provide the
first opportunity to explore the energy range up to about 30 TeV, (d) a
neutrino factory based on a muon storage ring would provide an exciting and
complementary scientific programme and a muon collider could be an interesting
later option.Comment: 14 pages, 1 figure, Prepared for the CERN Scientific Policy Committee
in September 2001, and presented to the CERN Council in December 200
Two-loop relation between the bare lattice coupling and the MSbar coupling in pure SU(N) gauge theories
We report the result of a computation of the relation between the
renormalized coupling in the MSbar scheme of dimensional regularization and the
bare coupling in the standard lattice formulation of the SU(N) Yang-Mills
theory to two-loop order of perturbation theory and discuss some of its
implications.Comment: 10 pages, postscript fil
Transcriptome analysis of cortical tissue reveals shared sets of downregulated genes in autism and schizophrenia.
Autism (AUT), schizophrenia (SCZ) and bipolar disorder (BPD) are three highly heritable neuropsychiatric conditions. Clinical similarities and genetic overlap between the three disorders have been reported; however, the causes and the downstream effects of this overlap remain elusive. By analyzing transcriptomic RNA-sequencing data generated from post-mortem cortical brain tissues from AUT, SCZ, BPD and control subjects, we have begun to characterize the extent of gene expression overlap between these disorders. We report that the AUT and SCZ transcriptomes are significantly correlated (P<0.001), whereas the other two cross-disorder comparisons (AUT-BPD and SCZ-BPD) are not. Among AUT and SCZ, we find that the genes differentially expressed across disorders are involved in neurotransmission and synapse regulation. Despite the lack of global transcriptomic overlap across all three disorders, we highlight two genes, IQSEC3 and COPS7A, which are significantly downregulated compared with controls across all three disorders, suggesting either shared etiology or compensatory changes across these neuropsychiatric conditions. Finally, we tested for enrichment of genes differentially expressed across disorders in genetic association signals in AUT, SCZ or BPD, reporting lack of signal in any of the previously published genome-wide association study (GWAS). Together, these studies highlight the importance of examining gene expression from the primary tissue involved in neuropsychiatric conditions-the cortical brain. We identify a shared role for altered neurotransmission and synapse regulation in AUT and SCZ, in addition to two genes that may more generally contribute to neurodevelopmental and neuropsychiatric conditions
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