290 research outputs found
Baryogenesis with Superheavy Squarks
We consider a setup where R-parity is violated in the framework of split
supersymmetry. The out-of-equilibrium decays of heavy squarks successfully lead
to the generation of a baryon asymmetry. We restrict the R-parity violating
couplings to the baryon number violating subset to keep the neutralino
sufficiently stable to provide the dark matter. The observed baryon asymmetry
can be generated for squark masses larger than 10^11 GeV, while neutralino dark
matter induces a stronger bound of 10^13 GeV. Some mass splitting between left-
and right-handed squarks may be needed to satisfy also constraints from gluino
cosmology.Comment: 18 pages, LaTeX, 4 figure
Direct probes of R-parity-violating supersymmetric couplings via single-top-squark production
We study the s-channel production of a single top squark in hadron collisions
through an R-parity-violating mechanism, examining in detail the case in which
the squark decays through an R-parity-conserving process into a bottom quark, a
lepton, and missing energy. We show that the top squark can be discovered if
its mass is less than 400 GeV, or that the current bound on the size of the
R-parity-violating couplings can be reduced by up to one order of magnitude
with existing data and by two orders of magnitude at the forthcoming run II of
the Fermilab Tevatron.Comment: To appear in Phys. Rev. D; 32 pgs., 17 ps figs., uses RevTeX; 1 new
fig., slight textual clarification
On the NLO QCD corrections to the production of the heaviest neutral Higgs scalar in the MSSM
We present a calculation of the two-loop top-stop-gluino contributions to
Higgs production via gluon fusion in the MSSM. By means of an asymptotic
expansion in the heavy particle masses, we obtain explicit and compact analytic
formulae that are valid when the Higgs and the top quark are lighter than stops
and gluino, without assuming a specific hierarchy between the Higgs mass and
the top mass. Being applicable to the heaviest Higgs scalar in a significant
region of the MSSM parameter space, our results complement earlier ones
obtained with a Taylor expansion in the Higgs mass, and can be easily
implemented in computer codes to provide an efficient and accurate
determination of the Higgs production cross section.Comment: 18 pages, 4 figure
On the two-loop sbottom corrections to the neutral Higgs boson masses in the MSSM
We compute the O(ab*as) two-loop corrections to the neutral Higgs boson
masses in the Minimal Supersymmetric Standard Model, using the effective
potential approach. Such corrections can be important in the region of
parameter space corresponding to tan(beta)>>1 and sizeable mu. In spite of the
formal analogy with the O(at*as) corrections, there are important differences,
since the dominant effects are controlled by the sbottom-Higgs scalar
couplings. We propose a convenient renormalization scheme that avoids
unphysically large threshold effects associated with the bottom mass, and
absorbs the bulk of the O(ab*as + ab*at) corrections into the one-loop
expression. We give general explicit formulae for the O(ab*as) corrections to
the neutral Higgs boson mass matrix. We also discuss the importance of the
O(ab^2) corrections and derive a formula for their contribution to mh in a
simple limiting case.Comment: 14 pages, 4 figures. Version to appear in Nucl. Phys.
Association of estradiol and visceral fat with structural brain networks and memory performance in adults
Importance Changes in estradiol during aging are associated with increased dementia risk. It remains unclear how estradiol supports cognitive health and whether risk factors, such as midlife obesity, are exacerbated by estrogen loss. Objectives To assess whether visceral adipose tissue (VAT) moderates the association between age and brain network structure and to investigate whether estradiol moderates the association between VAT and brain network structure. Design, Setting, and Participants Cross-sectional study of data from 974 cognitively healthy adults in Germany who participated in the Health Study of the Leipzig Research Centre for Civilization Diseases, a previously described population-based cohort study. Two moderation analyses were performed, including VAT as the moderator variable between age and brain network structure and estradiol as the moderator variable between VAT and brain network structure. The study was conducted from August 1, 2011, to November 23, 2014. Analyses were conducted from August 2017 to September 201
Giant and tunable excitonic optical anisotropy in single-crystal CsPbX halide perovskites
During the last years, giant optical anisotropy demonstrated its paramount
importance for light manipulation which resulted in numerous applications
ranging from subdiffraction light guiding to switchable nanolasers. In spite of
recent advances in the field, achieving continuous tunability of optical
anisotropy remains an outstanding challenge. Here, we present a solution to the
problem through chemical alteration of the ratio of halogen atoms (X = Br or
Cl) in single-crystal CsPbX halide perovskites. It turns out that the
anisotropy originates from an excitonic resonance in the perovskite, which
spectral position and strength are determined by the halogens composition. As a
result, we manage to continually modify the optical anisotropy by 0.14. We also
discover that the halide perovskite can demonstrate optical anisotropy up to
0.6 in the visible range -- the largest value among non-van der Waals
materials. Moreover, our results reveal that this anisotropy could be in-plane
and out-of-plane, depending on perovskite shape -- rectangular and square.
Hence, it can serve as an additional degree of freedom for anisotropy
manipulation. As a practical demonstration, we created perovskite anisotropic
nanowaveguides and show a significant impact of anisotropy on high-order
guiding modes. These findings pave the way for halide perovskites as a
next-generation platform for tunable anisotropic photonics.Comment: 18 pages, 3 figure
Les Houches "Physics at TeV Colliders 2003" Beyond the Standard Model Working Group: Summary Report
The work contained herein constitutes a report of the ``Beyond the Standard
Model'' working group for the Workshop "Physics at TeV Colliders", Les Houches,
France, 26 May--6 June, 2003. The research presented is original, and was
performed specifically for the workshop. Tools for calculations in the minimal
supersymmetric standard model are presented, including a comparison of the dark
matter relic density predicted by public codes. Reconstruction of
supersymmetric particle masses at the LHC and a future linear collider facility
is examined. Less orthodox supersymmetric signals such as non-pointing photons
and R-parity violating signals are studied. Features of extra dimensional
models are examined next, including measurement strategies for radions and
Higgs', as well as the virtual effects of Kaluza Klein modes of gluons. An LHC
search strategy for a heavy top found in many little Higgs model is presented
and finally, there is an update on LHC studies.Comment: 113 pages, ed B.C. Allanach, v5 has changes to part XV
NLO QCD bottom corrections to Higgs boson production in the MSSM
We present a calculation of the two-loop bottom-sbottom-gluino contributions
to Higgs boson production via gluon fusion in the MSSM. The calculation is
based on an asymptotic expansion in the masses of the supersymmetric particles,
which are assumed to be much heavier than the bottom quark and the Higgs
bosons. We obtain explicit analytic results that allow for a straightforward
identification of the dominant contributions in the NLO bottom corrections. We
emphasize the interplay between the calculations of the masses and the
production cross sections of the Higgs bosons, discussing sensible choices of
renormalization scheme for the parameters in the bottom/sbottom sector.Comment: 25 pages, 4 figures. v2: references and two figures added, version
published in JHE
Chiral photonic super-crystals based on helical van der Waals homostructures
Chirality is probably the most mysterious among all symmetry transformations.
Very readily broken in biological systems, it is practically absent in
naturally occurring inorganic materials and is very challenging to create
artificially. Chiral optical wavefronts are often used for the identification,
control and discrimination of left- and right-handed biological and other
molecules. Thus, it is crucially important to create materials capable of
chiral interaction with light, which would allow one to assign arbitrary chiral
properties to a light field. In this paper, we utilized van der Waals
technology to assemble helical homostructures with chiral properties (e. g.
circular dichroism). Because of the large range of van der Waals materials
available such helical homostructures can be assigned with very flexible
optical properties. We demonstrate our approach by creating helical
homostructures based on multilayer AsS, which offers the most
pronounced chiral properties even in thin structures due to its strong biaxial
optically anisotropy. Our work showcases that the chirality of an
electromagnetic system may emerge at an intermediate level between the
molecular and the mesoscopic one due to the tailored arrangement of non-chiral
layers of van der Waals crystals and without additional patterning
On the two-loop Yukawa corrections to the MSSM Higgs boson masses at large tan(beta)
We complete the effective potential calculation of the two-loop, top/bottom
Yukawa corrections to the Higgs boson masses in the Minimal Supersymmetric
Standard Model, by computing the O(at^2 + at*ab + ab^2) contributions for
arbitrary values of the bottom Yukawa coupling. We also compute the corrections
to the minimization conditions of the effective potential at the same
perturbative order. Our results extend the existing O(at^2) calculation, and
are relevant in regions of the parameter space corresponding to tan(beta) >> 1.
We extend to the Yukawa corrections a convenient renormalization scheme,
previously proposed for the O(ab*as) corrections, that avoids unphysically
large threshold effects associated with the bottom mass and absorbs the bulk of
the corrections into the one-loop expression. For large values of tan(beta),
the new contributions can account for a variation of several GeV in the
lightest Higgs boson mass.Comment: 19 pages, 4 eps figures. Some formulae corrected in the Appendi
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