773 research outputs found
The Casimir force on a surface with shallow nanoscale corrugations: Geometry and finite conductivity effects
We measure the Casimir force between a gold sphere and a silicon plate with
nanoscale, rectangular corrugations with depth comparable to the separation
between the surfaces. In the proximity force approximation (PFA), both the top
and bottom surfaces of the corrugations contribute to the force, leading to a
distance dependence that is distinct from a flat surface. The measured Casimir
force is found to deviate from the PFA by up to 15%, in good agreement with
calculations based on scattering theory that includes both geometry effects and
the optical properties of the material
Can multistate dark matter annihilation explain the high-energy cosmic ray lepton anomalies?
Multistate dark matter (DM) models with small mass splittings and couplings
to light hidden sector bosons have been proposed as an explanation for the
PAMELA/Fermi/H.E.S.S. high-energy lepton excesses. We investigate this proposal
over a wide range of DM density profiles, in the framework of concrete models
with doublet or triplet dark matter and a hidden SU(2) gauge sector that mixes
with standard model hypercharge. The gauge coupling is bounded from below by
the DM relic density, and the Sommerfeld enhancement factor is explicitly
computable for given values of the DM and gauge boson masses M, mu and the
(largest) dark matter mass splitting delta M_{12}. Sommerfeld enhancement is
stronger at the galactic center than near the Sun because of the radial
dependence of the DM velocity profile, which strengthens the inverse Compton
(IC) gamma ray constraints relative to usual assumptions. We find that the
PAMELA/Fermi/H.E.S.S. lepton excesses are marginally compatible with the model
predictions, and with CMB and Fermi gamma ray constraints, for M ~ 800 GeV, mu
~ 200 MeV, and a dark matter profile with noncuspy Einasto parameters alpha >
0.20, r_s ~ 30 kpc. We also find that the annihilating DM must provide only a
subdominant (< 0.4) component of the total DM mass density, since otherwise the
boost factor due to Sommerfeld enhancement is too large.Comment: 20 pages, 12 figures; v2: Corrected branching ratio for ground state
DM annihilations into leptons, leading to boost factors that are larger than
allowed. Added explicit results for doublet DM model. Some conclusions
changed; main conclusion of tension between inverse Compton constraints and
N-body simulations of halo profiles is unchange
Displaced Higgs production in type III seesaw
We point out that the type III seesaw mechanism introducing fermion triplets
predicts peculiar Higgs boson signatures of displaced vertices with two b jets
and one or two charged particles which can be cleanly identified. In a
supersymmetric theory, the scalar partner of the fermion triplet contains a
neutral dark matter candidate which is almost degenerate with its charged
components. A Higgs boson can be produced together with such a dark matter
triplet in the cascade decay chain of a strongly produced squark or gluino.
When the next lightest supersymmetric particle (NLSP) is bino/wino-like, there
appears a Higgs boson associated with two charged tracks of a charged lepton
and a heavy charged scalar at a displacement larger than about 1 mm. The
corresponding production cross-section is about 0.5 fb for the squark/gluino
mass of 1 TeV. In the case of the stau NLSP, it decays mainly to a Higgs boson
and a heavy charged scalar whose decay length is larger than 0.1 mm for the
stau NLSP mixing with the left-handed stau smaller than 0.3. As this process
can have a large cascade production pb for the squark/gluino mass
TeV, one may be able to probe it at the early stage of the LHC
experiment.Comment: 10 pages, 5 figure
Free circulating ICAM-1 in serum and cerebrospinal fluid of HIV-1 infected patients correlate with TNF-α and blood-brain barrier damage
The mechanism for the initiation of blood-brain barrier damage and intrathecal inflammation in patients infected with the human immunodeficiency virus (HIV) is poorly understood. We have recently reported that tumour necrosis factor-α (TNF-α) mediates active neural inflammation and blood-brain barrier damage in HIV-1 infection. Stimulation of endothelial cells by TNF-α induces the expression of intercellular adhesion molecule-1 (ICAM-1), which is an important early marker of immune activation and response. We report herein for the first time the detection of high levels of free circulating ICAM-1 in serum and cerebrospinal fluid of patients with HIV-1 infection. Free circulating ICAM-1 in these patients correlated with TNF-α concentrations and with the degree of blood-brain barrier damage and were detected predominantly in patients with neurologic involvement. These findings have important implications for the understanding and investigation of the intrathecal inflammatory response in HIV-1 infection
Geometrization of Quantum Mechanics
We show that it is possible to represent various descriptions of Quantum
Mechanics in geometrical terms. In particular we start with the space of
observables and use the momentum map associated with the unitary group to
provide an unified geometrical description for the different pictures of
Quantum Mechanics. This construction provides an alternative to the usual GNS
construction for pure states.Comment: 16 pages. To appear in Theor. Math. Phys. Some typos corrected.
Definition 2 in page 5 rewritte
Tumour necrosis factor-α mediates blood—brain barrier damage in HIV-1 infection of the central nervous system
The pathogenesis of brain inflammation and damage by human immunodeficiency virus (HIV) infection is unclear. Because blood–brain barrier damage and impaired cerebral perfusion are common features of HIV-1 infection, we evaluated the role of tumour necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in mediating disruption of the blood–brain barrier. Levels of TNF-α were more elevated in cerebrospinal fluid (CSF) than in serum of HIV-1 infected patients and were mainly detected in those patients who had neurologic involvement. Intrathecal TNF-α levels correlated with signs of blood–brain barrier damage, manifested by high CSF to serum albumin quotient, and with the degree of barrier impairment. In contrast, intrathecal IL-1β levels did not correlate with blood-brain barrier damage in HIV-1 infected patients. TNF-α seems to be related to active neural inflammation and to blood–brain barrier damage. The proinflammatory effects of TNF-α in the nervous system are dissociated from those of IL-1β
A simple inert model solves the little hierarchy problem and provides a dark matter candidate
We discuss a minimal extension to the standard model in which two singlet
scalar states that only interacts with the Higgs boson is added. Their masses
and interaction strengths are fixed by the two requirements of canceling the
one-loop quadratic corrections to the Higgs boson mass and providing a viable
dark matter candidate. Direct detection of the lightest of these new states in
nuclear scattering experiments is possible with a cross section within reach of
future experiments.Comment: Finite corrections included. Model modified. Conclusion unchange
Geometrical Description of Quantum Mechanics - Transformations and Dynamics
In this paper we review a proposed geometrical formulation of quantum
mechanics. We argue that this geometrization makes available mathematical
methods from classical mechanics to the quantum frame work. We apply this
formulation to the study of separability and entanglement for states of
composite quantum systems.Comment: 22 pages, to be published in Physica Script
Minimal dark matter in type III seesaw
We explore the possibility of a new dark matter candidate in the
supersymmetric type III seesaw mechanism where a neutral scalar component of
the Y=0 triplet can be the lightest supersymmetric particle. Its thermal
abundance can be in the right range if non-standard cosmology such as kination
domination is assumed. The enhanced cross-section of the dark matter
annihilation to W+W- can leave detectable astrophysical and cosmological
signals whose current observational data puts a lower bound on the dark matter
mass. The model predicts the existence of a charged scalar almost degenerate
with the dark matter scalar and its lifetime lies between 5.5 cm and 6.3 m. It
provides a novel opportunity of the dark mater mass measurement by identifying
slowly-moving and highly-ionizing tracks in the LHC experiments. If the
ordinary lightest supersymmetric particle is the usual Bino, its decay leads to
clean signatures of same-sign di-lepton and di-charged-scalar associated with
observable displaced vertices which are essentially background-free and can be
fully reconstructed.Comment: 3 figures, 12 pages; An error in the antiproton limit corrected; the
lower bound on the dark matter mass strengthened; references added; typos
correcte
PAMELA and FERMI-LAT limits on the neutralino-chargino mass degeneracy
Searches for Dark Matter (DM) particles with indirect detection techniques
have reached important milestones with the precise measurements of the
anti-proton and gamma-ray spectra, notably by the PAMELA and FERMI-LAT
experiments. While the gamma-ray results have been used to test the thermal
Dark Matter hypothesis and constrain the Dark Matter annihilation cross section
into Standard Model (SM) particles, the anti-proton flux measured by the PAMELA
experiment remains relatively unexploited. Here we show that the latter can be
used to set a constraint on the neutralino-chargino mass difference. To
illustrate our point we use a Supersymmetric model in which the gauginos are
light, the sfermions are heavy and the Lightest Supersymmetric Particle (LSP)
is the neutralino. In this framework the W^+ W^- production is expected to be
significant, thus leading to large anti-proton and gamma-ray fluxes. After
determining a generic limit on the Dark Matter pair annihilation cross section
into W^+ W^- from the anti-proton data only, we show that one can constrain
scenarios in which the neutralino-chargino mass difference is as large as ~ 20
GeV for a mixed neutralino (and intermediate choices of the anti-proton
propagation scheme). This result is consistent with the limit obtained by using
the FERMI-LAT data. As a result, we can safely rule out the pure wino
neutralino hypothesis if it is lighter than 450 GeV and constitutes all the
Dark Matter.Comment: 22page
- …