8,209 research outputs found
Decoding the Mechanism for the Origin of Dark Matter in the Early Universe Using LHC Data
It is shown that LHC data can allow one to decode the mechanism by which dark
matter is generated in the early universe in supersymmetric theories. We focus
on two of the major mechanisms for such generation of dark matter which are
known to be the Stau Coannihilation (Stau-Co) where the neutralino is typically
Bino like and annihilation on the Hyperbolic Branch (HB) where the neutralino
has a significant Higgsino component. An investigation of how one may
discriminate between the Stau-Co region and the HB region using LHC data is
given for the mSUGRA model. The analysis utilizes several signatures including
multi leptons, hadronic jets, b-tagging, and missing transverse momentum. A
study of the SUSY signatures reveals several correlated smoking gun signals
allowing a clear discrimination between the Stau-Co and the HB regions where
dark matter in the early universe can originate.Comment: 7 pages, 5 figs, 2 columns, Accepted for publication in Physical
Review
Signals of supersymmetry with inaccessible first two families at the Large Hadron Collider
We investigate the signals of supersymmetry (SUSY) in a scenario where only
the third family squarks and sleptons can be produced at the Large Hadron
Collider (LHC), in addition to the gluino, charginos and neutralinos. The final
states in such cases are marked by a multiplicity of top and/or bottom quarks.
We study in particular, the case when the stop, sbottom and gluino masses are
near the TeV scale due to which, the final state t's and b's are very
energetic. We point out the difficulty in b-tagging and identifying energetic
tops and suggest several event selection criteria which allow the signals to
remain significantly above the standard model background. We show that such
scenarios with gluino mass up to 2 TeV can be successfully probed at the LHC.
Information on can also be obtained by looking at associated Higgs
production in the cascades of accompanying neutralinos. We also show that a
combined analysis of event rates in the different channels and the effective
mass distribution allows one to differentiate this scenario from the one where
all three sfermion families are accessible.Comment: v3: 17 pages, 8 figures, 7 table
CP Violation and Dark Matter
A brief review is given of the effects of CP violation on the direct
detection of neutralinos in dark matter detectors. We first summarize the
current developments using the cancellation mechanism which allows for the
existence of large CP violating phases consistent with experimental limits on
the electron and on the neutron electric dipole moments in a broad class of
SUSY, string and D brane models. We then discuss their effects on the
scattering of neutralinos from quarks and on the event rates. It is found that
while CP effects on the event rates can be enormous such effects are reduced
significantly with the imposition of the EDM constraints. However, even with
the inclusion of the EDM constraints the effects are still very significant and
should be included in a precision prediction of event rates in any SUSY, string
or D brane model.Comment: Based on an invited talk at the conference "Sources and Detection of
Dark Matter in the Universe", at Marina del Rey, CA, Feb. 23-25, 2000; 12
pages, Latex including 2 figure
Faraday patterns in dipolar Bose-Einstein condensates
Faraday patterns can be induced in Bose-Einstein condensates by a periodic
modulation of the system nonlinearity. We show that these patterns are
remarkably different in dipolar gases with a roton-maxon excitation spectrum.
Whereas for non-dipolar gases the pattern size decreases monotonously with the
driving frequency, patterns in dipolar gases present, even for shallow roton
minima, a highly non trivial frequency dependence characterized by abrupt
pattern size transitions, which are especially pronounced when the dipolar
interaction is modulated. Faraday patterns constitute hence an optimal tool for
revealing the onset of the roton minimum, a major key feature of dipolar gases.Comment: 4 pages, 10 figure
Kelvon-roton instability of vortex lines in dipolar Bose-Einstein condensates
The physics of vortex lines in dipolar condensates is studied. Due to the
nonlocality of the dipolar interaction, the 3D character of the vortex plays a
more important role in dipolar gases than in typical short-range interacting
ones. In particular, the dipolar interaction significantly affects the
stability of the transverse modes of the vortex line. Remarkably, in the
presence of a periodic potential along the vortex line, a roton minimum may
develop in the spectrum of transverse modes. We discuss the appropriate
conditions at which this roton minimum may eventually lead to an instability of
the straight vortex line, opening new scenarios for vortices in dipolar gases.Comment: 4 pages, 3 eps figure
Phonon instability in two-dimensional dipolar Bose-Einstein Condensates
The partially attractive character of the dipole-dipole interaction leads to
phonon instability in dipolar condensates, which is followed by collapse in
three-dimensional geometries. We show that the nature of this instability is
fundamentally different in two-dimensional condensates, due to the
dipole-induced stabilization of two-dimensional bright solitons. As a
consequence, a transient gas of attractive solitons is formed, and collapse may
be avoided. In the presence of an harmonic confinement, the instability leads
to transient pattern formation followed by the creation of stable
two-dimensional solitons. This dynamics should be observable in on-going
experiments, allowing for the creation of stable two-dimensional solitons for
the first time ever in quantum gases.Comment: 4 pages, 4 figure
Cosmic rays, lithium abundance and excess entropy in galaxy clusters
We consider the production of Li in spallation reactions by cosmic rays
in order to explain the observed abundance in halo metal-poor stars. We show
that heating of ambient gas by cosmic rays is an inevitable consequence of this
process, and estimate the energy input required to reproduce the observed
abundance of Li/H to be of order a few hundred eV per
particle. We draw attention to the possibility that this could explain the
excess entropy in gas in galaxy groups and clusters. The evolution of Li
and the accompanying heating of gas is calculated for structures collapsing at
the present epoch with injection of cosmic rays at high redshift. We determine
the energy required to explain the abundance of Li at
corresponding to the formation epoch of halo metal-poor stars, and also an
increased entropy level of keV cm necessary to explain X-ray
observations of clusters. The energy budget for this process is consistent with
the expected energy output of radio-loud AGNs, and the diffusion length scale
of cosmic-ray protons responsible for heating is comparable to the size of
regions with excess entropy. We also discuss the constraints imposed by the
extragalactic gamma-ray background.Comment: 5 pages, 1 Figure, Accepted for publication in MNRAS (Letters
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