107 research outputs found
Slightly Non-Minimal Dark Matter in PAMELA and ATIC
We present a simple model in which dark matter couples to the standard model
through a light scalar intermediary that is itself unstable. We find this model
has several notable features, and allows a natural explanation for a surplus of
positrons, but no surplus of anti-protons, as has been suggested by early data
from PAMELA and ATIC. Moreover, this model yields a very small nucleon
coupling, well below the direct detection limits. In this paper we explore the
effect of this model in both the early universe and in the galaxy.Comment: 7 pages, 6 figures, v3: updated for new data, added discussion of
Ferm
Searches for Long Lived Neutral Particles
An intriguing possibility for TeV scale physics is the existence of neutral
long lived particles (LOLIPs) that subsequently decay into SM states. Such
particles are many cases indistinguishable from missing transverse energy (MET)
at colliders. We propose new methods to search for these particles using
neutrino telescopes. We study their detection prospects, assuming production
either at the LHC or through dark matter (DM) annihilations in the Sun and the
Earth. We find that the sensitivity for LOLIPs produced at the LHC is limited
by luminosity and detection energy thresholds. On the other hand, in the case
of DM annihilation into LOLIPs, the sensitivity of neutrino telescopes is
promising and may extend beyond the reach of upcoming direct detection
experiments. In the context of low scale hidden sectors weakly coupled to the
SM, such indirect searches allow to probe couplings as small as 10^-15.Comment: 22 pages, 6 figure
Discerning Secluded Sector gauge structures
New fundamental particles, charged under new gauge groups and only weakly
coupled to the standard sector, could exist at fairly low energy scales. In
this article we study a selection of such models, where the secluded group
either contains a softly broken U(1) or an unbroken SU(N). In the Abelian case
new {\gamma}v gauge bosons can be radiated off and decay back into visible
particles. In the non-Abelian case there will not only be a cascade in the
hidden sector, but also hadronization into new {\pi}v and {\rho}v mesons that
can decay back. This framework is developed to be applicable both for e+e- and
pp collisions, but for these first studies we concentrate on the former process
type. For each Abelian and non-Abelian group we study three different scenarios
for the communication between the standard sector and the secluded one. We
illustrate how to distinguish the various characteristics of the models and
especially study to what extent the underlying gauge structure can be
determined experimentally.Comment: removed extra figure
An Electron Fixed Target Experiment to Search for a New Vector Boson A' Decaying to e+e-
We describe an experiment to search for a new vector boson A' with weak
coupling alpha' > 6 x 10^{-8} alpha to electrons (alpha=e^2/4pi) in the mass
range 65 MeV < m_A' < 550 MeV. New vector bosons with such small couplings
arise naturally from a small kinetic mixing of the "dark photon" A' with the
photon -- one of the very few ways in which new forces can couple to the
Standard Model -- and have received considerable attention as an explanation of
various dark matter related anomalies. A' bosons are produced by radiation off
an electron beam, and could appear as narrow resonances with small production
cross-section in the trident e+e- spectrum. We summarize the experimental
approach described in a proposal submitted to Jefferson Laboratory's PAC35,
PR-10-009. This experiment, the A' Experiment (APEX), uses the electron beam of
the Continuous Electron Beam Accelerator Facility at Jefferson Laboratory
(CEBAF) at energies of ~1-4 GeV incident on 0.5-10% radiation length Tungsten
wire mesh targets, and measures the resulting e+e- pairs to search for the A'
using the High Resolution Spectrometer and the septum magnet in Hall A. With a
~1 month run, APEX will achieve very good sensitivity because the statistics of
e+e- pairs will be ~10,000 times larger in the explored mass range than any
previous search for the A' boson. These statistics and the excellent mass
resolution of the spectrometers allow sensitivity to alpha'/alpha one to three
orders of magnitude below current limits, in a region of parameter space of
great theoretical and phenomenological interest. Similar experiments could also
be performed at other facilities, such as the Mainz Microtron.Comment: 19 pages, 12 figures, 2 table
Age-dependent effects of low-dose nicotine treatment on cocaine-induced behavioral plasticity in rats
Epidemiological evidence of early adolescent tobacco use, prior to that of marijuana and other illicit drugs, has led to the hypothesis that nicotine is a “gateway” drug that sensitizes reward pathways to the addictive effects of other psychostimulants.
To test this hypothesis, we have compared the effect of a brief, low-dose nicotine pretreatment of adolescent and adult rats on subsequent locomotor response to acute and chronic cocaine.
Adolescents, aged postnatal day (P) 28, and adults, aged P86, were given four daily injections of saline or nicotine (0.06 mg/kg, i.v.). At P32 and P90, rats were given acute injections of cocaine (0, 0.4 or 1.0 mg/kg, i.v.) and monitored for locomotor activity in either a habituated or novel test environment. To examine cocaine sensitization, rats were treated for 3 days with saline or cocaine (0.4 mg/kg, i.v.), and, after 1 day of withdrawal, were given a challenge dose of cocaine (0.4 mg/kg, i.v.).
Nicotine pretreatment did not affect acute, drug-induced locomotor activity at either age. However, age differences in cocaine response were observed, with adolescent animals showing enhanced locomotor activity in the novel environment. Adolescent controls did not exhibit cocaine-induced locomotor sensitization, whereas adults did. Nicotine pretreatment during adolescence promoted the development and expression of a sensitized response to repeated cocaine exposure similar to that observed in saline-pretreated adult controls.
These findings show that brief pretreatment with nicotine, in a low dose comparable to that inhaled in 2–4 cigarettes, enhances cocaine-induced behavioral plasticity in adolescent rats
Decaying into the Hidden Sector
The existence of light hidden sectors is an exciting possibility that may be
tested in the near future. If DM is allowed to decay into such a hidden sector
through GUT suppressed operators, it can accommodate the recent cosmic ray
observations without over-producing antiprotons or interfering with the
attractive features of the thermal WIMP. Models of this kind are simple to
construct, generic and evade all astrophysical bounds. We provide tools for
constructing such models and present several distinct examples. The light
hidden spectrum and DM couplings can be probed in the near future, by measuring
astrophysical photon and neutrino fluxes. These indirect signatures are
complimentary to the direct production signals, such as lepton jets, predicted
by these models.Comment: 40 pages, 5 figure
Low-Energy Probes of a Warped Extra Dimension
We investigate a natural realization of a light Abelian hidden sector in an
extended Randall-Sundrum (RS) model. In addition to the usual RS bulk we
consider a second warped space containing a bulk U(1)_x gauge theory with a
characteristic IR scale of order a GeV. This Abelian hidden sector can couple
to the standard model via gauge kinetic mixing on a common UV brane. We show
that if such a coupling induces significant mixing between the lightest U(1)_x
gauge mode and the standard model photon and Z, it can also induce significant
mixing with the heavier U(1)_x Kaluza-Klein (KK) modes. As a result it might be
possible to probe several KK modes in upcoming fixed-target experiments and
meson factories, thereby offering a new way to investigate the structure of an
extra spacetime dimension.Comment: 26 pages, 1 figure, added references, corrected minor typos, same as
journal versio
R-parity Conservation via the Stueckelberg Mechanism: LHC and Dark Matter Signals
We investigate the connection between the conservation of R-parity in
supersymmetry and the Stueckelberg mechanism for the mass generation of the B-L
vector gauge boson. It is shown that with universal boundary conditions for
soft terms of sfermions in each family at the high scale and with the
Stueckelberg mechanism for generating mass for the B-L gauge boson present in
the theory, electric charge conservation guarantees the conservation of
R-parity in the minimal B-L extended supersymmetric standard model. We also
discuss non-minimal extensions. This includes extensions where the gauge
symmetries arise with an additional U(1)_{B-L} x U(1)_X, where U(1)_X is a
hidden sector gauge group. In this case the presence of the additional U(1)_X
allows for a Z' gauge boson mass with B-L interactions to lie in the sub-TeV
region overcoming the multi-TeV LEP constraints. The possible tests of the
models at colliders and in dark matter experiments are analyzed including
signals of a low mass Z' resonance and the production of spin zero bosons and
their decays into two photons. In this model two types of dark matter
candidates emerge which are Majorana and Dirac particles. Predictions are made
for a possible simultaneous observation of new physics events in dark matter
experiments and at the LHC.Comment: 38 pages, 7 fig
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