975 research outputs found
Direct Detection of Non-Chiral Dark Matter
Direct detection experiments rule out fermion dark matter that is a chiral
representation of the electroweak gauge group. Non-chiral real, complex and
singlet representations, however, provide viable fermion dark matter
candidates. Although any one of these candidates will be virtually impossible
to detect at the LHC, it is shown that they may be detected at future planned
direct detection experiments. For the real case, an irreducible radiative
coupling to quarks may allow a detection. The complex case in general has an
experimentally ruled out tree-level coupling to quarks via Z-boson exchange.
However, in the case of two SU(2)_L doublets, a higher dimensional coupling to
the Higgs can suppress this coupling, and a remaining irreducible radiative
coupling may allow a detection. Singlet dark matter could be detected through a
coupling to quarks via Higgs exchange. Since all non-chiral dark matter can
have a coupling to the Higgs, at least some of its mass can be obtained from
electroweak symmetry breaking, and this mass is a useful characterization of
its direct detection cross-section.Comment: 22 pages, 3 figures. References added. Minor corrections to match
published versio
Signatures of sub-GeV dark matter beams at neutrino experiments
We study the high-luminosity fixed-target neutrino experiments at MiniBooNE,
MINOS and T2K and analyze their sensitivity to light stable states, focusing on
MeV--GeV scale dark matter. Thermal relic dark matter scenarios in the sub-GeV
mass range require the presence of light mediators, whose coupling to the
Standard Model facilitates annihilation in the early universe and allows for
the correct thermal relic abundance. The mediators in turn provide a production
channel for dark matter at colliders or fixed targets, and as a consequence the
neutrino beams generated at fixed targets may contain an additional beam of
light dark matter. The signatures of this beam include elastic scattering off
electrons or nucleons in the (near-)detector, which closely mimics the neutral
current scattering of neutrinos. We determine the event rate at modern fixed
target facilities and the ensuing sensitivity to sub-GeV dark matter.Comment: 18 pages, 13 figures, revtex4-
Selfish Dark Matter
We present a mechanism where a particle asymmetry in one sector is used to
generate an asymmetry in another sector. The two sectors are not coupled
through particle number violating interactions and are not required to be in
thermal contact with each other. When this mechanism is applied to baryogenesis
in asymmetric dark matter models, we find that the dark matter particles can be
extremely light, e.g. much lighter than an eV, and that in some cases there is
no need to annihilate away the symmetric component of dark matter. We discuss a
concrete realization of the mechanism with signals in direct detection, at the
LHC, at -factories or future beam dump experiments.Comment: 18+5 pages, 2 figures; Journal version: Added references, small
changes to the free-streaming length estimate
Two Loop R-Symmetry Breaking
We analyze two loop quantum corrections for pseudomoduli in O'Raifeartaigh
like models. We argue that R-symmetry can be spontaneously broken at two loop
in non supersymmetric vacua. We provide a basic example with this property. We
discuss on phenomenological applications.Comment: 13 pages, 5 figures, JHEP3.cls, reference adde
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
Jet diffuser for simulating ram conditions on a turbojet-engine static test stand
A jet diffuser for simulating flight or ram conditions on a turbojet-engine static test stand was designed and investigated. The diffuser utilizes the kinetic energy of the jet from a turbojet engine to reduce the discharge pressure at the exhaust nozzle and thereby provides simulated ram-pressure ratios across the engine. The engine exhaust nozzle discharges into an exhaust chamber (flexibly sealed to the tail pipe), which is connected to a diffuser by a bell-shaped nozzle. The pressure in the exhaust chamber is controlled independently of engine speed by a variable-area shutter at the diffuser discharge. The jet diffuser simulated ram-pressure ratios from 0.95 to 2.2 at various simulated pressure altitudes for a range of engine speeds from 85 to 100 percent of maximum rpm. Agreement of data obtained with and without the jet diffuser for a ram-pressure ratio of 1.0 indicated that the presence of the diffuser did not interfere with the flow through the engine exhaust-nozzle outlet
R-symmetry and Supersymmetry Breaking at Finite Temperature
We analyze the spontaneous symmetry breaking at finite temperature
for the simple O'Raifeartaigh-type model introduced in [1] in connection with
spontaneous supersymmetry breaking. We calculate the finite temperature
effective potential (free energy) to one loop order and study the thermal
evolution of the model. We find that the R-symmetry breaking occurs through a
second order phase transition. Its associated meta-stable supersymmetry
breaking vacuum is thermodynamically favored at high temperatures and the model
remains trapped in this state by a potential barrier, as the temperature lowers
all the way until T=0.Comment: 19 pages, 4 figures - Minor revisions, references added. To appear in
JHE
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