4,411 research outputs found
Realistic calculations of nuclear disappearance lifetimes induced by neutron-antineutron oscillations
Realistic calculations of nuclear disappearance lifetimes induced by
neutron-antineutron oscillations are reported for oxygen and iron, using
antineutron nuclear potentials derived from a recent comprehensive analysis of
antiproton atomic X-ray and radiochemical data. A lower limit of 3.3 x 10E8 s
on the neutron-antineutron oscillation time is derived from the
Super-Kamiokande I new lower limit of 1.77 x 10E32 yr on the neutron lifetime
in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap
experiments using ultracold neutrons, are calculated from updated antinucleon
optical potentials at threshold, with results shown to be largely model
independent.Comment: version matching PRD publication, typos and references correcte
Decaying Dark Matter from Dark Instantons
We construct an explicit, TeV-scale model of decaying dark matter in which
the approximate stability of the dark matter candidate is a consequence of a
global symmetry that is broken only by instanton-induced operators generated by
a non-Abelian dark gauge group. The dominant dark matter decay channels are to
standard model leptons. Annihilation of the dark matter to standard model
states occurs primarily through the Higgs portal. We show that the mass and
lifetime of the dark matter candidate in this model can be chosen to be
consistent with the values favored by fits to data from the PAMELA and Fermi
LAT experiments.Comment: 19 pages LaTeX, 3 eps figures. v2,v3: references adde
Cosmic Coincidence and Asymmetric Dark Matter in a Stueckelberg Extension
We discuss the possibility of cogenesis generating the ratio of baryon
asymmetry to dark matter in a Stueckelberg U(1) extension of the standard model
and of the minimal supersymmetric standard model. For the U(1) we choose
which is anomaly free and can be gauged. The dark matter
candidate arising from this extension is a singlet of the standard model gauge
group but is charged under . Solutions to the Boltzmann
equations for relics in the presence of asymmetric dark matter are discussed.
It is shown that the ratio of the baryon asymmetry to dark matter consistent
with the current WMAP data, i.e., the cosmic coincidence, can be successfully
explained in this model with the depletion of the symmetric component of dark
matter from resonant annihilation via the Stueckelberg gauge boson. For the
extended MSSM model it is shown that one has a two component dark matter
picture with asymmetric dark matter being the dominant component and the
neutralino being the subdominant component (i.e., with relic density a small
fraction of the WMAP cold dark matter value). Remarkably, the subdominant
component can be detected in direct detection experiments such as SuperCDMS and
XENON-100. Further, it is shown that the class of Stueckelberg models with a
gauged will produce a dramatic signature at a muon collider
with the showing a detectable
resonance while is devoid of this
resonance. Asymmetric dark matter arising from a Stueckelberg
extension is also briefly discussed. Finally, in the models we propose the
asymmetric dark matter does not oscillate and there is no danger of it being
washed out from oscillations.Comment: 36 pages, 7 figure
The Electroweak Phase Transition in Ultra Minimal Technicolor
We unveil the temperature-dependent electroweak phase transition in new
extensions of the Standard Model in which the electroweak symmetry is
spontaneously broken via strongly coupled, nearly-conformal dynamics achieved
by the means of multiple matter representations. In particular, we focus on the
low energy effective theory introduced to describe Ultra Minimal Walking
Technicolor at the phase transition. Using the one-loop effective potential
with ring improvement, we identify regions of parameter space which yield a
strong first order transition. A striking feature of the model is the existence
of a second phase transition associated to the electroweak-singlet sector. The
interplay between these two transitions leads to an extremely rich phase
diagram.Comment: 38 RevTeX pages, 9 figure
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