243 research outputs found
A method to find quantum noiseless subsystems
We develop a structure theory for decoherence-free subspaces and noiseless
subsystems that applies to arbitrary (not necessarily unital) quantum
operations. The theory can be alternatively phrased in terms of the
superoperator perspective, or the algebraic noise commutant formalism. As an
application, we propose a method for finding all such subspaces and subsystems
for arbitrary quantum operations. We suggest that this work brings the
fundamental passive technique for error correction in quantum computing an
important step closer to practical realization.Comment: 5 pages, to appear in Physical Review Letter
Black hole evaporation with separated fermions
In models with a low quantum gravity scale, a well-motivated reason to expect
quark and lepton fields are localized but physically separated is to avoid
proton decay. This could happen in a ``fat-brane'' or in an additional,
orthogonal 1/TeV sized dimension in which the gauge and Higgs fields live
throughout. Black holes with masses of order the quantum gravity scale are
therefore expected to evaporate non-universally, preferentially radiating
directly into quarks or leptons but not both. Should black holes be copiously
produced at a future hadron collider, we find the ratio of final state jets to
charged leptons to photons is 113:8:1, which differs from previous analyses
that assumed all standard model fields live at the same point in the extra
dimensional space.Comment: 5 pages, REVTe
Heavy Charged Gauge Bosons with General CP Violating Couplings
Heavy gauge bosons such as are expected to exist in many
extensions of the Standard Model. In this paper, it is shown that the most
general Lagrangian for the interaction of with top and bottom
quarks which consists of V-A and V+A structure with in general complex
couplings produces an Electric Dipole Moment (EDM) for the top quark at one
loop level. We predict the allowed ranges for the mass and couplings of
by using the upper limit on the top quark EDM
Inelastic Dark Matter in Light of DAMA/LIBRA
Inelastic dark matter, in which WIMP-nucleus scatterings occur through a
transition to an excited WIMP state ~ 100 keV above the ground state, provides
a compelling explanation of the DAMA annual modulation signal. We demonstrate
that the relative sensitivities of various dark matter direct detection
experiments are modified such that the DAMA annual modulation signal can be
reconciled with the absence of a reported signal at CDMS-Soudan, XENON10,
ZEPLIN, CRESST, and KIMS for inelastic WIMPs with masses O(100 GeV). We review
the status of these experiments, and make predictions for upcoming ones. In
particular, we note that inelastic dark matter leads to highly suppressed
signals at low energy, with most events typically occurring between 20 to 45
keV (unquenched) at xenon and iodine experiments, and generally no events at
low (~ 10 keV) energies. Suppressing the background in this high energy region
is essential to testing this scenario. The recent CRESST data suggest seven
observed tungsten events, which is consistent with expectations from this
model. If the tungsten signal persists at future CRESST runs, it would provide
compelling evidence for inelastic dark matter, while its absence should exclude
it.Comment: 27 pages, 17 figures, minor revision
Report of the Subgroup on Alternative Models and New Ideas
We summarize some of the work done by the P3 subgroup on Alternative Models
and New Ideas. The working group covered a broad range of topics including a
constrained Standard Model from an extra dimension, a discussion of recent
ideas addressing the strong CP problem, searches for doubly charged higgs
bosons in e gamma collisions, and an update on discovery limits for extra
neutral gauge bosons at hadron colliders. The breadth of topics reflects the
many ideas and approaches to physics beyond the Standard Model.Comment: 10 pages, 5 figures. Contributed to the APS/DPF/DPB Summer Study on
the Future of Particle Physics (Snowmass 2001), Snowmass, Colorado, 30 Jun -
21 Jul 200
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