1,234,420 research outputs found
Localization and critical diffusion of quantum dipoles in two dimensions
We discuss quantum propagation of dipole excitations in two dimensions. This
problem differs from the conventional Anderson localization due to existence of
long range hops. We found that the critical wavefunctions of the dipoles always
exist which manifest themselves by a scale independent diffusion constant. If
the system is T-invariant the states are critical for all values of the
parameters. Otherwise, there can be a "metal-insulator" transition between this
"ordinary" diffusion and the Levy-flights (the diffusion constant
logarithmically increasing with the scale). These results follow from the
two-loop analysis of the modified non-linear supermatrix -model.Comment: 4.2 page
Quirks in supersymmetry with gauge coupling unification
I investigate the phenomenology of supersymmetric models with extra
vector-like supermultiplets that couple to the Standard Model gauge fields and
transform as the fundamental representation of a new confining non-Abelian
gauge interaction. If perturbative gauge coupling unification is to be
maintained, the new group can be SU(2), SU(3), or SO(3). The impact on the
sparticle mass spectrum is explored, with particular attention to the gaugino
mass dominated limit in which the supersymmetric flavor problem is naturally
solved. The new confinement length scale is astronomical for SO(3), so the new
particles are essentially free. For the SU(2) and SU(3) cases, the new
vector-like fermions are quirks; pair production at colliders yields
quirk-antiquirk states bound by stable flux tubes that are microscopic but long
compared to the new confinement scale. I study the reach of the Tevatron and
LHC for the optimistic case that in a significant fraction of events the
quirk-antiquirk bound state will lose most of its energy before annihilating as
quirkonium.Comment: 28 page
Conductance of Aharonov--Bohm Rings: From the Discrete to the Continuous Spectrum Limit
The dissipative conductance of an array of mesoscopic rings, subject to an
a.c. magnetic flux is investigated. The magneto--conductance may change sign
between canonical and grand-canonical statistical ensembles, as function of the
inelastic level broadening and as function of the temperature. Differences
between canonical and grand-canonical ensembles persist up to temperature of
the order of the Thouless energy.Comment: 13 pages, 2 figures, REVTeX v2.1, WIS--93/121/Dec.--P
Perturbative treatment of the multichannel interacting resonant level model in steady state non-equilibrium
We consider the steady state non-equilibrium physics of the multichannel
interacting resonant level model in the weak coupling regime. By using the
scattering state method we show in agreement with the rate equations that the
negative differential conductance at large enough voltages is due to the
renormalization of the hopping amplitude thus of the vertex.Comment: 3+ pages, 4 figure
Relic gravitational waves: latest revisions and preparations for new data
The forthcoming release of data from the Planck mission, and possibly from
the next round of Wilkinson Microwave Anisotropy Probe (WMAP) observations,
make it necessary to revise the evaluations of relic gravitational waves in the
existing data and, at the same time, to refine the assumptions and data
analysis techniques in preparation for the arrival of new data. We reconsider
with the help of the commonly used CosmoMC numerical package the previously
found indications of relic gravitational waves in the 7-year (WMAP7) data. The
CosmoMC approach reduces the confidence of these indications from approximately
2 level to approximately 1 level, but the indications do not
disappear altogether. We critically analyze the assumptions that are currently
used in the Cosmic Microwave Background (CMB) data analyzes and outline the
strategy that should help avoid the oversight of relic gravitational waves in
the future CMB data. In particular, it is important to keep away from the
unwarranted assumptions about density perturbations. The prospects of confident
detection of relic gravitational waves by the Planck satellite have worsened,
but they are still good. It appears that more effort will be required in order
to mitigate the foreground contamination.Comment: 11 pages, 4 figures, 3 tables; v.3: improvements, published versio
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