28,566 research outputs found
Radiation-Resistant Solar Cells - A Panel Discussion
Radiation resistant silicon cells for solar energy conversio
Apparent Violation of the Wiedemann-Franz law near a magnetic field tuned metal-antiferromagnetic quantum critical point
The temperature dependence of the interlayer electrical and thermal
resistivity in a layered metal are calculated for Fermi liquid quasiparticles
which are scattered inelastically by two-dimensional antiferromagnetic spin
fluctuations. Both resistivities have a linear temperature dependence over a
broad temperature range. Extrapolations to zero temperature made from this
linear- range give values that appear to violate the Wiedemann-Franz law.
However, below a low-temperature scale, which becomes small close to the
critical point, a recovery of this law occurs. Our results describe recent
measurements on CeCoIn near a magnetic field-induced quantum phase
transition. Hence, the experiments do not necessarily imply a non-Fermi liquid
ground state.Comment: 4 pages, 2 figures; accepted to Phys. Rev. Let
Classification of Standard Model Particles in Orbifold Grand Unified Theories
We classify the standard model fermions, which originate from bulk fields of
the or representation after orbifold breaking, in
grand unified theories on 5 or 6-dimensional space-time, under the
condition that , and survive as zero modes.Comment: 24 pages, typos corrected, to appear in IJMP
Fermi surface of underdoped cuprate superconductors from interlayer magnetoresistance: closed pockets versus open arcs
An outstanding question about the underdoped cuprates concerns the true nature of their Fermi surface which appears as a set of disconnected arcs. Theoretical models have proposed two distinct possibilities: (1) each arc is the observable part of a partially hidden closed pocket and (2) each arc is open, truncated at its apparent ends. We show that measurements of the variation in the interlayer resistance with the direction of a magnetic field parallel to the layers can qualitatively distinguish closed pockets from open arcs. This is possible because the field can be oriented such that all electrons on arcs encounter a large Lorentz force and resulting magnetoresistance whereas some electrons on pockets escape the effect by moving parallel to the field. © 2010 The American Physical Society
Squark and slepton masses as probes of supersymmetric SO(10) unification
We carry out an analysis of the non-universal supersymmetry breaking scalar
masses arising in SO(10) supersymmetric unification. By considering patterns of
squark and slepton masses, we derive a set of sum rules for the sfermion masses
which are independent of the manner in which SO(10) breaks to the Standard
Model gauge group via its SU(5) subgroups. The phenomenology arising from such
non-universality is unaffected by the symmetry breaking pattern, so long as the
breaking occurs via any of the SU(5) subgroups of the SO(10) group.Comment: 15 pages using RevTe
Controlled MOCVD growth of Bi2Se3 topological insulator nanoribbons
Topological insulators are a new class of materials that support
topologically protected electronic surface states. Potential applications of
the surface states in low dissipation electronic devices have motivated efforts
to create nanoscale samples with large surface-to-volume ratios and highly
controlled stoichiometry. Se vacancies in Bi2Se3 give rise to bulk conduction,
which masks the transport properties of the surface states. We have therefore
developed a new route for the synthesis of topological insulator nanostructures
using metalorganic chemical vapour deposition (MOCVD). MOCVD allows for control
of the Se/Bi flux ratio during growth. With the aim of rational growth, we vary
the Se/Bi flux ratio, growth time, and substrate temperature, and observe
morphological changes which indicate a growth regime in which nanoribbon
formation is limited by the Bi precursor mass-flow. MOCVD growth of Bi2Se3
nanostructures occurs via a distinct growth mechanism that is nucleated by gold
nanoparticles at the base of the nanowire. By tuning the reaction conditions,
we obtain either single-crystalline ribbons up to 10 microns long or thin
micron-sized platelets.Comment: Related papers at http://pettagroup.princeton.ed
Searching for bosons decaying to gluons
The production and decay of a new heavy vector boson, a chromophilic
vector boson, is described. The chromophilic couples only to two gluons,
but its two-body decays are absent, leading to a dominant decay mode of
. The unusual nature of the interaction predicts a
cross-section which grows with for a fixed coupling and an
accompanying gluon with a coupling that rises with its energy. We study the
decay mode, proposing distinct reconstruction techniques for the
observation of an excess and for the measurement of . We estimate the
sensitivity of current experimental datasets.Comment: For submission to PR
The thermodynamics of urban population flows
Orderliness, reflected via mathematical laws, is encountered in different
frameworks involving social groups. Here we show that a thermodynamics can be
constructed that macroscopically describes urban population flows. Microscopic
dynamic equations and simulations with random walkers underlie the macroscopic
approach. Our results might be regarded, via suitable analogies, as a step
towards building an explicit social thermodynamics
Large scale distribution of total mass versus luminous matter from Baryon Acoustic Oscillations: First search in the SDSS-III BOSS Data Release 10
Baryon Acoustic Oscillations (BAOs) in the early Universe are predicted to
leave an as yet undetected signature on the relative clustering of total mass
versus luminous matter. A detection of this effect would provide an important
confirmation of the standard cosmological paradigm and constrain alternatives
to dark matter as well as non-standard fluctuations such as Compensated
Isocurvature Perturbations (CIPs). We conduct the first observational search
for this effect, by comparing the number-weighted and luminosity-weighted
correlation functions, using the SDSS-III BOSS Data Release 10 CMASS sample.
When including CIPs in our model, we formally obtain evidence at of
the relative clustering signature and a limit that matches the existing upper
limits on the amplitude of CIPs. However, various tests suggest that these
results are not yet robust, perhaps due to systematic biases in the data. The
method developed in this Letter, used with more accurate future data such as
that from DESI, is likely to confirm or disprove our preliminary evidence.Comment: 6 pages, 2 figures, accepted for publication in PR
The weight for random quark masses
In theories in which the parameters of the low energy theory are not unique,
perhaps having different values in different domains of the universe as is
possible in some inflationary models, the fermion masses would be distributed
with respect to some weight. In such a situation the specifics of the fermion
masses do not have a unique explanation, yet the weight provides the visible
remnant of the structure of the underlying theory. This paper introduces this
concept of a weight for the distribution of masses and provides a quantitative
estimate of it from the observed quarks and leptons. The weight favors light
quark masses and appears roughly scale invariant (rho ~ 1/m). Some relevant
issues, such as the running of the weight with scale and the possible effects
of anthropic constraints, are also discussed.Comment: 35pages, 19 figure
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