3,741 research outputs found
Theoretical study of even denominator fractions in graphene: Fermi sea versus paired states of composite fermions
The physics of the state at even denominator fractional fillings of Landau
levels depends on the Coulomb pseudopotentials, and produces, in different GaAs
Landau levels, a composite fermion Fermi sea, a stripe phase, or, possibly, a
paired composite fermion state. We consider here even denominator fractions in
graphene, which has different pseudopotentials as well as a possible four fold
degeneracy of each Landau level. We test various composite fermion Fermi sea
wave functions (fully polarized, SU(2) singlet, SU(4) singlet) as well as the
paired composite fermion states in the n=0 and Landau levels and predict
that (i) the paired states are not favorable, (ii) CF Fermi seas occur in both
Landau levels, and (iii) an SU(4) singlet composite fermion Fermi sea is
stabilized in the appropriate limit. The results from detailed microscopic
calculations are generally consistent with the predictions of the mean field
model of composite fermions
General Position Subsets and Independent Hyperplanes in d-Space
Erd\H{o}s asked what is the maximum number such that every set of
points in the plane with no four on a line contains points in
general position. We consider variants of this question for -dimensional
point sets and generalize previously known bounds. In particular, we prove the
following two results for fixed :
- Every set of hyperplanes in contains a subset
of size at least , for some
constant , such that no cell of the arrangement of is bounded by
hyperplanes of only.
- Every set of points in , for some constant
, contains a subset of cohyperplanar points or points in
general position.
Two-dimensional versions of the above results were respectively proved by
Ackerman et al. [Electronic J. Combinatorics, 2014] and by Payne and Wood [SIAM
J. Discrete Math., 2013].Comment: 8 page
High Resolution Valley Spectroscopy of Si Quantum Dots
We study an accumulation mode Si/SiGe double quantum dot (DQD) containing a
single electron that is dipole coupled to microwave photons in a
superconducting cavity. Measurements of the cavity transmission reveal
dispersive features due to the DQD valley states in Si. The occupation of the
valley states can be increased by raising temperature or applying a finite
source-drain bias across the DQD, resulting in an increased signal. Using
cavity input-output theory and a four-level model of the DQD, it is possible to
efficiently extract valley splittings and the inter- and intra-valley tunnel
couplings
Odd Decays from Even Anomalies: Gauge Mediation Signatures Without SUSY
We analyze the theory and phenomenology of anomalous global chiral symmetries
in the presence of an extra dimension. We propose a simple extension of the
Standard Model in 5D whose signatures closely resemble those of supersymmetry
with gauge mediation, and we suggest a novel scalar dark matter candidate.Comment: 26 pages, 1 figure; v2: references added; discussion of direct
collider constraints added; v3: corrected dark matter calculation in chapter
4.2 and replaced figure 1
Towards a Realistic Model of Higgsless Electroweak Symmetry Breaking
We present a 5D gauge theory in warped space based on a bulk SU(2)_L x
SU(2)_R x U(1)_(B-L) gauge group where the gauge symmetry is broken by boundary
conditions. The symmetry breaking pattern and the mass spectrum resembles that
in the standard model (SM). To leading order in the warp factor the rho
parameter and the coupling of the Z (or equivalently the S-parameter) are as in
the SM, while corrections are expected at the level of a percent. From the
AdS/CFT point of view the model presented here can be viewed as the AdS dual of
a (walking) technicolor-like theory, in the sense that it is the presence of
the IR brane itself that breaks electroweak symmetry, and not a localized Higgs
on the IR brane (which should be interpreted as a composite Higgs model). This
model predicts the lightest W, Z and photon resonances to be at around 1.2 TeV,
and no fundamental (or composite) Higgs particles.Comment: 10 pages. v2: refs adde
Towards a chiral gauge theory by deconstruction in AdS5
We describe an implementation of a deconstructed gauge theory with charged
fermions defined on an interval in five dimensional AdS space. The four
dimensional slices are Minkowski, and the end slices support four dimensional
chiral zero modes. In such a theory, the energy scales warp down as we move
along the fifth dimension. If we augment this theory with localized neutral
4-dimensional Majorana fermions on the low energy end, and implement a Higgs
mechanism there, we can arrange the theory such that the lightest gauge boson
mode and the chiral mode on the wall at the high energy end are parametrically
lighter than all the other states in the theory. If this semiclassical
construction does not run into problems at the quantum level, this may provide
an explicit construction of a chiral gauge theory. Instanton effects are
expected to make the gauge boson heavy only if the resulting effective theory
is anomalous.Comment: 6 pages, 3 figures, presented at Lattice2005(Chiral fermions),
Dublin, July 25-30, 2005, to appear in Proceedings of Scienc
And the first shall be the last
This study analyzes the puzzle of Hungarian economic drifting in a long run perspective. The underlying puzzle for the investigation is why bad policies are invariably popular and good policies unpopular, thus why political and economic rationality never overlap. The first part of the article summarizes in eight points the basic features of the postwar period. Then six lessons are offered, which might be useful for other countries in transition or for students of comparative economics and politics, lessons that can be generalized on the basis of the individual country experience
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