10,679 research outputs found
Tests of non-standard electroweak couplings of right-handed quarks
The standard model can be interpreted as the leading order of a Low-Energy
Effective Theory (LEET) invariant under a higher non linearly realized symmetry
equipped with a systematic power
counting. Within the minimal version of this ``not quite decoupling'' LEET, the
dominant non-standard effect appears at next-to-leading order (NLO) and is a
modification of the couplings of fermions to W and Z. In particular, the
coupling of right-handed quarks to Z is modified and a direct coupling of
right-handed quarks to W emerges. Charged right-handed lepton currents are
forbidden by an additional discrete symmetry in the lepton sector originally
designed to suppress Dirac neutrino masses. A complete NLO analysis of
experimental constraints on these modified couplings is presented. Concerning
couplings of light quarks, the interface of the electroweak tests with QCD
aspects is discussed in detail.Comment: 56 pages, 14 figures, v2: references added, minor modifications in
the text, accepted for publication in JHE
Lie-Poisson Deformation of the Poincar\'e Algebra
We find a one parameter family of quadratic Poisson structures on which satisfies the property {\it a)} that it is preserved
under the Lie-Poisson action of the Lorentz group, as well as {\it b)} that it
reduces to the standard Poincar\'e algebra for a particular limiting value of
the parameter. (The Lie-Poisson transformations reduce to canonical ones in
that limit, which we therefore refer to as the `canonical limit'.) Like with
the Poincar\'e algebra, our deformed Poincar\'e algebra has two Casimir
functions which we associate with `mass' and `spin'. We parametrize the
symplectic leaves of with space-time coordinates,
momenta and spin, thereby obtaining realizations of the deformed algebra for
the cases of a spinless and a spinning particle. The formalism can be applied
for finding a one parameter family of canonically inequivalent descriptions of
the photon.Comment: Latex file, 26 page
Kondo insulator SmB6 under strain: surface dominated conduction near room temperature
SmB6 is a strongly correlated mixed-valence Kondo insulator with a newly
discovered surface state, proposed to be of non-trivial topological origin.
However, the surface state dominates electrical conduction only below T* ~ 4 K
limiting its scientific investigation and device application. Here, we report
the enhancement of T * in SmB6 under the application of tensile strain. With
0.7% tensile strain we report surface dominated conduction at up to a
temperature of 240 K, persisting even after the strain has been removed. This
can be explained in the framework of strain-tuned temporal and spatial
fluctuations of f-electron configurations, which might be generally applied to
other mixed-valence materials. We note that this amount of strain can be indued
in epitaxial SmB6 films via substrate in potential device applications.Comment: to appear in Nature Material
Radio Frequency Tunable Oscillator Device Based on SmB6 Microcrystal
Radio frequency tunable oscillators are vital electronic components for
signal generation, characterization, and processing. They are often constructed
with a resonant circuit and a 'negative' resistor, such as a Gunn-diode,
involving complex structure and large footprints. Here we report that a piece
of SmB6, 100 micron in size, works as a current-controlled oscillator in the 30
MHz frequency range. SmB6 is a strongly correlated Kondo insulator that was
recently found to have a robust surface state likely to be protected by the
topology of its electronics structure. We exploit its non-linear dynamics, and
demonstrate large AC voltage outputs with frequencies from 20 Hz to 30 MHz by
adjusting a small DC bias current. The behaviors of these oscillators agree
well with a theoretical model describing the thermal and electronic dynamics of
coupled surface and bulk states. With reduced crystal size we anticipate the
device to work at higher frequencies, even in the THz regime. This type of
oscillator might be realized in other materials with a metallic surface and a
semiconducting bulk.Comment: v3 to appear in Physical Review Letter
Lorentz Transformations as Lie-Poisson Symmetries
We write down the Poisson structure for a relativistic particle where the
Lorentz group does not act canonically, but instead as a Poisson-Lie group. In
so doing we obtain the classical limit of a particle moving on a noncommutative
space possessing invariance. We show that if the standard mass
shell constraint is chosen for the Hamiltonian function, then the particle
interacts with the space-time. We solve for the trajectory and find that it
originates and terminates at singularities.Comment: 18 page
Detecting Non-Abelian Statistics in the nu=5/2 Fractional Quantum Hall State
In this letter we propose an interferometric experiment to detect non-Abelian
quasiparticle statistics -- one of the hallmark characteristics of the
Moore-Read state expected to describe the observed FQHE plateau at nu=5/2. The
implications for using this state for constructing a topologically protected
qubit as has been recently proposed by Das Sarma et. al. are also addressed.Comment: 5 pages, 2 eps figures v2: A few minor changes and citation
corrections. In particular, the connection to cond-mat/9711087 has been
clarified. v3: Minor changes: fixed references to Fig. 2, updated citations,
changed a few words to conform to the version published in PR
Big bang nucleosynthesis as a probe of fundamental "constants"
Big Bang nucleosynthesis (BBN) is the earliest sensitive probe of the values
of many fundamental particle physics parameters. We have found the leading
linear dependences of primordial abundances on all relevant parameters of the
standard BBN code, including binding energies and nuclear reaction rates. This
enables us to set limits on possible variations of fundamental parameters. We
find that 7Li is expected to be significantly more sensitive than other species
to many fundamental parameters, a result which also holds for variations of
coupling strengths in grand unified (GUT) models. Our work also indicates which
areas of nuclear theory need further development if the values of ``constants''
are to be more accurately probed.Comment: Refereed article to be published in Nuclear Physics in Astrophysics
III Proceedings, J. Phys. G. Special Issue. Based on work in collaboration
with C. Wetterich (Heidelberg). 6 page
Topologically protected quantum gates for computation with non-Abelian anyons in the Pfaffian quantum Hall state
We extend the topological quantum computation scheme using the Pfaffian
quantum Hall state, which has been recently proposed by Das Sarma et al., in a
way that might potentially allow for the topologically protected construction
of a universal set of quantum gates. We construct, for the first time, a
topologically protected Controlled-NOT gate which is entirely based on
quasihole braidings of Pfaffian qubits. All single-qubit gates, except for the
pi/8 gate, are also explicitly implemented by quasihole braidings. Instead of
the pi/8 gate we try to construct a topologically protected Toffoli gate, in
terms of the Controlled-phase gate and CNOT or by a braid-group based
Controlled-Controlled-Z precursor. We also give a topologically protected
realization of the Bravyi-Kitaev two-qubit gate g_3.Comment: 6 pages, 7 figures, RevTeX; version 3: introduced section names, new
reference added; new comment added about the embedding of the one- and two-
qubit gates into a three-qubit syste
Superlong GRBs
We searched for anomalously long GRBs (GRBs) in the archival records of the
Burst and Transient Sources Experiment (BATSE). Ten obvious superlong (>500 s)
GRBs with almost continuous emission episodes were found. Nine of these events
are known from the BATSE catalog, but five have no duration estimates; we found
one burst for the first time. We also detected events with emission episodes
separated by a long period of silence (up to 1000 s) with a total duration of
1000--2000 s. In the latter case, we cannot reach an unequivocal conclusion
about a common origin of the episodes due to the BATSE poor angular resolution.
However, for most of these pairs, the probability of a coincidence of
independent GRBs is much lower than unity, and the probability that all of
these are coincidences is 10E-8. All of the events have a hardness ratio (the
ratio of the count rates in different energy channels) typical of GRBs, and
their unique duration is unlikely to be related to their high redshifts.
Superlong bursts do not differ in their properties from typical long (>2 s)
GRBs. We estimated the fraction of superlong GRBs (>500 s) among the long GRBs
in the BATSE sample with fluxes up to 0.1 ph cm^{-2} s^{-1} to be between 0.3
and 0.5%, which is higher than the estimate based on the BATSE catalog.Comment: 11 pages, 4 figures, 3 tables, translation is made by Astronomy
Letter
Mid-infrared Variability from the Spitzer Deep Wide-field Survey
We use the multi-epoch, mid-infrared Spitzer Deep Wide-Field Survey to investigate the variability of objects in 8.1 deg^2 of the NOAO Deep Wide Field Survey Boötes field. We perform a Difference Image Analysis of the four available epochs between 2004 and 2008, focusing on the deeper 3.6 and 4.5 μm bands. Out of 474, 179 analyzed sources, 1.1% meet our standard variability selection criteria that the two light curves are strongly correlated (r > 0.8) and that their joint variance (σ_(12)) exceeds that for all sources with the same magnitude by 2σ. We then examine the mid-IR colors of the variable sources and match them with X-ray sources from the XBoötes survey, radio catalogs, 24 μm selected active galactic nucleus (AGN) candidates, and spectroscopically identified AGNs from the AGN and Galaxy Evolution Survey (AGES). Based on their mid-IR colors, most of the variable sources are AGNs (76%), with smaller contributions from stars (11%), galaxies (6%), and unclassified objects, although most of the stellar, galaxy, and unclassified sources are false positives. For our standard selection criteria, 11%-12% of the mid-IR counterparts to X-ray sources, 24 μm AGN candidates, and spectroscopically identified AGNs show variability. The exact fractions depend on both the search depth and the selection criteria. For example, 12% of the 1131 known z>1 AGNs in the field and 14%-17% of the known AGNs with well-measured fluxes in all four Infrared Array Camera bands meet our standard selection criteria. The mid-IR AGN variability can be well described by a single power-law structure function with an index of γ ≈ 0.5 at both 3.6 and 4.5 μm, and an amplitude of S _0 ≃ 0.1 mag on rest-frame timescales of 2 yr. The variability amplitude is higher for shorter rest-frame wavelengths and lower luminosities
- …