18,222 research outputs found
The Physics of UHECRs: Spectra, Composition and the Transition Galactic-Extragalactic
We review the experimental evidences about flux and mass composition of ultra
high energy cosmic rays in connection with theoretical scenarios concerning
astrophysical sources. In this context, we also address the discussion about
the expected transition between cosmic rays produced inside the Galaxy and
those coming from the intergalactic space.Comment: 6 pages, 10 figures, invited talk given at the "2016 International
Conference on Ultra-High Energy Cosmic Rays (UHECR2016)", Kyoto (Japan),
11-14 October 2016, version accepted for publication on JPS Conference
Proceeding
Antiferromagnetism and phase separation in the t-J model at low doping: a variational study
Using Gutzwiller-projected wave functions, I estimate the ground-state energy
of the t-J model for several variational states relevant for high-temperature
cuprate superconductors. The results indicate antiferromagnetism and phase
separation at low doping both in the superconducting state and in the
staggered-flux normal state proposed for the vortex cores. While phase
separation in the underdoped superconducting state may be relevant for the
stripe formation mechanism, the results for the normal state suggest that
similar charge inhomogeneities may also appear in vortex cores up to relatively
high doping values.Comment: 4 pages, 3 figures, reference adde
Numerical study of fractionalization in an Easy-axis Kagome antiferromagnet
Based on exact numerical calculations, we show that the generalized Kagome
spin model in the easy axis limit exhibits a spin liquid, topologically
degenerate ground state over a broad range of phase space. We present an (to
our knowledge the first) explicit calculation of the gap (and dispersion) of
``vison'' excitations, and exponentially decaying spin and vison 2-point
correlators, hallmarks of deconfined, fractionalized and gapped spinons. The
region of the spin liquid phase includes a point at which the model is
equivalent to a Heisenberg model with purely two-spin interactions. Beyond this
range, a negative ``potential'' term tunes a first order transition to a
magnetic ordered state. The nature of the phase transition is also discussed in
light of the low energy spectrum. These results greatly expand the results and
range of a previous study of this model in the vicinity of an exactly soluble
point.Comment: 4 pages, 5 figure
Correlations of the local density of states in quasi-one-dimensional wires
We report a calculation of the correlation function of the local density of
states in a disordered quasi-one-dimensional wire in the unitary symmetry class
at a small energy difference. Using an expression from the supersymmetric
sigma-model, we obtain the full dependence of the two-point correlation
function on the distance between the points. In the limit of zero energy
difference, our calculation reproduces the statistics of a single localized
wave function. At logarithmically large distances of the order of the Mott
scale, we obtain a reentrant behavior similar to that in strictly
one-dimensional chains.Comment: Published version. Minor technical and notational improvements. 16
pages, 1 figur
Scalable quantum search using trapped ions
We propose a scalable implementation of Grover's quantum search algorithm in
a trapped-ion quantum information processor. The system is initialized in an
entangled Dicke state by using simple adiabatic techniques. The
inversion-about-average and the oracle operators take the form of single
off-resonant laser pulses, addressing, respectively, all and half of the ions
in the trap. This is made possible by utilizing the physical symmetrie of the
trapped-ion linear crystal. The physical realization of the algorithm
represents a dramatic simplification: each logical iteration (oracle and
inversion about average) requires only two physical interaction steps, in
contrast to the large number of concatenated gates required by previous
approaches. This does not only facilitate the implementation, but also
increases the overall fidelity of the algorithm.Comment: 6 pages, 2 figure
Semileptonic decays of heavy mesons
The semileptonic and leptonic decays of heavy mesons are studied as a
phenomenological application and exploration of a heavy-quark limit of
Dyson-Schwinger equations. The single form factor, , which
characterises the semileptonic decay in this limit, is calculated and compares
well with recent experimental extractions. We obtain a lower bound of 1/3 on
the slope-parameter , which, in calculations with
realistic input, is exceeded by a great deal: agreement with experimental data
requiring . The flavour and momentum dependence of the
light-quark propagators has observable consequences.Comment: 11 pages, LaTeX, epsfig.sty, elsart.st
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