25,599 research outputs found
Unified covariant treatment of hyperfine splitting for heavy and light mesons
This paper aims at proving the fundamental role of a relativistic formulation
for quarkonia models.
We present a completely covariant description of a two-quark system
interacting by the Cornell potential with a Breit term describing the hyperfine
splitting. Using an appropriate procedure to calculate the Breit correction, we
find heavy meson masses in excellent agreement with experimental data.
Moreover, also when applied to light quarks and even taking average values of
the running coupling constant, we prove that covariance properties and
hyperfine splitting are sufficient to explain the light mesons spectrum and to
give a very good agreement with the data.Comment: 4 page
Single-Particle Tunneling in Doped Graphene-Insulator-Graphene Junctions
The characteristics of tunnel junctions formed between n- and p-doped
graphene are investigated theoretically. The single-particle tunnel current
that flows between the two-dimensional electronic states of the graphene (2D-2D
tunneling) is evaluated. At a voltage bias such that the Dirac points of the
two electrodes are aligned, a large resonant current peak is produced. The
magnitude and width of this peak is computed, and its use for devices is
discussed. The influence of both rotational alignment of the graphene
electrodes and structural perfection of the graphene is discussed.Comment: 23 pages, 9 figures; added Section II(E) and associated figures, and
made other minor typographical correction
Generic Quantum Ratchet Accelerator with Full Classical Chaos
A simple model of quantum ratchet transport that can generate unbounded
linear acceleration of the quantum ratchet current is proposed, with the
underlying classical dynamics fully chaotic. The results demonstrate that
generic acceleration of quantum ratchet transport can occur with any type of
classical phase space structure. The quantum ratchet transport with full
classical chaos is also shown to be very robust to noise due to the large
linear acceleration afforded by the quantum dynamics. One possible experiment
allowing observation of these predictions is suggested.Comment: 4 pages, 4 figure
Adiabatic Creation of Atomic Squeezing in Dark States vs. Decoherences
We study the multipartite correlations of the multi-atom dark states, which
are characterized by the atomic squeezing beyond the pairwise entanglement. It
is shown that, in the photon storage process with atomic ensemble via
electromagnetically induced transparency (EIT) mechanism, the atomic squeezing
and the pairwise entanglement can be created by adiabatically manipulating the
Rabi frequency of the classical light field on the atomic ensemble. We also
consider the sudden death for the atomic squeezing and the pairwise
entanglement under various decoherence channels. An optimal time for generating
the greatest atomic squeezing and pairwise entanglement is obtained by studying
in details the competition between the adiabatic creation of quantum
correlation in the atomic ensemble and the decoherence that we describe with
three typical decoherence channels.Comment: 11 pages, 13 figure
Breaking scale invariance from a singular inflaton potential
In this paper we break the scale invariance of the primordial power spectrum
of curvature perturbations of inflation. Introducing a singular behaviour due
to spontaneous symmetry breaking in the inflaton potential, we obtain fully
analytic expressions of scale dependent oscillation and a modulation in power
on small scale in the primordial spectrum. And we give the associated cosmic
microwave background and matter power spectra which we can observe now and
discuss the signature of the scale dependence. We also address the possibility
of whether some inflationary model with featured potential might mimic the
predictions of the scale invariant power spectrum. We present some examples
which illustrate such degeneracies.Comment: 20 pages, 9 figures; Discussion expanded and references added;
Miscellaneous typos correcte
Two Component Model of Dark Energy
We consider the possibility that the dark energy is made up of two or more
independent components, each having a different equation of state. We fit the
model with supernova and gamma-ray burst (GRB) data from resent observations,
and use the Markov Chain Monte Carlo (MCMC) technique to estimate the allowed
parameter regions. We also use various model selection criteria to compare the
two component model with the LCDM, one component dark energy model with static
or variable w(XCDM), and with other multi-component models. We find that the
two component models can give reasonably good fit to the current data. For some
data sets, and depending somewhat on the model selection criteria, the two
component model can give better fit to the data than XCDM with static w and
XCDM with variable w parameterized by w = w_0 + w_az/(1+z).Comment: 10 pages, 8 figures, 3 tables; Version accepted by PR
SiS in the circumstellar envelope of IRC +10126: maser and quasi-thermal emission
We present new Effelsberg-100 m, ATCA, and VLA observations of rotational SiS
transitions in the circumstellar envelope (CSE) of IRC +10216. Thanks to the
high angular resolution achieved by the ATCA observations, we unambiguously
confirm that the molecule's J=1-0 transition exhibits maser action in this CSE,
as first suggested more than thirty years ago. The maser emission's radial
velocity peaking at a local standard of rest velocity of -39.8620.065 km/s
indicates that it arises from an almost fully accelerated shell. Monitoring
observations show time variability of the SiS (1-0) maser. The two lowest-
SiS quasi-thermal emission lines trace a much more extended emitting region
than previous high-J SiS observations. Their distributions show that the SiS
quasi-thermal emission consists of two components: one is very compact
(radius<1.5", corresponding to <3 cm), and the other extends
out to a radius >11". An incomplete shell-like structure is found in the
north-east, which is indicative of existing SiS shells. Clumpy structures are
also revealed in this CSE. The gain of the SiS (1-0) maser (optical depths of
about -5 at the blue-shifted side and, assuming inversion throughout the entire
line's velocity range, about -2 at the red-shifted side) suggests that it is
unsaturated. The SiS (1-0) maser can be explained in terms of ro-vibrational
excitation caused by infrared pumping, and we propose that infrared continuum
emission is the main pumping source.Comment: Accepted for publication in ApJ. A high-resolution version can be
found at https://gongyan2444.github.io/pdf/cw-leo-sis.pdf 3D movies of SiS
cubes can be found at https://gongyan2444.github.io/movie/sis10-3d.avi and
https://gongyan2444.github.io/movie/sis21-3d.av
The Wigner solution of quark gap equation at nonzero current quark mass and partial restoration of chiral symmetry at finite chemical potential
According to the generally accepted phase diagram of QCD, at low temperature
and high baryon number density the chiral phase transition of QCD is of first
order and the co-existence of the Nambu-Goldstone phase and the Wigner phase
should appear. This is in conflict with the usual claim that the quark gap
equation has no Wigner solution in the case of nonzero current quark mass. In
this paper we analyze the reason why the Wigner solution does not exist in the
usual treatment and try to propose a new approach to discuss this question. As
a first step, we adopt a modified Nambu-Jona-Lasinio (NJL) model to study the
Wigner solution at finite current quark mass. We then generalize this approach
to the case of finite chemical potential and discuss partial restoration of
chiral symmetry at finite chemical potential and compare our results with those
in the normal NJL model.Comment: 7 pages, 5 figures, and 1 table, discussion at finite chemical
potential adde
Indistinguishability and Interference in the Coherent Control of Atomic and Molecular Processes
The subtle and fundamental issue of indistinguishability and interference
between independent pathways to the same target state is examined in the
context of coherent control of atomic and molecular processes, with emphasis
placed on possible "which-way" information due to quantum entanglement
established in the quantum dynamics. Because quantum interference between
independent pathways to the same target state occurs only when the independent
pathways are indistinguishable, it is first shown that creating useful
coherence (as defined in the paper) between nondegenerate states of a molecule
for subsequent quantum interference manipulation cannot be achieved by
collisions between atoms or molecules that are prepared in momentum and energy
eigenstates. Coherence can, however, be transferred from light fields to atoms
or molecules. Using a particular coherent control scenario, it is shown that
this coherence transfer and the subsequent coherent phase control can be
readily realized by the most classical states of light, i.e., coherent states
of light. It is further demonstrated that quantum states of light may suppress
the extent of phase-sensitive coherent control by leaking out some which-way
information while "incoherent interference control" scenarios proposed in the
literature have automatically ensured the indistinguishability of multiple
excitation pathways. The possibility of quantum coherence in photodissociation
product states is also understood in terms of the disentanglement between
photodissociation fragments. Results offer deeper insights into quantum
coherence generation in atomic and molecular processes.Comment: 26 pages, based on one Chapter from first author's Ph.D thesis in
200
- …