20,511 research outputs found
Sectoral r modes and periodic RV variations of Sun-like stars
Radial velocity (RV) measurements are used to search for planets orbiting
late-type main-sequence stars and confirm the transiting planets. The most
advanced spectrometers are approaching a precision of cm/s that
implies the need to identify and correct for all possible sources of RV
oscillations intrinsic to the star down to this level and possibly beyond. The
recent discovery of global-scale equatorial Rossby waves in the Sun, also
called r modes, prompted us to investigate their possible signature in stellar
RV measurements. R modes are toroidal modes of oscillation whose restoring
force is the Coriolis force and propagate in the retrograde direction in a
frame that corotates with the star. The solar r modes with azimuthal orders were identified unambiguously because of their dispersion
relation and their long e-folding lifetimes of hundreds of days. Here we
simulate the RV oscillations produced by sectoral r modes with assuming a stellar rotation period of 25.54 days and a maximum amplitude of
the surface velocity of each mode of 2 m/s. This amplitude is representative of
the solar measurements, except for the mode which has not yet been
observed. Sectoral r modes with azimuthal orders and would produce RV
oscillations with amplitudes of 76.4 and 19.6 cm/s and periods of 19.16 and
10.22 days, respectively, for a star with an inclination of the rotation axis
. Therefore, they may produce rather sharp peaks in the Fourier
spectrum of the radial velocity time series that could lead to spurious
planetary detections. Sectoral r~modes may represent a source of confusion in
the case of slowly rotating inactive stars that are preferential targets for RV
planet search. The main limitation of the present investigation is the lack of
observational constraint on the amplitude of the mode on the Sun.Comment: 7 pages; 4 figures; 1 table; accepted to Astronomy & Astrophysic
Quantum Phase Interference for Quantum Tunneling in Spin Systems
The point-particle-like Hamiltonian of a biaxial spin particle with external
magnetic field along the hard axis is obtained in terms of the potential field
description of spin systems with exact spin-coordinate correspondence. The
Zeeman energy term turns out to be an effective gauge potential which leads to
a nonintegrable pha se of the Euclidean Feynman propagator.
The phase interference between clockwise and anticlockwise under barrier
propagations is recognized explicitly as the Aharonov-Bohm effect. An
additional phase which is significant for quantum phase interference is
discovered with the quantum theory of spin systems besides the known phase
obtained with the semiclassical treatment of spin. We also show the energ y
dependence of the effect and obtain the tunneling splitting at excited states
with the help of periodic instantons.Comment: 19 pages, no figure, to appear in PR
Classical and Intuitionistic Subexponential Logics are Equally Expressive
International audienceIt is standard to regard the intuitionistic restriction of a classical logic as increasing the expressivity of the logic because the classical logic can be adequately represented in the intuitionistic logic by double-negation, while the other direction has no truth-preserving propositional encodings. We show here that subexponential logic, which is a family of substructural refinements of classical logic, each parametric over a preorder over the subexponential connectives, does not suffer from this asymmetry if the preorder is systematically modified as part of the encoding. Precisely, we show a bijection between synthetic (i.e., focused) partial sequent derivations modulo a given encoding. Particular instances of our encoding for particular subexponential preorders give rise to both known and novel adequacy theorems for substructural logics
The Transverse-momentum-dependent Parton Distribution Function and Jet Transport in Medium
We show that the gauge-invariant transverse-momentum-dependent (TMD) quark
distribution function can be expressed as a sum of all higher-twist collinear
parton matrix elements in terms of a transport operator. From such a general
expression, we derive the nuclear broadening of the transverse momentum
distribution. Under the maximal two-gluon correlation approximation, in which
all higher-twist nuclear multiple-parton correlations with the leading nuclear
enhancement are given by products of twist-two nucleon parton distributions, we
find the nuclear transverse momentum distribution as a convolution of a
Gaussian distribution and the nucleon TMD quark distribution. The width of the
Gaussian, or the mean total transverse momentum broadening squared, is given by
the path integral of the quark transport parameter which can also be
expressed in a gauge invariant form and is given by the gluon distribution
density in the nuclear medium. We further show that contributions from
higher-twist nucleon gluon distributions can be resummed under the extended
adjoint two-gluon correlation approximation and the nuclear transverse momentum
distribution can be expressed in terms of a transverse scale dependent quark
transport parameter or gluon distribution density. We extend the study to hot
medium and compare to dipole model approximation and
Supersymmetric Yang-Mills (SYM) theory in the strong coupling limit. We find
that multiple gluon correlations become important in the strongly coupled
system such as SYM plasma.Comment: 22 pages in RevTex with 2 figures final published versio
Charged Dual String Vacua from Interacting Rotating Black Holes Via Discrete and Nonlinear Symmetries
Using the stationary formulation of the toroidally compactified heterotic
string theory in terms of a pair of matrix Ernst potentials we consider the
four-dimensional truncation of this theory with no U(1) vector fields excited.
Imposing one time-like Killing vector permits us to express the stationary
effective action as a model in which gravity is coupled to a matrix Ernst
potential which, under certain parametrization, allows us to interpret the
matter sector of this theory as a double Ernst system. We generate a web of
string vacua which are related to each other via a set of discrete symmetries
of the effective action (some of them involve S-duality transformations and
possess non-perturbative character). Some physical implications of these
discrete symmetries are analyzed and we find that, in some particular cases,
they relate rotating black holes coupled to a dilaton with no Kalb--Ramond
field, static black holes with non-trivial dilaton and antisymmetric tensor
fields, and rotating and static naked singularities. Further, by applying a
nonlinear symmetry, namely, the so-called normalized Harrison transformation,
on the seed field configurations corresponding to these neutral backgrounds, we
recover the U(1)^n Abelian vector sector of the four-dimensional action of the
heterotic string, charging in this way the double Ernst system which
corresponds to each one of the neutral string vacua, i.e., the stationary and
the static black holes and the naked singularities.Comment: 19 pages in latex, added referenc
Glueballs and Instantons
We study correlation functions and Bethe Salpeter amplitudes for the scalar,
the pseudoscalar and the tensor glueballs using an instanton-based model of the
QCD vacuum. We consider both the pure gauge case and the situation for real QCD
with two light quark flavors. We show that instantons lead to a strong
modification of the correlation functions as compared to their perturbative
behavior. In particular, we find a strong attractive force in the
channel and repulsion in the channel. Due to the
strong classical field of the instantons, these effects are much larger than
the spin splittings observed in mesons made of quarks. The resulting masses,
coupling constants and wave functions appear to be in agreement with lattice
gauge simulations.Comment: revised version published in Phys. Rev. Let
Neutron Transfer Dynamics and Doorway to Fusion in Time-Dependent Hartree-Fock Theory
We analyze the details of mass exchange in the vicinity of the Coulomb
barrier for heavy-ion collisions involving neutron-rich nuclei using the
time-dependent Hartree-Fock (TDHF) theory. We discuss the time-dependence of
transfer and show that the potential barriers seen by individual
single-particle states can be considerably different than the effective barrier
for the two interacting nuclei having a single center-of-mass. For this reason
we observe a substantial transfer probability even at energies below the
effective barrier.Comment: 6 pages, 9 figure
Bell's inequalities in the tomographic representation
The tomographic approach to quantum mechanics is revisited as a direct tool
to investigate violation of Bell-like inequalities. Since quantum tomograms are
well defined probability distributions, the tomographic approach is emphasized
to be the most natural one to compare the predictions of classical and quantum
theory. Examples of inequalities for two qubits an two qutrits are considered
in the tomographic probability representation of spin states.Comment: 11 pages, comments and references adde
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