16,627 research outputs found
Massive Spin-2 fields of Geometric Origin in Curved Spacetimes
We study the consistency of a model which includes torsion as well as the
metric as dynamical fields and has massive spin-2 particle in its spectrum. The
massive spin-2 mode resides in the torsion, rather than in the metric. It is
known that this model is tachyon- and ghost-free in Minkowski background. We
show that this property remains valid and no other pathologies emerge in de
Sitter and anti-de Sitter backgrounds, with some of our results extending to
arbirary Einstein space backgrounds. This suggests that the model is
consistent, at least at the classical level, unlike, e.g., the Fierz--Pauli
theory.Comment: 17 pages, Clarifying remarks added in section 5, minor changes,
version to be published in the Phys. Rev.
Nuclear Magnetic Relaxation Rate in a Noncentrosymmetric Superconductor
For a noncentrosymmetric superconductor such as CePt3Si, we consider a Cooper
pairing model with a two-component order parameter composed of spin-singlet and
spin-triplet pairing components.
We demonstrate that such a model on a qualitative level accounts for
experimentally observed features of the temperature dependence of the nuclear
spin-lattice relaxation rate 1/T1, namely a peak just below Tc and a line-node
gap behavior at low temperatures.Comment: 4 page
Quantum hypothesis testing with group symmetry
The asymptotic discrimination problem of two quantum states is studied in the
setting where measurements are required to be invariant under some symmetry
group of the system. We consider various asymptotic error exponents in
connection with the problems of the Chernoff bound, the Hoeffding bound and
Stein's lemma, and derive bounds on these quantities in terms of their
corresponding statistical distance measures. A special emphasis is put on the
comparison of the performances of group-invariant and unrestricted
measurements.Comment: 33 page
Exponents of quantum fixed-length pure state source coding
We derive the optimal exponent of the error probability of the quantum
fixed-length pure state source coding in both cases of blind coding and visible
coding. The optimal exponent is universally attained by Jozsa et al. (PRL, 81,
1714 (1998))'s universal code. In the direct part, a group representation
theoretical type method is essential. In the converse part, Nielsen and Kempe
(PRL, 86, 5184 (2001))'s lemma is essential.Comment: LaTeX2e and revetx4 with
aps,twocolumn,superscriptaddress,showpacs,pra,amssymb,amsmath. The previous
version has a mistak
Path Integral for Space-time Noncommutative Field Theory
The path integral for space-time noncommutative theory is formulated by means
of Schwinger's action principle which is based on the equations of motion and a
suitable ansatz of asymptotic conditions. The resulting path integral has
essentially the same physical basis as the Yang-Feldman formulation. It is
first shown that higher derivative theories are neatly dealt with by the path
integral formulation, and the underlying canonical structure is recovered by
the Bjorken-Johnson-Low (BJL) prescription from correlation functions defined
by the path integral. A simple theory which is non-local in time is then
analyzed for an illustration of the complications related to quantization,
unitarity and positive energy conditions. From the view point of BJL
prescription, the naive quantization in the interaction picture is justified
for space-time noncommutative theory but not for the simple theory non-local in
time. We finally show that the perturbative unitarity and the positive energy
condition, in the sense that only the positive energy flows in the positive
time direction for any fixed time-slice in space-time, are not simultaneously
satisfied for space-time noncommutative theory by the known methods of
quantization.Comment: 21 page
Charge transfer and weak bonding between molecular oxygen and graphene zigzag edges at low temperatures
Electron paramagnetic resonance (EPR) study of air-physisorbed defective
carbon nano-onions evidences in favor of microwave assisted formation of
weakly-bound paramagnetic complexes comprising negatively-charged O2- ions and
edge carbon atoms carrying pi-electronic spins. These complexes being located
on the graphene edges are stable at low temperatures but irreversibly
dissociate at temperatures above 50-60 K. These EPR findings are justified by
density functional theory (DFT) calculations demonstrating transfer of an
electron from the zigzag edge of graphene-like material to oxygen molecule
physisorbed on the graphene sheet edge. This charge transfer causes changing
the spin state of the adsorbed oxygen molecule from S = 1 to S = 1/2 one. DFT
calculations show significant changes of adsorption energy of oxygen molecule
and robustness of the charge transfer to variations of the graphene-like
substrate morphology (flat and corrugated mono- and bi-layered graphene) as
well as edges passivation. The presence of H- and COOH- terminated edge carbon
sites with such corrugated substrate morphology allows formation of ZE-O2-
paramagnetic complexes characterized by small (<50 meV) binding energies and
also explains their irreversible dissociation as revealed by EPR.Comment: 28 pages, 8 figures, 2 tables, accepted in Carbon journa
Nuclear transport models can reproduce charged-particle-inclusive measurements but are not strongly constrained by them
Nuclear transport models are important tools for interpretation of many heavy-ion experiments and are essential in efforts to probe the nuclear equation of state. In order to fulfill these roles, the model predictions should at least agree with observed single-particle-inclusive momentum spectra; however, this agreement has recently been questioned. The present work compares the Vlasov-Uehling-Uhlenbeck model to data for mass-symmetric systems ranging from 12C+12C to 139La+139La, and we find good agreement within experimental uncertainties at 0.4A and 0.8A GeV. For currently available data, these uncertainties are too large to permit effective nucleon-nucleon scattering cross sections in the nuclear medium to be extracted at a useful level of precision
Neumann problem for the Korteweg–de Vries equation
AbstractWe consider Neumann initial-boundary value problem for the Korteweg–de Vries equation on a half-line(0.1){ut+λuux+uxxx=0,t>0,x>0,u(x,0)=u0(x),x>0,ux(0,t)=0,t>0. We prove that if the initial data u0∈H10,214∩H21,72 and the norm ‖u0‖H10,214+‖u0‖H21,72⩽ε, where ε>0 is small enough Hps,k={f∈L2;‖f‖Hps,k=‖〈x〉k〈i∂x〉sf‖Lp<∞}, 〈x〉=1+x2 and λ∫0∞xu0(x)dx=λθ<0. Then there exists a unique solution u∈C([0,∞),H21,72)∩L2(0,∞;H22,3) of the initial-boundary value problem (0.1). Moreover there exists a constant C such that the solution has the following asymptoticsu(x,t)=Cθ(1+ηlogt)−1t−23Ai′(xt3)+O(ε2t−23(1+ηlogt)−65) for t→∞ uniformly with respect to x>0, where η=−9θλ∫0∞Ai′2(z)dz and Ai(q) is the Airy functionAi(q)=12πi∫−i∞i∞e−z3+zqdz=1πRe∫0∞e−iξ3+iξqdξ
Using intelligent optimization methods to improve the group method of data handling in time series prediction
In this paper we show how the performance of the basic algorithm of the Group Method of Data Handling (GMDH) can be improved using Genetic Algorithms (GA) and Particle Swarm Optimization (PSO). The new improved GMDH is then used to predict currency exchange rates: the US Dollar to the Euros. The performance of the hybrid GMDHs are compared with that of the conventional GMDH. Two performance measures, the root mean squared error and the mean absolute percentage errors show that the hybrid GMDH algorithm gives more accurate predictions than the conventional GMDH algorithm
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