14,794 research outputs found
Baryons and Skyrmions in QCD with Quarks in Higher Representations
We study the baryonic sector of QCD with quarks in the two index symmetric or
antisymmetric representation. The minimal gauge invariant state that carries
baryon number cannot be identified with the Skyrmion of the low energy chiral
effective Lagrangian. Mass, statistics and baryon number do not match. We
carefully investigate the properties of the minimal baryon in the large N limit
and we find that it is unstable under formation of bound states with higher
baryonic number. These states match exactly with the properties of the Skyrmion
of the effective Lagrangian.Comment: 23 pages, 13 figures. v2: minor changes. v3: corrected a mistake and
some typos. v4: modifyed the part about the stability of the Skyrmio
A PDE-constrained optimization formulation for discrete fracture network flows
We investigate a new numerical approach for the computation of the 3D flow in a discrete fracture network that does not require a conforming discretization of partial differential equations on complex 3D systems of planar fractures. The discretization within each fracture is performed independently of the discretization of the other fractures and of their intersections. Independent meshing process within each fracture is a very important issue for practical large scale simulations making easier mesh generation. Some numerical simulations are given to show the viability of the method. The resulting approach can be naturally parallelized for dealing with systems with a huge number of fractures
Non-Hermitian shortcut to stimulated Raman adiabatic passage
We propose a non-Hermitian generalization of stimulated Raman adiabatic
passage (STIRAP), which allows one to increase speed and fidelity of the
adiabatic passage. This is done by adding balanced imaginary (gain/loss) terms
in the diagonal (bare energy) terms of the Hamiltonian and choosing them such
that they cancel exactly the nonadiabatic couplings, providing in this way an
effective shortcut to adiabaticity. Remarkably, for a STIRAP using delayed
Gaussian-shaped pulses in the counter-intuitive scheme the imaginary terms of
the Hamiltonian turn out to be time independent. A possible physical
realization of non-Hermitian STIRAP, based on light transfer in three
evanescently-coupled optical waveguides, is proposed.Comment: 7 pages, 4 figure
Barkhausen noise in soft amorphous magnetic materials under applied stress
We report experimental measurements of Barkhausen noise on
Fe_{64}Co_{21}B_{15} amorphous alloy under tensile stress. We interpret the
scaling behavior of the noise distributions in terms of the depinning
transition of the domain walls. We show that stress induced anisotropy enhance
the effect of short-range elastic interactions that dominate over long-range
dipolar interactions. The universality class is thus different from the one
usually observed in Barkhausen noise measurements and is characterized by the
exponents \tau = 1.3 and \alpha = 1.5, for the decay of the distributions of
jump sizes and durations.Comment: 6 pages, 3 .eps figures. Submitted to the 43rd Magnetism and Magnetic
Materials Conference (J. Appl. Phys.
Quantum simulation of the Riemann-Hurwitz zeta function
We propose a simple realization of a quantum simulator of the Riemann-Hurwitz
(RH) \zeta\ function based on a truncation of its Dirichlet representation. We
synthesize a nearest-neighbour-interaction Hamiltonian, satisfying the property
that the temporal evolution of the autocorrelation function of an initial bare
state of the Hamiltonian reproduces the RH function along the line \sigma+i
\omega t of the complex plane, with \sigma>1. The tight-binding Hamiltonian
with engineered hopping rates and site energies can be implemented in a variety
of physical systems, including trapped ion systems and optical waveguide
arrays. The proposed method is scalable, which means that the simulation can be
in principle arbitrarily accurate. Practical limitations of the suggested
scheme, arising from a finite number of lattice sites N and from decoherence,
are briefly discussed.Comment: 6 pages, 3 figure
A Stabilization Mechanism of Zirconia Based on Oxygen Vacancies Only
The microscopic mechanism leading to stabilization of cubic and tetragonal
forms of zirconia (ZrO) is analyzed by means of a self-consistent
tight-binding model. Using this model, energies and structures of zirconia
containing different vacancy concentrations are calculated, equivalent in
concentration to the charge compensating vacancies associated with dissolved
yttria (YO) in the tetragonal and cubic phase fields (3.2 and 14.4% mol
respectively). The model is shown to predict the large relaxations around an
oxygen vacancy, and the clustering of vacancies along the directions,
in good agreement with experiments and first principles calculations. The
vacancies alone are shown to explain the stabilization of cubic zirconia, and
the mechanism is analyzed.Comment: 19 pages, 6 figures. To be published in J. Am. Ceram. So
Exact solution of time-dependent Lindblad equations with closed algebras
Time-dependent Lindblad master equations have important applications in areas
ranging from quantum thermodynamics to dissipative quantum computing. In this
paper we outline a general method for writing down exact solutions of
time-dependent Lindblad equations whose superoperators form closed algebras. We
focus on the particular case of a single qubit and study the exact solution
generated by both coherent and incoherent mechanisms. We also show that if the
time-dependence is periodic, the problem may be recast in terms of Floquet
theory. As an application, we give an exact solution for a two-levels quantum
heat engine operating in a finite-time.Comment: 15 pages, 12 figure
- …