224 research outputs found
Bubbling with -almost constant mean curvature and an Alexandrov-type theorem for crystals
A compactness theorem for volume-constrained almost-critical points of
elliptic integrands is proven. The result is new even for the area functional,
as almost-criticality is measured in an integral rather than in a uniform
sense. Two main applications of the compactness theorem are discussed. First,
we obtain a description of critical points/local minimizers of elliptic
energies interacting with a confinement potential. Second, we prove an
Alexandrov-type theorem for crystalline isoperimetric problems
Electron-phonon coupling in semimetals in a high magnetic field
We consider the effect of electron-phonon coupling in semimetals in high
magnetic fields, with regard to elastic modes that can lead to a redistribution
of carriers between pockets. We show that in a clean three dimensional system,
at each Landau level crossing, this leads to a discontinuity in the
magnetostriction, and a divergent contribution to the elastic modulus. We
estimate the magnitude of this effect in the group V semimetal Bismuth.Comment: 2 figure
Acoustic attenuation rate in the Fermi-Bose model with a finite-range fermion-fermion interaction
We study the acoustic attenuation rate in the Fermi-Bose model describing a
mixtures of bosonic and fermionic atom gases. We demonstrate the dramatic
change of the acoustic attenuation rate as the fermionic component is evolved
through the BEC-BCS crossover, in the context of a mean-field model applied to
a finite-range fermion-fermion interaction at zero temperature, such as
discussed previously by M.M. Parish et al. [Phys. Rev. B 71, 064513 (2005)] and
B. Mihaila et al. [Phys. Rev. Lett. 95, 090402 (2005)]. The shape of the
acoustic attenuation rate as a function of the boson energy represents a
signature for superfluidity in the fermionic component
Numerical Approximations Using Chebyshev Polynomial Expansions
We present numerical solutions for differential equations by expanding the
unknown function in terms of Chebyshev polynomials and solving a system of
linear equations directly for the values of the function at the extrema (or
zeros) of the Chebyshev polynomial of order N (El-gendi's method). The
solutions are exact at these points, apart from round-off computer errors and
the convergence of other numerical methods used in connection to solving the
linear system of equations. Applications to initial value problems in
time-dependent quantum field theory, and second order boundary value problems
in fluid dynamics are presented.Comment: minor wording changes, some typos have been eliminate
Ground state correlations and mean-field in O: Part II
We continue the investigations of the O ground state using the
coupled-cluster expansion [] method with realistic nuclear
interaction. In this stage of the project, we take into account the three
nucleon interaction, and examine in some detail the definition of the internal
Hamiltonian, thus trying to correct for the center-of-mass motion. We show that
this may result in a better separation of the internal and center-of-mass
degrees of freedom in the many-body nuclear wave function. The resulting ground
state wave function is used to calculate the "theoretical" charge form factor
and charge density. Using the "theoretical" charge density, we generate the
charge form factor in the DWBA picture, which is then compared with the
available experimental data. The longitudinal response function in inclusive
electron scattering for O is also computed.Comment: 9 pages, 7 figure
Spin noise spectroscopy to probe quantum states of ultracold fermionic atomic gases
Ultracold alkali atoms provide experimentally accessible model systems for
probing quantum states that manifest themselves at the macroscopic scale.
Recent experimental realizations of superfluidity in dilute gases of ultracold
fermionic (half-integer spin) atoms offer exciting opportunities to directly
test theoretical models of related many-body fermion systems that are
inaccessible to experimental manipulation, such as neutron stars and
quark-gluon plasmas. However, the microscopic interactions between fermions are
potentially quite complex, and experiments in ultracold gases to date cannot
clearly distinguish between the qualitatively different microscopic models that
have been proposed. Here, we theoretically demonstrate that optical
measurements of electron spin noise -- the intrinsic, random fluctuations of
spin -- can probe the entangled quantum states of ultracold fermionic atomic
gases and unambiguously reveal the detailed nature of the interatomic
interactions. We show that different models predict different sets of
resonances in the noise spectrum, and once the correct effective interatomic
interaction model is identified, the line-shapes of the spin noise can be used
to constrain this model. Further, experimental measurements of spin noise in
classical (Boltzmann) alkali vapors are used to estimate the expected signal
magnitudes for spin noise measurements in ultracold atom systems and to show
that these measurements are feasible
Staying Thermal with Hartree Ensemble Approximations
We study thermal behavior of a recently introduced Hartree ensemble
approximation, which allows for non-perturbative inhomogeneous field
configurations as well as for approximate thermalization, in the model
in 1+1 dimensions. Using ensembles with a free field thermal distribution as
out-of-equilibrium initial conditions we determine thermalization time scales.
The time scale for which the system stays in approximate quantum thermal
equilibrium is an indication of the time scales for which the approximation
method stays reasonable. This time scale turns out to be two orders of
magnitude larger than the time scale for thermalization, in the range of
couplings and temperatures studied. We also discuss simplifications of our
method which are numerically more efficient and make a comparison with
classical dynamics.Comment: 19 pages latex; extensively rewritten to improve presentation, data
essentially unchanged, analysis sharpened and one table adde
Renormalization constants and beta functions for the gauge couplings of the Standard Model to three-loop order
We compute the beta functions for the three gauge couplings of the Standard
Model in the minimal subtraction scheme to three loops. We take into account
contributions from all sectors of the Standard Model. The calculation is
performed using both Lorenz gauge in the unbroken phase of the Standard Model
and background field gauge in the spontaneously broken phase. Furthermore, we
describe in detail the treatment of and present the automated setup
which we use for the calculation of the Feynman diagrams. It starts with the
generation of the Feynman rules and leads to the bare result for the Green's
function of a given process.Comment: 44 pages, 9 figures; v2: sign in eq.(29) corrected; final result
unchange
Colloquial words and expressions in professional environment
Language generally represents a means of communications in society, a complex reality that may be conceptualized in various ways as it is differently approached. Due to the current explosive development of science and technology to satisfy the multi-folded demands and desires of people worldwide as well as the increase of inter-cultural changes, many words belonging to the “terminological bank” have passed into the common literary or even colloquial vocabulary. When we speak about professionalisms we refer to the lexical units used in a definite trade, profession or calling by people connected by common interests both at work and at home
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