109 research outputs found
Open problems in nuclear density functional theory
This note describes five subjects of some interest for the density functional
theory in nuclear physics. These are, respectively, i) the need for concave
functionals, ii) the nature of the Kohn-Sham potential for the radial density
theory, iii) a proper implementation of a density functional for an "intrinsic"
rotational density, iv) the possible existence of a potential driving the
square root of the density, and v) the existence of many models where a density
functional can be explicitly constructed.Comment: 10 page
Lattice methods and the nuclear few- and many-body problem
We begin with a brief overview of lattice calculations using chiral effective
field theory and some recent applications. We then describe several methods for
computing scattering on the lattice. After that we focus on the main goal,
explaining the theory and algorithms relevant to lattice simulations of nuclear
few- and many-body systems. We discuss the exact equivalence of four different
lattice formalisms, the Grassmann path integral, transfer matrix operator,
Grassmann path integral with auxiliary fields, and transfer matrix operator
with auxiliary fields. Along with our analysis we include several coding
examples and a number of exercises for the calculations of few- and many-body
systems at leading order in chiral effective field theory.Comment: 20 pages, 3 figures, Submitted to Lect. Notes Phys., "An advanced
course in computational nuclear physics: Bridging the scales from quarks to
neutron stars", M. Hjorth-Jensen, M. P. Lombardo, U. van Kolck, Editor
Nuclear energy density functional from chiral two- and three-nucleon interactions
An improved density-matrix expansion is used to calculate the nuclear energy
density functional from chiral two- and three-nucleon interactions. The
two-body interaction comprises long-range one- and two-pion exchange
contributions and a set of contact terms contributing up to fourth power in
momenta. In addition we employ the leading order chiral three-nucleon
interaction with its parameters and fixed in
calculations of nuclear few-body systems. With this input the nuclear energy
density functional is derived to first order in the two- and three-nucleon
interaction. We find that the strength functions and
of the surface and spin-orbit terms compare in the relevant
density range reasonably with results of phenomenological Skyrme forces.
However, an improved description requires (at least) the treatment of the
two-body interaction to second order. This observation is in line with the
deficiencies in the nuclear matter equation of state that remain
in the Hartree-Fock approximation with low-momentum two- and three-nucleon
interactions.Comment: 16 pages, 12 figures, submitted to Eur. Phys. J.
The effective fine structure constant of freestanding graphene measured in graphite
Electrons in graphene behave like Dirac fermions, permitting phenomena from
high energy physics to be studied in a solid state setting. A key question is
whether or not these Fermions are critically influenced by Coulomb
correlations. We performed inelastic x-ray scattering experiments on crystals
of graphite, and applied reconstruction algorithms to image the dynamical
screening of charge in a freestanding, graphene sheet. We found that the
polarizability of the Dirac fermions is amplified by excitonic effects,
improving screening of interactions between quasiparticles. The strength of
interactions is characterized by a scale-dependent, effective fine structure
constant, \alpha *(k,\omega), whose value approaches \alpha * ~ 1/7 at low
energy and large distances. This value is substantially smaller than the
nominal \alpha = 2.2, suggesting that, on the whole, graphene is more weakly
interacting than previously believed.Comment: 28 pages, 10 figures, 2 animation
Microscopically-constrained Fock energy density functionals from chiral effective field theory. I. Two-nucleon interactions
The density matrix expansion (DME) of Negele and Vautherin is a convenient
tool to map finite-range physics associated with vacuum two- and three-nucleon
interactions into the form of a Skyme-like energy density functional (EDF) with
density-dependent couplings. In this work, we apply the improved formulation of
the DME proposed recently in arXiv:0910.4979 by Gebremariam {\it et al.} to the
non-local Fock energy obtained from chiral effective field theory (EFT)
two-nucleon (NN) interactions at next-to-next-to-leading-order (NLO). The
structure of the chiral interactions is such that each coupling in the DME Fock
functional can be decomposed into a cutoff-dependent coupling {\it constant}
arising from zero-range contact interactions and a cutoff-independent coupling
{\it function} of the density arising from the universal long-range pion
exchanges. This motivates a new microscopically-guided Skyrme phenomenology
where the density-dependent couplings associated with the underlying
pion-exchange interactions are added to standard empirical Skyrme functionals,
and the density-independent Skyrme parameters subsequently refit to data. A
Mathematica notebook containing the novel density-dependent couplings is
provided.Comment: 28 pages, 12 figures. Mathematica notebook provided with submission
Morfología de la mucosa gástrica oxíntica en ratones jóvenes tratados con omeprazol
El omeprazol es un potente inhibidor de la bomba de protones usado como antiácido en la práctica diaria. Actúa uniéndose en forma covalente a la enzima de membrana H+/K+ ATPasa en la etapa final de la estimulación secretora. En pacientes adultos y pediátricos se describen cambios en la mucosa gástrica con altas dosis en cortos periodos de tiempo.Facultad de Ciencias Médica
Ab Initio Nuclear Thermodynamics
We propose a new Monte Carlo method called the pinhole trace algorithm for ab initio calculations of the thermodynamics of nuclear systems. For typical simulations of interest, the computational speedup relative to conventional grand-canonical ensemble calculations can be as large as a factor of one thousand. Using a leading-order effective interaction that reproduces the properties of many atomic nuclei and neutron matter to a few percent accuracy, we determine the location of the critical point and the liquid-vapor coexistence line for symmetric nuclear matter with equal numbers of protons and neutrons. We also present the first ab initio study of the density and temperature dependence of nuclear clustering
Artificial graphene as a tunable Dirac material
Artificial honeycomb lattices offer a tunable platform to study massless
Dirac quasiparticles and their topological and correlated phases. Here we
review recent progress in the design and fabrication of such synthetic
structures focusing on nanopatterning of two-dimensional electron gases in
semiconductors, molecule-by-molecule assembly by scanning probe methods, and
optical trapping of ultracold atoms in crystals of light. We also discuss
photonic crystals with Dirac cone dispersion and topologically protected edge
states. We emphasize how the interplay between single-particle band structure
engineering and cooperative effects leads to spectacular manifestations in
tunneling and optical spectroscopies.Comment: Review article, 14 pages, 5 figures, 112 Reference
Properties of Graphene: A Theoretical Perspective
In this review, we provide an in-depth description of the physics of
monolayer and bilayer graphene from a theorist's perspective. We discuss the
physical properties of graphene in an external magnetic field, reflecting the
chiral nature of the quasiparticles near the Dirac point with a Landau level at
zero energy. We address the unique integer quantum Hall effects, the role of
electron correlations, and the recent observation of the fractional quantum
Hall effect in the monolayer graphene. The quantum Hall effect in bilayer
graphene is fundamentally different from that of a monolayer, reflecting the
unique band structure of this system. The theory of transport in the absence of
an external magnetic field is discussed in detail, along with the role of
disorder studied in various theoretical models. We highlight the differences
and similarities between monolayer and bilayer graphene, and focus on
thermodynamic properties such as the compressibility, the plasmon spectra, the
weak localization correction, quantum Hall effect, and optical properties.
Confinement of electrons in graphene is nontrivial due to Klein tunneling. We
review various theoretical and experimental studies of quantum confined
structures made from graphene. The band structure of graphene nanoribbons and
the role of the sublattice symmetry, edge geometry and the size of the
nanoribbon on the electronic and magnetic properties are very active areas of
research, and a detailed review of these topics is presented. Also, the effects
of substrate interactions, adsorbed atoms, lattice defects and doping on the
band structure of finite-sized graphene systems are discussed. We also include
a brief description of graphane -- gapped material obtained from graphene by
attaching hydrogen atoms to each carbon atom in the lattice.Comment: 189 pages. submitted in Advances in Physic
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