11,954 research outputs found
Perturbative Tamm-Dancoff Renormalization
A new two-step renormalization procedure is proposed. In the first step, the
effects of high-energy states are considered in the conventional (Feynman)
perturbation theory. In the second step, the coupling to many-body states is
eliminated by a similarity transformation. The resultant effective Hamiltonian
contains only interactions which do not change particle number. It is subject
to numerical diagonalization. We apply the general procedure to a simple
example for the purpose of illustration.Comment: 20 pages, RevTeX, 10 figure
Haemoglobin and size dependent constraints on swimbladder inflation in fish larvae
In developmental studies of fish species (especially physostomians) it could be demonstrated,
that the lack of haemoglobin during larval and juvenile stages is a relatively common phenomenon.
Generally it is linked with body translucency. In representatives of the families Galaxiidae,
Osmeridae and Clupeidae, partly reared, partly observed immediately after being caught in the wild, it
turned out, that this condition coincides with a considerable delay in swimbladder inflation. To determine
the moment of its first inflation, larvae placed in a hermetic chamber were observed under a
dissecting microscope. While lowering the pressure, the expanding swimbladder showed whether or
not its content is really gaseous. The reason postulated to be responsible for the delayed inflation is
that larvae lacking haemoglobin do not have the possibility of oxygen transport to their buoyancy
organ by means of the blood. Apart of this, capillarity force calculations and body force estimations
show that with decreasing size the constraints linked with surface tension increase overproportionally.
While in larger sized larvae like trout we could demonstrate inflation by swallowing air, in species with
small larvae this was not the case. Below a certain size, even in physostomians, the ductus pneumaticus
is no alternative to the blood pathway for swimbladder inflation
The Peierls substitution in an engineered lattice potential
Artificial gauge fields open new possibilities to realize quantum many-body
systems with ultracold atoms, by engineering Hamiltonians usually associated
with electronic systems. In the presence of a periodic potential, artificial
gauge fields may bring ultracold atoms closer to the quantum Hall regime. Here,
we describe a one-dimensional lattice derived purely from effective
Zeeman-shifts resulting from a combination of Raman coupling and radiofrequency
magnetic fields. In this lattice, the tunneling matrix element is generally
complex. We control both the amplitude and the phase of this tunneling
parameter, experimentally realizing the Peierls substitution for ultracold
neutral atoms.Comment: 6 pages, 5 figure
Nonperturbative renormalization group in a light-front three-dimensional real scalar model
The three-dimensional real scalar model, in which the symmetry
spontaneously breaks, is renormalized in a nonperturbative manner based on the
Tamm-Dancoff truncation of the Fock space. A critical line is calculated by
diagonalizing the Hamiltonian regularized with basis functions. The marginal
() coupling dependence of the critical line is weak. In the broken
phase the canonical Hamiltonian is tachyonic, so the field is shifted as
. The shifted value is determined as a function of
running mass and coupling so that the mass of the ground state vanishes.Comment: 23 pages, LaTeX, 6 Postscript figures, uses revTeX and epsbox.sty. A
slight revision of statements made, some references added, typos correcte
SHG microscopic observations of polar state in Li-doped KTaO3 under electric field
Incipient ferroelectric KTaO3 with off-center Li impurity of the critical
concentration of 2.8 mol% was investigated in order to clarify the dipole glass
state under electric field. Using optical second-harmonic generation (SHG)
microscope, we observed a marked history dependence of SHG intensity through
zero-field cooling (ZFC), zero-field heating (ZFH), field heating after ZFC
(FH/ZFC) and FH after field cooling (FH/FC). These show different paths with
respect to temperature: In the ZFC/ZFH process, weak SHG was observed at low
temperature, while in the FH/ZFC process, relatively high SHG appears in a
limited temperature range below TF depending on the field strength, and in the
FC and FH/FC processes, the SHG exhibits ferroelectric-like temperature
dependence: it appears at the freezing temperature of 50K, increases with
decreasing temperature and has a tendency of saturation. These experimental
results strongly suggest that dipole glass state or polar nano-clusters which
gradually freezes with decreasing temperature is transformed into
semi-macroscopic polar state under the electric field. However at sufficiently
low temperature, the freezing is so strong that the electric field cannot
enlarge the polar clusters. These experimental results show that the polar
nano-cluster model similar to relaxors would be more relevant in KTaO3 doped
with the critical concentration of Li. Further experiments on the anisotropy of
SHG determine that the average symmetry of the field-induced polar phase is
tetragonal 4mm or 4, which is also confirmed by the X-ray diffraction
measurement.Comment: 26 pages, 8 figures, 1 tabl
Glueballs in a Hamiltonian Light-Front Approach to Pure-Glue QCD
We calculate a renormalized Hamiltonian for pure-glue QCD and diagonalize it.
The renormalization procedure is designed to produce a Hamiltonian that will
yield physical states that rapidly converge in an expansion in free-particle
Fock-space sectors. To make this possible, we use light-front field theory to
isolate vacuum effects, and we place a smooth cutoff on the Hamiltonian to
force its free-state matrix elements to quickly decrease as the difference of
the free masses of the states increases. The cutoff violates a number of
physical principles of light-front pure-glue QCD, including Lorentz covariance
and gauge covariance. This means that the operators in the Hamiltonian are not
required to respect these physical principles. However, by requiring the
Hamiltonian to produce cutoff-independent physical quantities and by requiring
it to respect the unviolated physical principles of pure-glue QCD, we are able
to derive recursion relations that define the Hamiltonian to all orders in
perturbation theory in terms of the running coupling. We approximate all
physical states as two-gluon states, and use our recursion relations to
calculate to second order the part of the Hamiltonian that is required to
compute the spectrum. We diagonalize the Hamiltonian using basis-function
expansions for the gluons' color, spin, and momentum degrees of freedom. We
examine the sensitivity of our results to the cutoff and use them to analyze
the nonperturbative scale dependence of the coupling. We investigate the effect
of the dynamical rotational symmetry of light-front field theory on the
rotational degeneracies of the spectrum and compare the spectrum to recent
lattice results. Finally, we examine our wave functions and analyze the various
sources of error in our calculation.Comment: 75 pages, 17 figures, 1 tabl
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