176,497 research outputs found
From Popov-Fedotov trick to universal fermionization
We show that Popov-Fedotov trick of mapping spin-1/2 lattice systems on
two-component fermions with imaginary chemical potential readily generalizes to
bosons with a fixed (but not limited) maximal site occupation number, as well
as to fermionic Hamiltonians with various constraints on the site Fock states.
In a general case, the mapping---fermionization---is on multi-component
fermions with many-body non-Hermitian interactions. Additionally, the
fermionization approach allows one to convert large many-body couplings into
single-particle energies, rendering the diagrammatic series free of large
expansion parameters; the latter is essential for the efficiency and
convergence of the diagrammatic Monte Carlo method.Comment: 4 pages, no figures (v2 contains some improvements; the most
important one is the generic complex chemical potential trick for
spins/bosons
Diffusion of solar cosmic rays and the power spectrum of the interplanetary magnetic field
Solar cosmic ray diffusion and interplanetary magnetic field power spectru
Schwinger-Dyson equations in large-N quantum field theories and nonlinear random processes
We propose a stochastic method for solving Schwinger-Dyson equations in
large-N quantum field theories. Expectation values of single-trace operators
are sampled by stationary probability distributions of the so-called nonlinear
random processes. The set of all histories of such processes corresponds to the
set of all planar diagrams in the perturbative expansions of the expectation
values of singlet operators. We illustrate the method on the examples of the
matrix-valued scalar field theory and the Weingarten model of random planar
surfaces on the lattice. For theories with compact field variables, such as
sigma-models or non-Abelian lattice gauge theories, the method does not
converge in the physically most interesting weak-coupling limit. In this case
one can absorb the divergences into a self-consistent redefinition of expansion
parameters. Stochastic solution of the self-consistency conditions can be
implemented as a "memory" of the random process, so that some parameters of the
process are estimated from its previous history. We illustrate this idea on the
example of two-dimensional O(N) sigma-model. Extension to non-Abelian lattice
gauge theories is discussed.Comment: 16 pages RevTeX, 14 figures; v2: Algorithm for the Weingarten model
corrected; v3: published versio
Radio Quiet Pulsars with Ultra-Strong Magnetic Fields
The notable absence of radio pulsars having measured magnetic dipole surface
field strengths above Gauss naturally raises the
question of whether this forms an upper limit to pulsar magnetization. Recently
there has been increasing evidence that neutron stars possessing higher dipole
spin-down fields do in fact exist, including a growing list of anomalous X-ray
pulsars (AXPs) with long periods and spinning down with high period
derivatives, implying surface fields of -- Gauss.
Furthermore, the recently reported X-ray period and period derivative for the
Soft Gamma-ray Repeater (SGR) source SGR1806-20 suggest a surface field around
Gauss. None of these high-field pulsars have yet been detected as
radio pulsars. We propose that high-field pulsars should be radio-quiet because
electron-positron pair production in their magnetospheres, thought to be
essential for radio emission, is efficiently suppressed in ultra-strong fields
( Gauss) by the action of photon splitting, a
quantum electrodynamical process in which a photon splits into two. Our
computed radio quiescence boundary in the radio pulsar diagram,
where photon splitting overtakes pair creation, is located just above the
boundary of the known radio pulsar population, neatly dividing them from the
AXPs. We thus identify a physical mechanism that defines a new class of
high-field radio-quiet neutron stars that should be detectable by their pulsed
emission at X-ray and perhaps -ray energies.Comment: 4 pages, including one figure and one table, in AASTeX emulatapj
format, Astrophysical Journal Letters, in pres
Warm water deuterium fractionation in IRAS 16293-2422 - The high-resolution ALMA and SMA view
Measuring the water deuterium fractionation in the inner warm regions of
low-mass protostars has so far been hampered by poor angular resolution
obtainable with single-dish ground- and space-based telescopes. Observations of
water isotopologues using (sub)millimeter wavelength interferometers have the
potential to shed light on this matter. Observations toward IRAS 16293-2422 of
the 5(3,2)-4(4,1) transition of H2-18O at 692.07914 GHz from Atacama Large
Millimeter/submillimeter Array (ALMA) as well as the 3(1,3)-2(2,0) of H2-18O at
203.40752 GHz and the 3(1,2)-2(2,1) transition of HDO at 225.89672 GHz from the
Submillimeter Array (SMA) are presented. The 692 GHz H2-18O line is seen toward
both components of the binary protostar. Toward one of the components, "source
B", the line is seen in absorption toward the continuum, slightly red-shifted
from the systemic velocity, whereas emission is seen off-source at the systemic
velocity. Toward the other component, "source A", the two HDO and H2-18O lines
are detected as well with the SMA. From the H2-18O transitions the excitation
temperature is estimated at 124 +/- 12 K. The calculated HDO/H2O ratio is (9.2
+/- 2.6)*10^(-4) - significantly lower than previous estimates in the warm gas
close to the source. It is also lower by a factor of ~5 than the ratio deduced
in the outer envelope. Our observations reveal the physical and chemical
structure of water vapor close to the protostars on solar-system scales. The
red-shifted absorption detected toward source B is indicative of infall. The
excitation temperature is consistent with the picture of water ice evaporation
close to the protostar. The low HDO/H2O ratio deduced here suggests that the
differences between the inner regions of the protostars and the Earth's oceans
and comets are smaller than previously thought.Comment: Accepted for publication in Astronomy & Astrophysic
Criticality in the configuration-mixed interacting boson model : (1) mixing
The case of U(5)-- mixing in the
configuration-mixed Interacting Boson Model is studied in its mean-field
approximation. Phase diagrams with analytical and numerical solutions are
constructed and discussed. Indications for first-order and second-order shape
phase transitions can be obtained from binding energies and from critical
exponents, respectively
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