3,355 research outputs found
Electron spin resonance shifts in S=1 antiferromagnetic chains
We discuss electron spin resonance (ESR) shifts in spin-1 Heisenberg
antiferromagnetic chains with a weak single-ion anisotropy based on several
effective field theories, the O(3) nonlinear sigma model (NLSM) in the Haldane
phase, free fermion theories around the lower and the upper critical fields. In
the O(3) NLSM, the single-ion anisotropy corresponds to a composite operator
which creates two magnons at the same time and position. Therefore, even inside
a parameter range where free magnon approximation is valid, we have to take
interactions among magnons into account. Though the O(3) NLSM is only valid in
the Haldane phase, an appropriate translation of Faddeev-Zamolodchikov
operators of the O(3) NLSM to fermion operators enables one to treat ESR shifts
near the lower critical field in a similar manner to discussions in Haldane
phase. We present that our theory gives quantitative agreements with recent ESR
experimental results on an spin-1 chain compounds NDMAP
Junctions of three quantum wires and the dissipative Hofstadter model
We study a junction of three quantum wires enclosing a magnetic flux. This is
the simplest problem of a quantum junction between Tomonaga-Luttinger liquids
in which Fermi statistics enter in a non-trivial way. We present a direct
connection between this problem and the dissipative Hofstadter problem, or
quantum Brownian motion in two dimensions in a periodic potential and an
external magnetic field, which in turn is connected to open string theory in a
background electromagnetic field. We find non-trivial fixed points
corresponding to a chiral conductance tensor leading to an asymmetric flow of
the current.Comment: 4 pages, 1 figur
Calculation of transition probabilities and ac Stark shifts in two-photon laser transitions of antiprotonic helium
Numerical ab initio variational calculations of the transition probabilities
and ac Stark shifts in two-photon transitions of antiprotonic helium atoms
driven by two counter-propagating laser beams are presented. We found that
sub-Doppler spectroscopy is in principle possible by exciting transitions of
the type (n,L)->(n-2,L-2) between antiprotonic states of principal and angular
momentum quantum numbers n~L-1~35, first by using highly monochromatic,
nanosecond laser beams of intensities 10^4-10^5 W/cm^2, and then by tuning the
virtual intermediate state close (e.g., within 10-20 GHz) to the real state
(n-1,L-1) to enhance the nonlinear transition probability. We expect that ac
Stark shifts of a few MHz or more will become an important source of systematic
error at fractional precisions of better than a few parts in 10^9. These shifts
can in principle be minimized and even canceled by selecting an optimum
combination of laser intensities and frequencies. We simulated the resonance
profiles of some two-photon transitions in the regions n=30-40 of the
\bar{p}^4He^+ and \bar{p} ^3He^+ isotopes to find the best conditions that
would allow this.Comment: 18 pages 2 tables 12 figures, submitted to Phys. Rev.
Classical Nonrelativistic Effective Field Theory and the Role of Gravitational Interactions
Coherent oscillation of axions or axion-like particles may give rise to
long-lived clumps, called axion stars, because of the attractive gravitational
force or its self-interaction. Such a kind of configuration has been
extensively studied in the context of oscillons without the effect of gravity,
and its stability can be understood by an approximate conservation of particle
number in a non-relativistic effective field theory (EFT). We extend this
analysis to the case with gravity to discuss the longevity of axion stars and
clarify the EFT expansion scheme in terms of gradient energy and Newton's
constant. Our EFT is useful to calculate the axion star configuration and its
classical lifetime without any ad hoc assumption. In addition, we derive a
simple stability condition against small perturbations. Finally, we discuss the
consistency of other non-relativistic effective field theories proposed in the
literature.Comment: 37 pages, 3 figure
Asymmetric function theory
The classical theory of symmetric functions has a central position in
algebraic combinatorics, bridging aspects of representation theory,
combinatorics, and enumerative geometry. More recently, this theory has been
fruitfully extended to the larger ring of quasisymmetric functions, with
corresponding applications. Here, we survey recent work extending this theory
further to general asymmetric polynomials.Comment: 36 pages, 8 figures, 1 table. Written for the proceedings of the
Schubert calculus conference in Guangzhou, Nov. 201
Boundary Critical Phenomena in SU(3) "Spin" Chains
SU(3)-invariant "spin" chains with a single impurity, such as a modified
exchange coupling on one link, are analyzed using boundary conformal field
theory techniques. These chains are equivalent to a special case of the "tJV"
model, i.e. the t-J model with a nearest neighbour repulsion added. In the
continuum limit they are equivalent to two free bosons at a special value of
the compactification radii. The SU(3) symmetry, which is made explicit in this
formulation, provides insight into the exact solution of a non-trivial boundary
critical point found earlier in another formulation of this model as a theory
of quantum Brownian motion.Comment: 19 pages, Rev Te
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