3,809 research outputs found
Spin Chains with Periodic Array of Impurities
We investigate the spin chain model composed of periodic array of two kinds
of spins and , which allows us to study the spin chains with
impurities as well as the alternating spin chains in a unified fashion. By
using the Lieb-Shultz-Mattis theorem, we first study the model rigorously, and
then by mapping it to the non-linear sigma model, we extensively investigate
low-energy properties with particular emphasis on the competition between the
massive and massless phases.Comment: 5 pages, revtex, To appear in PR
Prepotential of Supersymmetric Yang-Mills Theories in the Weak Coupling Region
We show how to obtain the explicite form of the low energy quantum effective
action for supersymmetric Yang-Mills theory in the weak coupling region
from the underlying hyperelliptic Riemann surface. This is achieved by
evaluating the integral representation of the fields explicitly. We calculate
the leading instanton corrections for the group SU(\nc), SO(N) and
and find that the one-instanton contribution of the prepotentials for the these
group coincide with the one obtained recently by using the direct instanton
caluculation.Comment: 13 pages, LaTe
Fuzzy Algebrae of the General Kaehler Coset Space G/H\otimesU(1)^k
We study the fuzzy structure of the general Kaehler coset space
G/S\otimes{U(1)}^k deformed by the Fedosov formalism. It is shown that the
Killing potentials satisfy the fuzzy algebrae working in the Darboux
coordinates.Comment: 8 pages, LaTex, no figur
Prepotentials, Bi-linear Forms on Periods and Enhanced Gauge Symmetries in Type-II Strings
We construct a bi-linear form on the periods of Calabi-Yau spaces. These are
used to obtain the prepotentials around conifold singularities in type-II
strings compactified on Calabi-Yau space. The explicit construction of the
bi-linear forms is achieved for the one-moduli models as well as two moduli
models with K3-fibrations where the enhanced gauge symmetry is known to be
observed at conifold locus. We also show how these bi-linear forms are related
with the existence of flat coordinates. We list the resulting prepotentials in
two moduli models around the conifold locus, which contains alpha' corrections
of 4-D N=2 SUSY SU(2) Yang-Mills theory as the stringy effect.Comment: Latex file(34pp), a reference added, typos correcte
Ground-State Phase Diagram of the Two-Dimensional Extended Bose-Hubbard Model
We investigate the ground-state phase diagram of the soft-core Bose-Hubbard
model with the nearest-neighbor repulsion on a square lattice by using an
unbiased quantum Monte Carlo method. In contrast to the previous study[P.
Sengupta {\it et. al.}, Phys. Rev. Lett. {\bf 94}, 207202 (2005)], we present
the ground-state phase diagrams up to large hopping parameters. As a result, in
addition to the known supersolid above half-filling, we find supersolid even
below and at half-filling for large hopping parameters. Furthermore, for the
strong nearest-neighbor repulsion, we show that the supersolid phase occupies a
remarkably broad region in the phase diagram. The results are in qualitative
agreement with that obtained by the Gutzwiller mean-field approximation[M.
Iskin, Phys. Rev. A {\bf 83}, 051606(R) (2011) and T. Kimura, Phys. Rev. A {\bf
84}, 063630 (2011)]
Unwrapping of DNA-protein complexes under external stretching
A DNA-protein complex modelled by a semiflexible chain and an attractive
spherical core is studied in the situation when an external stretching force is
acting on one end monomer of the chain while the other end monomer is kept
fixed in space. Without stretching force, the chain is wrapped around the core.
By applying an external stretching force, unwrapping of the complex is induced.
We study the statics and the dynamics of the unwrapping process by computer
simulation and simple phenomenological theory. We find two different scenarios
depending on the chain stiffness: For a flexible chain, the extension of the
complex scales linearly with the external force applied. The sphere-chain
complex is disordered, i.e. there is no clear winding of the chain around the
sphere. For a stiff chain, on the other hand, the complex structure is ordered,
which is reminiscent to nucleosome. There is a clear winding number and the
unwrapping process under external stretching is discontinuous with jumps of the
distance-force curve. This is associated to discrete unwinding processes of the
complex. Our predictions are of relevance for experiments, which measure
force-extension curves of DNA-protein complexes, such as nucleosome, using
optical tweezers.Comment: 8 pages, 7 figure
Ring polymers in melts and solutions: scaling and crossover
We propose a simple mean-field theory for the structure of ring polymer
melts. By combining the notion of topological volume fraction and a classical
van der Waals theory of fluids, we take into account many body effects of
topological origin in dense systems. We predict that although the compact
statistics with the Flory exponent is realized for very long chains,
most practical cases fall into the crossover regime with the apparent exponent
during which the system evolves toward a topological dense-packed
limit.Comment: 4 pages, 3 figure
Efficient Hamiltonian programming in qubit arrays with nearest-neighbour couplings
We consider the problem of selectively controlling couplings in a practical
quantum processor with always-on interactions that are diagonal in the
computational basis, using sequences of local NOT gates. This methodology is
well-known in NMR implementations, but previous approaches do not scale
efficiently for the general fully-connected Hamiltonian, where the complexity
of finding time-optimal solutions makes them only practical up to a few tens of
qubits. Given the rapid growth in the number of qubits in cutting-edge quantum
processors, it is of interest to investigate the applicability of this control
scheme to much larger scale systems with realistic restrictions on
connectivity. Here we present an efficient scheme to find near time-optimal
solutions that can be applied to engineered qubit arrays with local
connectivity for any number of qubits, indicating the potential for practical
quantum computing in such systems.Comment: 5 pages, 5 figures. Shortened and clarified from previous versio
Isovector multiphonon excitations in near spherical nuclei
The lowest isoscalar and isovector quadrupole and octupole excitations in
near spherical nuclei are studied within the the proton-neutron version of the
interacting boson model including quadrupole and octupole bosons (sdf-IBM-2).
The main decay modes of these states in near spherical nuclei are discussed.Comment: 4 pages, 1 figure, LaTeX, sprocl, epsfig. Proc. Int. Conf. on
Structure of the Nucleus at the Dawn of the Century (Bologna, 29 May - 3 June
2000); in pres
- …