891 research outputs found
Spin systems with dimerized ground states
In view of the numerous examples in the literature it is attempted to outline
a theory of Heisenberg spin systems possessing dimerized ground states (``DGS
systems") which comprises all known examples. Whereas classical DGS systems can
be completely characterized, it was only possible to provide necessary or
sufficient conditions for the quantum case. First, for all DGS systems the
interaction between the dimers must be balanced in a certain sense. Moreover,
one can identify four special classes of DGS systems: (i) Uniform pyramids,
(ii) systems close to isolated dimer systems, (iii) classical DGS systems, and
(iv), in the case of , systems of two dimers satisfying four
inequalities. Geometrically, the set of all DGS systems may be visualized as a
convex cone in the linear space of all exchange constants. Hence one can
generate new examples of DGS systems by positive linear combinations of
examples from the above four classes.Comment: With corrections of proposition 4 and other minor change
The State-Vector Space for Two-Mode Parabosons and Charged Parabose Coherent States
The structure of the state-vector space for the two-mode parabose system is
investigated and a complete set of state-vectors is constructed. The basis
vectors are orthonormal in order . In order , conserved-charge
parabose coherent states are constructed and an explicit completeness relation
is obtained.Comment: 13 pages, LaTeX file, no figures and no macro
Coherent states for the hydrogen atom
We construct wave packets for the hydrogen atom labelled by the classical
action-angle variables with the following properties. i) The time evolution is
exactly given by classical evolution of the angle variables. (The angle
variable corresponding to the position on the orbit is now non-compact and we
do not get exactly the same state after one period. However the gross features
do not change. In particular the wave packet remains peaked around the labels.)
ii) Resolution of identity using this overcomplete set involves exactly the
classical phase space measure. iii) Semi-classical limit is related to
Bohr-Sommerfield quantization. iv) They are almost minimum uncertainty wave
packets in position and momentum.Comment: 9 pages, 2 figures, minor change in language and journal reference
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The Heisenberg antiferromagnet on an anisotropic triangular lattice: linear spin-wave theory
We consider the effect of quantum spin fluctuations on the ground state
properties of the Heisenberg antiferromagnet on an anisotropic triangular
lattice using linear spin-wave theory. This model should describe the magnetic
properties of the insulating phase of the kappa-(BEDT-TTF)_2 X family of
superconducting molecular crystals. The ground state energy, the staggered
magnetization, magnon excitation spectra and spin-wave velocities are computed
as a function of the ratio between the second and first neighbours, J2/J1. We
find that near J2/J1 = 0.5, i.e., in the region where the classical spin
configuration changes from a Neel ordered phase to a spiral phase, the
staggered magnetization vanishes, suggesting the possibility of a quantum
disordered state. In this region, the quantum correction to the magnetization
is large but finite. This is in contrast to the frustrated Heisenberg model on
a square lattice, for which the quantum correction diverges logarithmically at
the transition from the Neel to the collinear phase. For large J2/J1, the model
becomes a set of chains with frustrated interchain coupling. For J2 > 4 J1, the
quantum correction to the magnetization, within LSW, becomes comparable to the
classical magnetization, suggesting the possibility of a quantum disordered
state. We show that, in this regime, quantum fluctuations are much larger than
for a set of weakly coupled chains with non-frustated interchain coupling.Comment: 10 pages, RevTeX + epsf, 5 figures Replaced with published version.
Comparison to series expansions energies include
Search for binary black hole mergers in the third observing run of Advanced LIGO-Virgo using coherent WaveBurst enhanced with machine learning
In this work, we use the coherent WaveBurst (cWB) pipeline enhanced with machine learning (ML) to search for binary black hole (BBH) mergers in the Advanced LIGO-Virgo strain data from the third observing run. We detect, with equivalent or higher significance, all gravitational-wave (GW) events previously reported by the standard cWB search for BBH mergers in the third GW Transient Catalog. The ML-enhanced cWB search identifies five additional GW candidate events from the catalog that were previously missed by the standard cWB search. Moreover, we identify three marginal candidate events not listed in third GW Transient Catalog. For simulated events distributed uniformly in a fiducial volume, we improve the sensitive hypervolume with respect to the standard cWB search by approximately 28% and 34% for the stellar-mass and intermediate mass black hole binary mergers respectively, detected with a false-alarm rate less than 1/100 yr-1. We show the robustness of the ML-enhanced search for detection of generic BBH signals by reporting increased sensitivity to the spin-precessing and eccentric BBH events as compared to the standard cWB search. Furthermore, we compare the improvement of the ML-enhanced cWB search for different detector networks
Coherent states for the hydrogen atom: discrete and continuous spectra
We construct the systems of generalised coherent states for the discrete and
continuous spectra of the hydrogen atom. These systems are expressed in
elementary functions and are invariant under the (discrete spectrum)
and (continuous spectrum) subgroups of the dynamical symmetry group
of the hydrogen atom. Both systems of coherent states are particular
cases of the kernel of integral operator which interwines irreducible
representations of the group.Comment: 15 pages, LATEX, minor sign corrections, to appear in J.Phys.
Reassessing candidate eccentric binary black holes: Results with a model including higher-order modes
The detection of eccentricity from a gravitational wave signal is expected to
help distinguish between formation channels for a given binary. In this study,
we reassess all previously-reported binary black holes with previous claims of
possible eccentricity as well as a few binaries with more interesting source
parameters, for the first time using a model (TEOBResumSGeneral) which accounts
for the full eccentricity range possible and incorporates higher-order
gravitational emission critical to model emission from highly eccentric orbits.
We estimate the eccentricity of these five events. For the first time, we
present marginal evidence of eccentricity for one of the events: GW190929.
Contrary to previous work with different settings, we do not find evidence
supporting eccentric orbits for the same systems. We find the incorporation of
eccentricity in our analyses dramatically shifts the posterior in multiple
parameters for several events, features could negatively impact other analyses
Correlation search for coherent pion emission in heavy ion collisions
The methods allowing to extract the coherent component of pion emission
conditioned by the formation of a quasi-classical pion source in heavy ion
collisions are suggested. They exploit a nontrivial modification of the quantum
statistical and final state interaction effects on the correlation functions of
like and unlike pions in the presence of the coherent radiation. The extraction
of the coherent pion spectrum from pi+pi-, pi+pi+ and pi-pi- correlation
functions and single--pion spectra is discussed in detail for large expanding
systems produced in ultra-relativistic heavy ion collisions.Comment: 21 pages, 3 eps figures, ReVTeX, corrected submission abstract.
Version published in PRC 65 (2002) 064904. Added is a detailed explanation of
the differences between pure coherent states and charge constrained coherent
states in the case of a simple example model. The expressions for
two-particle spectra taking into account both the final state interaction and
the coherent component of pion emission are derived in a more general and
transparent wa
Ownership identity, strategy and performance:business group affiliates versus independent firms in India
We consider whether the impact of entrepreneurial orientation on business performance is moderated by the company affiliation with business groups. Within business groups, we explore the trade-off between inter-firm insurance that enables risk-taking, and inefficient resource allocation. Risk-taking in group affiliated firms leads to higher performance, compared to independent firms, but the impact of proactivity is attenuated. Utilizing Indian data, we show that risk-taking may undermine rather than improve business performance, but this effect is not present in business groups. Proactivity enhances performance, but less so in business groups. Firms can also enhance performance by technological knowledge acquisition, but these effects are not significantly different for various ownership categories
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