72 research outputs found
Protocol for developing, disseminating and implementing a core outcome set for endometriosis
Peer reviewedPublisher PD
Order-Disorder Transition in a Two-Layer Quantum Antiferromagnet
We have studied the antiferromagnetic order -- disorder transition occurring
at in a 2-layer quantum Heisenberg antiferromagnet as the inter-plane
coupling is increased. Quantum Monte Carlo results for the staggered structure
factor in combination with finite-size scaling theory give the critical ratio
between the inter-plane and in-plane coupling constants.
The critical behavior is consistent with the 3D classical Heisenberg
universality class. Results for the uniform magnetic susceptibility and the
correlation length at finite temperature are compared with recent predictions
for the 2+1-dimensional nonlinear -model. The susceptibility is found
to exhibit quantum critical behavior at temperatures significantly higher than
the correlation length.Comment: 11 pages (5 postscript figures available upon request), Revtex 3.
Disorder Induced Phase Transition in a Random Quantum Antiferromagnet
A two-dimensional Heisenberg model with random antiferromagnetic
nearest-neighbor exchange is studied using quantum Monte Carlo techniques. As
the strength of the randomness is increased, the system undergoes a transition
from an antiferromagnetically ordered ground state to a gapless disordered
state. The finite-size scaling of the staggered structure factor and
susceptibility is consistent with a dynamic exponent .Comment: Revtex 3.0, 10 pages + 5 postscript figures available upon request,
UCSBTH-94-1
Programming Groups of Rational Agents
Abstract. In this paper, we consider the problem of effectively pro-gramming groups of agents. These groups should capture structuring mechanisms common in multi-agent systems, such as teams, cooperative groups, and organisations. Not only should individual agents be dynamic and evolving, but the groups in which the agents occur must be open, flexible and capable of similar evolution and restructuring. We enable the description and implementation of such groups by providing an extension to our previous work on programming languages for agent-based systems based on executable temporal and modal logics. With such formalism as a basis, we consider the grouping aspects within multi-agent systems. In particular, we describe how this logic-based approach to grouping has been implemented in Java and consider how this language can be used for developing multi-agent systems.
Leptogenesis, CP violation and neutrino data: What can we learn?
A detailed analytic and numerical study of baryogenesis through leptogenesis
is performed in the framework of the standard model of electroweak interactions
extended by the addition of three right-handed neutrinos, leading to the seesaw
mechanism. We analyze the connection between GUT-motivated relations for the
quark and lepton mass matrices and the possibility of obtaining a viable
leptogenesis scenario. In particular, we analyze whether the constraints
imposed by SO(10) GUTs can be compatible with all the available solar,
atmospheric and reactor neutrino data and, simultaneously, be capable of
producing the required baryon asymmetry via the leptogenesis mechanism. It is
found that the Just-So^2 and SMA solar solutions lead to a viable leptogenesis
even for the simplest SO(10) GUT, while the LMA, LOW and VO solar solutions
would require a different hierarchy for the Dirac neutrino masses in order to
generate the observed baryon asymmetry. Some implications on CP violation at
low energies and on neutrinoless double beta decay are also considered.Comment: 36 pages, 6 figures; new references added, final version to appear in
Nucl. Phys.
The Interplay Between the "Low" and "High" Energy CP-Violation in Leptogenesis
We analyse within the "flavoured" leptogenesis scenario of baryon asymmetry
generation, the interplay of the "low energy" CP-violation, originating from
the PMNS neutrino mixing matrix , and the "high energy" CP-violation which
can be present in the matrix of neutrino Yukawa couplings, , and can
manifest itself only in "high" energy scale processes. The type I see-saw model
with three heavy right-handed Majorana neutrinos having hierarchical spectrum
is considered. The "orthogonal" parametrisation of the matrix of neutrino
Yukawa couplings, which involves a complex orthogonal matrix , is employed.
In this approach the matrix is the source of "high energy" CP-violation.
Results for normal hierarchical (NH) and inverted hierarchical (IH) light
neutrino mass spectrum are derived in the case of decoupling of the heaviest RH
Majorana neutrino. It is shown that taking into account the contribution to
due to the CP-violating phases in the neutrino mixing matrix can
change drastically the predictions for , obtained assuming only "high
energy" CP-violation from the -matrix is operative in leptogenesis. In the
case of IH spectrum, in particular, there exist significant regions in the
corresponding parameter space where the purely "high energy" contribution in
plays a subdominant role in the production of baryon asymmetry compatible
with the observations.Comment: Results unchanged; comments and references added; version to be
puplished in Eur.Phys.J.
Minimal Scenarios for Leptogenesis and CP Violation
The relation between leptogenesis and CP violation at low energies is
analyzed in detail in the framework of the minimal seesaw mechanism. Working,
without loss of generality, in a weak basis where both the charged lepton and
the right-handed Majorana mass matrices are diagonal and real, we consider a
convenient generic parametrization of the Dirac neutrino Yukawa coupling matrix
and identify the necessary condition which has to be satisfied in order to
establish a direct link between leptogenesis and CP violation at low energies.
In the context of the LMA solution of the solar neutrino problem, we present
minimal scenarios which allow for the full determination of the cosmological
baryon asymmetry and the strength of CP violation in neutrino oscillations.
Some specific realizations of these minimal scenarios are considered. The
question of the relative sign between the baryon asymmetry and CP violation at
low energies is also discussed.Comment: 36 pages, 5 figures; minor corrections and references updated. Final
version to appear in Phys. Rev.
Thermal leptogenesis in a model with mass varying neutrinos
In this paper we consider the possibility of neutrino mass varying during the
evolution of the Universe and study its implications on leptogenesis.
Specifically, we take the minimal seesaw model of neutrino masses and introduce
a coupling between the right-handed neutrinos and the dark energy scalar field,
the Quintessence. In our model, the right-handed neutrino masses change as the
Quintessence scalar evolves. We then examine in detail the parameter space of
this model allowed by the observed baryon number asymmetry. Our results show
that it is possible to lower the reheating temperature in this scenario in
comparison with the case that the neutrino masses are unchanged, which helps
solve the gravitino problem. Furthermore, a degenerate neutrino mass patten
with larger than the upper limit given in the minimal leptogenesis
scenario is permitted.Comment: 18 pages, 7 figures, version to appear in PR
The TESS-keck survey. III. A stellar obliquity measurement of TOI-1726 c
We report the measurement of a spectroscopic transit of TOI-1726c, one of two planets transiting a G-type star with V = 6.9 in the Ursa Major Moving Group (∼400 Myr). With a precise age constraint from cluster membership, TOI-1726 provides a great opportunity to test various obliquity excitation scenarios that operate on different timescales. By modeling the Rossiter-McLaughlin (RM) effect, we derived a sky-projected obliquity of -1-+3235∘. This result rules out a polar/retrograde orbit and is consistent with an aligned orbit for planet c. Considering the previously reported, similarly prograde RM measurement of planet b and the transiting nature of both planets, TOI-1726 tentatively conforms to the overall picture that compact multitransiting planetary systems tend to have coplanar, likely aligned orbits. TOI-1726 is also a great atmospheric target for understanding differential atmospheric loss of sub-Neptune planets (planet b 2.2 R☉ and c 2.7 R☉ both likely underwent photoevaporation). The coplanar geometry points to a dynamically cold history of the system that simplifies any future modeling of atmospheric escape
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