2,774 research outputs found
Quantum spin glass in anisotropic dipolar systems
The spin-glass phase in the \LHx compound is considered. At zero transverse
field this system is well described by the classical Ising model. At finite
transverse field deviations from the transverse field quantum Ising model are
significant, and one must take properly into account the hyperfine
interactions, the off-diagonal terms in the dipolar interactions, and details
of the full J=8 spin Hamiltonian to obtain the correct physical picture. In
particular, the system is not a spin glass at finite transverse fields and does
not show quantum criticality.Comment: 6 pages, 2 figures, to appear in J. Phys. Condens. Matter
(proceedings of the HFM2006 conference
Quantum spin glass and the dipolar interaction
Systems in which the dipolar energy dominates the magnetic interaction, and
the crystal field generates strong anisotropy favoring the longitudinal
interaction terms, are considered. Such systems in external magnetic field are
expected to be a good experimental realization of the transverse field Ising
model. With random interactions this model yields a spin glass to paramagnet
phase transition as function of the transverse field. Here we show that the
off-diagonal dipolar interaction, although effectively reduced, destroys the
spin glass order at any finite transverse field. Moreover, the resulting
correlation length is shown to be small near the crossover to the paramagnetic
phase, in agreement with the behavior of the nonlinear susceptibility in the
experiments on \LHx. Thus, we argue that the in these experiments a
cross-over to the paramagnetic phase, and not quantum criticality, was
observed.Comment: To appear in Phys. Rev. Let
Semi-leptonic (1968) decays as a scalar meson probe
The unusual multiplet structures associated with the light spin zero mesons
have recently attracted a good deal of theoretical attention. Here we discuss
some aspects associated with the possibility of getting new experimental
information on this topic from semi-leptonic decays of heavy charged mesons
into an isosinglet scalar or pseudoscalar plus leptons.Comment: 11 pages, 4 figure
Doubly perturbed neutrinos and the mixing parameter
We further study a predictive model for the masses and mixing matrix of three
Majorana neutrinos. At zeroth order the model yielded degenerate neutrinos and
a generalized ``tribimaximal" mixing matrix. At first order the mass
splitting was incorporated and the tribimaximal mixing matrix emerged with
very small corrections but with a zero value for the parameter . In the
present paper a different, assumed weaker, perturbation is included which gives
a non zero value for and further corrections to other quantities.
These corrections are worked out and their consequences discussed under the
simplifying assumption that the conventional CP violation phase vanishes. It is
shown that the existing measurements of the parameter provide strong
bounds on in this model.Comment: 8 page
Comment on ``Confirmation of the Sigma Meson''
We comment on the recent paper by N.A. Tornqvist and M. Roos published in
Phys. Rev. Lett. 76, 1575 (1996).Comment: 3 pages (LaTeX), 1 PostScript Figur
An approach to permutation symmetry for the electroweak theory
The form of the leptonic mixing matrix emerging from experiment has, in the
last few years, generated a lot of interest in the so-called tribimaximal type.
This form may be naturally associated with the possibility of a discrete
permutation symmetry () among the three generations. However, trying to
implement this attractive symmetry has resulted in some problems and it seems
to have fallen out of favor. We suggest an approach in which the holds to
first approximation, somewhat in the manner of the old SU(3) flavor symmetry of
the three flavor quark model. It is shown that in the case of the neutrino
sector, a presently large experimentally allowed region can be fairly well
described in this first approximation.
We briefly discuss the nature of the perturbations which are the analogs of
the Gell-Mann Okubo perturbations but confine our attention for the most part
to the invariant model. We postulate that the invariant mass
spectrum consists of non zero masses for the and zero masses for
the other charged fermions but approximately degenerate masses for the three
neutrinos. The mixing matrices are assumed to be trivial for the charged
fermions but of tribimaximal type for the neutrinos in the first approximation.
It is shown that this can be implemented by allowing complex entries for the
mass matrix and spontaneous breakdown of the invariance of the
Lagrangian.Comment: 24 pages, 1 figure, minor corrections and acknowledgment added. To
appear in IJM
Case Report: Psychotherapy of a 10-year-old Afghani refugee with post-traumatic stress disorder and dissociative absences.
Violence-related post-traumatic stress disorder (PTSD) in the context of war and terrorism has become an increasingly pressing public health issue relevant to refugee children and families. PTSD and related psychopathology in children can adversely affect all domains of development and, in particular, interfere with learning and socialization. When the experience of violent trauma and related loss is shared with the entire family, resulting impairment and distress may prevent caregivers from being psychologically available to process their traumatized children's emotional communication and otherwise meet their children's developmental needs. When children suffer from PTSD, it may be impossible to put their experience and related thoughts and feelings into words, let alone a coherent narrative. The latter difficulty can be even more pronounced when the child displays dissociative symptoms, possibly signaling a dissociative subtype of PTSD. Thus, the narrative within the child's play during psychotherapy becomes all the more important as an indicator of the child's internal world. This case report is an example both of evaluation and of psychotherapy that is both psychodynamic and trauma-informed with a 10-year-old Afghani boy who suffered the violent loss of his father at age of 3 years, leading to his immigration to Switzerland. This paper addresses the question of how the psychotherapist can accompany the child through the elaboration of his trauma and how the therapist can contribute to the co-construction of a coherent narrative of the child's experience and to the restoration of an intersubjective connection between the traumatized child and caregiver
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