Gap ratio in anharmonic charge-density-wave systems

Many experimental systems exist that possess charge-density-wave order in their ground state. While this order should be able to be described with models similar to those used for superconductivity, nearly all systems have a ratio of the charge-density-wave order parameter to the transition temperature that is too high for conventional theories. Recent work explained how this can happen in harmonic systems, but when the lattice distortion gets large, anharmonic effects must play an increasingly important role. Here we study the gap ratio for anharmonic charge-density wave systems to see whether the low-temperature properties possess universality as was seen previously in the transition temperature and to see whether the explanation for the large gap ratios survives for anharmonic systems as well.Comment: (5 pages, 3 figures, ReVTeX

Electronic dynamic Hubbard model: exact diagonalization study

A model to describe electronic correlations in energy bands is considered. The model is a generalization of the conventional Hubbard model that allows for the fact that the wavefunction for two electrons occupying the same Wannier orbital is different from the product of single electron wavefunctions. We diagonalize the Hamiltonian exactly on a four-site cluster and study its properties as function of band filling. The quasiparticle weight is found to decrease and the quasiparticle effective mass to increase as the electronic band filling increases, and spectral weight in one- and two-particle spectral functions is transfered from low to high frequencies as the band filling increases. Quasiparticles at the Fermi energy are found to be more 'dressed' when the Fermi level is in the upper half of the band (hole carriers) than when it is in the lower half of the band (electron carriers). The effective interaction between carriers is found to be strongly dependent on band filling becoming less repulsive as the band filling increases, and attractive near the top of the band in certain parameter ranges. The effective interaction is most attractive when the single hole carriers are most heavily dressed, and in the parameter regime where the effective interaction is attractive, hole carriers are found to 'undress', hence become more like electrons, when they pair. It is proposed that these are generic properties of electronic energy bands in solids that reflect a fundamental electron-hole asymmetry of condensed matter. The relation of these results to the understanding of superconductivity in solids is discussed.Comment: Small changes following referee's comment

Associations of psychological thriving with coping efficacy, expectations for future growth, and depressive symptoms over time in people with arthritis.

OBJECTIVE: Psychological thriving reflects a trajectory of growth over time as opposed to scaling back expectations. Whether thriving is a product, precursor, or process of coping with arthritis-related limitations is unclear. We examined associations between thriving, coping efficacy, and expectations for future growth in individuals with arthritis, and the relations of thriving to depressive symptoms and retrospective perceptions of personal growth over a six-month period. METHODS: A sample of 423 people with arthritis completed measures of thriving, coping efficacy, depressive symptoms, and expectations for future growth; 168 individuals completed a six-month follow-up survey. Structural equation modeling analyses compared three possible models of psychological thriving, controlling for disease-related variables. Hierarchical regression analyses of the cross-lagged associations of thriving with retrospective perceptions of positive personal change and depressive symptoms were also conducted. RESULTS: Structural equation analyses suggest that the process model in which thriving and coping efficacy jointly predicted expectations for future growth best fit the data. Baseline thriving was also associated with retrospective perceptions of personal growth at follow-up and fewer depressive symptoms at baseline and follow-up, after controlling for disease-related variables. CONCLUSION: Overall, these findings suggest that psychological thriving is synergistically related to coping efficacy, and to expectations for future growth and less depression, in people with arthritis. Importantly, our findings support the notion that psychological thriving is more than scaling back expectations, and that thriving may be an important quality to cultivate to address the burden of depression in people with arthritis

Hope and fatigue in chronic illness: The role of perceived stress

Fatigue is a debilitating symptom of chronic illness that is deleteriously affected by perceived stress, a process particularly relevant to inflammatory disease. Hopefulness, a goal-based motivational construct, may beneficially influence stress and fatigue, yet little research has examined these associations. We assessed the relation between hope and fatigue, and the mediating effect of stress, in individuals with fibromyalgia, arthritis, and inflammatory bowel disease. Covarying age, sex, and pain, stress partially mediated the association between hope and fatigue; those with greater hope reported less stress and consequent fatigue. Therapeutically, bolstering hope may allow proactive management of stressors, resulting in less fatigue

Functional impairment and depressive symptoms in older adults: Mitigating effects of hope.

OBJECTIVES: We examined trait hopefulness and its component subscales of agency and pathways as potential moderators of the association between functional impairment and depressive symptoms, hypothesizing that hopefulness would buffer this association. DESIGN: Cross-sectional, interview-based. METHODS: Older adult, primary care patients (N= 105; 62% female) completed measures of cognitive functioning, functional impairment, medical illness burden, trait hope, and depressive symptoms. RESULTS: Functional impairment was significantly positively associated with depressive symptoms and dispositional hope total score moderated this relationship. Independently, the pathways subscale was a significant moderator and agency neared significance, yet their interaction was not significant. CONCLUSIONS: Older adults with functional impairment appear to benefit from agency and pathways; either subcomponent alone or their additive effect can activate hopefulness. Facilitation of infrastructure (pathways), primarily, and self-efficacy (agency), secondarily, may be important strategies for reducing depressive symptoms in elderly patients with functional impairment

Effective R-parity violation from supersymmetry breaking

We present a scenario in which Yukawa-like R-parity violating (RPV) couplings are naturally suppressed. In our framework, RPV is assumed to originate from the SUSY breaking mechanism and then transmitted into the SUSY Lagrangian only through soft SUSY breaking operators in the scalar potential. The RPV Yukawa-like operators of the superpotential, conventionally parametrized by the couplings \lambda, \lambda' and \lambda'', are then generated through loops containing the SUSY scalars, the gauginos and the soft RPV interactions and are, therefore, manifest as effective operators with a typical strength of order 10^{-3}.Comment: 4 pages, 2 figures, Revtex4. Main changes with respect to Version 1 are: improved discussions on RGE effects, discussion added on neutrino masses, a toy model added for the proposed scenario. Conclusions remain unchanged. As will appear in Phys. Rev.

Health beliefs, attitudes, and health-related quality of life in persons with fibromyalgia : mediating role of treatment adherence

Fibromyalgia is a chronic illness characterized by pain and fatigue. Persons with fibromyalgia experience increased the risk for poor mental and physical health-related quality of life, which may be dependent on multiple factors, including health beliefs, such as confidence in physicians and the health-care system, and health behaviors, such as treatment adherence. Respondents with fibromyalgia (n = 409) were recruited nationally, via support organizations, and completed self-report measures: Multidimensional Health Profile – Health Functioning Index (MHP-H), Short-Form-36 Health Survey (SF-36v2), and Medical Outcomes Study (MOS) Measure of Patient Adherence – General Adherence Items. In mediation models, belief in the healthcare system and health-care personnel, and health efficacy exerted an indirect effect through treatment adherence on mental and physical quality of life. Adaptive health beliefs and attitudes were related to greater treatment adherence and, in turn, to a better quality of life. Maladaptive health beliefs and mistrusting attitudes about physician-level and systemic-level healthcare provision are negatively related to both treatment adherence and consequent physical and mental health-related quality of life in persons with fibromyalgia. Future randomized controlled trials are needed to determine if therapeutic strategies to alter health values might improve adherence and self-rated health

Self-compassion and suicide risk in veterans : when the going gets tough, do the tough benefit more from self-kindness?

Objectives: Veterans are at particular risk for suicide due to psychopathological, emotional, and interpersonal risk factors. However, the presence of individual-level protective factors, such as self-compassion, may reduce risk, becoming more salient at increasing levels of distress and psychopathology, per theory. We examined the relation between self-compassion and suicide risk, and the moderating effects of depression, PTSD symptoms, anger, shame, and thwarted interpersonal needs. Methods: Our sample of United States veterans (n=541) in our cross-sectional study were mostly male (69.1%) with an average age of 49.90 (SD=16.78), who completed online self-report measures: Suicidal Behaviors Questionnaire-Revised, Multidimensional Health Profile-Psychosocial Functioning Screening Tool, PTSD Checklist-Military Version, Differential Emotions Scale-IV, and the Interpersonal Needs Questionnaire. Results: The linkage between self-compassion and suicidal behavior in our veteran sample was moderated by distress-evoking risk factors, including depression, anger, shame, and thwarted interpersonal needs, such that, as level of risk severity increases, the inverse association between self-compassion and suicidal behavior is strengthened. Conclusions: Our findings highlight an emergent protective process that may prevent suicide in times of distress. Therapeutically bolstering the ability for self-compassion may provide a proactive coping strategy that can be brought to bear in times of crisis, reducing suicide risk for veterans

Effects of Boson Dispersion in Fermion-Boson Coupled Systems

We study the nonlinear feedback in a fermion-boson system using an extension of dynamical mean-field theory and the quantum Monte Carlo method. In the perturbative regimes (weak-coupling and atomic limits) the effective interaction among fermions increases as the width of the boson dispersion increases. In the strong coupling regime away from the anti-adiabatic limit, the effective interaction decreases as we increase the width of the boson dispersion. This behavior is closely related with complete softening of the boson field. We elucidate the parameters that control this nonperturbative region where fluctuations of the dispersive bosons enhance the delocalization of fermions.Comment: 14 pages RevTeX including 12 PS figure

Symmetry breaking in the Hubbard model at weak coupling

The phase diagram of the Hubbard model is studied at weak coupling in two and three spatial dimensions. It is shown that the Neel temperature and the order parameter in d=3 are smaller than the Hartree-Fock predictions by a factor of q=0.2599. For d=2 we show that the self-consistent (sc) perturbation series bears no relevance to the behavior of the exact solution of the Hubbard model in the symmetry-broken phase. We also investigate an anisotropic model and show that the coupling between planes is essential for the validity of mean-field-type order parameters