Non-linear quantum critical transport and the Schwinger Mechanism

Scaling arguments imply that quantum critical points exhibit universal non-linear responses to external probes. We investigate the origins of such non-linearities in transport, which is especially problematic since the system is necessarily driven far from equilibrium. We argue that for a wide class of systems the new ingredient that enters is the Schwinger mechanism--the production of carriers from the vacuum by the applied field-- which is then balanced against a scattering rate which is itself set by the field. We show by explicit computation how this works for the case of the symmetric superfluid-Mott insulator transition of bosons

Nonlinear quantum critical transport and the Schwinger mechanism for a superfluid-Mott-insulator transition of bosons

Scaling arguments imply that quantum-critical points exhibit universal nonlinear responses to external probes. We investigate the origins of such nonlinearities in transport, which is especially problematic since the system is necessarily driven far from equilibrium. We argue that for a wide class of systems the new ingredient that enters is the Schwinger mechanism-the production of carriers from the vacuum by the applied field-which is then balanced against a scattering rate that is itself set by the field. We show by explicit computation how this works for the case of the symmetric superfluid-Mott insulator transition of bosons

Magnetothermoelectric response at a superfluid-mott-insulator transition (vol 98, art no 166801, 2007)

Publisher’s Note: Magnetothermoelectric Response at a Superfluid–Mott-Insulator Transition [Phys. Rev. Lett. 98, 166801 (2007)

Magnetothermoelectric response at a superfluid-Mott-insulator transition

We investigate the finite temperature magnetothermoelectric response in the vicinity of a superfluid-Mott-insulator quantum phase transition. We focus on the particle-hole symmetric transitions of the Bose-Hubbard model, and combine Lorentz invariance arguments with quantum Boltzmann calculations. By means of an epsilon expansion, we find that a nonvanishing thermoelectric tensor and a finite thermal transport coefficient are supported in this quantum critical regime. We comment on the singular Nernst effect in this problem

Current noise in the vicinity of the 2D superconductor-insulator quantum critical point

Systems near to quantum critical points show universal scaling in response to external probes. We consider whether this scaling is reflected in their out-of-equilibrium fluctuations. We study current noise in the metallic state at the z=1 quantum critical point between a superconductor and an insulator in two dimensions. Using a Boltzmann-Langevin approach within a 1/N expansion, we show that the current noise obeys a universal scaling form S-j=T Phi[T/T-eff(E)], with T-eff proportional to root E. This treatment recovers Johnson noise in thermal equilibrium and S-j proportional to root E at strong electric fields. The latter differs significantly from both the shot noise in conventional metals (diffusive Fermi liquids) and the free carrier result, due to strong correlations between the critical bosonic excitations. Current-noise measurements could therefore help clarify the physics of the destruction of superconductivity in thin film superconductors

Improving health and well-being through community health champions: a thematic evaluation of a programme in Yorkshire and Humber.

AIMS: The contribution that lay people can make to the public health agenda is being increasingly recognised in research and policy literature. This paper examines the role of lay workers (referred to as 'community health champions') involved in community projects delivered by Altogether Better across Yorkshire and Humber. The aim of the paper is to describe key features of the community health champion approach and to examine the evidence that this type of intervention can have an impact on health. METHODS: A qualitative approach was taken to the evaluation, with two strands to gathering evidence: interviews conducted with different stakeholder groups including project leads, key partners from community and statutory sectors and community workers, plus two participatory workshops to gather the views of community health champions. Seven projects (from a possible 12) were identified to be involved in the evaluation. Those projects that allowed the evaluation team to explore fully the champion role (training, infrastructure, etc.) and how that works in practice as a mechanism for empowerment were selected. In total, 29 semi-structured interviews were conducted with project staff and partners, and 30 champions, varying in terms of age, gender, ethnicity and disability, took part in the workshops. RESULTS: Becoming a community health champion has health benefits such as increased self-esteem and confidence and improved well-being. For some champions, this was the start of a journey to other opportunities such as education or paid employment. There were many examples of the influence of champions extending to the wider community of family, friends and neighbours, including helping to support people to take part in community life. Champions recognised the value of connecting people through social networks, group activities, and linking people into services and the impact that that had on health and well-being. Project staff and partners also recognised that champions were promoting social cohesiveness and helping to integrate people into their community. CONCLUSIONS: The recent public health White Paper suggested that the Altogether Better programme is improving individual and community health as well as increasing social capital, voluntary activity and wider civic participation. This evaluation supports this statement and suggests that the community health champion role can be a catalyst for change for both individuals and communities

R^4 counterterm and E7(7) symmetry in maximal supergravity

The coefficient of a potential R^4 counterterm in N=8 supergravity has been shown previously to vanish in an explicit three-loop calculation. The R^4 term respects N=8 supersymmetry; hence this result poses the question of whether another symmetry could be responsible for the cancellation of the three-loop divergence. In this article we investigate possible restrictions from the coset symmetry E7(7)/SU(8), exploring the limits as a single scalar becomes soft, as well as a double-soft scalar limit relation derived recently by Arkani-Hamed et al. We implement these relations for the matrix elements of the R^4 term that occurs in the low-energy expansion of closed-string tree-level amplitudes. We find that the matrix elements of R^4 that we investigated all obey the double-soft scalar limit relation, including certain non-maximally-helicity-violating six-point amplitudes. However, the single-soft limit does not vanish for this latter set of amplitudes, which suggests that the E7(7) symmetry is broken by the R^4 term.Comment: 33 pages, typos corrected, published versio

Stigma of living as an autism carer: a brief psycho-social support intervention (SOLACE). Study protocol for a randomised controlled feasibility study.

Stigma is prominent in the lives of autistic individuals and their families and contributes significantly to the challenges faced by families raising an autistic child. Parents and carers can feel blamed for their child's behaviour, feel socially excluded and isolated and suffer from low self-esteem and poor psychological well-being. This increases the risk of experiencing self-stigma which further exacerbates these and other negative consequences. Therefore, there is a need for interventions that help parents/family carers cope with autism-related stigma as well as prevent the internalisation of stigma. The primary objective of this study is to assess the feasibility and acceptability of a stigma support intervention for parents and carers of autistic children titled 'Stigma of Living as an Autism Carer (SOLACE)'. The secondary objective is to explore the preliminary impact of the intervention on the mental health of the parents and carers. tests for differences within the group. Other outcomes of interest are stigma, self-stigma, self-esteem, self-blame, social isolation, self-compassion and perceived responsibility and control. Results from the feasibility randomised controlled trial will be used to refine the study protocol and inform the design of an intervention for future use in a larger, powered trial. SOLACE could potentially improve the psychological well-being of parents/family carers of autistic children through increased resistance to stigma. ISRCTN Registry number ISRCTN61093625 (October 13, 2017)

Evolution of Plasma Composition in an Eruptive Flux Rope

Magnetic flux ropes are bundles of twisted magnetic field enveloping a central axis. They harbor free magnetic energy and can be progenitors of coronal mass ejections (CMEs). However, identifying flux ropes on the Sun can be challenging. One of the key coronal observables that has been shown to indicate the presence of a flux rope is a peculiar bright coronal structure called a sigmoid. In this work, we show Hinode EUV Imaging Spectrometer observations of sigmoidal active region (AR) 10977. We analyze the coronal plasma composition in the AR and its evolution as a sigmoid (flux rope) forms and erupts as a CME. Plasma with photospheric composition was observed in coronal loops close to the main polarity inversion line during episodes of significant flux cancellation, suggestive of the injection of photospheric plasma into these loops driven by photospheric flux cancellation. Concurrently, the increasingly sheared core field contained plasma with coronal composition. As flux cancellation decreased and a sigmoid/flux rope formed, the plasma evolved to an intermediate composition in between photospheric and typical AR coronal compositions. Finally, the flux rope contained predominantly photospheric plasma during and after a failed eruption preceding the CME. Hence, plasma composition observations of AR 10977 strongly support models of flux rope formation by photospheric flux cancellation forcing magnetic reconnection first at the photospheric level then at the coronal level