152 research outputs found
PT symmetry and large-N models
Recently developed methods for PT-symmetric models can be applied to
quantum-mechanical matrix and vector models. In matrix models, the calculation
of all singlet wave functions can be reduced to the solution a one-dimensional
PT-symmetric model. The large-N limit of a wide class of matrix models exists,
and properties of the lowest-lying singlet state can be computed using WKB. For
models with cubic and quartic interactions, the ground state energy appears to
show rapid convergence to the large-N limit. For the special case of a quartic
model, we find explicitly an isospectral Hermitian matrix model. The Hermitian
form for a vector model with O(N) symmetry can also be found, and shows many
unusual features. The effective potential obtained in the large-N limit of the
Hermitian form is shown to be identical to the form obtained from the original
PT-symmetric model using familiar constraint field methods. The analogous
constraint field prescription in four dimensions suggests that PT-symmetric
scalar field theories are asymptotically free.Comment: 15 pages, to be published in J. Phys. A special issue on Pseudo
Hermitian Hamiltonians in Quantum Physic
Confinement in a Higgs Model on
We determine the phase structure of an SU(2) gauge theory with an adjoint
scalar on using semiclassical methods. There are two global
symmetries: a symmetry associated with the Higgs field and a
center symmetry. We analyze the order of the deconfining phase
transition when different deformation terms are used. After finding order
parameters for the global symmetries, we show that there are four distinct
phases: a deconfined phase, a confined phase, a Higgs phase, and a mixed
confined phase. The mixed confined phase occurs where one might expect a phase
in which there is both confinement and the Higgs mechanism, but the behavior of
the order parameters distinguishes the two phases. In the mixed confined phase,
the global symmetry breaks spontaneously to a Z(2)
subgroup that acts non-trivially on both the scalar field and the Polyakov
loop. We find explicitly the BPS and KK monopole solutions of the Euclidean
field equations in the BPS limit. In the mixed phase, a linear combination of
and enters into the monopole solutions. In all four phases,
Wilson loops orthogonal to the compact direction are expected to show area-law
behavior. We show that this confining behavior can be attributed to a dilute
monopole gas in a broad region that includes portions of all four phases. A
duality argument similar to that applied recently [Poppitz and Unsal, 2011] to
the Seiberg-Witten model on shows that the monopole gas
picture, arrived at using Euclidean instanton methods, can be interpreted as a
gas of finite-energy dyons.Comment: 23 pages, 5 figure
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Judging nudging: can nudging improve population health?
If people didn’t smoke, drank less, ate healthier diets and were more active, the huge burden of chronic diseases such as cancer, heart disease, and type 2 diabetes would be much reduced.1 The prospect of being able to nudge populations into changing their behaviour has generated great interest among policymakers worldwide, including the UK government.2 We explore what nudging is and assess the prospect of nudging our way to a healthier population
Complete High Temperature Expansions for One-Loop Finite Temperature Effects
We develop exact, simple closed form expressions for partition functions
associated with relativistic bosons and fermions in odd spatial dimensions.
These expressions, valid at high temperature, include the effects of a
non-trivial Polyakov loop and generalize well-known high temperature
expansions. The key technical point is the proof of a set of Bessel function
identities which resum low temperature expansions into high temperature
expansions. The complete expressions for these partition functions can be used
to obtain one-loop finite temperature contributions to effective potentials,
and thus free energies and pressures.Comment: 9 pages, RevTeX, no figures. To be published in Phys. Rev D. v2 has
revised introduction and conclusions, plus a few typographical errors are
corrected; v3 corrects one typ
Economic instruments for population diet and physical activity behaviour change: a systematic scoping review.
BACKGROUND: Unhealthy diet and low levels of physical activity are common behavioural factors in the aetiology of many non-communicable diseases. Recent years have witnessed an upsurge of policy and research interest in the use of taxes and other economic instruments to improve population health. OBJECTIVE: To assemble, configure and analyse empirical research studies available to inform the public health case for using economic instruments to promote dietary and physical activity behaviour change. METHODS: We conducted a systematic scoping review of evidence for the effects of specific interventions to change, or general exposure to variations in, prices or income on dietary and physical activity behaviours and corollary outcomes. Systematic electronic searches and parallel snowball searches retrieved >1 million study records. Text mining technologies were used to prioritise title-abstract records for screening. Eligible studies were selected, classified and analysed in terms of key characteristics and principal findings, using a narrative, configuring synthesis focused on implications for policy and further research. RESULTS: We identified 880 eligible studies, including 192 intervention studies and 768 studies that incorporated evidence for prices or income as correlates or determinants of target outcomes. Current evidence for the effects of economic instruments and exposures on diet and physical activity is limited in quality and equivocal in terms of its policy implications. Direct evidence for the effects of economic instruments is heavily skewed towards impacts on diet, with a relative lack of evidence for impacts on physical activity. CONCLUSIONS: The evidence-based case for using economic instruments to promote dietary and physical activity behaviour change may be less compelling than some proponents have claimed. Future research should include measurement of people's actual behavioural responses using study designs capable of generating reliable causal inferences regarding intervention effects. Policy implementation needs to be carefully aligned with evaluation planning and design
Pinpointing needles in giant haystacks: use of text mining to reduce impractical screening workload in extremely large scoping reviews.
In scoping reviews, boundaries of relevant evidence may be initially fuzzy, with refined conceptual understanding of interventions and their proposed mechanisms of action an intended output of the scoping process rather than its starting point. Electronic searches are therefore sensitive, often retrieving very large record sets that are impractical to screen in their entirety. This paper describes methods for applying and evaluating the use of text mining (TM) technologies to reduce impractical screening workload in reviews, using examples of two extremely large-scale scoping reviews of public health evidence (choice architecture (CA) and economic environment (EE)). Electronic searches retrieved >800,000 (CA) and >1 million (EE) records. TM technologies were used to prioritise records for manual screening. TM performance was measured prospectively. TM reduced manual screening workload by 90% (CA) and 88% (EE) compared with conventional screening (absolute reductions of ≈430 000 (CA) and ≈378 000 (EE) records). This study expands an emerging corpus of empirical evidence for the use of TM to expedite study selection in reviews. By reducing screening workload to manageable levels, TM made it possible to assemble and configure large, complex evidence bases that crossed research discipline boundaries. These methods are transferable to other scoping and systematic reviews incorporating conceptual development or explanatory dimensions
Well-posedness of boundary layer equations for time-dependent flow of non-Newtonian fluids
We consider the flow of an upper convected Maxwell fluid in the limit of high
Weissenberg and Reynolds number. In this limit, the no-slip condition cannot be
imposed on the solutions. We derive equations for the resulting boundary layer
and prove the well-posedness of these equations. A transformation to Lagrangian
coordinates is crucial in the argument
Phenomenological Equations of State for the Quark-Gluon Plasma
Two phenomenological models describing an SU(N) quark-gluon plasma are
presented. The first is obtained from high temperature expansions of the free
energy of a massive gluon, while the second is derived by demanding color
neutrality over a certain length scale. Each model has a single free parameter,
exhibits behavior similar to lattice simulations over the range T_d - 5T_d, and
has the correct blackbody behavior for large temperatures. The N = 2
deconfinement transition is second order in both models, while N = 3,4, and 5
are first order. Both models appear to have a smooth large-N limit. For N >= 4,
it is shown that the trace of the Polyakov loop is insufficient to characterize
the phase structure; the free energy is best described using the eigenvalues of
the Polyakov loop. In both models, the confined phase is characterized by a
mutual repulsion of Polyakov loop eigenvalues that makes the Polyakov loop
expectation value zero. In the deconfined phase, the rotation of the
eigenvalues in the complex plane towards 1 is responsible for the approach to
the blackbody limit over the range T_d - 5T_d. The addition of massless quarks
in SU(3) breaks Z(3) symmetry weakly and eliminates the deconfining phase
transition. In contrast, a first-order phase transition persists with
sufficiently heavy quarks.Comment: 22 pages, RevTeX, 9 eps file
A review of ureteral injuries after external trauma
<p>Abstract</p> <p>Introduction</p> <p>Ureteral trauma is rare, accounting for less than 1% of all urologic traumas. However, a missed ureteral injury can result in significant morbidity and mortality. The purpose of this article is to review the literature since 1961 with the primary objective to present the largest medical literature review, to date, regarding ureteral trauma. Several anatomic and physiologic considerations are paramount regarding ureteral injuries management.</p> <p>Literature review</p> <p>Eighty-one articles pertaining to traumatic ureteral injuries were reviewed. Data from these studies were compiled and analyzed. The majority of the study population was young males. The proximal ureter was the most frequently injured portion. Associated injuries were present in 90.4% of patients. Admission urinalysis demonstrated hematuria in only 44.4% patients. Intravenous ureterogram (IVU) failed to diagnose ureteral injuries either upon admission or in the operating room in 42.8% of cases. Ureteroureterostomy, with or without indwelling stent, was the surgical procedure of choice for both trauma surgeons and urologists (59%). Complications occurred in 36.2% of cases. The mortality rate was 17%.</p> <p>Conclusion</p> <p>The mechanism for ureteral injuries in adults is more commonly penetrating than blunt. The upper third of the ureter is more often injured than the middle and lower thirds. Associated injuries are frequently present. CT scan and retrograde pyelography accurately identify ureteral injuries when performed together. Ureteroureterostomy, with or without indwelling stent, is the surgical procedure of choice of both trauma surgeons and urologists alike. Delay in diagnosis is correlated with a poor prognosis.</p
The Finite Temperature SU(2) Savvidy Model with a Non-trivial Polyakov Loop
We calculate the complete one-loop effective potential for SU(2) gauge bosons
at temperature T as a function of two variables: phi, the angle associated with
a non-trivial Polyakov loop, and H, a constant background chromomagnetic field.
Using techniques broadly applicable to finite temperature field theories, we
develop both low and high temperature expansions. At low temperatures, the real
part of the effective potential V_R indicates a rich phase structure, with a
discontinuous alternation between confined (phi=pi) and deconfined phases
(phi=0). The background field H moves slowly upward from its zero-temperature
value as T increases, in such a way that sqrt(gH)/(pi T) is approximately an
integer. Beyond a certain temperature on the order of sqrt(gH), the deconfined
phase is always preferred. At high temperatures, where asymptotic freedom
applies, the deconfined phase phi=0 is always preferred, and sqrt(gH) is of
order g^2(T)T. The imaginary part of the effective potential is non-zero at the
global minimum of V_R for all temperatures. A non-perturbative magnetic
screening mass of the form M_m = cg^2(T)T with a sufficiently large coefficient
c removes this instability at high temperature, leading to a stable
high-temperature phase with phi=0 and H=0, characteristic of a
weakly-interacting gas of gauge particles. The value of M_m obtained is
comparable with lattice estimates.Comment: 28 pages, 5 eps figures; RevTeX 3 with graphic
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