Complex Scalar Singlet Dark Matter: Vacuum Stability and Phenomenology

We analyze one-loop vacuum stability, perturbativity, and phenomenological constraints on a complex singlet extension of the Standard Model (SM) scalar sector containing a scalar dark matter candidate. We study vacuum stability considerations using a gauge-invariant approach and compare with the conventional gauge-dependent procedure. We show that, if new physics exists at the TeV scale, the vacuum stability analysis and experimental constraints from the dark matter sector, electroweak precision data, and LEP allow both a Higgs-like scalar in the mass range allowed by the latest results from CMS and ATLAS and a lighter singlet-like scalar with weak couplings to SM particles. If instead no new physics appears until higher energy scales, there may be significant tension between the vacuum stability analysis and phenomenological constraints (in particular electroweak precision data) to the extent that the complex singlet extension with light Higgs and singlet masses would be ruled out. We comment on the possible implications of a scalar with ~125 GeV mass and future ATLAS invisible decay searches.Comment: 24 pages, 12 figures; v2 - fixed minor typos, added reference, changed layou

Stronger prediction of motor recovery and outcome post-stroke by cortico-spinal tract integrity than functional connectivity

<div><p>Objectives</p><p>To examine longitudinal changes in structural and functional connectivity post-stroke in patients with motor impairment, and define their importance for recovery and outcome at 12 months.</p><p>Methods</p><p>First-time stroke patients (N = 31) were studied at 1–2 weeks, 3 months, and 12 months post-injury with a validated motor battery and resting-state fMRI to measure inter-hemispheric functional connectivity (FC). Fractional anisotropy (FA) of the cortico-spinal tract (CST) was derived from diffusion tensor imaging as a measure of white matter organization. ANOVAs were used to test for changes in FC, FA, and motor performance scores over time, and regression analysis related motor outcome to clinical and neuroimaging variables.</p><p>Results</p><p>FA of the ipsilesional CST improved significantly from 3 to 12 months and was strongly correlated with motor performance. FA improved even in the absence of direct damage to the CST. Inter-hemispheric FC also improved over time, but did not correlate with motor performance at 12 months. Clinical variables (early motor score, education level, and age) predicted 80.4% of the variation of motor outcome, and FA increased the predictability to 84.6%. FC did not contribute to the prediction of motor outcome.</p><p>Conclusions</p><p>Stroke causes changes to the CST microstructure that can account for behavioral variability even in the absence of demonstrable lesion. Ipsilesional CST undergoes remodeling post-stroke, even past the three-month window when most of the motor recovery happens. FA of the CST, but not inter-hemispheric FC, can improve to the prediction of motor outcome based on early motor scores.</p></div

Collisional shifts in optical-lattice atom clocks

We theoretically study the effects of elastic collisions on the determination of frequency standards via Ramsey fringe spectroscopy in optical-lattice atom clocks. Interparticle interactions of bosonic atoms in multiply-occupied lattice sites can cause a linear frequency shift, as well as generate asymmetric Ramsey fringe patterns and reduce fringe visibility due to interparticle entanglement. We propose a method of reducing these collisional effects in an optical lattice by introducing a phase difference of $\pi$ between the Ramsey driving fields in adjacent sites. This configuration suppresses site to site hopping due to interference of two tunneling pathways, without degrading fringe visibility. Consequently, the probability of double occupancy is reduced, leading to cancellation of collisional shifts.Comment: 15 pages, 11 figure

Classical and Quantum Interaction of the Dipole

A unified and fully relativistic treatment of the interaction of the electric and magnetic dipole moments of a particle with the electromagnetic field is given. New forces on the particle due to the combined effect of electric and magnetic dipoles are obtained. Four new experiments are proposed, three of which would observe topological phase shifts.Comment: 10 pages, Latex/Revtex. Some minor errors have been correcte

Hadronic Parity Violation: a New View through the Looking Glass

Studies of the strangeness changing hadronic weak interaction have produced a number of puzzles that have so far evaded a complete explanation within the Standard Model. Their origin may lie either in dynamics peculiar to weak interactions involving strange quarks or in more general aspects of the interplay between strong and weak interactions. In principle, studies of the strangeness conserving hadronic weak interaction using parity violating hadronic and nuclear observables provide a complementary window on this question. However, progress in this direction has been hampered by the lack of a suitable theoretical framework for interpreting hadronic parity violation measurements in a model-independent way. Recent work involving effective field theory ideas has led to the formulation of such a framework while motivating the development of a number of new hadronic parity violation experiments in few-body systems. In this article, we review these recent developments and discuss the prospects and opportunities for further experimental and theoretical progress.Comment: Manuscript submitted to Annual Reviews of Nuclear and Particle Scienc

Identification of a QTL on chromosome 7AS for sodium exclusion in bread wheat

Tese de doutoramento em Engenharia Física (Instrumentação), apresentada à Faculdade de Ciências e Tecnologia da Universidade de CoimbraO número de ciclotrões com capacidade para acelerar protões até cerca de 20 MeV tem vindo a aumentar em todo o mundo. Apesar de o objectivo principal das instalaçõoes que contêm estas máquinas ser a produção de radionuclídeos para tomografia por emissão de positrões (PET, do inglês positron emission tomography), algumas dessas instalações estão equipadas com várias linhas de feixe que podem ser adaptadas para investigação científica. Por exemplo, radiobiologia, radiofisiolgia e outros estudos de dosimetria podem ser realizados utilizando uma destas linhas de feixe devidamente adaptada para o efeito. Neste trabalho, uma das linhas de feixe do ciclotrão PET da Universidade de Coimbra foi complementada e instrumentada por forma a possibilitar a irradiação de um arranjo experimental com um feixe de protões de elevada qualidade. Esta nova linha de feixe foi construída de raíz e sem causar qualquer interferência com as demais linhas do ciclotrão, dedicadas à produção de radionuclídeos. São apresentados resultados tanto experimentais como de simulação, estes últimos obtidos através dos pacotes de simulação SRIM/TRIM e Geant4, tendo como objectivo a medição do pico de Bragg depositado pelo feixe de protões do ciclotrão PET, com uma energia nominal de 18 MeV. Utilizando um bloco de plástico cintilador e uma câmara fotográfica com ligação à internet da marca D-link foi possível medir tanto o alcance como a largura do feixe de protões com uma resolução espacial inferior a 0,1 mm. Os alcances do feixe medidos após este passar pelo meio de um tubo de alumínio com vácuo com 40 cm de comprimento e um segundo tubo com 2,4 m de comprimento permitiram confirmar que a energia efectiva do feixe é de 18 MeV. Mediu-se também o pico de Bragg utilizando um alvo constituído por várias folhas de alumínio intercaladas com lâminas de polietileno. O sinal de corrente foi recolhido das várias folhas de alumínio através de amplificadores de transimpedância fabricados no âmbito desta tese. Verificou-se que o pico de Bragg assim medido é consistente com simulações realizadas utilizando o pacote SRIM/TRIM. Após a instalação da linha de feixe no perímetro exterior do ciclotrão, esta foi caracterizada, calibrada e validada. Para tal, o sinal induzido pela passagem do feixe por uma folha de alumínio com 20 μm de espessura é lido através do amplificador de transimpedância mencionado. Este sinal amplificado providencia informação de dose em tempo real através de um programa desenvolvido em C/C++. Para além da dose, as principais variáveis de monitorização que este programa providencia incluem a corrente do feixe, a carga integrada em conjunto com a taxa de dose. Deste modo a dose e a corrente integrada (carga total) entregue até um dado instante na montagem experimental pode ser controlada por meio de um obturador controlado por computador. Feixes de protões com correntes tão baixas como 10 pA podem deste modo ser aferidas. A folha de alumínio foi escolhida por ser resistente à radiação, possuir baixa densidade e baixa probabilidade de radioactividade induzida pelo feixe e, finalmente, por representar um custo negligenciável. Junta-se a estas vantagens o facto de o método potenciar o cálculo da dose entregue a um alvo durante uma irradiação, com uma perda mínima da energia do feixe de protões, e com dispersão igualmente mínima. Resultados experimentais e simulações com o Geant4 são apresentados que revelam a aplicação, pela primeira vez, de um feixe de 18 MeV proveniente de um ciclotrão para irradiação de uma região seleccionada de um alvo. Fazendo uso do sistema de dosimetria apresentado no parágrafo anterior foi possível irradiar de modo homogéneo uma região circular com 18 mm de diâmetro. Torna-se assim possível irradiar culturas celulares localizadas em placas multi-poços com um diâmetro por poço de 16 mm, como é usual em experiências de radiobiologia. Verificou-se que o controlo do campo magnético aplicado dentro do ciclotrão é crucial para se obter uma irradiação uniforme em todo o campo do alvo. Para tal, efetua-se antes de cada irradiação e com o obturador fechado, um varrimento à corrente que gera o campo magnético dentro do ciclotrão, medindo-se um perfil quase gaussiano e tomando-se o seu valor central para se obter uma irradiação homogénea. As taxas de dose no alvo (entre 500 mGy/s e 5 mGy/s) são obtidas através de um disco em rotação posicionado na trajectória do feixe. O disco, com 150 mm de raio e uma fenda de 0,5 mm na sua extermidade, permite reduzir a taxa de dose por um factor de 5×10−4. Finalmente, vários filmes do tipo Gafchromic EBT2 foram expostos a diferente valores de dose por forma a validar toda a instalação para irradiação de um alvo com feixes de protões. Para tal validação fez-se uso do sistema de dosimetria em filme 2D do Serviço de Radioterapia do Centro Hospitalar Universitário de Coimbra. A dose absoluta nos filmes irradiados com protões foi verificada neste sistema e apresentou uma precisão melhor que 2%.The number of cyclotrons capable of accelerating protons to about 20MeV is increasing throughout the world. Originally aiming at the production of positron emission tomography (PET) radionuclides, some of these facilities are equipped with several beamlines suitable for scientific research. Radiobiology, radiophysiology, and other dosimetric studies can be performed using these beamlines. In this work, a PET cyclotron was fitted with a long beam transport line to irradiate with a good quality proton beam experimental setups. The beamline was configured as a natural extension of one of the cyclotron beam ports, while keeping available the other beam ports for PET radionuclides production. Experimental results are reported, together with SRIM/TRIM and Geant4 simulations, which aim at measuring the Bragg peak of the 18 -MeV proton beam from the PET cyclotron. By using a piece of plastic scintillator and a D-link Ethernet-based camera, the proton beam range and width were measured with a spatial resolution of 0.1mm. The ranges of the proton beam in the plastic scintillator were used to assess its energy after trespassing one or two Havar R windows and either a 40-cm-long or a 2.4-m-long aluminum pipe. The initial energy of the proton beam from the PET cyclotron was found to be 18 MeV. Additionally, the Bragg peak of the protons from the PET cyclotron was assessed using a stacked target consisting of several aluminum foils interleaved with polyethylene sheets, readout by in-house made transimpedance electronics. The measured Bragg peak is consistent with simulations performed using the SRIM/TRIM simulation toolkit. An out-of-yoke irradiation setup using the accelerated proton beam coming from the PET cyclotron was developed, characterized, calibrated, and validated. A 20-μm-thick aluminum transmission foil is readout by in-house made transimpedance electronics, providing online dose information via a C/C++ program. xvii Overview The main monitoring variables include beam current, integrated charge together with dose rate. The beam monitor is able to readout and deliver these variables in real-time. Hence the dose and integrated current (total charge) delivered upto a given instant to an experimental setup may be controlled via a computercontrolled shutter that was installed in the beam path. Proton beam currents down to 10 pA can be assessed using the thin aluminum foil. The aluminum was chosen for this task because it is radiation hard, it has low density and low radiation activity, and finally because it is easily available at negligible cost. In addition, this method allows for calculating the dose delivered to a target during an irradiation with high efficiency, and with minimal proton energy loss and scattering. Experimental results and Geant4 simulations are reported, which aim at using for the first time the 18 -MeV proton beam from a PET cyclotron to irradiate a selected region of a target using the developed dosimetry system. By using this system, a homogeneous beam spot on target with a diameter of 18mm can be controlled. This allows controlled irradiation of cell cultures located in typical biological multi-well dishes with diameters of 16mm each. It was found that the control of the magnetic field applied inside the cyclotron plays a major role for achieving said homogeneity. For that, scanning the magnet current and measuring the corresponding dose rate reveals a quasi-Gaussian shaped curve that must be known before any irradiation procedure (the final shutter is closed during such measurements). The optimum magnet current is taken from the center of the Gaussian-shaped curve, hence producing a homogenous dose on target. The measured dose rate on target ranges from 500mGy/s down to 5mGy/s. This is achieved with a 150mm radius rotating disk with a slit of 0.5mm width, that decreases target dose rates by a factor of 5 × 10−4. Several Gafchromic R EBT2 films were exposed to different values of dose for validating the developed irradiation setup using the 2D film dosimetry system of the Department of Radiotherapy of Coimbra University Hospital Center. The absolute dose in the irradiated films were assessed with a precision better than 2%. It is planned, in the near future, to irradiate small animals, cell cultures, or other materials or samples

Message on a bottle: are alcohol warning labels about cancer appropriate?

Background Although most Australians are unaware of the risk, there is strong evidence for a direct link between alcohol consumption and many types of cancer. Warning labels on alcohol products have been proposed as a cost-effective strategy to inform the community of this health risk. We aimed to identify how Australians might respond to such an approach. Methods We conducted a national online survey canvassing responses to four separate cancer warning messages on labels. The graphically presented messages were informed by qualitative data from a series of focus groups among self-identified ‘light-to-moderate’ drinkers. For each label, participants were asked their level of agreement with impact statements about raising awareness, prompting conversation, influencing drinking behaviour and educating others about cancer risk. We analysed responses according to demographic and other factors, including self-reported drinking behaviour (using the 3-item Alcohol Use Disorder Test – AUDIT-C – scores). Results Approximately 1600 participants completed the survey, which was open to all Australian adults over a period of 1 month in 2014. Overall, the labels were well received, with the majority (>70 %) agreeing all labels could raise awareness and prompt conversations about the cancer risk associated with alcohol. Around 50 % or less agreed that the labels could influence drinking behaviour, but larger proportions agreed that the labels would prompt them to discuss the issue with family and friends. Although sex, AUDIT-C score and age were significantly associated with agreement on bivariate analysis, multivariate analyses demonstrated that being inclined to act upon warning label recommendations in general was the most important predictor of agreement with all of the impact statements. Having a low AUDIT-C score also predicted agreement that the labels might prompt behaviour change in friends. Conclusions The findings suggest that providing detailed warnings about cancer risk on alcohol products is a viable means of increasing public awareness of the health risks associated with alcohol consumption. Further research is needed to explore the ability of such warnings to influence behavioural intentions and actual drinking behaviour

Nonequilibrium dynamics of fermions in a spatially homogeneous scalar background field

We consider the time evolution of systems in which a spatially homogeneous scalar field is coupled to fermions. The quantum back-reaction is taken into account in one-loop approximation. We set up the basic equations and their renormalization in a form suitable for numerical computations. The initial singularities appearing in the renormalized equations are removed by a Bogoliubov transformation. The equations are then generalized to those in a spatially flat Friedmann-Robertson-Walker universe. We have implemented the Minkowski space equations numerically and present results for the time evolution with various parameter sets. We find that fermion fluctuations are not in general as ineffective as assumed previously but show interesting features which should be studied further. In an especially interesting example we find that fermionic fluctuations can ``catalyze'' the evolution of bosonic fluctuations.Comment: 36 pages, 18 figures in one postscript file, references added, a few misprints corrected, figures and figure captions slightly modifie

Optical analog of Rabi oscillation suppression due to atomic motion

The Rabi oscillations of a two-level atom illuminated by a laser on resonance with the atomic transition may be suppressed by the atomic motion through averaging or filtering mechanisms. The optical analogs of these velocity effects are described. The two atomic levels correspond in the optical analogy to orthogonal polarizations of light and the Rabi oscillations to polarization oscillations in a medium which is optically active, naturally or due to a magnetic field. In the later case, the two orthogonal polarizations could be selected by choosing the orientation of the magnetic field, and one of them be filtered out. It is argued that the time-dependent optical polarization oscillations or their suppression are observable with current technology.Comment: 10 pages, 10 figure