Influence of the photon - neutrino processes on magnetar cooling

The photon-neutrino processes $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$, $\gamma \to \nu \bar \nu$ and $\gamma \gamma \to \nu \bar \nu$ are investigated in the presence of a strongly magnetized and dense electron-positron plasma. The amplitudes of the reactions $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$ and $\gamma \gamma \to \nu \bar \nu$ are obtained. In the case of a cold degenerate plasma contributions of the considering processes to neutrino emissivity are calculated. It is shown that contribution of the process $\gamma \gamma \to \nu \bar \nu$ to neutrino emissivity is supressed in comparision with the contributions of the processes $\gamma e^{\pm} \to e^{\pm} \nu \bar \nu$ and $\gamma \to \nu \bar \nu$. The constraint on the magnetic field strength in the magnetar outer crust is obtained.Comment: 8 pages, LaTeX, 2 PS figures, based on the talk presented by D.A. Rumyantsev at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow Region, May 23-29, 2008, to appear in the Proceeding

High resolution spectroscopic analysis of seven giants in the bulge globular cluster NGC 6723

Globular clusters associated with the Galactic bulge are important tracers of stellar populations in the inner Galaxy. High resolution analysis of stars in these clusters allows us to characterize them in terms of kinematics, metallicity, and individual abundances, and to compare these fingerprints with those characterizing field populations. We present iron and element ratios for seven red giant stars in the globular cluster NGC~6723, based on high resolution spectroscopy. High resolution spectra ($R\sim48~000$) of seven K giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the MPG/ESO 2.2m telescope. Photospheric parameters were derived from $\sim130$ FeI and FeII transitions. Abundance ratios were obtained from line-to-line spectrum synthesis calculations on clean selected features. An intermediate metallicity of [Fe/H]$=-0.98\pm0.08$ dex and a heliocentric radial velocity of $v_{hel}=-96.6\pm1.3~km s^{-1}$ were found for NGC 6723. Alpha-element abundances present enhancements of $[O/Fe]=0.29\pm0.18$ dex, $[Mg/Fe]=0.23\pm0.10$ dex, $[Si/Fe]=0.36\pm0.05$ dex, and $[Ca/Fe]=0.30\pm0.07$ dex. Similar overabundance is found for the iron-peak Ti with $[Ti/Fe]=0.24\pm0.09$ dex. Odd-Z elements Na and Al present abundances of $[Na/Fe]=0.00\pm0.21$ dex and $[Al/Fe]=0.31\pm0.21$ dex, respectively. Finally, the s-element Ba is also enhanced by $[Ba/Fe]=0.22\pm0.21$ dex. The enhancement levels of NGC 6723 are comparable to those of other metal-intermediate bulge globular clusters. In turn, these enhancement levels are compatible with the abundance profiles displayed by bulge field stars at that metallicity. This hints at a possible similar chemical evolution with globular clusters and the metal-poor of the bulge going through an early prompt chemical enrichment

Coexistence of Non-Conventional Condensates in Two-Level Bose Atom System

In the framework of the Bogolyubov approximation and using the Bogolyubov inequalities we give a simple proof of the coexistence of two non-conventional Bose-Einstein condensates in the case of some superstable Bose system whose atoms have an internal two-level structure and their energy operators in the second quantized form depend on the number operators only.Comment: 17 page

QED vacuum fluctuations and induced electric dipole moment of the neutron

Quantum fluctuations in the QED vacuum generate non-linear effects, such as peculiar induced electromagnetic fields. In particular, we show here that an electrically neutral particle, possessing a magnetic dipole moment, develops an induced electric dipole-type moment with unusual angular dependence, when immersed in a quasistatic, constant external electric field. The calculation of this effect is done in the framework of the Euler-Heisenberg effective QED Lagrangian, corresponding to the weak field asymptotic expansion of the effective action to one-loop order. It is argued that the neutron might be a good candidate to probe this signal of non-linearity in QED.Comment: A misprint has been corrected, and three new references have been adde

Electric field of a pointlike charge in a strong magnetic field and ground state of a hydrogenlike atom

In an external constant magnetic field, so strong that the electron Larmour length is much shorter than its Compton length, we consider the modification of the Coulomb potential of a point charge owing to the vacuum polarization. We establish a short-range component of the static interaction in the Larmour scale, expressed as a Yukawa-like law, and reveal the corresponding "photon mass" parameter. The electrostatic force regains its long-range character in the Compton scale: the tail of the potential follows an anisotropic Coulomb law, decreasing away from the charge slower along the magnetic field and faster across. In the infinite-magnetic-field limit the potential is confined to an infinitely thin string passing though the charge parallel to the external field. This is the first evidence for dimensional reduction in the photon sector of quantum electrodynamics. The one-dimensional form of the potential on the string is derived that includes a delta-function centered in the charge. The nonrelativistic ground-state energy of a hydrogenlike atom is found with its use and shown not to be infinite in the infinite-field limit, contrary to what was commonly accepted before, when the vacuum polarization had been ignored. These results may be useful for studying properties of matter at the surface of extremely magnetized neutron stars.Comment: 45 pages, 6 figures, accepted to Phys. Rev.

Hamiltonian Frenet-Serret dynamics

The Hamiltonian formulation of the dynamics of a relativistic particle described by a higher-derivative action that depends both on the first and the second Frenet-Serret curvatures is considered from a geometrical perspective. We demonstrate how reparametrization covariant dynamical variables and their projections onto the Frenet-Serret frame can be exploited to provide not only a significant simplification of but also novel insights into the canonical analysis. The constraint algebra and the Hamiltonian equations of motion are written down and a geometrical interpretation is provided for the canonical variables.Comment: Latex file, 14 pages, no figures. Revised version to appear in Class. Quant. Gra

Density-dependent interactions and structure of charged colloidal dispersions in the weak screening regime

We determine the structure of charge-stabilized colloidal suspensions at low ionic strength over an extended range of particle volume fractions using a combination of light and small angle neutron scattering experiments. The variation of the structure factor with concentration is analyzed within a one-component model of a colloidal suspension. We show that the observed structural behavior corresponds to a non-monotonic density dependence of the colloid effective charge and the mean interparticle interaction energy. Our findings are corroborated by similar observations from primitive model computer simulations of salt-free colloidal suspensions.Comment: Revised version, accepted to Phys. Rev. Let

A systematic review of behaviour change techniques used in interventions to increase physical activity among breast cancer survivors

BACKGROUND: Despite evidence that physical activity (PA) can help reduce recurrence and mortality, many breast cancer survivors are less active than recommended levels. The aim of this systematic review is to advance our understanding of which behaviour change techniques (BCTs) have been used in interventions promoting breast cancer survivors' PA and to evaluate their potential to increase PA. METHODS: A systematic search was conducted in five databases (Medline; PsycInfo; Embase; CINAHL and Scopus) for studies published between 2005 and 2019. Following a rigorous screening process, 27 studies were retained. These were reviewed and analysed for quality, coded for BCTs (k = 0.65) and interventions categorised according to their potential to increase PA using an established methodology. RESULTS: The majority of studies were moderate quality (64%). Demonstration on how to perform the behaviour was the most commonly used BCT (n = 23). Adding objects to the environment, (pedometer or accelerometer) was the BCT with the highest potential to increase PA. This was followed by, goal setting and self-monitoring of behaviour. A theory-based approach to evaluation was used in only 59% (n = 16) of the studies. CONCLUSIONS: The results of this review inform which BCTs have the potential to increase PA for breast cancer survivors and inform intervention development. Future research, is encouraged to properly report intervention procedures around dose and frequency of intervention components to allow for review and replication