The decay of unstable k-strings in SU(N) gauge theories at zero and finite temperature

Sources in higher representations of SU(N) gauge theory at T=0 couple with apparently stable strings with tensions depending on the specific representation rather than on its N-ality. Similarly at the deconfining temperature these sources carry their own representation-dependent critical exponents. It is pointed out that in some instances one can evaluate exactly these exponents by fully exploiting the correspondence between the 2+1 dimensional critical gauge theory and the 2d conformal field theory in the same universality class. The emerging functional form of the Polyakov-line correlators suggests a similar form for Wilson loops in higher representations which helps in understanding the behaviour of unstable strings at T=0. A generalised Wilson loop in which along part of its trajectory a source is converted in a gauge invariant way into higher representations with same N-ality could be used as a tool to estimate the decay scale of the unstable strings.Comment: 18 pages, 4 figures v2: typos correcte

Vortex solution in 2+1 dimensional Yang-Mills theory at high temperatures

At high temperatures the A_0 component of the Yang--Mills field plays the role of the Higgs field, and the 1-loop potential V(A_0) plays the role of the Higgs potential. We find a new stable vortex solution of the Abrikosov-Nielsen-Olesen type, and discuss its properties and possible implications.Comment: 8 p., three .eps figures include

Conformal vs confining scenario in SU(2) with adjoint fermions

The masses of the lowest-lying states in the meson and in the gluonic sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are measured on the lattice at a fixed value of the lattice coupling $\beta = 4/g_0^2 = 2.25$ for values of the bare fermion mass $m_0$ that span a range between the quenched regime and the massless limit, and for various lattice volumes. Even for light constituent fermions the lightest glueballs are found to be lighter than the lightest mesons. Moreover, the string tension between two static fundamental sources strongly depends on the mass of the dynamical fermions and becomes of the order of the inverse squared lattice linear size before the chiral limit is reached. The implications of these findings for the phase of the theory in the massless limit are discussed and a strategy for discriminating between the (near--)conformal and the confining scenario is outlined.Comment: 5 pages, 4 figures using RevTeX4, Typos corrected, references added. Versions to appear on PR

Sub-structure formation in starless cores

Motivated by recent observational searches of sub-structure in starless molecular cloud cores, we investigate the evolution of density perturbations on scales smaller than the Jeans length embedded in contracting isothermal clouds, adopting the same formalism developed for the expanding Universe and the solar wind. We find that initially small amplitude, Jeans-stable perturbations (propagating as sound waves in the absence of a magnetic field), are amplified adiabatically during the contraction, approximately conserving the wave action density, until they either become nonlinear and steepen into shocks at a time $t_{\rm nl}$, or become gravitationally unstable when the Jeans length decreases below the scale of the perturbations at a time $t_{\rm gr}$. We evaluate analytically the time $t_{\rm nl}$ at which the perturbations enter the non-linear stage using a Burgers' equation approach, and we verify numerically that this time marks the beginning of the phase of rapid dissipation of the kinetic energy of the perturbations. We then show that for typical values of the rms Mach number in molecular cloud cores, $t_{\rm nl}$ is smaller than $t_{\rm gr}$, and therefore density perturbations likely dissipate before becoming gravitational unstable. Solenoidal modes grow at a faster rate than compressible modes, and may eventually promote fragmentation through the formation of vortical structures.Comment: 8 pages, 4 figure

Deep-inelastic scattering and the operator product expansion in lattice QCD

We discuss the determination of deep-inelastic hadron structure in lattice QCD. By using a fictitious heavy quark, direct calculations of the Compton scattering tensor can be performed in Euclidean space that allow the extraction of the moments of structure functions. This overcomes issues of operator mixing and renormalisation that have so far prohibited lattice computations of higher moments. This approach is especially suitable for the study of the twist-two contributions to isovector quark distributions, which is practical with current computing resources. While we focus on the isovector unpolarised distribution, our method is equally applicable to other quark distributions and to generalised parton distributions. By looking at matrix elements such as $$ (where $V^\mu$ and $A^\nu$ are vector and axial-vector heavy-light currents) within the same formalism, moments of meson distribution amplitudes can also be extracted.Comment: 10 pages, 5 figures, version accepted for publicatio

Topical analgesia for acute otitis media

BACKGROUND: Acute otitis media (AOM) is a spontaneously remitting disease of which pain is the most distressing symptom. Antibiotics are now known to have less benefit than previously assumed. Topical pain relief may be a satisfactory intervention for AOM sufferers and encourage clinicians to prescribe fewer antibiotics. OBJECTIVES: To assess the effectiveness of topical analgesia for AOM in adults and children. SEARCH METHODS: For this second update we searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2011, Issue 1), Ovid MEDLINE (2008 to February Week 1 2011), Ovid MEDLINE (In‐Process & Other Non‐Indexed Citations 10 February 2011), Ovid EMBASE (2008 to 2011 Week 05), EBSCO CINAHL (2008 to 4 February 2011) and Ovid AMED (2008 to April 2011). SELECTION CRITERIA: Double‐blind randomised controlled trials (RCTs) or quasi‐RCTs comparing an otic preparation with an analgesic effect (excluding antibiotics) versus placebo or an otic preparation with an analgesic effect (excluding antibiotics) versus any other otic preparation with an analgesic effect, in adults or children presenting at primary care settings with AOM without perforation. DATA COLLECTION AND ANALYSIS: Three review authors independently screened studies, assessed trial quality and extracted data. Attempts to obtain additional information from the trial authors of the included trials were unsuccessful. MAIN RESULTS: Five trials including 391 children aged three to 18 years met our criteria. Two studies (117 children) compared anaesthetic ear drops versus placebo immediately at diagnosis. All children received some form of oral pain relief. In all five studies it was clear that ear pain diminishes rapidly for most sufferers. Nevertheless there was a statistically significant difference in the proportion of children achieving a 50% reduction in pain in favour of anaesthetic drops 10 minutes after instillation (risk ratio (RR) 2.13, 95% confidence interval (CI) 1.19 to 3.80) and 30 minutes after instillation (RR 1.43, 95% CI 1.12 to 1.81) on the day AOM was diagnosed but not at 20 minutes (RR 1.24, 95% CI 0.88 to 1.74). Three trials (274 children) compared anaesthetic ear drops with naturopathic herbal ear drops. Naturopathic drops were favoured 15 and 30 minutes after instillation, one to three days after diagnosis, but the differences were not statistically significant. Only one trial looked at adverse reactions and found none. Overall the findings of this review are based on trial evidence that is at low or unclear risk of bias. AUTHORS' CONCLUSIONS: Evidence from five RCTs, only two of which addressed the most relevant question of primary effectiveness, provides limited evidence that ear drops are effective 30 minutes after administration in older children with AOM. Uncertainty exists as to the magnitude of this effect and more high‐quality studies are needed

DNA waves and water

Some bacterial and viral DNA sequences have been found to induce low frequency electromagnetic waves in high aqueous dilutions. This phenomenon appears to be triggered by the ambient electromagnetic background of very low frequency. We discuss this phenomenon in the framework of quantum field theory. A scheme able to account for the observations is proposed. The reported phenomenon could allow to develop highly sensitive detection systems for chronic bacterial and viral infections.Comment: Invited talk at the DICE2010 Conference, Castiglioncello, Italy September 201

Evershed clouds as precursors of moving magnetic features around sunspots

The relation between the Evershed flow and moving magnetic features (MMFs) is studied using high-cadence, simultaneous spectropolarimetric measurements of a sunspot in visible (630.2 nm) and near-infrared (1565 nm) lines. Doppler velocities, magnetograms, and total linear polarization maps are calculated from the observed Stokes profiles. We follow the temporal evolution of two Evershed clouds that move radially outward along the same penumbral filament. Eventually, the clouds cross the visible border of the spot and enter the moat region, where they become MMFs. The flux patch farther from the sunspot has the same polarity of the spot, while the MMF closer to it has opposite polarity and exhibits abnormal circular polarization profiles. Our results provide strong evidence that at least some MMFs are the continuation of the penumbral Evershed flow into the moat. This, in turn, suggests that MMFs are magnetically connected to sunspots.Comment: To appear in ApJ Letters, Vol 649, 2006 September 20 issu

Quark mixings and flavor changing interactions with singlet quarks

Aspects of the quark mixings and flavor changing interactions are investigated in electroweak models with singlet quarks. The effects on the ordinary quark mixing are determined in terms of the quark masses and the parameters describing the mixing between the ordinary quarks q and the singlet quarks Q (q-Q mixing). Some salient features arise in the flavor changing interactions through the q-Q mixing. The unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix within the ordinary quark sector is violated, and the flavor changing neutral currents (FCNC's) appear both in the gauge and scalar couplings. The flavor changing interactions are calculated appropriately in terms of the q-Q mixing parameters and the quark masses, which really exhibit specific flavor structures. It is found that there are reasonable ranges of the model parameters to reproduce the ordinary quark mass hierarchy and the actual CKM structure even in the presence of q-Q mixing. Some phenomenological effects of the singlet quarks are also discussed. In particular, the scalar FCNC's may be more important in some cases, if the singlet quarks as well as the extra scalar particles from the singlet Higgs fields have masses $\sim$ 100 GeV -- 1 TeV.Comment: 32 pages, 7 figures, added reference