Glimpses of a strange star

There are about 2000 gamma ray burst (GRB) events known to us with data pouring in at the rate of one per day. While the afterglows of GRBs in radio, optical and X-ray bands are successfully explained by the fireball model, a significant difficulty with the proposed mechanisms for GRBs is that a small amount ($\le 10^{-6} M_{\odot}$) of baryons in the ejecta can be involved. There are very few models that fulfill this criteria together with other observational features, among which are the differentially rotating collapsed object model and the "supernova" model. These models generally invoke rapidly rotating neutron stars, and may be subject to uncertainties in the formation mechanisms and the equations of state of neutron stars. According to Spruit, the problem of making a GRB from an X-ray binary is reduced to finding a plausible way to make the star rotate differentially. We suggest that a model of strange star (SS) can naturally explain many of these bursts with not only their low baryon content, but the differential rotation which leads to an enhanced magnetic field that surfaces up and is responsible for GRBs

Corrigendum to “Integrals of motion in the many-body localized phase” [Nucl. Phys. B 891 (2015) 420–465]

We correct a small error in our article Integrals of motion in the many body localized phase [1] . The correction does not alter the main result regarding the convergence of the perturbative expansion for integrals of motion in forward approximation, but reduces the estimate of the radius of convergence by a numerical factor of roughly ≃1.79

The Higgs-like boson spin from the center–edge asymmetry in the diphoton channel at the LHC

We discuss the discrimination of the 125 GeV spin-parity 0+ Higgs-like boson observed at the LHC, decaying into two photons, H→γγ , against the hypothesis of a minimally coupled JP=2+ narrow diphoton resonance with the same mass and giving the same total number of signal events under the peak. We apply, as the basic observable of the analysis, the center–edge asymmetry ACE of the cosine of the polar angle of the produced photons in the diphoton rest frame to distinguish between the tested spin hypotheses. We show that the center–edge asymmetry ACE should provide a strong discrimination between the possibilities of spin-0 and spin-2 with graviton-like couplings, depending on the fraction of qq¯ production of the spin-2 signal, reaching CLs<10-6 for fqq=0 . Indeed, the ACE has the potential to do better than existing analyses for fqq<0.4

MFV reductions of MSSM parameter space

The 100+ free parameters of the minimal supersymmetric standard model (MSSM) make it computationally difficult to compare systematically with data, motivating the study of specific parameter reductions such as the cMSSM and pMSSM. Here we instead study the reductions of parameter space implied by using minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with a view towards systematically building in constraints on flavour-violating physics. Within this framework the space of parameters is reduced by expanding soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a 24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42 respectively), depending on the order kept in the expansion. We provide a Bayesian global fit to data of the MSSM-30 parameter set to show that this is manageable with current tools. We compare the MFV reductions to the 19-parameter pMSSM choice and show that the pMSSM is not contained as a subset. The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs boson and tan β ∼ 10 with multi-TeV sparticles

Magneto-transport from momentum dissipating holography

We obtain explicit expressions for the thermoelectric transport coefficients of a strongly coupled, planar medium in the presence of an orthogonal magnetic field and momentum-dissipating processes. The computations are performed within the gauge/gravity framework where the momentum dissipation mechanism is introduced by including a mass term for the bulk graviton. Relying on the structure of the computed transport coefficients and promoting the parameters to become dynamical functions, we propose a holography inspired phenomenology open to a direct comparison with experimental data from the cuprates

Distributed SUSY breaking: dark energy, Newton’s law and the LHC

We identify the underlying symmetry mechanism that suppresses the low-energy effective 4D cosmological constant within some 6D supergravity models, generically leading to results suppressed by powers of the KK scale, m K K 2 , relative to the much larger size, m 4 , associated with mass- m particles localized in these models on codimension-2 branes. These models are examples for which the local conditions for unbroken supersymmetry can be satisfied locally everywhere within the extra dimensions, but are obstructed only by global conditions like flux quantization or by the mutual inconsistency of the boundary conditions required at the various branes. Consequently quantities (like vacuum energies) forbidden by supersymmetry cannot become nonzero until wavelengths of order the KK scale are integrated out, since only such long wavelength modes can see the entire space and so ‘know’ that supersymmetry has broken. We verify these arguments by extending earlier rugby-ball calculations of one-loop vacuum energies within these models to more general pairs of branes within two warped extra dimensions. For the Standard Model confined to one of two otherwise identical branes, the predicted effective 4D vacuum energy density is of order ρ vac ⋍ C ( mM g / 4 πM p ) 4 = C (5 . 6 × 10 −5 eV) 4 , where M g ≳ 10 TeV (corresponding to extra-dimensional size r ≲ 1 μ m) and M p = 2 . 44 × 10 18 GeV are the 6D and 4D rationalized Planck scales, and m is the heaviest brane-localized particle. (For numerical purposes we take m to be the top-quark mass and take M g as small as possible, consistent with energy-loss bounds from supernovae.) C is a constant depending on the details of the bulk spectrum, which could easily be of order 500 for each of hundreds of fields in the bulk. The value C ∼ 6 × 10 6 would give the observed Dark Energy density

Heat kernels on the AdS 2 cone and logarithmic corrections to extremal black hole entropy

We develop new techniques to efficiently evaluate heat kernel coefficients for the Laplacian in the short-time expansion on spheres and hyperboloids with conical singularities. We then apply these techniques to explicitly compute the logarithmic contribution to black hole entropy from an $\mathcal{N}$ = 4 vector multiplet about a $\mathbb{Z}$ N orbifold of the nearhorizon geometry of quarter-BPS black holes in $\mathcal{N}$ = 4 supergravity. We find that this vanishes, matching perfectly with the prediction from the microstate counting. We also discuss possible generalisations of our heat kernel results to higher-spin fields over $\mathbb{Z}$ N orbifolds of higher-dimensional spheres and hyperboloids

A note on the magnitude of the flux superpotential

The magnitude of the flux superpotential W flux plays a crucial role in determining the scales of IIB string compactifications after moduli stabilisation. It has been argued that values of W flux ≪ 1 are preferred, and even required for physical and consistency reasons. This note revisits these arguments. We establish that the couplings of heavy Kaluza-Klein modes to light states scale with the internal volume as g ~ M KK /M P ~ $\mathcal{V}$ −2/3 ≪ 1 and argue that consistency of the superspace derivative expansion requires gF/M 2 ~ m 3/2 /M KK ≪ 1, where F is the auxiliary field of the light fields and M the ultraviolet cutoff. This gives only a mild constraint on the flux superpotential, W flux ≪ $\mathcal{V}$ 1/3 , which can be easily satisfied for $\mathcal{O}$ (1) values of W flux . This regime is also statistically favoured and makes the Bousso-Polchinski mechanism for the vacuum energy hierarchically more efficient

Bounds on charge and heat diffusivities in momentum dissipating holography

Inspired by a recently conjectured universal bound for thermo-electric diffusion constants in quantum critical, strongly coupled systems and relying on holographic analytical computations, we investigate the possibility of formulating Planckian bounds in different holographic models featuring momentum dissipation. For a certain family of solutions to a simple massive gravity dilaton model at zero charge density we find linear in temperature resistivity and entropy density alongside a constant electric susceptibility. In addition we explicitly find that the sum of the thermo-electric diffusion constants is bounded

Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise