In a previous work, we showed that it is possible to detect keV scale sterile neutrino dark matter ${\nu }_s$ in a $\beta$ decay experiment using radioactive sources such as ${}^3\mathrm{T}$ or ${}^{106}\mathrm{Ru}$. The signals of this dark matter candidate are monoenergetic electrons produced in the neutrino capture process ${\nu }_s+N^{\prime }\to N+e^{-}$. These electrons have energy greater than the maximum energy of the electrons produced in the associated decay process $N^{\prime }\to N+e^{-}+{\overline{\nu }}_e$. Hence, signal electron events are well beyond the end point of the $\beta$ decay spectrum and are not polluted by the $\beta$ decay process. Another possible background, which is a potential threat to the detection of ${\nu }_s$ dark matter, is the electron event produced by the scattering of solar neutrinos with electrons in target matter. In this article, we study in detail this possible background and discuss its implications for the detection of keV scale sterile neutrino dark matter. In particular, bound state features of electrons in Ru atoms are considered with care in the scattering process when the kinetic energy of the final electron is the same order of magnitude of the binding energy.

The anomalous magnetic moment of the electron is determined experimentally with an accuracy of $2.8\times 10^{-13}$ and the uncertainty may decrease by an order of magnitude in the future. While the current data are in excellent agreement with the standard model, the possible future improvement in the error in $\mathrm{\Delta }{a}_e=a_e^{\exp }-a_e^{\text{theory}}$ has recently drawn interest in the electron anomalous magnetic moment as a possible probe of new physics beyond the standard model. In this work we give an analysis of such physics in an extension of the minimal supersymmetric standard model with a vector multiplet. In the extended model the electroweak contribution to the anomalous magnetic moment of the electron includes loop diagrams involving in addition to the exchange of W and Z, the exchange of charginos, sneutrinos and mirror sneutrinos, and the exchange of neutralinos, sleptons and mirror sleptons. The analysis shows that a contribution to the electron magnetic moment much larger than expected by $m_e^2/m_{\mu }^2$ scaling of the deviation of the muon anomalous magnetic moment over the standard model prediction, i.e., $\mathrm{\Delta }{a}_{\mu }=3\times 10^{-9}$ as given by the Brookhaven experiment, can be gotten within the minimal supersymmetric standard model (MSSM) extension. Effects of $CP$ violating phases in the extended MSSM model on the corrections to the supersymmetric electroweak contributions to $a_e$ are also investigated. The analysis points to the possibility of detection of new physics effects with modest improvement on the error in $\mathrm{\Delta }{a}_e=a_e^{\exp }-a_e^{\text{theory}}$.

We develop a model for hadrons in the framework of the worldline formalism. While being based wholly in four-dimensional quantum field theory, it shares many features with holographic approaches: Already by the use of the worldline formalism the approach appears intrinsically quantum mechanical. As auxiliary fifth dimension Schwinger’s proper time is grouped with the physical four spacetime dimensions into an ${\mathrm{AdS}}_5$ geometry, which is warped due to conformal-symmetry breaking effects. Hidden local symmetry is emergent. The four-dimensional sources are extended to five-dimensional fields by a Wilson flow (gradient flow). A variational principle for the flow reproduces exactly the corresponding holographic computation. The worldline approach also yields the higher-dimensional description in the nonrelativistic case.

Given a gauge theory with gauge group $G$, it is sometimes useful to find an equivalent formulation in terms of a nontrivial gauge subgroup $H\subset G$. This amounts to fixing the gauge partially from $G$ down to $H$. We study this problem systematically, both from the algebraic and from the path integral points of view. We find that the usual BRST cohomology must be replaced by an equivariant version and that the ghost Lagrangian must always include quartic ghost terms, even at tree level. Both the Cartan and Weil models for equivariant cohomology play a role and find natural interpretations within the physics framework. Applications include the construction of D-brane models of emergent space, the ’t Hooft Abelian projection scenario in quantum chromodynamics and the formulation of the low-energy effective theories of grand unified models.

This article investigates the construction of fermions and the formulation of the Standard Model of particle physics in a theory in which the Lorentz signature emerges from an underlying microscopic purely Euclidean $SO(4)$ theory. Couplings to a clock field are responsible for triggering the change of signature of the effective metric in which the standard fields propagate. We demonstrate that Weyl and Majorana fermions can be constructed in this framework. This construction differs from other studies of Euclidean fermions, as the coupling to the clock field allows us to write down an action which flows to the usual action in Minkowski spacetime. We then show how the Standard Model can be obtained in this theory and consider the constraints on non-Standard-Model operators which can appear in the QED sector due to $CPT$ and Lorentz violation.

We consider the two-point correlators of Yang-Mills theories at finite temperature in the Landau gauge. We employ a model for the corresponding Yang-Mills correlators based on the inclusion of an effective mass term for gluons. The latter is expected to have its origin in the existence of Gribov copies. One-loop calculations at zero temperature have been shown to agree remarkably well with the corresponding lattice data. We extend on this and perform a one-loop calculation of the Matsubara gluon and ghost two-point correlators at finite temperature. We show that, as in the vacuum, an effective gluon mass accurately captures the dominant infrared physics for the magnetic gluon and ghost propagators. It also reproduces the gross qualitative features of the electric gluon propagator. In particular, we find a slight nonmonotonous behavior of the Debye mass as a function of temperature, however not as pronounced asin existing lattice results. A more quantitative description of the electric sector near the deconfinement phase transition certainly requires another physical ingredient sensitive to the order parameter of the transition.

We extend the Wald solution to a black hole that is also moving at constant velocity. More specifically, we derive analytic solutions for the Maxwell equations for a rotating black hole moving at constant speed in an asymptotically uniform magnetic test field. By adopting Kerr-Schild coordinates we avoid singular behaviors at the horizon and obtain a complete description of the charge and current distributions in terms of the black-hole spin and velocity. Using this solution, we compute the energy losses expected when charged particles are accelerated along the magnetic field lines, improving previous estimates that had to cope with singular electromagnetic fields on the horizon. When used to approximate the emission from binary black holes in a uniform magnetic field, our estimates match reasonably well those from numerical-relativity calculations in the force-free approximation.

We incorporate realistic, tabulated equations of state into fully relativistic simulations of magnetized neutron stars along with a neutrino leakage scheme which accounts for cooling via neutrino emission. Both these improvements utilize open-source code (GR1D) and tables from the Web site stellarcollapse.org. Our implementation makes use of a novel method for the calculation of the optical depth, which simplifies its use with distributed adaptive mesh refinement. We present various tests with and without magnetization and preliminary results both from single stars and from the merger of a binary system.

Emergent theory assumes that the universe originates from an Einstein static (ES) state rather than the big bang singularity, and, thus, provides a possible way to resolve the singularity problem. The stability against all kinds of perturbations that ensures the past eternity of the ES state is crucial for a successful realization of the emergent scenario. Recently, it has been found that in the context of the Jordan-Brans-Dicke (JBD) theory there exists a stable ES solution under homogenous and anisotropic perturbations. In this paper, we extend the analysis to the stability against tensor and inhomogeneous scalar perturbations. We find that, different from general relativity and $f(R)$ theory, a stable ES solution is allowed in the JBD theory when different kinds of perturbations are considered, although the stability conditions are tighter for tensor and inhomogeneous scalar perturbations than those for homogenous and anisotropic ones.

The propagation of plane electromagnetic waves in the gravitational field inside a rotating cloud of dark matter is analyzed. Formulas for the deflection and absorption of light and the rotation of the polarization plane are obtained in closed form in terms of the mass density and the angular velocity of the cloud. It is shown that the formulas can be considerably simplified for axisymmetric configurations. As an example, the formalism is applied to a rotating massive cloud described by a Plummer potential.

This paper investigates the Faraday effect as a different source of $B$-mode polarization. The $E$-mode polarization is Faraday rotated provided a stochastic large-scale magnetic field is present prior to photon decoupling. In the first part of the paper we discuss the case where the tensor modes of the geometry are absent and we argue that the $B$ mode recently detected by the BICEP2 Collaboration cannot be explained by a large-scale magnetic field rotating, through the Faraday effect, the well-established $E$-mode polarization. In this case, the observed temperature autocorrelations would be excessively distorted by the magnetic field. In the second part of the paper the formation of Faraday rotation is treated as a stationary, random and Markovian process with the aim of generalizing a set of scaling laws originally derived in the absence of the tensor modes of the geometry. We show that the scalar, vector and tensor modes of the brightness perturbations can all be Faraday rotated even if the vector and tensor parts of the effect have been neglected, so far, by focussing the attention on the scalar aspects of the problem. The mixing between the power spectra of the $E$-mode and $B$-mode polarizations involves a unitary transformation depending nonlinearly on the Faraday rotation rate. The present approach is suitable for a general scrutiny of the polarization observables and of their frequency dependence.

Current searches for gravitational waves from coalescing binary black holes (BBH) use templates that only include the dominant harmonic. In this study we use effective-one-body multipolar waveforms calibrated to numerical-relativity simulations to quantify the effect of neglecting subdominant harmonics on the sensitivity of searches. We consider both signal-to-noise ratio (SNR) and the signal-based vetoes that are used to reweight SNR. We find that neglecting subdominant modes when searching for nonspinning BBHs with component masses $3{\mathrm{M}}_{\odot }\le m_1$, $m_2\le 200{\mathrm{M}}_{\odot }$ and total mass $M<360{\mathrm{M}}_{\odot }$ in advanced LIGO results in a negligible reduction of the reweighted SNR at detection thresholds. Subdominant modes therefore have no effect on the detection rates predicted for advanced LIGO. Furthermore, we find that if subdominant modes are included in templates the sensitivity of the search becomes worse if we use current search priors, due to an increase in false alarm probability. Templates would need to be weighted differently than what is currently done to compensate for the increase in false alarms. If we split the template bank such that subdominant modes are only used when $M\gtrsim 100{\mathrm{M}}_{\odot }$ and mass ratio $q\gtrsim 4$, we find that the sensitivity does improve for these intermediate mass-ratio BBHs, but the sensitive volume associated with these systems is still small compared to equal-mass systems. Using subdominant modes is therefore unlikely to substantially increase the probability of detecting gravitational waves from nonspinning BBH signals unless there is a relatively large population of intermediate mass-ratio BBHs in the universe.

The recent detection by the BICEP2 Collaboration of a high level of tensor modes has relevant implications which we briefly discuss in this short note. In particular, the large angle CMB B-mode polarization seems to imply problematic super-Planckian excursions of the inflaton field. We provide some comments about this point and in particular we stress a natural resolution to it: given our current (and probably future) observational ignorance about the true source of the scalar perturbations, one should abandon the theoretical prejudice that they are associated to the inflaton fluctuations.

Recent LHCb measurements show small discrepancies with respect to the Standard Model (SM) predictions in selected angular distributions of the mode $B^0\to K^{*0}{\mu }^{+}{\mu }^{-}$. The possibility of explaining such tensions within theories beyond the SM crucially depends on the size of the deviations of the Wilson coefficients of the effective Hamiltonian for this mode, in comparison to their SM values. We analyze this issue in the framework of the Randall–Sundrum model with custodial protection (${\mathrm{RS}}_c$); in our study we also consider the mode with $\tau$ leptons in the final state. We discuss the small deviations of ${\mathrm{RS}}_c$ results from SM ones, found scanning the parameter space of the model.

In this exploratory lattice study, low-energy scattering of the $(D{\overline{D}}^{*}{)}^{\pm }$ meson system is analyzed using lattice QCD with $N_f=2$ twisted mass fermion configurations with three pion mass values. The calculation is performed within single-channel Lüscher’s finite-size formalism. The threshold scattering parameters, namely the scattering length $a_0$ and the effective range $r_0$, for the $s$-wave scattering in $J^P=1^{+}$ channel are extracted. For the cases in our study, the interaction between the two charmed mesons is weakly repulsive. Our lattice results therefore do not support the possibility of a shallow bound state for the two mesons for the pion mass values we studied. This calculation provides some useful information on the nature of the newly discovered resonance-like structure $Z_c(3900)$ by various experimental groups.

The covariant spectator quark model is applied to the ${\gamma }^{*}N\to N^{*}(1520)$ reaction in the spacelike region. The spin quark core contributions to the electromagnetic form factors and helicity transition amplitudes are estimated from the covariant structure of the $N^{*}(1520)$ wave function calibrated by the experimental data for large squared momentum transfer $Q^2$. The difference between the model results and the experimental data is then used to parametrize the low $Q^2$ behavior, where meson cloud effects are assumed to dominate. This parametrization can be very useful for future studies of the reaction, as well as for the extension of the transition form factors to the timelike region.

Triple gauge boson hadroproduction, in particular the production of three $W$-bosons at the LHC, is considered at next-to leading order accuracy in QCD. The NLO matrix elements are combined with parton showers. Multijet merging is invoked such that NLO matrix elements with one additional jet are also included. The studies here incorporate both the signal and all relevant backgrounds for $VH$ production with the subsequent decay of the Higgs boson into $W$– or $\tau$–pairs. They have been performed using Sherpa$+$OpenLoops in combination with Collier.

The frequency dependent conductivity $\sigma (\omega )$ of the strongly coupled quark-gluon plasma is estimated using a bottom up holographic model that can adequately describe recent lattice data for QCD thermodynamics at zero chemical potential. Different choices for the coupling between the bulk gauge field and the other bulk fields that define the background (the metric and a scalar field) are used in order to fit the lattice data for the electric charge susceptibility ${\chi }_2^Q/T^2$. The ratio ${\sigma }_{\mathrm{DC}}/T$ is found to vary near the deconfinement transition in a way that is similar to recent lattice results. This model is used to compute the charge diffusion coefficient $D$ of the strongly coupled plasma. We find that the dimensionless combination $DT$ has the same type of temperature dependence displayed by ${\sigma }_{\mathrm{DC}}/T$, and, thus, charge diffusion is suppressed at low temperatures. The frequency dependent conductivity $\sigma (\omega )$ reveals some nontrivial structure for values of the temperature near the phase transition. None of these structures appears in the associated Euclidean correlator, which we also compute. Our results suggest that the conformal invariance violation near the QCD deconfinement phase transition may be seen in the Euclidean correlator through a downward shift of its value at the minimum, which gives a rough estimate of the temperature dependence of the DC conductivity in the plasma.