The atomic transition from an excited state $|\mathrm{e}⟩$ to the ground state $|\mathrm{g}⟩$ by emitting a neutrino pair and a photon, i.e., $|\mathrm{e}⟩\to |\mathrm{g}⟩+|\gamma ⟩+|{\nu }_i⟩+|{\overline{\nu }}_j⟩$ with $i$, $j=1$, 2, 3, has been proposed by Yoshimura and his collaborators as an alternative way to determine the absolute scale $m_0$ of neutrino masses. More recently, a statistical analysis of the fine structure of the photon spectrum from this atomic process has been performed [N. Song et al. Phys. Rev. D 93, 013020 (2016)] to quantitatively examine the experimental requirements for a realistic determination of absolute neutrino masses. In this paper, we show how to improve the statistical analysis and demonstrate that the previously required detection time can be reduced by one order of magnitude for the case of a $3\sigma$ determination of $m_0\sim 0.01\mathrm{eV}$ with an accuracy better than 10%. Such an improvement is very encouraging for further investigations on measuring absolute neutrino masses through atomic processes.

We develop the consequences of introducing a purely leptonic, lepton number violating nonstandard interaction (NSI) and standard model neutrino mixing with a fourth, sterile neutrino in the analysis of short baseline, neutrino experiments. We focus on the muon decay at rest (DAR) results from the Liquid Scintillation Neutrino Experiment (LSND) and the Karlsruhe and Rutherford Medium Energy Neutrino Experiment. We make a comprehensive analysis of lepton number violating, NSI effective operators and find nine that affect muon decay relevant to LSND results. Two of these preserve the standard model value $3/4$ for the Michel $\rho$ and $\delta$ parameters and, overall, show favorable agreement with precision data and the ${\overline{\nu }}_e$ signal from LSND data. We display theoretical models that lead to these two effective operators. In the model we choose to apply to DAR data, both ${\overline{\nu }}_e$ appearance from ${\overline{\nu }}_{\mu }$ oscillation and ${\overline{\nu }}_e$ survival after production from NSI decay of the ${\mu }^{+}$ contribute to the expected signal. This is a unique feature of our scheme. We find a range of parameters where both experiments can be accommodated consistently with recent global, sterile neutrino fits to short baseline data. We comment on implications of the models for new physics searches at colliders and comment on further implications of the lepton number violating interactions plus sterile neutrino-standard neutrino mixing.

The recent proposal of a photon and a neutrino-pair beam is investigated in detail. Production rates, both differential and total, of a single photon, two photons, and a neutrino pair emitted from quantum ions in circular motion are given for any velocity of ion. This part is an extension of our previous calculations at highest energies to lower energies of circulating ions, and hopefully helps to identify the new process of quantum ion circulation at a low energy ring. We clarify how to utilize the circulating ion for a new source of coherent neutrino beam despite much stronger background photons. Once one verifies that the coherence is maintained in the initial phases of time evolution after laser irradiation, large background photon emission rates are not an obstacle against utilizing the extracted neutrino-pair beam.

Majorana neutrinos naturally lead to a lepton number violation (LNV). A superposition of Majorana states can mimic Dirac-type neutrinos, leading to lepton number conservation. Using the example of specific observables related to high- and low-energy processes, we demonstrate how the strength of LNV correlates with neutrino parameters, such as $CP$ phases, flavor mixings, and mass ratios. We stress the coaction of low- and high-energy studies for quantitatively testing phenomenological models. Second, we conclude that in order to fully study the role of heavy neutrinos in the search for new physics signals, a departure from trivial scenarios assuming degeneracy in mass and no flavor mixing or $CP$ phases becomes necessary for a proper physical analysis.

Many studies have been carried out in the literature to evaluate the number of polarization modes of gravitational waves in modified theories, in particular in $f(R)$ theories. In the latter ones, besides the usual two transverse-traceless tensor modes present in general relativity, there are two additional scalar ones: a massive longitudinal mode and a massless transverse mode (the so-called breathing mode). This last mode has often been overlooked in the literature, due to the assumption that the application of the Lorenz gauge implies transverse-traceless wave solutions. We however show that this is in general not possible and, in particular, that the traceless condition cannot be imposed due to the fact that we no longer have a Minkowski background metric. Our findings are in agreement with the results found using the Newman-Penrose formalism and thus clarify the inconsistencies found so far in the literature.

We study here, using the Mannheim-Kazanas solution of Weyl conformal theory, the mass decomposition in the representative subsample of 57 early-type elliptical lens galaxies of the Sloan Lens Advanced Camera for Surveys (SLACS) on board the Hubble Space Telescope. We begin by showing that the solution need not be an exclusive solution of conformal gravity but can also be viewed as a solution of a class of $f(R)$ gravity theories coupled to nonlinear electrodynamics thereby rendering the ensuing results more universal. Since lensing involves light bending, we shall first show that the solution adds to Schwarzschild light bending caused by the luminous mass ($M_{*}$) a positive contribution $+\gamma R$ contrary to the previous results in the literature, thereby resolving a long-standing problem. The cause of the error is critically examined. Next, applying the expressions for light bending together with an input equating Einstein and Weyl angles, we develop a novel algorithm for separating the luminous component from the total lens mass ($\text{luminous}+\text{dark}$) within the Einstein radius. Our results indicate that the luminous mass estimates differ from the observed total lens masses by a linear proportionality factor across the subsample, which qualitatively agrees with the common conclusion from a number of different simulations in the literature. In quantitative detail, we observe that the ratios of luminous over total lens mass ($f^{*}$) within the Einstein radius of individual galaxies take on values near unity, many of which remarkably fall inside or just marginally outside the specified error bars obtained from a simulation based on the Bruzual-Charlot stellar population synthesis model together with the Salpeter initial mass function favored on the ground of metallicity [Grillo et al., Astron. Astrophys. 501, 461 (2009)]. We shall also calculate the average dark matter density ${⟨\rho ⟩}_{\mathrm{av}}$ of individual galaxies within their respective Einstein spheres. To our knowledge, the present approach, being truly analytic, seems to be the first of its kind attempting to provide a new decomposition scheme distinct from the simulational ones.

We formulate an effective theory of structure formation (ETHOS) that enables cosmological structure formation to be computed in almost any microphysical model of dark matter physics. This framework maps the detailed microphysical theories of particle dark matter interactions into the physical effective parameters that shape the linear matter power spectrum and the self-interaction transfer cross section of nonrelativistic dark matter. These are the input to structure formation simulations, which follow the evolution of the cosmological and galactic dark matter distributions. Models with similar effective parameters in ETHOS but with different dark particle physics would nevertheless result in similar dark matter distributions. We present a general method to map an ultraviolet complete or effective field theory of low-energy dark matter physics into parameters that affect the linear matter power spectrum and carry out this mapping for several representative particle models. We further propose a simple but useful choice for characterizing the dark matter self-interaction transfer cross section that parametrizes self-scattering in structure formation simulations. Taken together, these effective parameters in ETHOS allow the classification of dark matter theories according to their structure formation properties rather than their intrinsic particle properties, paving the way for future simulations to span the space of viable dark matter physics relevant for structure formation.

Axionlike particles (ALPs) and photons interconvert in the presence of a magnetic field. At keV energies in the environment of galaxy clusters, the conversion probability can become unsuppressed for light ALPs. Conversion of thermal x-ray photons into ALPs can introduce a steplike feature into the cluster thermal bremsstrahlung spectrum, and we argue that existing x-ray data on galaxy clusters should be sufficient to extend bounds on ALPs in the low-mass region $m_a\lesssim 1\times {10}^{-12}\mathrm{eV}$ down to $M\sim 7\times {10}^{11}\mathrm{GeV}$, and that for ${10}^{11}\mathrm{GeV}<M\lesssim {10}^{12}\mathrm{GeV}$ light ALPs give rise to interesting and unique observational signatures that may be probed by existing and upcoming x-ray (and potentially x-ray polarization) observations of galaxy clusters.

The two-pion low-energy contribution to the anomalous magnetic moment of the muon, $a_{\mu }\equiv (g-2{)}_{\mu }/2$, expressed as an integral over the modulus squared of the pion electromagnetic form factor, brings a relatively large contribution to the theoretical error, since the low accuracy of experimental measurements in this region is amplified by the drastic increase of the integration kernel. We derive stringent constraints on the two-pion contribution by exploiting analyticity and unitarity of the pion electromagnetic form factor. To avoid the poor knowledge of the modulus of this function, we use instead its phase, known with high precision in the elastic region from Roy equations for pion-pion scattering via the Fermi-Watson theorem. Above the inelastic threshold we adopt a conservative integral condition on the modulus, determined from data and perturbative QCD. Additional high precision data on the modulus in the range 0.65–0.71 GeV, obtained from $e^{+}{e}^{-}$ annihilation and $\tau$-decay experiments, are used to improve the predictions on the modulus at lower energies by means of a parametrization-free analytic extrapolation. The results are optimal for a given input and do not depend on the unknown phase of the form factor above the inelastic threshold. The present work improves a previous analysis based on the same technique, including more experimental data and employing better statistical tools for their treatment. We obtain for the contribution to $a_{\mu }$ from below 0.63 GeV the value $(133.258\pm 0.723)\times {10}^{-10}$, which amounts to a reduction of the theoretical error by about $6\times {10}^{-11}$.

We revisit the WIMP-type dark matter scattering on electrons that results in atomic ionization and can manifest itself in a variety of existing direct-detection experiments. Unlike the WIMP-nucleon scattering, where current experiments probe typical interaction strengths much smaller than the Fermi constant, the scattering on electrons requires a much stronger interaction to be detectable, which in turn requires new light force carriers. We account for such new forces explicitly, by introducing a mediator particle with scalar or vector couplings to dark matter and to electrons. We then perform state-of-the-art numerical calculations of atomic ionization relevant to the existing experiments. Our goals are to consistently take into account the atomic physics aspect of the problem (e.g., the relativistic effects, which can be quite significant) and to scan the parameter space—the dark matter mass, the mediator mass, and the effective coupling strength—to see if there is any part of the parameter space that could potentially explain the DAMA modulation signal. While we find that the modulation fraction of all events with energy deposition above 2 keV in NaI can be quite significant, reaching $\sim 50\%$, the relevant parts of the parameter space are excluded by the XENON10 and XENON100 experiments.

Dark matter may interact with the Standard Model through the kinetic mixing of dark photons, $A^{\prime }$, with Standard Model photons. Such dark matter will accumulate in the Sun and annihilate into dark photons. The dark photons may then leave the Sun and decay into pairs of charged Standard Model particles that can be detected by the Alpha Magnetic Spectrometer (AMS). The directionality of this “dark sunshine” is distinct from all astrophysical backgrounds, providing an opportunity for unambiguous dark matter discovery by AMS. We perform a complete analysis of this scenario including Sommerfeld enhancements of dark matter annihilation and the effect of the Sun’s magnetic field on the signal, and we define a set of cuts to optimize the signal probability. With the three years of data already collected, AMS may discover dark matter with mass $1\mathrm{TeV}\lesssim m_X\lesssim 10\mathrm{TeV}$, dark photon masses $m_{A^{\prime }}\sim \mathcal{O}(100)\mathrm{MeV}$, and kinetic mixing parameters ${10}^{-11}\lesssim ϵ\lesssim {10}^{-8}$. The proposed search extends beyond existing beam dump and supernova bounds, and it is complementary to direct detection, probing the same region of parameter space.

For quantum field theories with topological sectors, Monte Carlo simulations on fine lattices tend to be obstructed by an extremely long autocorrelation time with respect to the topological charge. Then reliable numerical measurements are feasible only within individual sectors. The challenge is to assemble such restricted measurements in a way that leads to a substantiated approximation to the fully fledged result, which corresponds to the correct sampling over the entire set of configurations. We test an approach for such a topological summation, which was suggested by Brower, Chandrasekharan, Negele and Wiese. Under suitable conditions, energy levels and susceptibilities can be obtained to a good accuracy, as we demonstrate for $\mathrm{O}(N)$ models, SU(2) Yang-Mills theory, and for the Schwinger model.

Recently, both ATLAS and CMS Collaborations report an excess at 750 GeV in the diphoton invariant mass spectrum at 13 TeV LHC. If it is a new (pseudo)scalar produced via a loop-induced gluon-gluon fusion process, it is important to know what the particle in the loop is. In this work, we investigate the possibility of determining the fraction of the contribution from the standard-model top quark in the loop.

We calculate—for the first time in three-flavor lattice QCD—the hadronic matrix elements of all five local operators that contribute to neutral $B^0$- and $B_s$-meson mixing in and beyond the Standard Model. We present a complete error budget for each matrix element and also provide the full set of correlations among the matrix elements. We also present the corresponding bag parameters and their correlations, as well as specific combinations of the mixing matrix elements that enter the expression for the neutral $B$-meson width difference. We obtain the most precise determination to date of the SU(3)-breaking ratio $\xi =1.206(18)(6)$, where the second error stems from the omission of charm-sea quarks, while the first encompasses all other uncertainties. The threefold reduction in total uncertainty, relative to the 2013 Flavor Lattice Averaging Group results, tightens the constraint from $B$ mixing on the Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle. Our calculation employs gauge-field ensembles generated by the MILC Collaboration with four lattice spacings and pion masses close to the physical value. We use the asqtad-improved staggered action for the light-valence quarks and the Fermilab method for the bottom quark. We use heavy-light meson chiral perturbation theory modified to include lattice-spacing effects to extrapolate the five matrix elements to the physical point. We combine our results with experimental measurements of the neutral $B$-meson oscillation frequencies to determine the CKM matrix elements $|V_{td}|=8.00(34)(8)\times {10}^{-3}$, $|V_{ts}|=39.0(1.2)(0.4)\times {10}^{-3}$, and $|V_{td}/V_{ts}|=0.2052(31)(10)$, which differ from CKM-unitarity expectations by about $2\sigma$. These results and others from flavor-changing-neutral currents point towards an emerging tension between weak processes that are mediated at the loop and tree levels.

At the Fermilab Tevatron proton-antiproton ($p\overline{p}$) collider, Drell-Yan lepton pairs are produced in the process $p\overline{p}\to e^{+}{e}^{-}+X$ through an intermediate ${\gamma }^{*}/Z$ boson. The forward-backward asymmetry in the polar-angle distribution of the $e^{-}$ as a function of the $e^{+}{e}^{-}$-pair mass is used to obtain ${\sin }^2{\theta }_{\text{eff}}^{\text{lept}}$, the effective leptonic determination of the electroweak-mixing parameter ${\sin }^2{\theta }_W$. The measurement sample, recorded by the Collider Detector at Fermilab (CDF), corresponds to $9.4{\mathrm{fb}}^{-1}$ of integrated luminosity from $p\overline{p}$ collisions at a center-of-momentum energy of 1.96 TeV, and is the full CDF Run II data set. The value of ${\sin }^2{\theta }_{\text{eff}}^{\text{lept}}$ is found to be $0.23248\pm 0.00053$. The combination with the previous CDF measurement based on ${\mu }^{+}{\mu }^{-}$ pairs yields ${\sin }^2{\theta }_{\text{eff}}^{\text{lept}}=0.23221\pm 0.00046$. This result, when interpreted within the specified context of the standard model assuming ${\sin }^2{\theta }_W=1-M_W^2/M_Z^2$ and that the $W$- and $Z$-boson masses are on-shell, yields ${\sin }^2{\theta }_W=0.22400\pm 0.00045$, or equivalently a $W$-boson mass of $80.328\pm 0.024\mathrm{GeV}/c^2$.

This paper presents a search for massive charged long-lived particles produced in $pp$ collisions at $\sqrt{s}=13\mathrm{TeV}$ at the LHC using the ATLAS experiment. The data set used corresponds to an integrated luminosity of $3.2{\mathrm{fb}}^{-1}$. Many extensions of the Standard Model predict the existence of massive charged long-lived particles, such as $R$-hadrons. These massive particles are expected to be produced with a velocity significantly below the speed of light, and therefore to have a specific ionization higher than any Standard Model particle of unit charge at high momenta. The Pixel subsystem of the ATLAS detector is used to measure the ionization energy loss of reconstructed charged particles and to search for such highly ionizing particles. The search presented here has much greater sensitivity than a similar search performed using the ATLAS detector in the $\sqrt{s}=8\mathrm{TeV}$ data set, thanks to the increase in expected signal cross section due to the higher center-of-mass energy of collisions, to an upgraded detector with a new silicon layer close to the interaction point, and to analysis improvements. No significant deviation from Standard Model background expectations is observed, and lifetime-dependent upper limits on $R$-hadron production cross sections and masses are set. Gluino $R$-hadrons with lifetimes above 0.4 ns and decaying to $q\overline{q}$ plus a 100 GeV neutralino are excluded at the 95% confidence level, with lower mass limit ranging between 740 and 1590 GeV. In the case of stable $R$-hadrons the lower mass limit at the 95% confidence level is 1570 GeV.

We perform the first measurement on the $D^0-{\overline{D}}^0$ mixing parameters using a time-dependent amplitude analysis of the decay $D^0\to {\pi }^{+}{\pi }^{-}{\pi }^0$. The data were recorded with the BABAR detector at center-of-mass energies at and near the $\Upsilon (4S)$ resonance, and correspond to an integrated luminosity of approximately $468.1{\mathrm{fb}}^{-1}$. The neutral $D$ meson candidates are selected from $D^{*}(2010{)}^{+}\to D^0{\pi }_s^{+}$ decays where the flavor at the production is identified by the charge of the low-momentum pion, ${\pi }_s^{+}$. The measured mixing parameters are $x=(1.5\pm 1.2\pm 0.6)\%$ and $y=(0.2\pm 0.9\pm 0.5)\%$, where the quoted uncertainties are statistical and systematic, respectively.

A known feature of electrically charged Reissner–Nordström–anti-de Sitter planar black holes is that they can become unstable when considered as solutions of Einstein-Yang-Mills theory. The mechanism for this is that the linearized Yang-Mills equations in the background of the Reissner-Nordström (RN) black holes possess a normalizable zero mode, resulting in non-Abelian (nA) magnetic clouds near the horizon. In this work we show that the same pattern may occur also for asymptotically flat RN black holes. Different from the anti–de Sitter case, in the Minkowskian background the prerequisites for the existence of the nA clouds are (i) a large enough gauge group, and (ii) the presence of some extra interaction terms in the matter Lagrangian. To illustrate this mechanism we present two specific examples, one in four- and the other in five-dimensional asymptotically flat spacetime. In the first case, we augment the usual $SU(3)$ Yang-Mills Lagrangian with a higher-order (quartic) curvature term, while for the second one we add the Chern-Simons density to the $SO(6)$ Yang-Mills system. In both cases, an Abelian gauge symmetry is spontaneously broken near a RN black hole horizon with the appearance of a condensate of nA gauge fields. In addition to these two examples, we review the corresponding picture for anti–de Sitter black holes. All these solutions are studied both analytically and numerically, existence proofs being provided for nA clouds in the background of RN black holes. The proofs use shooting techniques which are suggested by and in turn offer insights for our numerical methods. They indicate that, for a black hole of given mass, appropriate electric charge values are required to ensure the existence of solutions interpolating desired boundary behavior at the horizons and spatial infinity.

In this work, we consider electromagnetic dynamics in Randall-Sundrum branes. It is derived from a family of four-dimensional spacetimes compatible with Randall-Sundrum brane worlds, focusing on asymptotic flat backgrounds. Maximal extensions of the solutions are constructed, and their causal structures are discussed. These spacetimes include singular, nonsingular, and extreme black holes. Maxwell’s electromagnetic field is introduced, and its evolution is studied in an extensive numerical survey. Electromagnetic quasinormal mode spectra are derived and analyzed with time-dependent and high-order WKB methods. Our results indicate that the black holes in the brane are electromagnetically stable.

Consistency of the unconventional view of de Sitter space as a quantum theory of gravity with a finite number of degrees of freedom requires that Coleman–De Luccia tunneling rates to vacua with negative cosmological constant should be interpreted as recurrences to low-entropy states. This demand translates into two constraints, or consistency conditions, on the scalar potential that are generically as follows: (1) the distance in field space between the de Sitter vacuum and any other vacuum with negative cosmological constant must be of the order of the reduced Planck mass or larger and (2) the fourth root of the vacuum energy density of the de Sitter vacuum must be smaller than the fourth root of the typical scale of the scalar potential. These consistency conditions shed a different light on both outstanding hierarchy problems of the standard model of particle physics: the scale of electroweak symmetry breaking and the scale of the cosmological constant. Beyond the unconventional interpretation of quantum de Sitter space, we complete the analytic understanding of the thin-wall approximation of Coleman–De Luccia tunneling, extend its numerical analysis to generic potentials and discuss the role of gravity in stabilizing the standard model potential.