We present the most general actions of a single scalar field and two scalar fields coupled to gravity, consistent with second-order field equations in four dimensions, possessing local scale invariance. We apply two different methods to arrive at our results. One method, Ricci gauging, was known to the literature and we find this to produce the same result for the case of one scalar field as a more efficient method presented here. However, we also find our more efficient method to be much more general when we consider two scalar fields. Locally scale invariant actions are also presented for theories with more than two scalar fields coupled to gravity and we explain how one could construct the most general actions for any number of scalar fields. Our generalized scale invariant actions have obvious applications to early Universe cosmology and include, for example, the Bezrukov-Shaposhnikov action as a subset.

We show that in the limit where the number of spacetime dimensions $D$ grows to infinity a very large class of black holes (including nonextremal, static, asymptotically flat ones, with any number of gauge-field charges, possibly coupled to dilatons) possess a universal set of quasinormal modes whose complex frequencies depend only on the horizon radius and no other black hole parameters. The damping ratio of these modes vanishes like $D^{-2/3}$, so they are almost normal modes, or “quasiparticle” excitations of the black hole. The structure responsible for the existence of these modes at large $D$ is also present very generally in other black holes.

Several years ago we demonstrated that the Casimir energy for perfectly reflecting and imperfectly reflecting parallel plates gravitated normally, that is, obeyed the equivalence principle. At that time the divergences in the theory were treated only formally, without proper regularization, and the coupling to gravity was limited to the canonical energy-momentum-stress tensor. Here we strengthen the result by removing both of those limitations. We consider, as a toy model, massless scalar fields interacting with semitransparent ($\delta$-function) potentials defining parallel plates, which become Dirichlet plates for strong coupling. We insert space and time point-split regulation parameters, and obtain well-defined contributions to the self-energy of each plate, and the interaction energy between the plates. (This self-energy does not vanish even in the conformally coupled, strong-coupled limit.) We also compute the local energy density, which requires regularization near the plates. In general, the energy density includes a surface energy that resides precisely on the boundaries. This energy is also regulated. The gravitational interaction of this well-defined system is then investigated, and it is verified that the equivalence principle is satisfied.

Recent perturbative self-force computations [Shah et al., Phys. Rev. D 89, DM11229 (2014)], both numerical and analytical, have determined that half-integral post-Newtonian terms arise in the conservative dynamics of black hole binaries moving on exactly circular orbits. We look at the possible origin of these terms within the post-Newtonian approximation, find that they essentially originate from nonlinear “tail-of-tail” integrals and show that, as demonstrated in the previous paper, their first occurrence is at the 5.5PN order. The post-Newtonian method we use is based on a multipolar–post-Minkowskian treatment of the field outside a general matter source, which is reexpanded in the near zone and extended inside the source thanks to a matching argument. Applying the formula obtained for generic sources to compact binaries, we obtain the redshift factor of circular black hole binaries (without spins) at 5.5PN order in the extreme mass ratio limit. Our result fully agrees with the determination of the 5.5PN coefficient by means of perturbative self-force computations reported in the previously cited paper.

Recently it has been suggested that dark radiation in the form of axions produced during the decay of string theory moduli fields could be responsible for the soft x-ray excess in galaxy clusters. These soft x-ray photons come about due to the conversion of these axions into photons in the magnetic fields of the clusters. In this work we calculate the conversion of axionic dark radiation into x-ray photons in the magnetic field of our own Galaxy. We consider $\mathrm{\Delta }{N}_{\nu }\sim 0.5$ worth of dark radiation made up of axions with energy of order 0.1–1 keV. We show that it is possible, if a little optimistic, to explain the large regions of x-ray emission located above and below the center of the Galactic plane detected in the $3/4\mathrm{keV}$ ROSAT all-sky map completely due to the conversion of dark radiation into photons with an inverse axion-photon coupling of $M\sim 3\times 10^{13}\mathrm{GeV}$ and an axion mass of $m\le 10^{-12}\mathrm{eV}$. Different parameter values could explain both these features and the $3/4\mathrm{keV}$ x-ray background. More conservatively, these x-ray observations are a good way to constrain such models of axionic dark radiation.

The Fermi-LAT data appear to have an excess of gamma-rays from the inner 150 pc of the Galactic Center. The main explanations proposed for this are an unresolved population of millisecond pulsars (MSPs), dark matter (DM) annihilation, and nonthermal bremsstrahlung produced by a population of electrons interacting with neutral gas in molecular clouds. The first two options have spatial templates well fitted by the square of a generalized Navarro-Frenk-White (NFW) profile with inner slope $\gamma =1.2$. We model the third option with a 20-cm continuum emission Galactic Ridge template. A template based on the High Energy Stereoscopic System residuals is shown to give similar results. The gamma-ray excess is found to be best fit by a combination of the generalized NFW squared template and a Galactic Ridge template. We also find that the spectra of each template is not significantly affected in the combined fit and is consistent with previous single-template fits. That is the generalized NFW squared spectrum can be fit by either of order 1000 unresolved MSPs or DM with mass around 30 GeV, a thermal cross section, and mainly annihilating to $b\overline{b}$ quarks, while the Galactic Ridge continues to have a spectrum consistent with a population of nonthermal electrons whose spectrum also provides a good fit to synchrotron emission measurements. We also show that the current DM fit may be hard to test, even with 10 years of Fermi-LAT data, especially if there is a mixture of DM and MSPs contributing to the signal, in which case the implied DM cross section will be suppressed.

A natural model of realizing effective supersymmetry is presented. Two sets of the Standard Model-like gauge group $G_1\times G_2$ are introduced, where $G_i=\mathrm{SU}(3{)}_i\times \mathrm{SU}(2{)}_i\times \mathrm{U}(1{)}_i$, which break diagonally to the Standard Model gauge group at the energy scale $M\sim {10}^7\mathrm{GeV}$. Gauge couplings in $G_1$ are assumed to be much larger than those in $G_2$. Gauge-mediated supersymmetry breaking is adopted. The first two generations (third generation) are only charged only under $G_1$ ($G_2$). The effective supersymmetry spectrum is obtained. The reproduction of realistic Yukawa couplings is studied. The fine-tuning for a 126 GeV Higgs is reduced by the large $A$ term due to direct Higgs-messenger interaction. Finally, $G_2$ is found to be a nontrivial realization of the strong unification scenario in which case we can predict ${\alpha }_s(M_Z)$ without real unification.

Naturalness arguments imply the existence of Higgsinos lighter than 200–300 GeV. However, because these Higgsinos are nearly mass degenerate, they release very little visible energy in their decays, and signals from electroweak Higgsino pair production typically remain buried under Standard Model backgrounds. Moreover, gluinos, squarks and winos may plausibly lie beyond the reach of the LHC14, so that signals from naturalness-inspired supersymmetric models may well remain hidden via conventional searches. We examine instead prospects for detecting Higgsino pair production via monojets or monophotons from initial-state radiation. We find typical signal-to-background rates at best at the 1% level and without any spectral distortions, leading to rather pessimistic conclusions regarding detectability via these channels.

Nonperturbative treatment of the quark-hadron transition at nonzero temperature $T$ and chemical potential $\mu$ in the framework of the field correlator method is generalized to the case of nonzero magnetic field B. A compact form of the quark pressure for arbitrary $B,\mu ,T$ is derived. As a result, the transition temperature is found as a function of B and $\mu$, which depends only on the following parameters: the vacuum gluonic condensate $G_2$ and the field correlator $D_1^E(x)$, which defines the Polyakov loops and is known both analytically and on the lattice. A moderate (25%) decrease of $T_c(\mu =0)$ for $eB$ changing from zero to $1{\mathrm{GeV}}^2$ is found. A sequence of transition curves in the $(\mu ,T)$ plane is obtained for $B$ in the same interval, monotonically decreasing in scale for growing $B$.

We present a study of $W^{+}{W}^{+}jj$ and $W^{-}{W}^{-}jj$ production including leptonic decays in hadron-hadron collisions. The full electroweak and QCD induced contributions and their interferences are calculated at leading order. We find that, for inclusive cuts, the interference effects can be large if the jets are produced with large transverse momentum where, however, the production rate is suppressed. We also discuss the vector-boson-fusion cuts and show the validity of the vector-boson-fusion approximation. The next-to-leading order QCD corrections to the QCD-induced channels are also calculated. Compared to the previous calculation, we allow the intermediate $W$ bosons to be off shell. For on-shell $W$ production, we obtain an excellent agreement with previous results. Our code will be publicly available as part of the parton level Monte Carlo program vbflno.

The ${\mathrm{\Xi }}_Q^{\prime }\text{−}{\mathrm{\Xi }}_Q$ transition magnetic moments are calculated in a framework of the light cone QCD sum rules method. The values of the transition magnetic moments obtained are compared with the predictions of the other theoretical approaches.

We present a simple and predictive model of radiative neutrino masses. It is a special case of the Zee model which introduces two Higgs doublets and a charged singlet. We impose a family-dependent $Z_4$ symmetry acting on the leptons, which reduces the number of parameters describing neutrino oscillations to four. A variety of predictions follow: the hierarchy of neutrino masses must be inverted; the lightest neutrino mass is extremely small and calculable; one of the neutrino mixing angles is determined in terms of the other two; the phase parameters take $CP$-conserving values with ${\delta }_{CP}=\pi$; and the effective mass in neutrinoless double beta decay lies in a narrow range, $m_{\beta \beta }=(17.6–18.5)\mathrm{meV}$. The ratio of vacuum expectation values of the two Higgs doublets, $\tan \beta$, is determined to be either 1.9 or 0.19 from neutrino oscillation data. Flavor-conserving and flavor-changing couplings of the Higgs doublets are also determined from neutrino data. The nonstandard neutral Higgs bosons, if they are moderately heavy, would decay dominantly into $\mu$ and $\tau$ with prescribed branching ratios. Observable rates for the decays $\mu \to e\gamma$ and $\tau \to 3\mu$ are predicted if these scalars have masses in the range of 150–500 GeV.

We perform an analysis of the $D^{+}\to K_S^0{\pi }^{+}{\pi }^0$ Dalitz plot using a data set of $2.92{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collisions at the $\psi (3770)$ mass accumulated by the BESIII experiment, in which 166694 candidate events are selected with a background of 15.1%. The Dalitz plot is found to be well represented by a combination of six quasi-two-body decay channels [$K_S^0{\rho }^{+}$, $K_S^0\rho (1450{)}^{+}$, ${\overline{K}}^{*0}{\pi }^{+}$, ${\overline{K}}_0(1430{)}^0{\pi }^{+}$, $\overline{K}(1680{)}^0{\pi }^{+}$, ${\overline{\kappa }}^0{\pi }^{+}$] plus a small nonresonant component. Using the fit fractions from this analysis, partial branching ratios are updated with higher precision than previous measurements.

In this paper, we investigate the Randall-Sundrum–type braneworld models in the scalar-tensor theory with field derivative coupling to the Einstein tensor. We first formulate the generalized junction conditions of the metric and the scalar field on the timelike codimension-one hypersurface ($=\text{brane}$). With the use of these junction conditions, we then derive the Minkowski and de Sitter brane solutions embedded into the $Z_2$-symmetric five-dimensional anti–de Sitter (AdS) bulk spacetime. The configuration of the scalar field depends on the slice of the AdS spacetime. These branes are supported by the tension and not coupled to the scalar field. The Minkowski brane solution can be obtained when the brane tension is tuned to the bulk contributions. Once this tuning relation is broken, the de Sitter brane solutions are obtained. The de Sitter brane solutions have two branches. One has the smooth limit to the case where the scalar field becomes trivial, while the other branch does not. The latter branch has the upper bound on the brane tension, where the expansion rate vanishes. Finally, we investigate the low energy effective gravitational theory realized on the brane, which is given by the four-dimensional Einstein-scalar theory with the corrections from the bulk.

We derive the master equation that completely determines the time evolution of the density matrix of the Unruh-DeWitt detector in an arbitrary background geometry. We apply the equation to reveal a nonequilibrium thermodynamic character of de Sitter space. This generalizes an earlier study on the thermodynamic property of the Bunch-Davies vacuum that an Unruh-DeWitt detector staying in the Poincaré patch and interacting with a scalar field in the Bunch-Davies vacuum behaves as if it is in a thermal bath of finite temperature. In this paper, instead of the Bunch-Davies vacuum, we consider a class of initial states of scalar field, for which the detector behaves as if it is in a medium that is not in thermodynamic equilibrium and that undergoes a relaxation to the equilibrium corresponding to the Bunch-Davies vacuum. We give a prescription for calculating the relaxation times of the nonequilibrium processes. We particularly show that, when the initial state of the scalar field is the instantaneous ground state at a finite past, the relaxation time is always given by a universal value of half the curvature radius of de Sitter space. We expect that the relaxation time gives a nonequilibrium thermodynamic quantity intrinsic to de Sitter space.

The standard multidetector $\mathcal{F}$-statistic for continuous gravitational waves is susceptible to false alarms from instrumental artifacts, for example monochromatic sinusoidal disturbances (“lines”). This vulnerability to line artifacts arises because the $\mathcal{F}$-statistic compares the signal hypothesis to a Gaussian-noise hypothesis, and hence is triggered by anything that resembles the signal hypothesis more than Gaussian noise. Various ad-hoc veto methods to deal with such line artifacts have been proposed and used in the past. Here we develop a Bayesian framework that includes an explicit alternative hypothesis to model disturbed data. We introduce a simple line model that defines lines as signal candidates appearing only in one detector. This allows us to explicitly compute the odds between the signal hypothesis and an extended noise hypothesis, resulting in a new detection statistic that is more robust to instrumental artifacts. We present and discuss results from Monte-Carlo tests on both simulated data and on detector data from the fifth LIGO science run. We find that the line-robust statistic retains the detection power of the standard $\mathcal{F}$-statistic in Gaussian noise. In the presence of line artifacts it is more sensitive, even compared to the popular $\mathcal{F}$-statistic consistency veto, over which it improves by as much as a factor of two in detectable signal strength.

We enumerate the $4(1+F)+2S$ independent arbitrary functions of space required to describe a general relativistic cosmology containing an arbitrary number of noninteracting fluid ($F$) and scalar fields ($S$). Results are also given for arbitrary space dimension and for higher-order gravity theories, where the number increases to $16+4F+2S$. Both counts are subject to assumptions about whether the dark energy is a cosmological constant. A more detailed analysis is provided when global homogeneity is assumed and the functions become constants. This situation is also studied in the case where the flat and open universes have compact spatial topologies. This changes the relative generalities significantly and places new constraints on the types of expansion anisotropy that are permitted. The most general compact homogeneous universes containing Friedmann models are spatially flat and described by $8+4F+2S$ constants. Comparisons are made with the simple six-parameter lambda-CDM model and physical interpretations provided for the parameters needed to describe the most general cosmological models.

I study the corrections engendered by the insertion of a “melon” graph in the bulk of the first-order spinfoam used for the graviton propagator. I find that these corrections are highly nontrivial and, in particular, that they concern those terms which disappear in the Bojowald-Bianchi-Magliaro-Perini limit of vanishing Barbero-Immirzi parameter at fixed area ($\gamma \to 0,\gamma j\sim cst$). This fact is the first realization of the often cited idea that the spinfoam amplitude receives higher order corrections under the refinement of the underlying two-complex.

We consider general relativity with matter and radiation, with one of these fluids being coupled to a vacuum. We find that the Universe dynamics starts by an inflation phase if the coupled fluid has a negative energy density at an early time. Then, there is always a finite scale factor singularity except when vacuum and matter are coupled and matter density behaves like a negative radiation density. Moreover, the convergence to the $\mathrm{\Lambda }CDM$ model is clearly easier to reach when a vacuum is coupled to matter rather than to radiation. Two classes of theories are studied to illustrate these results.

The IsoDAR antineutrino source, which produces a flux from ${}^8\mathrm{Li}$ isotope decay at rest, when paired with the proposed Jiangmen Underground Neutrino Observatory detector, has unprecedented sensitivity to ${\overline{\nu }}_e$ disappearance for oscillations at high $\mathrm{\Delta }{m}^2$. Assuming charge conjugation, parity transformation, and time reversal $(CPT)$ invariance, the sensitive region for ${\overline{\nu }}_e$ disappearance can be used to restrict the allowed parameter space of a ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ appearance signal. The $5\sigma$ sensitivity of this experiment covers the entire ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ allowed parameter space from a combined fit to short-baseline experiments. This represents a decisive test of the LSND neutrino experiment and MiniBooNE antineutrino appearance signals within all models that are $CPT$ invariant. Running IsoDAR at KamLAND restricts a large part of the appearance signal region in a similar way.