We construct multipole moments for stationary, asymptotically flat, spacetime solutions to higher-order curvature theories of gravity. The moments are defined using $3+1$ techniques involving timelike Killing vector constructions as in the classic papers by Geroch and Hansen. Using the fact that the Kerr-Newman metric is a vacuum solution to a particular class of $f(R)$ theories of gravity, we compute all its moments, and find that they admit recurrence relations similar to those for the Kerr solution in general relativity. It has been proposed previously that modeling the measured frequencies of quasiperiodic oscillations from galactic microquasars enables experimental tests of the no-hair theorem. We explore the possibility that, even if the no-hair relation is found to break down in the context of general relativity, there may be an $f(R)$ counterpart that is preserved. We apply the results to the microquasars GRS $1915+105$ and GRO J1655-40 using the diskoseismology and kinematic resonance models, and constrain the spins and “charges” of their black holes.

This paper examines the behavior of closed “lattice universes” wherein masses are distributed in a regular lattice on the Cauchy surfaces of closed vacuum universes. Such universes are approximated using a form of Regge calculus originally developed by Collins and Williams to model closed Friedmann-Lemaître-Robertson-Walker universes. We consider two types of lattice universes, one where all masses are identical to each other and another where one mass gets perturbed in magnitude. In the unperturbed universe, we consider the possible arrangements of the masses in the Regge Cauchy surfaces and demonstrate that the model will only be stable if each mass lies within some spherical region of convergence. We also briefly discuss the existence of Regge models that are dual to the ones we have considered. We then model a perturbed lattice universe and demonstrate that the model’s evolution is well behaved, with the expansion increasing in magnitude as the perturbation is increased.

Fast radio bursts are mysterious transient sources likely located at cosmological distances. The derived brightness temperatures exceed by many orders of magnitude the self-absorption limit of incoherent synchrotron radiation, implying the operation of a coherent emission process. We propose a radiation mechanism for fast radio bursts where the emission arises from collisionless bremsstrahlung in strong plasma turbulence excited by relativistic electron beams. We discuss possible astrophysical scenarios in which this process might operate. The emitting region is a turbulent plasma hit by a relativistic jet, where Langmuir plasma waves produce a concentration of intense electrostatic soliton-like regions (cavitons). The resulting radiation is coherent and, under some physical conditions, can be polarized and have a power-law distribution in energy. We obtain radio luminosities in agreement with the inferred values for fast radio bursts. The time scale of the radio flare in some cases can be extremely fast, of the order of $10^{-3}\mathrm{s}$. The mechanism we present here can explain the main features of fast radio bursts and is plausible in different astrophysical sources, such as gamma-ray bursts and some active galactic nuclei.

We incorporate the effective restoration of $U(1{)}_{\mathrm{A}}$ symmetry in the $2+1$-flavor entanglement Polyakov-loop extended Nambu–Jona-Lasinio (EPNJL) model by introducing a temperature-dependent strength $K(T)$ to the Kobayashi–Maskawa–’t Hooft determinant interaction. $T$ dependence of $K(T)$ is well determined from pion and $a_0$-meson screening masses obtained by lattice QCD (LQCD) simulations with improved p4 staggered fermions. The strength is strongly suppressed in the vicinity of the pseudocritical temperature of chiral transition. The EPNJL model with the $K(T)$ well reproduces meson susceptibilities calculated by LQCD with domain-wall fermions. The model shows that the chiral transition is second order at the “light-quark chiral-limit” point where the light quark mass is zero and the strange quark mass is fixed at the physical value. This indicates that there exists a tricritical point. Hence, the location is estimated.

Starting from an earlier representation of the independent dimension-6 gluon operators in terms of color electric and magnetic fields, we estimate their changes near the critical temperature $T_c$ using the temperature dependence of the dimension-4 electric and magnetic condensates extracted from pure gauge theory on the lattice. We then improve the previous QCD sum rules for the $J/\psi$ mass near $T_c$ based on dimension-4 operators, by including the contribution of the dimension-6 operators to the OPE. We find an enhanced stability in the sum rule and confirm that the $J/\psi$ will undergo an abrupt change in the property across $T_c$.

Despite the discovery of a Higgs boson $h$ (125 GeV) at the LHC run 1, its self-interaction has fully evaded direct experimental probe so far. Such self-interaction is vital for electroweak symmetry breaking, vacuum stability, and electroweak phase transition. It is a most likely place to encode new physics beyond the standard model. We parametrize such new physics by model-independent dimension-six effective operators and study their tests via Higgs pair production at hadron colliders. We analyze three major di-Higgs production channels at the parton level and compare the parameter dependence of total cross sections and kinematic distributions at the LHC (14 TeV) and $pp$ (100 TeV) hadron collider. We further perform full simulations for the di-Higgs production channel $gg\to hh\to b\overline{b}\gamma \gamma$ and its backgrounds at the $pp$ (100 TeV) hadron collider. We construct four kinds of benchmark points and study the sensitivities to probing different regions of the parameter space of cubic Higgs interactions. We find that for a one-parameter analysis and with a $3{\mathrm{ab}}^{-1}$ ($30{\mathrm{ab}}^{-1}$) integrated luminosity, the $gg\to hh\to b\overline{b}\gamma \gamma$ channel can measure the SM cubic Higgs coupling and the derivative cubic Higgs coupling to an accuracy of about 13% (4.2%) and 5% (1.6%), respectively.

We consider lepton flavor violating Higgs decay, specifically $h\to \mu \tau$, in a leptoquark model. We introduce two scalar leptoquarks with the $SU(3{)}_c\times SU(2{)}_L\times U(1{)}_Y$ quantum numbers, $(3,2,7/6)$ and $(3,2,1/6)$, which do not generate dimension-4 operators mediating proton decay. They can mix with each other by interactions with the standard model Higgs. The constraint from the charged lepton flavor violating process, ${\tau }^{-}\to {\mu }^{-}\gamma$, is very strong when only one leptoquark contribution is considered. However, we demonstrate that significant cancellation is possible between the two leptoquark contributions. We show that we can explain the CMS (ATLAS) excess in $h\to \mu \tau$. We also show that muon ($g-2$) anomaly can also be accommodated.

We study the superstring inspired $E_6$ model motivated $U(1{)}_N$ extension of the supersymmetric standard model to explore the possibility of explaining the recent excess CMS events and the baryon asymmetry of the Universe in eight possible variants of the model. In light of the hints from short-baseline neutrino experiments at the existence of one or more light sterile neutrinos, we also study the neutrino mass matrices dictated by the field assignments and the discrete symmetries in these variants. We find that all the variants can explain the excess CMS events via the exotic slepton decay, while for a standard choice of the discrete symmetry four of the variants have the feature of allowing high scale baryogenesis (leptogenesis). For one other variant three body decay induced soft baryogenesis mechanism is possible which can induce baryon number violating neutron-antineutron oscillation. We also point out a new discrete symmetry which has the feature of ensuring proton stability and forbidding tree level flavor changing neutral current processes while allowing for the possibility of high scale leptogenesis for two of the variants. On the other hand, neutrino mass matrix of the $U(1{)}_N$ model variants naturally accommodates three active and two sterile neutrinos which acquire masses through their mixing with extra neutral fermions giving rise to interesting textures for neutrino masses.

The D0 collaboration at FermiLab has recently measured the top-quark pair forward-backward asymmetry in $\overline{p}p\to t\overline{t}X$ reactions as a function of the $t\overline{t}$ invariant mass $M_{t\overline{t}}$. The D0 result for $A_{\mathrm{FB}}(M_{t\overline{t}}>650\mathrm{GeV})$ is smaller than $A_{\mathrm{FB}}(M_{t\overline{t}})$ obtained for small values of $M_{t\overline{t}}$, which may indicate an “increasing-decreasing” behavior for $A_{\mathrm{FB}}(M_{t\overline{t}}>M_{\text{cut}})$. This behavior is not explained using conventional renormalization scale setting, or even by a next-to-next-to-leading order (${\mathrm{N}}^2\mathrm{LO}$) QCD calculation—one predicts a monotonically increasing behavior. In the conventional scale-setting method, one simply guesses a single renormalization scale ${\mu }_r$ for the argument of the QCD running coupling and then varies it over an arbitrary range. However, the conventional method has inherent difficulties. For example, the resulting perturbative quantum chromodynamics (pQCD) predictions depend on the choice of renormalization scheme, in contradiction to the principle of “renormalization scheme invariance”—predictions for physical observables cannot depend on a theoretical convention. The error estimate obtained by varying ${\mu }_r$ is unreliable since it is only sensitive to perturbative contributions involving the pQCD $\beta$-function. Worse, guessing the renormalization scale gives predictions for precision QED observables which are in contradiction to results obtained using the standard Gell-Mann-Low method. In contrast, if one fixes the scale using the principle of maximum conformality (PMC), the resulting pQCD predictions are renormalization-scheme independent since all of the scheme-dependent $\{{\beta }_i\}$-terms in the QCD perturbative series are resummed into the QCD running couplings at each order. The $\{{\beta }_i\}$-terms at each order can be unambiguously identified using renormalization group methods such as the $R_{\delta }$ method. The PMC then determines the renormalization scales of the running coupling at each order and provides unambiguous scale-fixed and scheme-independent predictions. The PMC reduces in the $N_C\to 0$ Abelian limit to the standard Gell-Mann-Low scale-setting method used in QED, including precise scheme-independent predictions for the forward-backward symmetry of the $e^{+}{e}^{-}\to {\mu }^{+}{\mu }^{-}$ cross section. By using the rigorous PMC scale-setting procedure, one obtains a comprehensive, self-consistent pQCD explanation for the Tevatron measurements of the top-quark pair forward-backward asymmetry. In this paper we show that if one applies the PMC to determine the top versus antitop quark forward-backward asymmetry by properly using the pQCD predictions up to ${\mathrm{N}}^2\mathrm{LO}$ level, one obtains the predictions without renormalization-scheme or scale ambiguities. For example, the PMC predicts $A_{\mathrm{FB}}^{\mathrm{PMC}}(M_{t\overline{t}}>450\mathrm{GeV})=29.9\%$ at the Tevatron, which is consistent with the CDF measurements. In addition, the PMC prediction for $A_{\mathrm{FB}}(M_{t\overline{t}}>M_{\text{cut}})$ shows an increasing-decreasing behavior for increasing values of $M_{\text{cut}}$ which is not observed in the NLO and ${\mathrm{N}}^2\mathrm{LO}$ predictions for $A_{\mathrm{FB}}(M_{t\overline{t}}>M_{\text{cut}})$ with conventional scale setting. This behavior could be tested by the future more precise measurements at the LHC.

We study the radiative decays of the $Z_c(3900{)}^0$ in a hadronic molecule picture, where the $Z_c(3900)$ is treated as a $D{\overline{D}}^{*}+\mathrm{c}.\mathrm{c}$ hadronic molecule. The partial widths of $\mathrm{\Gamma }(Z_c(3900{)}^0\to \gamma {\eta }_c(2S))$ and $\mathrm{\Gamma }(Z_c(3900{)}^0\to \gamma {\chi }_{c0})$ are predicted to be of order 10 keV, and the cross sections for $\sigma (e^{+}{e}^{-}\to {\pi }^0{Z}_c(3900)\to {\pi }^0\gamma {\eta }_c(2S))$ and $\sigma (e^{+}{e}^{-}\to {\pi }^0{Z}_c(3900)\to {\pi }^0\gamma {\chi }_{c0})$ are of order 0.1 pb at 4.23 GeV, which may be accessible for the BESIII and forthcoming Belle II.

Light scalar hadrons can be understood as dynamically generated resonances. These arise as “companion poles” in the propagators of quark-antiquark seed states when accounting for meson-loop contributions to the self-energies of the latter. Along this line, we extend previous calculations of Törnqvist and Roos and of Boglione and Pennington, where the resonance $a_0(980)$ appears as a companion pole in the propagator of $a_0(1450)$ which is predominantly a quark-antiquark state. We also construct an effective Lagrangian where $a_0(1450)$ couples to pseudoscalar mesons with both nonderivative and derivative interactions. Computing the one-loop self-energy, we demonstrate that the propagator has two poles: a companion pole corresponding to $a_0(980)$ and a pole of the seed state $a_0(1450)$. The positions of these poles are in quantitative agreement with experimental data.

We propose a new type of a three-loop induced neutrino mass model with dark matter candidates which are required for the neutrino mass generation. The smallness of neutrino masses can be naturally explained without introducing super heavy particles, namely, much heavier than a TeV scale and quite small couplings as compared to the gauge couplings. We find that as a bonus, the anomaly of the muon anomalous magnetic moment can simultaneously be explained by loop effects of new particles. In our model, there are doubly charged scalar bosons and leptons from isospin doublet fields which give characteristic collider signatures. In particular, the doubly charged scalar bosons can decay into the same-sign dilepton with its chirality of both right-handed or left- and right-handed. This can be a smoking gun signature to identify our model and be useful to distinguish other models with doubly charged scalar bosons at collider experiments.

PHENIX measurements are presented for the cross section and double-helicity asymmetry ($A_{LL}$) in inclusive ${\pi }^0$ production at midrapidity from $p+p$ collisions at $\sqrt{s}=510\mathrm{GeV}$ from data taken in 2012 and 2013 at the Relativistic Heavy Ion Collider. The next-to-leading-order perturbative-quantum-chromodynamics theory calculation is in excellent agreement with the presented cross section results. The calculation utilized parton-to-pion fragmentation functions from the recent DSS14 global analysis, which prefer a smaller gluon-to-pion fragmentation function. The ${\pi }^0{A}_{LL}$ results follow an increasingly positive asymmetry trend with $p_T$ and $\sqrt{s}$ with respect to the predictions and are in excellent agreement with the latest global analysis results. This analysis incorporated earlier results on ${\pi }^0$ and jet $A_{LL}$ and suggested a positive contribution of gluon polarization to the spin of the proton $\mathrm{\Delta }G$ for the gluon momentum fraction range $x>0.05$. The data presented here extend to a currently unexplored region, down to $x\sim 0.01$, and thus provide additional constraints on the value of $\mathrm{\Delta }G$.

We study the fermionic Schwinger effect in two-dimensional de Sitter spacetime. To do so, we first present a method to semiclassically compute the number of pairs created per momentum mode for general time dependent fields. In addition, the constant electric field is studied in depth. In this case, solutions for the Dirac equation can be found and the number of pairs can be computed using the standard Bogoliubov method. This result is shown to agree with the semiclassical one in the appropriate limit. The solutions are also used to compute the expectation value of the induced current. Comparing these results to similar studies for bosons, we find that while the results agree in the semiclassical limit, they do not generally agree. In particular, there is no occurrence of a strong current for small electric fields.

We consider new regular exact spherically symmetric solutions of a nonminimal Einstein–Yang-Mills theory with a cosmological constant and a gauge field of magnetic Wu-Yang type. The most interesting solutions found are black holes with metric and curvature invariants that are regular everywhere, i.e., regular black holes. We set up a classification of the solutions according to the number and type of horizons. The structure of these regular black holes is characterized by four specific features: a small cavity in the neighborhood of the center, a repulsion barrier off the small cavity, a distant equilibrium point, in which the metric function has a minimum, and a region of Newtonian attraction. Depending on the sign and value of the cosmological constant, the solutions are asymptotically de Sitter (dS), asymptotically flat, or asymptotically anti–de Sitter (AdS).

We compare the science capabilities of different eLISA mission designs, including four-link (two-arm) and six-link (three-arm) configurations with different arm lengths, low-frequency noise sensitivities and mission durations. For each of these configurations we consider a few representative massive black hole formation scenarios. These scenarios are chosen to explore two physical mechanisms that greatly affect eLISA rates, namely (i) black hole seeding, and (ii) the delays between the merger of two galaxies and the merger of the black holes hosted by those galaxies. We assess the eLISA parameter estimation accuracy using a Fisher matrix analysis with spin-precessing, inspiral-only waveforms. We quantify the information present in the merger and ringdown by rescaling the inspiral-only Fisher matrix estimates using the signal-to-noise ratio from nonprecessing inspiral-merger-ringdown phenomenological waveforms, and from a reduced set of precessing numerical relativity/post-Newtonian hybrid waveforms. We find that all of the eLISA configurations considered in our study should detect some massive black hole binaries. However, configurations with six links and better low-frequency noise will provide much more information on the origin of black holes at high redshifts and on their accretion history, and they may allow the identification of electromagnetic counterparts to massive black hole mergers.

We discuss the mass-radius diagram for static neutron star models obtained by the numerical solution of modified Tolman-Oppenheimer-Volkoff equations in $f(R)$ gravity where the Lagrangians $f(R)=R+\alpha R^2(1+\gamma R)$ and $f(R)=R^{1+\epsilon }$ are adopted. Unlike the case of the perturbative approach previously reported, the solutions are constrained by the presence of an extra degree of freedom, coming from the trace of the field equations. In particular, the stiffness of the equation of state determines an upper limit on the central density ${\rho }_{\mathrm{c}}$ above which the positivity condition of energy-matter tensor trace $T^{\mathrm{m}}=\rho -3p$ holds. In the case of quadratic $f(R)$ gravity, we find higher masses and radii at lower central densities with an inversion of the behavior around a pivoting ${\rho }_c$ which depends on the choice of the equation of state. When considering the cubic corrections, we find solutions converging to the required asymptotic behavior of the flat metric only for $\gamma <0$. A similar analysis is performed for $f(R)=R^{1+\epsilon }$ considering $\epsilon$ as the leading parameter. We work strictly in the Jordan frame in order to consider matter minimally coupled with respect to geometry. This fact allows us to avoid ambiguities that could emerge in adopting the Einstein frame.

We derive the decay widths for the leptonic decays of heavy charged pseudoscalars to massive sterile neutrinos, $M^{\pm }\to {\ell }^{\pm }+N$, within the frameworks involving the Standard Model and two-Higgs doublets (type II). We then apply the result to $B^{\pm }\to {\tau }^{\pm }+“\text{missing momentum}”$ of the Belle/BABAR experimental results, in order to measure directly the relevant parameter space, including the mixing parameter $U_{\tau N}$.

We discuss a possibility that the domain wall problem in the next-to-minimal supersymmetric standard model is alleviated without introducing a small explicit $Z_3$ breaking term by analyzing the evolution of the singlet scalar field within an inflationary paradigm. The singlet scalar field which explains the $\mu$-term tracks a time-varying minimum of the effective potential after inflation and slowly rolls down to its global minimum if there exist sufficiently large negative Hubble-induced corrections on the effective potential for the singlet field, which arise through supergravity. As a consequence, the whole Universe is confined within a single domain during and after inflation, which prevents the formation of domain walls. This will further constrain the history of the early Universe along with the Higgs-singlet coupling.

A scenario with two subsequent periods of inflationary expansion in the very early Universe is examined. The model is based on a potential motivated by symmetries being found in field theory at high energy. For various parameter sets of the potential, the spectra of scalar and tensor perturbations that are expected to originate from this scenario are calculated. Also the beginning of the reheating epoch connecting the second inflation with thermal equilibrium is studied. Perturbations with wavelengths leaving the horizon around the transition between the two inflations are special: It is demonstrated that the power spectrum at such scales deviates significantly from expectations based on measurements of the cosmic microwave background. This supports the conclusion that parameters for which this part of the spectrum leaves observable traces in the cosmic microwave background must be excluded. Parameters entailing a very efficient second inflation correspond to standard small-field inflation and can meet observational constraints. Particular attention is paid to the case where the second inflation leads solely to a shift of the observable spectrum from the first inflation. A viable scenario requires this shift to be small.