Stationary and axisymmetric ideal magnetohydrodynamic (MHD) accretion onto a black hole is studied analytically. The accreting plasma ejected from a plasma source with low velocity must be superfast magnetosonic before passing through the event horizon. We work out and apply a trans-fast magnetosonic solution without detailed analysis of the regularity conditions at the magnetosonic point, by introducing the bending angle $\beta$ of the magnetic field line, which is the ratio of the toroidal and poloidal components of the magnetic field. To accrete onto a black hole, the trans-magnetosonic solution has some restrictions on $\beta$, which are related to the field-aligned parameters of the MHD flows. One of the restrictions gives the boundary condition at the event horizon for the inclination of a magnetic field line. We find that this inclination is related to the energy and angular momentum transport to the black hole. Then, we discuss the spin-up/down process of a rotating black hole by cold MHD inflows in a secular evolution time scale. There are two asymptotic states for the spin evolution. One is that the angular velocity of the black hole approaches to that of the magnetic field line, and the other is that the spin-up effect by the positive angular momentum influx and the spin-down effect by the energy influx (as the mass-energy influx) are canceled. We also show that the MHD inflows prevents the evolution to the maximally rotating black hole.

The coincidence problem of late cosmic acceleration constitutes a serious riddle with regard to our understanding of the evolution of the Universe. Here we argue that this problem may someday be solved—or better understood—by expressing the Hubble expansion rate as a function of the ratio of densities (dark matter/dark energy) and observationally determining the said rate in terms of the redshift.

The size of the branching ratios for the $\tau \to \mu \gamma$ and $\tau \to \mu \gamma \gamma$ decays induced by a lepton flavor violating Higgs interaction $H\tau \mu$ is studied in the framework of effective field theories. The best constraint on the $H\tau \mu$ vertex, derived from the know measurement on the muon anomalous magnetic moment, is used to impose the upper bounds $\mathrm{Br}(\tau \to \mu \gamma )<7.5\times {10}^{-10}$ and $\mathrm{Br}(\tau \to \mu \gamma \gamma )<2.3\times {10}^{-12}$, which are more stringent than current experimental limits on this class of transitions.

Realistic calculations of nuclear disappearance lifetimes induced by $n\overline{n}$ oscillations are reported for oxygen and iron, using $\overline{n}$ nuclear potentials derived from a recent comprehensive analysis of $\overline{p}$ atomic X-ray and radiochemical data. A lower limit ${\tau }_{n\overline{n}}>3.3\times {10}^8\mathrm{s}$ on the $n\overline{n}$ oscillation time is derived from the Super-Kamiokande I new lower limit $T_d(\mathrm{O})>1.77\times {10}^{32}\mathrm{yr}$ on the neutron lifetime in oxygen. Antineutron scattering lengths in carbon and nickel, needed in trap experiments using ultracold neutrons, are calculated from updated $\overline{N}$ optical potentials at threshold, with results shown to be largely model independent.

In theories with universal extra dimensions, all standard model fields propagate in the bulk and the lightest state of the first Kaluza-Klein (KK) level can be made stable by imposing a $Z_2$ parity. We consider a framework where the lightest KK particle (LKP) is a neutral, extremely weakly interacting particle such as the first KK excitation of the graviton, while the next-to-lightest KK particle (NLKP) is the first KK mode of a charged right-handed lepton. In such a scenario, due to its very small couplings to the LKP, the NLKP is long-lived. We investigate the production of these particles from the interaction of high energy neutrinos with nucleons in the Earth and determine the rate of NLKP events in neutrino telescopes. Using the Waxman-Bahcall limit for the neutrino flux, we find that the rate can be as large as a few hundreds of events a year for realistic values of the NLKP mass.

Recently, it was pointed out that the mixing phase in the $B_s-{\overline{B}}_s$ system is large, contrary to the expectations in the standard model as well as in minimal flavor violation models. The leptonic decay widths of the $D_s$ meson are also found to be larger than expected. We show how a minimal set of four $R$-parity violating ${\lambda }^{\prime }$-type couplings can explain both these anomalies. We also point out other phenomenological implications of such new physics.

In a class of new physics models, the new physics sector is completely or partly hidden, namely, a singlet under the standard model (SM) gauge group. Hidden fields included in such new physics models communicate with the standard model sector through higher-dimensional operators. If a cutoff lies in the TeV range, such hidden fields can be produced at future colliders. We consider a scalar field as an example of the hidden fields. Collider phenomenology on this hidden scalar is similar to that of the SM Higgs boson, but there are several features quite different from those of the Higgs boson. We investigate productions of the hidden scalar at the International Linear Collider (ILC) and study the feasibility of its measurements, in particular, how well the ILC distinguishes the scalar from the Higgs boson, through realistic Monte Carlo simulations.

We investigate the relevance of the meson loops in the $f_0(1710)$ scalar meson decay into one photon and one vector meson, ($\rho$, $\omega$, and $\varphi$). In particular we estimate the size of the loops coming from the decay of the $f_0(1710)$ into two pseudoscalar mesons, containing three pseudoscalar mesons in the loop or two pseudoscalar mesons and one vector meson. The results, despite having large uncertainties, manifest that the contribution of the meson loops to these radiative decays is quite relevant and should be taken into account by the theoretical calculations which use these observables as a test of the possible glueball nature of this resonance. At the same time we also evaluate the relevance of the same loops in the two lighter scalar mesons, the $f_0(1370)$ and $f_0(1500)$, providing information of relevance in the search for the nature of the second nonet of scalar mesons.

We report a theoretical study of the axial nucleon-to-delta (1232) ($N\to \Delta$) transition form factors up to one-loop order in relativistic baryon chiral perturbation theory. We adopt a formalism in which the $\Delta$ couplings obey the spin-$3/2$ gauge symmetry and, therefore, decouple the unphysical spin-$1/2$ fields. We compare the results with phenomenological form factors obtained from neutrino bubble-chamber data and in quark models.

We present first evidence for the production of single top quarks in the D0 detector at the Fermilab Tevatron $p\overline{p}$ collider. The standard model predicts that the electroweak interaction can produce a top quark together with an antibottom quark or light quark, without the antiparticle top-quark partner that is always produced from strong-coupling processes. Top quarks were first observed in pair production in 1995, and since then, single top-quark production has been searched for in ever larger data sets. In this analysis, we select events from a $0.9{\mathrm{fb}}^{-1}$ data set that have an electron or muon and missing transverse energy from the decay of a $W$ boson from the top-quark decay, and two, three, or four jets, with one or two of the jets identified as originating from a $b$ hadron decay. The selected events are mostly backgrounds such as $W+\mathrm{\text{jets}}$ and $t\overline{t}$ events, which we separate from the expected signals using three multivariate analysis techniques: boosted decision trees, Bayesian neural networks, and matrix-element calculations. A binned likelihood fit of the signal cross section plus background to the data from the combination of the results from the three analysis methods gives a cross section for single top-quark production of $\sigma (p\overline{p}\to tb+X,tqb+X)=4.7\pm 1.3\mathrm{pb}$. The probability to measure a cross section at this value or higher in the absence of signal is 0.014%, corresponding to a 3.6 standard deviation significance. The measured cross section value is compatible at the 10% level with the standard model prediction for electroweak top-quark production. We use the cross section measurement to directly determine the Cabibbo-Kobayashi-Maskawa quark mixing matrix element that describes the $Wtb$ coupling and find $|V_{tb}{f}_1^L|={1.31}_{-0.21}^{+0.25}$, where $f_1^L$ is a generic vector coupling. This model-independent measurement translates into $0.68<|V_{tb}|\le 1$ at the 95% C.L. in the standard model.

We report a Dalitz-plot analysis of the charmless hadronic decays of charged $B$ mesons to the final state $K^{\pm }{\pi }^{\mp }{\pi }^{\pm }$. Using a sample of $(383.2\pm 4.2)\times {10}^6$ $B\overline{B}$ pairs collected by the BABAR detector, we measure $CP$-averaged branching fractions and direct $CP$ asymmetries for intermediate resonant and nonresonant contributions. We find evidence for direct $CP$ violation in the decay $B^{\pm }\to {\rho }^0(770)K^{\pm }$, with a $CP$-violation parameter $A_{CP}=(+44\pm 10\pm 4_{-13}^{+5})\%$.

We present a new method for studying high-$p_T$ dilepton events ($e^{\pm }{e}^{\mp }$, ${\mu }^{\pm }{\mu }^{\mp }$, $e^{\pm }{\mu }^{\mp }$) and simultaneously extracting the production cross sections of $p\overline{p}\to t\overline{t}$, $p\overline{p}\to W^{+}{W}^{-}$, and $p\overline{p}\to Z^0\to {\tau }^{+}{\tau }^{-}$ at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$. We perform a likelihood fit to the dilepton data in a parameter space defined by the missing transverse energy and the number of jets in the event. Our results, which use $360\mathrm{p}{\mathrm{b}}^{-1}$ of data recorded with the CDF II detector at the Fermilab Tevatron Collider, are $\sigma (t\overline{t})={8.5}_{-2.2}^{+2.7}\mathrm{pb}$, $\sigma (W^{+}{W}^{-})={16.3}_{-4.4}^{+5.2}\mathrm{pb}$, and $\sigma (Z^0\to {\tau }^{+}{\tau }^{-})={291}_{-46}^{+50}\mathrm{pb}$.

We calculate the light meson spectrum and the light quark masses by lattice QCD simulation, treating all light quarks dynamically and employing the Iwasaki gluon action and the nonperturbatively $O(a)$-improved Wilson quark action. The calculations are made at the squared lattice spacings at an equal distance $a^2\simeq 0.005$, 0.01, and $0.015{\mathrm{fm}}^2$, and the continuum limit is taken assuming an $O(a^2)$ discretization error. The light meson spectrum is consistent with experiment. The up, down, and strange quark masses in the $\overline{\mathrm{MS}}$ scheme at 2 GeV are $\overline{m}=(m_u+m_d)/2={3.55}_{-0.28}^{+0.65}\mathrm{MeV}$ and $m_s={90.1}_{-6.1}^{+17.2}\mathrm{MeV}$ where the error includes statistical and all systematic errors added in quadrature. These values contain the previous estimates obtained with the dynamical $u$ and $d$ quarks within the error.

The presence of a strong magnetic background can modify the nature and the dynamics of the chiral phase transition at finite temperature. We compute the modified effective potential in the linear sigma model with quarks to one loop in the $\overline{\mathrm{MS}}$ scheme for $N_f=2$. For fields $eB\sim 5m_{\pi }^2$ and larger a crossover is turned into a weak first-order transition. We discuss possible implications for noncentral heavy ion collisions at the Relativistic Heavy Ion Collider and the Large Hadron Collider and for the primordial QCD transition.

We consider the running coupling from the four-gluon vertex in Landau gauge, $\mathrm{SU}(N_c)$ Yang-Mills theory as given by a combination of dressing functions of the vertex and the gluon propagator. We determine these functions numerically from a coupled set of Dyson-Schwinger equations. We reproduce asymptotic freedom in the ultraviolet momentum region and find a coupling of order one at mid-momenta. In the infrared we find a nontrivial (i.e. nonzero) fixed point which is 3 orders of magnitude smaller than the corresponding fixed point in the coupling of the ghost-gluon vertex. This result explains why the Dyson-Schwinger and the functional renormalization group equations for the two point functions can agree in the infrared, although their structure is quite different. Our findings also support Zwanziger’s notion of an infrared effective theory driven by the Faddeev-Popov determinant.

We consider nontopological, “bell-shaped” localized and regular solutions available in some $1+1$-dimensional scalar field theories. Several properties of such solutions are studied, namely, their stability and the occurrence of fermion bound states in the background of a kink and a kink-antikink solution of the sine-Gordon model.

We consider the problem of calculating the Green’s functions associated to a massive scalar field with modified dispersion relations. We analyze the case when dispersion is modified by higher derivative spatial operators acting on the field orthogonally to a preferred direction, determined by a unit timelike vector field. By assuming that the integral curves of the vector field are geodesics, we expand the modified Klein-Gordon equation in Fermi normal coordinates. By means of a Fourier transform, we find a series representation in momentum-space of the Green’s functions. The coefficients of the series are geometrical terms containing combinations of the Ricci tensor and the vector field, as expected from previous calculations with different methods and for specific backgrounds.

In this work we discuss the time evolution of nonspherical perturbations of a nonrotating neutron star described by a realistic equation of state (EOS). We analyze 10 different EOS for a large sample of neutron star models. Various kinds of generic initial data are evolved and the gravitational signals are computed. We focus on the dynamical excitation of fluid and spacetime modes and extract the corresponding frequencies. We employ a constrained numerical algorithm based on standard finite-differencing schemes which permits stable and long-term evolutions. Our code provides accurate waveforms and allows one to capture, via Fourier analysis, the frequencies of the fluid modes with an accuracy comparable to that of frequency-domain calculations. The results we present here are useful for providing comparisons with simulations of nonlinear oscillations of (rotating) neutron star models as well as test beds for 3D nonlinear codes.

Many systems of current interest in relativistic astrophysics require a knowledge of radiative transfer in a magnetized gas flowing in a strongly curved, dynamical spacetime. Such systems include coalescing compact binaries containing neutron stars or white dwarfs, disks around merging black holes, core-collapse supernovae, collapsars, and gamma-ray burst sources. To model these phenomena, all of which involve general relativity, radiation (photon and/or neutrino), and magnetohydrodynamics (MHD), we have developed a general relativistic code capable of evolving MHD fluids and radiation in dynamical spacetimes. Our code solves the coupled Einstein-Maxwell-MHD-radiation system of equations both in axisymmetry and in full $3+1$ dimensions. We evolve the metric by integrating the BSSN (Baumgarte-Shapiro-Shibata-Nakamura) equations, and use a conservative, high-resolution shock-capturing scheme to evolve both the MHD and radiation moment equations. In this paper, we implement our scheme for optically thick gases and gray-body opacities. Our code gives accurate results in a suite of tests involving radiating shocks and nonlinear waves propagating in Minkowski spacetime. In addition, to test our code’s ability to evolve the relativistic radiation-MHD equations in strong-field dynamical spacetimes, we study “thermal Oppenheimer-Snyder collapse” to a black hole and find good agreement between analytic and numerical solutions.

This is the second in a series of papers whose aim is to generate adiabatic gravitational waveforms from the inspiral of stellar-mass compact objects into massive black holes. In earlier work, we presented an accurate $(2+1)\mathrm{D}$ finite-difference time-domain code to solve the Teukolsky equation, which evolves curvature perturbations near rotating (Kerr) black holes. The key new ingredient there was a simple but accurate model of the singular source term based on a discrete representation of the Dirac-delta function and its derivatives. Our earlier work was intended as a proof of concept, using simple circular, equatorial geodesic orbits as a test bed. Such a source is effectively static, in that the smaller body remains at the same coordinate radius and orbital inclination over an orbit. (It of course moves through axial angle, but we separate that degree of freedom from the problem. Our numerical grid has only radial, polar, and time coordinates.) We now extend the time-domain code so that it can accommodate dynamic sources that move on a variety of physically interesting world lines. We validate the code with extensive comparison to frequency-domain waveforms for cases in which the source moves along generic (inclined and eccentric) bound geodesic orbits. We also demonstrate the ability of the time-domain code to accommodate sources moving on interesting nongeodesic worldlines. We do this by computing the waveform produced by a test mass following a kludged inspiral trajectory, made of bound geodesic segments driven toward merger by an approximate radiation loss formula.