We present an improved version of the approximate scheme for generating inspirals of test bodies into a Kerr black hole recently developed by Glampedakis, Hughes and Kennefick. Their original “hybrid” scheme was based on combining exact relativistic expressions for the evolution of the orbital elements (the semilatus rectum $p$ and eccentricity $e$) with an approximate, weak-field, formula for the energy and angular momentum fluxes, amended by the assumption of constant inclination angle $\iota$ during the inspiral. Despite the fact that the resulting inspirals were overall well behaved, certain pathologies remained for orbits in the strong-field regime and for orbits which are nearly circular and/or nearly polar. In this paper we eliminate these problems by incorporating an array of improvements in the approximate fluxes. First, we add certain corrections which ensure the correct behavior of the fluxes in the limit of vanishing eccentricity and/or 90° inclination. Second, we use higher order post-Newtonian formulas, adapted for generic orbits. Third, we drop the assumption of constant inclination. Instead, we first evolve the Carter constant by means of an approximate post-Newtonian expression and subsequently extract the evolution of $\iota$. Finally, we improve the evolution of circular orbits by using fits to the angular momentum and inclination evolution determined by Teukolsky-based calculations. As an application of our improved scheme, we provide a sample of generic Kerr inspirals which we expect to be the most accurate to date, and for the specific case of nearly circular orbits we locate the critical radius where orbits begin to decircularize under radiation reaction. These easy-to-generate inspirals should become a useful tool for exploring LISA data analysis issues and may ultimately play a role in the detection of inspiral signals in the LISA data.

We revisit a scenario in which the cosmological constant is cancelled by the potential energy of a slowly evolving scalar field, or cosmon. The cosmon’s evolution is tied to the cosmological constant by a feedback mechanism. This feedback is achieved by an unconventional coupling of the cosmon field to the Ricci curvature scalar. The solutions show that the effective cosmological constant evolves approximately as $t^{-2}$ and remains always of the same order as the density of ordinary matter and radiation. Newton’s constant varies on cosmological time scales, with ${\dot{G}}_N/G_N\ll 1/t$. $G_N$ could have been somewhat different, and possibly smaller, at the time of Big Bang nucleosynthesis.

We provide exact solutions to the Einstein equations when the universe contains vacuum energy plus a uniform arrangement of magnetic fields, strings, or domain walls. Such a universe has planar symmetry; i.e., it is homogeneous but not isotropic. Further exact solutions are obtained when dust is included and approximate solutions are found for $w\ne 0$ matter. These cosmologies also have planar symmetry. These results may eventually be used to explain some features in the Wilkinson Microwave Anisotropy Probe data. The magnetic field case is the easiest to motivate and has the highest possibility of yielding reliable constraints on observational cosmology.

We analyze the impact of Higgs-mediated amplitudes on the rare decays $K_L\to {\pi }^0\nu \overline{\nu }$ and $K^{+}\to {\pi }^{+}\nu \overline{\nu }$ in the MSSM with large $\tan \beta$ and general flavor mixing. We point out that, going beyond the minimal flavor violation hypothesis, $Z$-penguin amplitudes generated by charged-Higgs exchange can induce sizable modifications of $K\to \pi \nu \overline{\nu }$ rates. Interestingly, these effects scale as ${tan}^4\beta$ at the amplitude level. For large values of $\tan \beta$, this mechanism allows deviations from the SM expectations even for tiny (Cabibbo-Kobayashi-Maskawa–type) off-diagonal mixing terms in the right-handed squark sector.

The high-statistical KLOE data on the $\varphi \to {\pi }^0{\pi }^0\gamma$ decay are described simultaneously with the data on the $\pi \pi$ scattering and the $\pi \pi \to K\overline{K}$ reaction. The description is carried out taking into account the chiral shielding of the putative $\sigma (600)$ meson and its mixing with the well-established $f_0(980)$ meson. It is shown that the data do not contradict the existence of the $\sigma (600)$ meson and yield evidence in favor of the four-quark nature of the $\sigma (600)$ and $f_0(980)$ mesons.

We discuss and compare different approaches to include gluon transverse momenta for heavy quark-antiquark pair production. The correlations in azimuthal angle and in the heavy quark, heavy antiquark transverse momenta are studied in detail. The results are illustrated with the help of different unintegrated gluon distribution functions (UGDF) from the literature. We compare results obtained with on-shell and off-shell matrix elements and kinematics and quantify where these effects are negligible and where they are essential. We concentrate on the region of asymmetric transverse momenta of charm quark and charm antiquark. Most of UGDFs lead in this corner of the phase space to almost full decorrelation in the azimuthal angle. We propose correlation observables to be best suited in order to test the existing models of UGDFs.

We consider the production of a lepton-antilepton pair by real photons off a hadronic target. The interference of one and two-photon exchange amplitudes leads to a charge asymmetry term that may be calculated explicitly in the large-$t$ limit in terms of hadronic distribution amplitudes. A rather compact expression emerges for the leading order asymmetry at fixed angle in the center-of-mass of the lepton pair. The magnitude appears sizeable and is approximately independent of the pair mass in the asymptotic limit.

A tree-level flavor changing neutral current in the uplike quark sector appears in one of the variations of the littlest Higgs model. We investigate the effects of this coupling in the $D^{+}\to {\pi }^{+}{l}^{+}{l}^{-}$ and $D^0\to {\rho }^0{l}^{+}{l}^{-}$ decays, which are the most appropriate candidates for the experimental studies. However, the effects are found to be too small to be observed in the current and the foreseen experimental facilities. These decays are still dominated by the standard model long-distance contributions, which are reevaluated based on the new experimental input.

Neutrino oscillations are treated from the point of view of relativistic first quantized theories and compared to second quantized treatments. Within first quantized theories, general oscillation probabilities can be found for Dirac fermions and charged spin 0 bosons. A clear modification in the oscillation formulas can be obtained and its origin is elucidated and confirmed to be inevitable from completeness and causality requirements. The left-handed nature of created and detected neutrinos can also be implemented in the first quantized Dirac theory in the presence of mixing; the probability loss due to the changing of initially left-handed neutrinos to the undetected right-handed neutrinos can be obtained in analytic form. Concerning second quantized approaches, it is shown in a calculation using virtual neutrino propagation that both neutrinos and antineutrinos may also contribute as intermediate particles. The sign of the contributing neutrino energy may have to be chosen explicitly without being automatic in the formalism. At last, a simple second quantized description of the flavor oscillation phenomenon is devised. In this description there is no interference terms between positive and negative components, but it still gives simple normalized oscillation probabilities. A new effect appearing in this context is an inevitable but tiny violation of the initial flavor of neutrinos. The probability loss due to the conversion of left-handed neutrinos to right-handed neutrinos is also presented.

Recent BES data on $J/\psi \to \varphi \pi \pi$ indicate that there is a possible new spin-0 state ($f_0(1790)$) with a mass of $m={1790}_{-30}^{+40}\mathrm{MeV}/{\mathrm{c}}^2$. Assuming it to be an isosinglet $0^{+}$, $(0^{++})$, we propose a new mixing scheme to describe this and the other three known isosinglet $f_0(1370)$, $f_0(1500)$, $f_0(1710)$ states by adding isosinglet hybrid states to the usual basis of two isosinglet quarkonia and one glueball. Since there are two isosinglet hybrid states, $(u\overline{u}+d\overline{d})g/\sqrt{2}$ and $s\overline{s}g$, this new basis implies existence of another isosinglet state $X$. Using known data, we estimate the ranges of the mixing parameters. We find two sets of solutions with $X$ mass predicted to be about 1820 MeV and 1760 MeV, respectively. We also study implications on the decay properties of these new states.

In a previous paper [G. V. Dunne and C. Schubert, Phys. Rev. D 72, 105004 (2005).], it was shown that the worldline expression for the nonperturbative imaginary part of the QED effective action can be approximated by the contribution of a special closed classical path in Euclidean spacetime, known as a worldline instanton. Here we extend this formalism to compute also the prefactor arising from quantum fluctuations about this classical closed path. We present a direct numerical approach for determining this prefactor, and we find a simple explicit formula for the prefactor in the cases where the inhomogeneous electric field is a function of just one spacetime coordinate. We find excellent agreement between our semiclassical approximation, conventional WKB, and recent numerical results using numerical worldline loops.

We present a formulation of gravity in terms of a theory based on complex $SU(2)$ gauge fields with a general coordinate invariant action functional quadratic in the field strength. Self-duality or anti-self-duality of the field strength emerges as a constraint from the equations of motion of this theory. This in turn leads to Einstein gravity equations for a dilaton and an axion conformally coupled to gravity for the self-dual constraint. The analysis has also been extended to $N=1$ and 2 super Yang-Mills theory of complex $SU(2)$ gauge fields. This leads to, besides other equations of motion, self-duality/anti-self-duality of generalized supercovariant field strengths. The self-dual case is then shown to yield as its solutions $N=1$, 2 supergravity equations, respectively.

We study the one-loop radiative corrections for massless fermions in de Sitter space induced by a Yukawa coupling to a light, nearly minimally coupled scalar field. We show that the fermions acquire a mass. Next we construct the corresponding (nonlocal) effective fermionic action, which—in contrast to the case of a massive Dirac fermion—preserves chirality. Nevertheless, the resulting fermion dynamics is precisely that of a Dirac fermion with a mass proportional to the expansion rate. Our finding supports the view that an observer or a test particle responds to a scalar field in inflation by shifting its energy rather than seeing a thermal bath.

We revisit the constraint on the primordial helium mass fraction $Y_p$ from observations of cosmic microwave background (CMB) alone. By minimizing ${\chi }^2$ of recent CMB experiments over 6 other cosmological parameters, we obtained rather weak constraints as $0.17\le Y_p\le 0.52$ at $1\sigma$ C.L. for a particular data set. We also study the future constraint on cosmological parameters when we take account of the prediction of the standard big bang nucleosynthesis (BBN) theory as a prior on the helium mass fraction where $Y_p$ can be fixed for a given energy density of baryon. We discuss the implications of the prediction of the standard BBN on the analysis of CMB.

We explore observational constraints on a cosmological brane world scenario in which the bulk is not empty. Rather, exchange of mass energy between the bulk and the brane is allowed. The evolution of matter fields to an observer on the brane is then modified due to new terms in the energy-momentum tensor describing this exchange. We investigate the constraints from various cosmological observations on the flow of matter from the bulk into the brane. Interestingly, we show that it is possible to have a $\Lambda =0$ cosmology to an observer in the brane which satisfies standard cosmological constraints including the cosmic microwave background (CMB) temperature fluctuations, Type Ia supernovae at high redshift, and the matter power spectrum. This model even accounts for the observed suppression of the CMB power spectrum at low multipoles. In this cosmology, the observed cosmic acceleration is attributable to the flow of matter from the bulk to the brane. A peculiar aspect of this cosmology is that the present dark-matter content of the Universe may be significantly larger than that of a $\Lambda \mathrm{CDM}$ cosmology. Its influence, however, is offset by the dark-radiation term. Possible additional observational tests of this new cosmological paradigm are suggested.

We show that high-energy neutrinos can be efficiently produced in X-ray binaries with relativistic jets and high-mass primary stars. We consider a system where the star presents a dense equatorial wind and the jet has a small content of relativistic protons. In this scenario, neutrinos and correlated gamma-rays result from $pp$ interactions and the subsequent pion decays. As a particular example we consider the microquasar LS I $+61$ 303. Above 1 TeV, we obtain a mean-orbital ${\nu }_{\mu }$-luminosity of $\sim 5{10}^{34}\mathrm{erg}/\mathrm{s}$ which can be related to an event rate of 4–5 muon-type neutrinos per kilometer-squared per year after considering the signal attenuation due to maximal neutrino oscillations. The maximal neutrino energies here considered will range between 20 and 85 TeV along the orbit. The local infrared photon field is responsible for opacity effects on the associated gamma radiation at high energies, but below 50 GeV the source could be detected by MAGIC telescope. GLAST observations at $E_{\gamma }>100\mathrm{MeV}$ should also reveal a strong source.

In the supersymmetric seesaw model of neutrino masses, augmented by the non-Abelian discrete tetrahedral symmetry $A_4$, a specific pattern of neutrino mixing is automatically generated if one of the three heavy singlet neutrino superfields acquires a nonzero vacuum expectation value. This pattern turns out to be exactly that of tribimaximal mixing, i.e. ${sin}^2{\theta }_{23}=1/2$, ${sin}^2{\theta }_{12}=1/3$, and ${sin}^2{\theta }_{13}=0$, in good agreement with data.

We demonstrate that the effects of matter upon neutrino propagation may be recast as the scattering of the initial neutrino wave function. Exchanging the differential, Schrodinger equation for an integral equation for the scattering matrix $S$ permits a Monte Carlo method for the computation of $S$ that removes many of the numerical difficulties associated with direct integration techniques.

We study the effects of dimension six effective operators on the production of single top quarks at the CERN LHC. The operator set considered includes terms with effective gluon interactions and four-fermion terms. Analytic expressions for the several partonic cross sections of single top production will be presented, as well as the results of their integration on the parton density functions.

Data from the Fermilab E835 experiment have been used to study the reaction $\overline{p}p\to \eta \eta {\pi }^0$ at $5.2\mathrm{GeV}/c$. A sample of 22 million six photon events has been analyzed to construct the Dalitz plot containing $\sim 80k$ $\eta \eta {\pi }^0$ events. A partial wave analysis of the data has been done. Six $f_J$-states decaying into $\eta \eta$ and five $a_J$-states decaying into $\eta {\pi }^0$ are identified in the mass region $\sim 1.3$ and 2.4 GeV, and their masses, widths, and spins are determined by maximum likelihood analysis of the data. Two $f_0$ states are identified with the popular candidates for the lightest scalar glueball, $f_0(1500)$ and $f_0(1710)$.