Pulsars inside binary systems can accrete matter that arrives up to the pulsar surface provided that its period is long enough. During the accretion process, matter has to be accelerated to the rotational velocity of the pulsar magnetosphere at the distance where the balance between the pressure of matter and the magnetic field is achieved. At this distance, a very turbulent and magnetized region is formed in which hadrons can be accelerated to relativistic energies. These hadrons can interact with the very strong radiation field coming from the hot polar cap on the neutron star surface created by the in-falling matter. We calculate the neutrino event rates produced in a ${\mathrm{km}}^2$ detector that can be expected from accreting millisecond and classical x-ray pulsars at a typical distance within our own Galaxy.

We estimate the diphoton coupling of $f_0(600)$, $f_0(980)$, and $f_2(1270)$ resonances in a coupled channel dispersive approach. The $f_0(600)$ diphoton coupling is also reinvestigated using a single channel $T$ matrix for $\pi \pi$ scattering with better analyticity property, and it is found to be significantly smaller than that of a $\overline{q}q$ state. Especially we also estimate the diphoton coupling of the third-sheet pole located near $\overline{K}K$ threshold, denoted as $f_0^{III}(980)$. It is argued that this third-sheet pole may be originated from a coupled channel Breit-Wigner description of the $f_0(980)$ resonance.

Pseudoscalar particles, with almost zero mass and very weak coupling to the visible matter, arise in many extensions of the standard model of particle physics. Their mixing with photons in the presence of an external magnetic field leads to many interesting astrophysical and cosmological consequences. This mixing depends on the medium properties, the momentum of the photon, and the background magnetic field. Here we give a general treatment of pseudoscalar-photon oscillations in a background magnetic field, taking the Faraday term into account. We give predictions valid in all regimes, under the assumption that the frequency of the wave is much higher than the plasma frequency and the gyration frequency of the medium. At sufficiently high frequencies, the Faraday effect is negligible and we reproduce the standard pseudoscalar-photon mixing phenomenon. However at low frequencies, where Faraday effect is important, the mixing formulas are considerably modified. We extend the formalism to the low frequency regime and explicitly determine the coherency matrix elements in different limits. We apply our formalism to some astrophysical phenomena in order to illustrate the new contributions we obtain. We explicitly compute the contribution due to the longitudinal mode of the photon and show that it is negligible in a certain parameter regime.

We present a detailed analysis together with exact numerical calculations on one-loop contributions to the branching ratio of the radiative decay of $\mu$ and $\tau$, namely $\mu \to e\gamma$, $\tau \to e\gamma$, and $\tau \to \mu \gamma$ from supersymmetry without $R$ parity, focusing on contributions involving bilinear couplings. A numerical study is performed to obtain explicit bounds on the parameters under the present experimental limit. We present, and use in the calculation, formulas for exact mass eigenstate effective couplings. In this sense, we present an exact analysis free from approximation for the first time. After comparing our results against the closest early analysis, we discovered a major difference in resulted constraints on some ${\mu }_i^{*}{B}_j$ combinations. Constraints from neutrino masses on the parameters were considered. Our result indicates that the branching ratio measurement on $\mu \to e\gamma$ down to ${10}^{-13}–{10}^{-14}$ and beyond, as targeted by the MEG experiment, has a chance of observing decay from the $R$-parity violating scenario.

Recently, it was shown that in inclusive $B\to X_s{\ell }^{+}{\ell }^{-}$ decay, an angular decomposition provides three independent ($q^2$ dependent) observables. A strategy was formulated to extract all measurable Wilson coefficients in $B\to X_s{\ell }^{+}{\ell }^{-}$ from a few simple integrals of these observables in the low $q^2$ region. The experimental measurements in the low $q^2$ region require a cut on the hadronic invariant mass, which introduces a dependence on nonperturbative $b$ quark distribution functions. The associated hadronic uncertainties could potentially limit the sensitivity of these decays to new physics. We compute the nonperturbative corrections to all three observables at leading and subleading order in the power expansion in ${\Lambda }_{\mathrm{QCD}}/m_b$. We find that the subleading power corrections give sizeable corrections, of order $-5\%$ to $-10\%$ depending on the observable and the precise value of the hadronic mass cut. They cause a shift of order $-0.05{\mathrm{GeV}}^2$ to $-0.1{\mathrm{GeV}}^2$ in the zero of the forward-backward asymmetry.

Based on the color-singlet model, we investigate the photoproduction of $J/\psi$ associated with a $c\overline{c}$ pair with all subprocesses including the direct, single-resolved, and double-resolved channels. The amplitude squared of these subprocesses are obtained analytically. By choosing corresponding parameters, we give theoretical predictions for the $J/\psi$ transverse momentum and rapidity distributions both at the LEPII and at the future photon colliders for these subprocesses. The numerical results show that at the LEPII these processes cannot give enough contributions to account for the experimental data, and it indicates that the color-octet mechanism may still be needed. At the photon collider with the laser backscattering photons, the resolved photon channel will dominate over the direct one in small and moderate $p_t$ regions with large $\sqrt{s}$. For their rapidity distribution with the laser backscattering photons, the resolved processes will be dominant in the whole region $-2<y<2$. By measuring the $J/\psi$ production associated with a $c\overline{c}$ pair, this process can be separated from the inclusive $J/\psi$ production and may provide a new chance to test the color-singlet contributions.

We discover new vacuum solutions of the Jalilian-Marian–Iancu–McLerran–Weigert–Leonidov–Kovner equation, which correspond to the center of a gauge group. We improve the color glass condensate (CGC) model by an explicit usage of a density matrix. Studying scattering of CGC states in an external color field, we observe that an amplitude is naturally expressed via group characters. We construct an example that shows how new thin effects may be potentially observed in peripheral collisions. We prove that at any parton density a gluonic CGC state does not become a true black disk. We find a wave function of a true black disk and show that it necessarily contains many quarks. This result corresponds to the necessity of nonvacuum Reggeon loops in a formation of a true black disk.

In the covariant light-front quark model, we investigate the $B_c\to h_c$, ${\chi }_{c0,1,2}$ form factors. The form factors are evaluated in the spacelike kinematic region and are recasted to the physical region by adopting the exponential parametrization. We also study the semileptonic $B_c$ decays and find that branching fractions for the $B_c\to (h_c,{\chi }_{c0,1,2})l\overline{\nu }(l=e,\mu )$ decays have the order ${10}^{-3}$, while branching fractions for $B_c\to (h_c,{\chi }_{c0,1,2})\tau {\overline{\nu }}_{\tau }$ are suppressed by one order. These predictions will be tested on the forthcoming hadron colliders.

CKM mixing between third-family quarks and a possible fourth family is constrained by global fits to the precision electroweak data. The dominant constraint is from nondecoupling oblique corrections rather than the vertex correction to $Z\to \overline{b}b$ used in previous analyses. The possibility of large mixing suggested by some recent analyses of flavor-changing neutral-current processes is excluded, but 3–4 mixing of the same order as the Cabbibo mixing of the first two families is allowed.

We present a measurement of the $B^0\to \overline{\Lambda }p{\pi }^{-}$ branching fraction performed using the BABAR detector at the PEP-II asymmetric $e^{+}{e}^{-}$ collider. Based on a sample of $467\times {10}^6$ $B\overline{B}$ pairs we measure $\mathcal{B}(B^0\to \overline{\Lambda }p{\pi }^{-})=[3.07\pm 0.31(\mathrm{stat})\pm 0.23(\mathrm{syst})]\times {10}^{-6}$. The measured differential spectrum as a function of the dibaryon invariant mass $m(\overline{\Lambda }p)$ shows a near-threshold enhancement similar to that observed in other baryonic $B$ decays. We study the $\overline{\Lambda }$ polarization as a function of $\overline{\Lambda }$ energy in the $B^0$ rest frame ($E_{\overline{\Lambda }}^{*}$) and compare it with theoretical expectations of fully longitudinally right-polarized $\overline{\Lambda }$ at large $E_{\overline{\Lambda }}^{*}$.

We show that the long known puzzling branching ratios of open-charm decays in $e^{+}{e}^{-}$ annihilation can be reasonably described with a simple form factor, which strongly suppresses open channels far above threshold. Application to the $e^{+}{e}^{-}\to J/\psi \pi \pi$ data on the $X(4260)$ enhancement recently reported by the BABAR Collaboration [B. Aubert (BABAR Collaboration), arXiv:0808.1543] allows a good fit with a simple nonresonant cusp structure around the $D_s^{*}{D}_s^{*}$ threshold. Moreover, we argue that a closer look at the data reveals an oscillatory pattern, which we model as an interference effect between a fast—OZI-allowed—and a slow—OZI-forbidden—$J/\psi f_0(980)$ mode. Other candidates for similar nonresonant enhancements are discussed.

The minimal coupling procedure, which is employed in standard Yang-Mills theories, appears to be ambiguous in the case of gravity. We propose a slight modification of this procedure, which removes the ambiguity. Our modification justifies some earlier results concerning the consequences of the Poincaré gauge theory of gravity. In particular, the predictions of the Einstein-Cartan theory with fermionic matter are rendered unique.

The fact that certain nonlinear $W_{2,s}$ algebras can be linearized by the inclusion of a spin-1 current can provide a simple way to realize $W_{2,s}$ algebras from linear $W_{1,2,s}$ algebras. In this paper, we first construct the explicit field realizations of linear $W_{1,2,s}$ algebras with double scalar and double spinor, respectively. Then, after a change of basis, the realizations of $W_{2,s}$ algebras are presented. The results show that all these realizations are Romans-type realizations.

We study the supersymmetric Wilson loops in the four-dimensional $\mathcal{N}=4$ super Yang-Mills theory in the context of AdS/CFT correspondence. In the gauge theory side, it is known that the expectation value of the Wilson loops of circular shape with winding number $k$, $W_k(C)$, is calculable by using a Gaussian matrix model. In the gravity side, the expectation value of the loop is conjectured to be given by the classical value of the action $S_{\mathrm{D}3}$ for a probe $\mathrm{D}3$-brane with $k$ electric fluxes as $⟨W_k(C)⟩={\mathrm{e}}^{-S_{\mathrm{D}3}}$. Given such correspondence, we pursue the interpretation of the matrix model eigenvalue density, or more precisely the resolvent, from the viewpoint of the probe $\mathrm{D}3$-brane. We see that the position of an eigenvalue appears as the gauge field plus the scalar field integrated over the boundary of the probe $\mathrm{D}3$-brane. In the course of our analysis, we also clarify the boundary condition on the $\mathrm{D}3$-brane in terms of the Wilson loop.

We investigate the gravitational one-loop divergences of the standard model in large extra dimensions, with gravitons propagating in the ($4+\delta$)-dimensional bulk and gauge fields as well as scalar and fermionic multiplets confined to a three-brane. To determine the divergences we establish a cutoff regularization which allows us to extract gauge-invariant counterterms. In contrast to the claim of a recent paper [F. Wu and M. Zhong, Phys. Rev. D 78, 085010 (2008).], we show that the fermionic and scalar higher derivative counterterms do not coincide with the higher derivative terms in the Lee-Wick standard model. We argue that even if the exact Lee-Wick higher derivative terms were found, as in the case of the pure gauge sector, this would not allow to conclude the existence of the massive ghost fields corresponding to these higher derivative terms in the Lee-Wick standard model.

We consider a string-inspired torsion-dilaton-gravity action in a Randall-Sundrum braneworld scenario and show that, in an effective four-dimensional theory on the visible brane, the rank-2 antisymmetric Kalb-Ramond field (source of torsion) is exponentially suppressed. The result is similar to our earlier result in [B. Mukhopadhyaya, S. Sen, and S. SenGupta, Phys. Rev. Lett. 89, 121101 (2002); Phys. Rev. Lett. 89, 259902(E) (2002)], where no dilaton was present in the bulk. This offers an explanation of the apparent invisibility of torsion in our space-time. However, in this case the trilinear couplings $\sim {\mathrm{TeV}}^{-1}$ between the dilaton and torsion may lead to new signals in TeV-scale experiments, bearing the stamp of extra warped dimensions.

We present a formalism to calculate the nonlinear matter power spectrum in modified gravity models that explain the late-time acceleration of the Universe without dark energy. Any successful modified gravity models should contain a mechanism to recover general relativity (GR) on small scales in order to avoid the stringent constrains on deviations from GR at solar system scales. Based on our formalism, the quasi-nonlinear power spectrum in the Dvali-Gabadadze-Porratti braneworld models and $f(R)$ gravity models are derived by taking into account the mechanism to recover GR properly. We also extrapolate our predictions to fully nonlinear scales using the parametrized post-Friedmann framework. In the Dvali-Gabadadze-Porratti and $f(R)$ gravity models, the predicted nonlinear power spectrum is shown to reproduce $N$-body results. We find that the mechanism to recover GR suppresses the difference between the modified gravity models and dark energy models with the same expansion history, but the difference remains large at the weakly nonlinear regime in these models. Our formalism is applicable to a wide variety of modified gravity models and it is ready to use once consistent models for modified gravity are developed.

Axionlike particles (ALPs) are predicted to couple with photons in the presence of magnetic fields. This effect may lead to a significant change in the observed spectra of gamma-ray sources such as active galactic nuclei (AGNs). Here we carry out a detailed study that for the first time simultaneously considers in the same framework both the photon/axion mixing that takes place in the gamma-ray source and that one expected to occur in the intergalactic magnetic fields. An efficient photon/axion mixing in the source always means an attenuation in the photon flux, whereas the mixing in the intergalactic medium may result in a decrement and/or enhancement of the photon flux, depending on the distance of the source and the energy considered. Interestingly, we find that decreasing the value of the intergalactic magnetic field strength, which decreases the probability for photon/axion mixing, could result in an increase of the expected photon flux at Earth if the source is far enough. We also find a 30% attenuation in the intensity spectrum of distant sources, which occurs at an energy that only depends on the properties of the ALPs and the intensity of the intergalactic magnetic field, and thus independent of the AGN source being observed. Moreover, we show that this mechanism can easily explain recent puzzles in the spectra of distant gamma-ray sources, like the possible detection of TeV photons from 3C 66A (a source located at $z=0.444$) by MAGIC and VERITAS, which should not happen according to conventional models of photon propagation over cosmological distances. Another puzzle is the recent published lower limit to the extragalactic background light intensity at $3.6\mu \mathrm{m}$ (which is almost twice larger as the previous one), which implies very hard spectra for some detected TeV gamma-ray sources located at $z=0.1–0.2$. The consequences that come from this work are testable with the current generation of gamma-ray instruments, namely Fermi (formerly known as GLAST) and imaging atmospheric Cherenkov telescopes like CANGAROO, HESS, MAGIC, and VERITAS.

We perform a detailed numerical investigation of the approximate moduli space metric proposed by Diakonov and Petrov [Phys. Rev. D 76, 056001 (2007)] for a confining model of dyons. Our findings strongly indicate that this metric is positive definite (and, therefore, a valid moduli space metric) throughout a considerable part of configuration space only for a small number of dyons at sufficiently low density. This poses strong limitations on results obtained by an unrestricted integration over collective coordinates in this model. It also indicates that strong correlations between collective coordinates will be essential for the physical content of a dyon model, which could be exhibited by a suitable simulation algorithm.