We investigate a novel approach to measuring the Hubble constant using gravitational-wave (GW) signals from compact binaries by exploiting the narrowness of the distribution of masses of the underlying neutron-star population. Gravitational-wave observations with a network of detectors will permit a direct, independent measurement of the distance to the source systems. If the redshift of the source is known, these inspiraling double-neutron-star binary systems can be used as standard sirens to extract cosmological information. Unfortunately, the redshift and the system chirp mass are degenerate in GW observations. Thus, most previous work has assumed that the source redshift is obtained from electromagnetic counterparts. However, we investigate a novel method of using these systems as standard sirens with GW observations alone. In this paper, we explore what we can learn about the background cosmology and the mass distribution of neutron stars from the set of neutron-star (NS) mergers detected by such a network. We use a Bayesian formalism to analyze catalogs of NS-NS inspiral detections. We find that it is possible to constrain the Hubble constant, $H_0$, and the parameters of the NS mass function using gravitational-wave data alone, without relying on electromagnetic counterparts. Under reasonable assumptions, we will be able to determine $H_0$ to $\pm 10\%$ using $\sim 100$ observations, provided the Gaussian half-width of the underlying double NS mass distribution is less than $0.04M_{\odot }$. The expected precision depends linearly on the intrinsic width of the NS mass function, but has only a weak dependence on $H_0$ near the default parameter values. Finally, we consider what happens if, for some fraction of our data catalog, we have an electromagnetically measured redshift. The detection, and cataloging, of these compact-object mergers will allow precision astronomy, and provide a determination of $H_0$ which is independent of the local distance scale.

We show that, because of their effective electromagnetic interaction in matter, transition radiation is emitted whenever neutrinos goes across the boundary between two media with different indices of refraction. This effect occurs in the context of the standard model and does not depend on any exotic neutrino property. We examine such a phenomena and compare it with the transition radiation of a neutrino endowed with an intrinsic dipole moment.

A well-known connection between $n$ strings winding around a circle and permutations of $n$ objects plays a fundamental role in the string theory of large $N$ two-dimensional Yang-Mills theory and elsewhere in topological and physical string theories. Basic questions in the enumeration of Feynman graphs can be expressed elegantly in terms of permutation groups. We show that these permutation techniques for Feynman graph enumeration, along with the Burnside counting lemma, lead to equalities between counting problems of Feynman graphs in scalar field theories and quantum electrodynamics with the counting of amplitudes in a string theory with torus or cylinder target space. This string theory arises in the large $N$ expansion of two-dimensional Yang-Mills and is closely related to lattice gauge theory with $S_n$ gauge group. We collect and extend results on generating functions for Feynman graph counting, which connect directly with the string picture. We propose that the connection between string combinatorics and permutations has implications for quantum-field-theory-string dualities, beyond the framework of large $N$ gauge theory.

In this note, we study a large class of four-dimensional $R$-symmetric theories, and we describe a new quantity ${\tau }_U$ which is well defined in these theories. Furthermore, we conjecture that this quantity is larger in the ultraviolet (UV) than in the infrared (IR), i.e., that ${\tau }_U^{\mathrm{UV}}>{\tau }_U^{\mathrm{IR}}$. While we do not prove this inequality in full generality, it is straightforward to show that our conjecture holds in the subset of theories that do not have accidental symmetries. In addition, we subject our inequality to an array of nontrivial tests in theories with accidental symmetries and dramatically different dynamics both in $\mathcal{N}=1$ and $\mathcal{N}=2$ supersymmetry and find that our inequality is obeyed. One interesting consequence of this conjecture is that the mixing of accidental symmetries with the IR superconformal $R$ current is bounded by the UV quantity, ${\tau }_U^{\mathrm{UV}}$. To demonstrate the potential utility of this bound, we apply it to the somewhat mysterious $SU(2)$ gauge theory of Intriligator, Seiberg, and Shenker and show that our conjecture, if correct, implies that this theory flows in the IR to an interacting superconformal field theory.

We discuss the Hawking temperature of near-equilibrium black holes using a semiclassical analysis. We introduce a useful expansion method for slowly evolving spacetime, and evaluate the Bogoliubov coefficients using the saddle point approximation. For a spacetime whose evolution is sufficiently slow, such as a black hole with slowly changing mass, we find that the temperature is determined by the surface gravity of the past horizon. As an example of applications of these results, we study the Hawking temperature of black holes with null shell accretion in asymptotically flat space and the AdS-Vaidya spacetime. We discuss implications of our results in the context of the AdS/CFT correspondence.

A generalization to the theory of massive gravity is presented which includes three dynamical metrics. It is shown that at the linear level, the theory predicts a massless spin-2 field which is decoupled from the other two gravitons, which are massive and interacting. In this regime, the matter should naturally couple to massless gravitons which introduce a preferred metric that is the average of the primary metrics. The cosmological solution of the theory shows the de Sitter behavior with a function of mass as its cosmological constant. Surprisingly, it lacks any nontrivial solution when one of the metrics is taken to be Minkowskian and seems to enhance the predictions which suggest that there is no homogeneous, isotropic, and flat solution for the standard massive cosmology.

It is expected that black holes are formed dynamically under gravitational collapses and approach stationary states. In this paper, we show that the asymptotic Killing vector at late time should exist on the horizon and then that it can be extended outside of black holes under the assumption of the analyticity of spacetimes. This fact implies that if there is another asymptotic Killing vector which becomes a stationary Killing at a far region and spacelike in the “ergoregion,” the rotating black holes may have the asymptotically axisymmetric Killing vector at late time. Thus, we may expect that the asymptotic rigidity of the black holes holds.

Inflation typically predicts a quasiscale-invariant spectrum of gravitational waves. In models of slow-roll inflation, the amplitude of such a background is too small to allow direct detection without a dedicated space-based experiment such as the proposed BBO or DECIGO. In this paper we note that particle production during inflation can generate a feature in the spectrum of primordial gravitational waves. We discuss the possibility that such a feature might be detected by ground-based laser interferometers such as Advanced LIGO and Advanced Virgo, which will become operational in the next few years. We also discuss the prospects of detection by a space interferometer like LISA. We first study gravitational waves induced by nonperturbative, explosive particle production during inflation: while explosive production of scalar quanta does not generate a significant bump in the primordial tensor spectrum, production of vectors can. We also show that chiral gravitational waves produced by electromagnetic fields amplified by an axionlike inflaton could be detectable by Advanced LIGO.

We introduce the generalized Lorentz gauge condition in the theory of quantum electrodynamics into the general vector-tensor theories of gravity. Then we explore the cosmic evolution and the static, spherically symmetric solution of the four dimensional vector field with the generalized Lorenz gauge. We find that, if the vector field is minimally coupled to the gravitation, it behaves as the cosmological constant. On the other hand, if it is nonminimally coupled to the gravitation, the vector field could behave as vast matters in the background of the spatially flat Friedmann-Robertson-Walker Universe. But it may not be the case. The weak, strong and dominant energy conditions, the stability analysis of classical and quantum aspects would put constraints on the parameters and so the equation of state of matters would be greatly constrained.

We have recently shown [S. A. Kim, A. R. Liddle, and D. Seery, Phys. Rev. Lett. 105, 181302 (2010)] that multifield axion $N$-flation can lead to observable non-Gaussianity in much of its parameter range, with the assisted-inflation mechanism ensuring that the density perturbations are sufficiently close to scale invariance. In this paper, we extend our analysis in several directions. In the case of equal-mass axions, we compute the probability distributions of observables and their correlations across the parameter space. We examine the case of unequal masses, and show that the mass spectrum must be very densely packed if the model is to remain in agreement with observations. The model makes specific testable predictions for all major perturbative observables, namely, the spectral index, tensor-to-scalar ratio, bispectrum, and trispectrum.

We discuss the interplay between spectral shape and detector response beyond a simple $E^{-2}$ neutrino flux at neutrino telescopes, using the example of time-integrated point source searches using IceCube-40 data. We use a self-consistent model for the neutrino production, in which protons interact with synchrotron photons from coaccelerated electrons, and we fully take into account the relevant pion and kaon production modes, the flavor composition at the source, flavor mixing, and magnetic field effects on the secondaries (pions, muon, and kaons). Since some of the model parameters can be related to the Hillas parameters $R$ (size of the acceleration region) and $B$ (magnetic field), we relate the detector response to the Hillas plane. In order to compare the response to different spectral shapes, we use the energy flux density as a measure for the pion production efficiency times luminosity of the source. We demonstrate that IceCube has a very good reach in this quantity for active galactic nuclei and jets for all source declinations, while the spectra of sources with strong magnetic fields are found outside the optimal reach. We also demonstrate where neutrinos from kaon decays and muon tracks from $\tau$ decays can be relevant for the detector response. Finally, we point out the complementarity between IceCube and other experiments sensitive to high-energy neutrinos, using the example of 2004–2008 Earth-skimming neutrino data from Auger. We illustrate that Auger, in principle, is more sensitive to the parameter region in the Hillas plane from which the highest-energetic cosmic rays may be expected in this model.

We consider the perturbative (weak field) limit of the small $x$ QCD evolution equation for the quadrupole, the normalized trace of four Wilson lines in the fundamental representation, which appears in dihadron angular correlation in high-energy collisions. We linearize the quadrupole evolution equation and then expand the Wilson lines in powers of $g{A}_{\mu }$ where $A_{\mu }$ is the gauge field. The quadratic terms in the expansion ($\sim g^2{A}^2$) satisfy the Balitsky-Fadin-Kuraev-Lipatov equation as has been recently shown. We then consider the quartic terms ($\sim g^4{A}^4$) in the expansion and show that the linearized quadrupole evolution equation, written in terms of color charge density $\rho$, reduces to the well-known Bartels-Jaroszewicz-Kwiecinski-Praszalowicz equation for the imaginary part of the four-Reggeized-gluon exchange amplitude. We comment on the possibility that the Bartels-Jaroszewicz-Kwiecinski-Praszalowicz equation for the evolution of an $n$-Reggeized-gluon state can be obtained from the Jalilian-Marian-Iancu-McLerran-Weigert-Leonidov-Kovner evolution equation for the normalized trace of $n$ fundamental Wilson lines when nonlinear (recombination) terms are neglected.

Partial decay widths of the heavy-light mesons, $D$, $D_s$, $B$, and $B_s$, emitting one chiral particle ($\pi$ or $K$) are evaluated in the framework of a relativistic potential model. Decay amplitudes are calculated by keeping the Lorentz invariance as far as possible and use has been made of the Lorentz-boosted relativistic wave functions of the heavy-light mesons. One of predictions of our calculation is very narrow widths of a few keV for yet undiscovered $B_s(0^{+},1^{+})$ mesons corresponding to ${}^{2S+1}L_J={}^{3}P_0$ and “${}^{3}P_1$” assuming their masses to be 5617 and 5682 MeV, respectively, as calculated in our former paper. In the course of our calculation, new sum rules are discovered on the decay widths in the limit of $m_Q\to \infty$. Among these rules, $\Gamma (D_{s0}^{*}(2317)\to D_s+\pi )=\Gamma (D_{s1}(2460)\to D_s^{*}+\pi )$ and $\Gamma (B_{s0}^{*}(5615)\to B_s+\pi )=\Gamma (B_{s1}(5679)\to B_s^{*}+\pi )$ are predicted to hold with a good accuracy.

We present a systematic discussion of ${\Lambda }_b\to \Lambda$ transition form factors in the framework of soft-collinear effective theory (SCET). The universal soft form factor, which enters the symmetry relations in the limit of large recoil energy, is calculated from a sum-rule analysis of a suitable SCET correlation function. The same method is applied to derive the leading corrections from hard-collinear gluon exchange at first order in the strong coupling constant. We present numerical estimates for form factors and form-factor ratios and their impact on decay observables in ${\Lambda }_b\to \Lambda {\mu }^{+}{\mu }^{-}$ decays.

In the framework of the $k_T$-factorization approach, the production and polarization of prompt $J/\psi$ mesons in $pp$ collisions at the LHC energy $\sqrt{s}=7\mathrm{TeV}$ is studied. Both the direct production mechanism as well as feed-down contributions from ${\chi }_{c1}$, ${\chi }_{c2}$, and ${\psi }^{\prime }$ decays are taken into account. Our consideration is based on the color singlet model supplemented with the off-shell matrix elements for the corresponding partonic subprocesses. The unintegrated gluon densities in a proton are determined using the CCFM evolution equation as well the Kimber-Martin-Ryskin prescription. We compare our numerical predictions with the first experimental data taken by the CMS, ATLAS, and LHCb collaborations. The estimation of polarization parameters ${\lambda }_{\theta }$, ${\lambda }_{\varphi }$, and ${\lambda }_{\theta \varphi }$ which determine $J/\psi$ spin density matrix is performed.

We study some properties of nucleons with a simplified version of a Faddeev equation at finite temperature and baryon chemical potential in the framework of the Nambu–Jona-Lasinio model. By taking diquark-quark bubble summation, we constructed the nucleon propagator and calculated the dynamical masses of the diquark and the nucleon in the pole approximation. We show that diquarks can survive as resonant states in the chiral symmetry restored phase at high temperature, and that nucleons are restricted in the chiral symmetry broken phase at low temperature. The phase diagram of the strongly interacting matter is then given.

We report on a measurement of $CP$-violating asymmetries ($A_{CP}$) in the Cabibbo-suppressed $D^0\to {\pi }^{+}{\pi }^{-}$ and $D^0\to K^{+}{K}^{-}$ decays reconstructed in a data sample corresponding to $5.9{\mathrm{fb}}^{-1}$ of integrated luminosity collected by the upgraded Collider Detector at Fermilab. We use the strong decay $D^{*+}\to D^0{\pi }^{+}$ to identify the flavor of the charmed meson at production and exploit $CP$-conserving strong $c\overline{c}$ pair production in $p\overline{p}$ collisions. High-statistics samples of Cabibbo-favored $D^0\to K^{-}{\pi }^{+}$ decays with and without a $D^{*\pm }$ tag are used to correct for instrumental effects and significantly reduce systematic uncertainties. We measure $A_{CP}(D^0\to {\pi }^{+}{\pi }^{-})=(+0.22\pm 0.24(\mathrm{stat})\pm 0.11(\mathrm{syst}))\%$ and $A_{CP}(D^0\to K^{+}{K}^{-})=(-0.24\pm 0.22(\mathrm{stat})\pm 0.09(\mathrm{syst}))\%$, in agreement with $CP$ conservation. These are the most precise determinations from a single experiment to date. Under the assumption of negligible direct $CP$ violation in $D^0\to {\pi }^{+}{\pi }^{-}$ and $D^0\to K^{+}{K}^{-}$ decays, the results provide an upper limit to the $CP$-violating asymmetry in $D^0$ mixing, $|A_{CP}^{\mathrm{ind}}(D^0)|<0.13\%$ at the 90% confidence level.

A maximum entropy principle was proven in my recent paper [S. Gao, Phys. Rev. D 84, 104023 (2011)]. I show that a crucial condition $p=p(\rho )$ used in the proof can be removed and the conclusion remains valid.

Recently, the possibility of so-called twinlike field theories has been demonstrated, that is, of different field theories which share the same topological defect solution with the same energy density. Further, purely algebraic conditions have been derived which the corresponding Lagrangians have to obey in order that the field theories be twins of each other. A further diagnostical tool which, in general, allows us to distinguish the topological defects of a given theory from the corresponding defects of its twins is the spectrum of linear fluctuations about these defects. Very recently, however, explicit examples of twin theories have been constructed such that not only their shapes and energy densities coincide, but also their linear fluctuation spectra are the same. Here we show that, again, there exist purely algebraic conditions for the Lagrangian densities which imply that the corresponding field theories are twins and that the fluctuation spectra about their defects coincide. These algebraic conditions allow us to construct an infinite number of twins with coinciding fluctuation spectra for a given theory, and we provide some explicit examples. The importance of this result is related to the fact that coinciding defects with coinciding energy densities and identical fluctuation spectra are almost indistinguishable physically, that is, indistinguishable in a linear or semiclassical approximation. This implies that the measurable physical properties of a kink, in general, do not allow us to determine the theory which provides the kink uniquely. Instead, in principle, an infinite number of possible theories has to be considered.