We investigate quantum entanglement of a scalar field in the inflationary universe. By introducing a bipartite system using a lattice model of scalar field, we apply the separability criterion based on the partial transpose operation and numerically calculate the bipartite entanglement between separate spatial regions. We find that the initial entangled state becomes separable or disentangled when the size of the spatial regions exceed the Hubble horizon. This is a necessary condition for the appearance of classicality of the quantum fluctuation. We further investigate the condition for the appearance of the classical distribution function and find that the condition is given by the inequality for the symplectic eigenvalue of the covariance matrix of the scalar field.

Experimental bounds on induced vacuum magnetic birefringence can be used to improve present photon-photon scattering limits in the electronvolt energy range. Measurements with the Polarizzazione del Vuoto con Laser apparatus [E. Zavattini et al., Phys. Rev. D 77, 032006 (2008)] at both $\lambda =1064$ and 532 nm lead to bounds on the parameter $A_e$, describing nonlinear effects in QED, of $A_e^{(1064)}<6.6\times {10}^{-21}{\mathrm{T}}^{-2}@1064\mathrm{nm}$ and $A_e^{(532)}<6.3\times {10}^{-21}{\mathrm{T}}^{-2}@532\mathrm{nm}$, respectively, at 95% confidence level, compared to the predicted value of $A_e=1.32\times {10}^{-24}{\mathrm{T}}^{-2}$. The total photon-photon scattering cross section may also be expressed in terms of $A_e$, setting bounds for unpolarized light of ${\sigma }_{\gamma \gamma }^{(1064)}<4.6\times {10}^{-62}{\mathrm{m}}^2$ and ${\sigma }_{\gamma \gamma }^{(532)}<2.7\times {10}^{-60}{\mathrm{m}}^2$. Compared to the expected QED scattering cross section these results are a factor of $\simeq 2\times {10}^7$ higher and represent an improvement of a factor about 500 on previous bounds based on ellipticity measurements and of a factor of about ${10}^{10}$ on bounds based on direct stimulated scattering measurements.

We give a representation of the parity-even part of the planar two-loop six-gluon maximally helicity violating (MHV) amplitude of $\mathcal{N}=4$ super-Yang-Mills theory, in terms of loop-momentum integrals with simple dual conformal properties. We evaluate the integrals numerically in order to test directly the Anastasiou-Bern-Dixon-Kosower/Bern-Dixon-Smirnov all-loop ansatz for planar MHV amplitudes. We find that the ansatz requires an additive remainder function, in accord with previous indications from strong-coupling and Regge limits. The planar six-gluon amplitude can also be compared with the hexagonal Wilson loop computed by Drummond, Henn, Korchemsky, and Sokatchev in arXiv:0803.1466. After accounting for differing singularities and other constants independent of the kinematics, we find that the Wilson loop and MHV-amplitude remainders are identical, to within our numerical precision. This result provides nontrivial confirmation of a proposed $n$-point equivalence between Wilson loops and planar MHV amplitudes, and suggests that an additional mechanism besides dual conformal symmetry fixes their form at six points and beyond.

We study conformal gravity as an alternative theory of gravitation. For conformal gravity to be phenomenologically viable requires that the conformal symmetry is not manifest at the energy scales of the other known physical forces. Hence we are required to find a mechanism for the spontaneous breaking of conformal invariance. In this paper we study the possibility that conformal invariance is spontaneously broken due to interactions with conformally coupled matter fields. The vacuum of the theory admits conformally noninvariant solutions corresponding to maximally symmetric space-times and variants thereof. These are either de Sitter space-time or anti-de Sitter space-time in the full four space-time dimensions and we find new solutions corresponding to maximal symmetry restricted to a lower dimensional subspace. We also consider normalizable, linearized gravitational perturbations around the anti-de Sitter background. We show to second order, that these gravitational fluctuations carry zero energy momentum. Finally we also show the possibility of domain wall solitons interpolating between the ground states of spontaneously broken conformal symmetry that we have found. These solitons necessarily require the vanishing of the scalar field. This offers a way of eschewing the recent suggestion and its consequences [E. Flanagan, Phys. Rev. D 74, 023002 (2006).] that the conformal symmetry could be quarantined to a sterile sector of the theory by choosing an appropriate field redefinition.

We analyze in detail the spin precession equations in binary black hole systems, when the tidal torque on a Kerr black hole due to quadrupole-monopole coupling is taken into account. We show that completing the precession equations with this term reveals the existence of a conserved quantity at 2PN order when averaging over orbital motion. This quantity allows one to solve the (orbit-averaged) precession equations exactly in the case of equal masses and arbitrary spins, neglecting radiation reaction. For unequal masses, an exact solution does not exist in closed form, but we are still able to derive accurate approximate analytic solutions. We also show how to incorporate radiation-reaction effects into our analytic solutions adiabatically, and compare the results to solutions obtained numerically. For various configurations of the binary, the relative difference in the accumulated orbital phase computed using our analytic solutions versus a full numerical solution varies from $\sim 0.3\%$ to $\sim 1.8\%$ over $\sim 80–140$ orbital cycles accumulated while sweeping over the orbital frequency range $\sim 20–300\mathrm{Hz}$. This typically corresponds to a discrepancy of order $\sim 5–6$ radians. While this may not be accurate enough for implementation in LIGO template banks, we still believe that our new solutions are potentially quite useful for comparing numerical relativity simulations of spinning binary black hole systems with post-Newtonian theory. They can also be used to gain more understanding of precession effects, with potential application to the gravitational recoil problem, and to provide semianalytical templates for spinning, precessing binaries.

We show that all thermodynamic quantities of the Einstein-Born-Infeld black holes in three dimensions can be obtained from the dilaton and its potential of two-dimensional dilaton gravity through dimensional reduction. These are all between nonrotating uncharged BTZ (Banados-Teitelboim-Zanelli) black hole (NBTZ) and charged BTZ black hole (CBTZ).

We present the first results from BlackHat, an automated C++ program for calculating one-loop amplitudes. The program implements the unitarity method and on-shell recursion to construct amplitudes. As input to the calculation, it uses compact analytic formulæ for tree amplitudes for four-dimensional helicity states. The program performs all related computations numerically. We make use of recently developed on-shell methods for evaluating coefficients of loop integrals, introducing a discrete Fourier projection as a means of improving efficiency and numerical stability. We illustrate the numerical stability of our approach by computing and analyzing six-, seven-, and eight-gluon amplitudes in QCD and comparing against previously obtained analytic results.

We calculate nonperturbative renormalization factors at hadronic scale for $\Delta S=2$ four-quark operators in quenched domain-wall QCD using the Schrödinger functional method. Combining them with the nonperturbative renormalization group running by the Alpha Collaboration, our result yields the fully nonperturbative renormalization factor, which converts the lattice bare $B_K$ to the renormalization group invariant (RGI) ${\widehat{B}}_K$. Applying this to the bare $B_K$ previously obtained by the CP-PACS Collaboration at $a^{-1}\simeq 2,3,4\mathrm{GeV}$, we obtain ${\widehat{B}}_K=0.782(5)(7)$ [equivalent to $B_K^{\overline{\mathrm{MS}}}(\mathrm{NDR},2\mathrm{GeV})=0.565(4)(5)$ by two-loop running] in the continuum limit, where the first error is statistical and the second is systematic due to the continuum extrapolation. Except the quenching error, the total error we have achieved is less than 2%, which is much smaller than the previous ones. Taking the same procedure, we obtain $m_{u,d}^{\mathrm{RGI}}=5.613(66)\mathrm{MeV}$ and $m_s^{\mathrm{RGI}}=147.1(17)\mathrm{MeV}$ [equivalent to $m_{u,d}^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=4.026(48)\mathrm{MeV}$ and $m_s^{\overline{\mathrm{MS}}}(2\mathrm{GeV})=105.6(12)\mathrm{MeV}$ by four-loop running] in the continuum limit.

The properties of the $\Xi (1530)$ resonance are investigated in the ${\Lambda }_c^{+}\to {\Xi }^{-}{\pi }^{+}{K}^{+}$ decay process. The data sample was collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider operating at center-of-mass energies 10.58 and 10.54 GeV. The corresponding integrated luminosity is approximately $230{\mathrm{fb}}^{-1}$. The spin of the $\Xi (1530)$ is established to be $3/2$. The existence of an $S$-wave amplitude in the ${\Xi }^{-}{\pi }^{+}$ system is inferred, and its interference with the $\Xi (1530{)}^0$ amplitude provides the first clear demonstration of the Breit-Wigner phase motion expected for the $\Xi (1530)$. The $P_1(\cos {\theta }_{{\Xi }^{-}})$ Legendre polynomial moment indicates the presence of a significant $S$-wave amplitude for ${\Xi }^{-}{\pi }^{+}$ mass values above $1.6\mathrm{GeV}/c^2$, and a dip in the mass distribution at approximately $1.7\mathrm{GeV}/c^2$ is interpreted as due to the coherent addition of a $\Xi (1690{)}^0$ contribution to this amplitude. This would imply $J^P=1/2^{-}$ for the $\Xi (1690)$. Attempts at fitting the $\Xi (1530{)}^0$ line shape yield unsatisfactory results, and this failure is attributed to interference effects associated with the amplitudes describing the $K^{+}{\pi }^{+}$ and/or ${\Xi }^{-}{K}^{+}$ systems.

We point out that the observed $CP$ violation in $B_d-{\overline{B}}_d$ mixing, taking into account the measured ratio $\Delta M_d/\Delta M_s$, the recently decreased lattice value of the nonperturbative parameter ${\widehat{B}}_K$ and an additional effective suppression factor ${\kappa }_{ϵ}\simeq 0.92$ in ${ϵ}_K$ neglected so far in most analyses, may be insufficient to describe the measured value of ${ϵ}_K$ within the standard model (SM), thus hinting at new $CP$ violating contributions to the $K-\overline{K}$ and/or $B_d-{\overline{B}}_d$ systems. Furthermore, assuming that $\Delta M_d/\Delta M_s$ is SM-like, the signs and the magnitudes of new-physics effects in ${ϵ}_K$ and in the $CP$ asymmetries $S_{\psi K_s}$ and $S_{\psi \varphi }$ may turn out to be correlated. For example, in a scenario with new $CP$ phases in $B_d$ and $B_s$ mixings being approximately equal and negative, a common new phase $\approx -5°$ could remove the tension between ${ϵ}_K$ and $S_{\psi K_s}$ present in the SM and simultaneously accommodate, at least partly, the recent claim of $S_{\psi \varphi }$ being much larger than the SM expectation. We emphasize the importance of precise determinations of $V_{cb}$, ${\widehat{B}}_K$, $F_K$, and ${\xi }_s$, to which the parameter ${ϵ}_K$ and its correlation with the $CP$ violation in the $B_d-{\overline{B}}_d$ system are very sensitive.

We report the measurement of the branching fractions of the rare decays $B^0\to D_s^{(*)+}{\pi }^{-}$, $B^0\to D_s^{(*)+}{\rho }^{-}$, and $B^0\to D_s^{(*)-}{K}^{(*)+}$ in a sample of $381\times {10}^6\mathit{{\rm Y}}(4S)$ decays into $B\overline{B}$ pairs collected with the BABAR detector at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ storage ring. We present evidence for the decay $B^0\to D_s^{-}{K}^{*+}$ and the vector-vector decays $B^0\to D_s^{*+}{\rho }^{-}$ and $B^0\to D_s^{*-}{K}^{*+}$, as well as the first measurement of the vector meson polarization in these decays. We also determine the ratios of the CKM-suppressed to CKM-favored amplitudes $r(D^{(*)}\pi )$ and $r(D^{(*)}\rho )$ in decays $B^0\to D^{(*)\pm }{\pi }^{\mp }$ and $B^0\to D^{(*)\pm }{\rho }^{\mp }$, and comment on the prospects for measuring the $CP$ observable $\sin (2\beta +\gamma )$.

In this paper, a protocol is proposed in which energy extraction from local vacuum states is possible by using quantum measurement information for the vacuum state of quantum fields. In the protocol, Alice, who stays at a spatial point, excites the ground state of the fields by a local measurement. Consequently, wave packets generated by Alice’s measurement propagate the vacuum to spatial infinity. Let us assume that Bob stays away from Alice and fails to catch the excitation energy when the wave packets pass in front of him. Next Alice announces her local measurement result to Bob by classical communication. Bob performs a local unitary operation depending on the measurement result. In this process, positive energy is released from the fields to Bob’s apparatus of the unitary operation. In the field systems, wave packets are generated with negative energy around Bob’s location. Soon afterwards, the negative-energy wave packets begin to chase after the positive-energy wave packets generated by Alice and form loosely bound states.

In this work, analyzing the propagation of electromagnetic waves in the field of gravitational waves, we show the presence and significance of the so-called surfing effect for pulsar timing measurements. It is shown that, due to the transverse nature of gravitational waves, the surfing effect leads to enormous pulsar timing residuals if the speed of gravitational waves is smaller than the speed of light. This fact allows one to place significant constraints on parameter $ϵ$, which characterizes the relative deviation of the speed of gravitational waves from the speed of light. We show that the existing constraints from pulsar timing measurements already place stringent limits on $ϵ$ and consequently on the mass of the graviton $m_g$. The limits on $m_g\lesssim 8.5\times {10}^{-24}$ are 2 orders of magnitude stronger than the current constraints from Solar System tests. The current constraints also allow one to rule out massive gravitons as possible candidates for cold dark matter in the galactic halo. In the near future, the gravitational wave background from extragalactic super massive black hole binaries, along with the expected submicrosecond pulsar timing accuracy, will allow one to achieve constraints of $ϵ\lesssim 0.4\%$ and possibly stronger.

We study a braneworld model in which a phantom-like behavior occurs with only cold dark matter and a cosmological constant, due to a large distance modification of gravity. With the addition of curvature, the geometrical tests are not strict enough to rule out models in which gravity is modified significantly on large scales. We show that this degeneracy in the parameter space is broken by the structure formation tests, such as the integrated Sachs-Wolfe effect, which can probe general relativity on large scales.

We present results from numerical evolution of a boosted black hole, perturbed nonlinearly by an axisymmetric distribution of matter in the realm of Robinson-Trautman spacetimes. Characteristic initial data for the system were constructed and the Robinson-Trautmann equation was integrated for these data using a numerical code based on the Galerkin-collocation method. The emission of gravitational waves by the system is typical of bremsstrahlung at early times, a consequence of the deceleration of the black hole as it interacts with the perturbation; part of the perturbation is radiated away and another part is absorbed into the hole. The angular pattern evolves to the quadrupole form for later times. The final configuration is a black hole in motion with larger (Bondi) rest mass and smaller boost parameter. The efficiency $\Delta$ of mass-energy extraction by gravitational wave emission was also computed. The relation of $\Delta$ to the mass of the remnant black hole satisfies a nonextensive thermostatistics distribution with entropic index $q\simeq 1/2$. The result extends analytical evaluations based on the linearized theory of gravitational wave emission. For each initial boost parameter, there always exists a (large) value of the perturbation parameter $A_0$ for which the momentum of the remnant black hole has opposite sign to that of the unperturbed black hole, due to the strong deceleration during the process of gravitational wave emission. The temporal wave form is that of an initial burst and we evaluate that for a large range of $A_0$ the process corresponds to a high power output in the initial dominant pulse.

We discuss a new inflationary scenario that is realized within the extended supersymmetric Pati-Salam model which yields an acceptable $b$-quark mass for universal boundary conditions and $\mu >0$ by modestly violating Yukawa unification and leads to new shifted, new smooth, or standard-smooth hybrid inflation. Inflation takes place along a “semishifted” classically flat direction on which the $\mathrm{U}(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge group remains unbroken. After the end of inflation, $\mathrm{U}(1{)}_{\mathrm{B}-\mathrm{L}}$ breaks spontaneously and a network of local cosmic strings, which contribute a small amount to the curvature perturbation, is produced. We show that, in minimal supergravity, this semishifted inflationary scenario is compatible with a recent fit to data which uses field-theory simulations of a local string network. Taking into account the requirement of gauge unification, we find that, for spectral index $n_{\mathrm{s}}=1$, the predicted fractional contribution of strings to the temperature power spectrum at multipole $\ell =10$ is $f_{10}\simeq 0.039$. Also, for $f_{10}=0.10$, which is the best-fit value, we obtain $n_{\mathrm{s}}\simeq 1.0254$. Spectral indices lower than about 0.98 are excluded and blue spectra are slightly favored. Magnetic monopoles are not formed at the end of semishifted hybrid inflation.

Gravitational waves potentially represent our only direct probe of the universe when it was less than one second old. In particular, first-order phase transitions in the early universe can generate a stochastic background of gravitational waves which may be detectable today. We briefly summarize the physical sources of gravitational radiation from phase transitions and present semianalytic expressions for the resulting gravitational wave spectra from three distinct realistic sources: bubble collisions, turbulent plasma motions, and inverse-cascade helical magnetohydrodynamic turbulence. Using phenomenological parameters to describe phase transition properties, we determine the region of parameter space for which gravitational waves can be detected by the proposed Laser Interferometer Space Antenna. The electroweak phase transition is detectable for a wide range of parameters.

We use a generalization of chiral perturbation theory to account for the effects of flavor twisted boundary conditions in the Breit frame. The relevant framework for two light flavors is an $SU(6|4)$ partially quenched theory, where the extra valence quarks differ only by their boundary conditions. Focusing on the pion electromagnetic form factor, finite volume corrections are calculated at next-to-leading order in the chiral expansion and are estimated to be small on current lattices.

The momentum spectrum and the polarization of charginos and neutralinos in squark decays are affected by gluon radiation in the decay process $\tilde{q}\to q\tilde{\chi }(g)$. We determine these corrections and study their impact on the $[q\ell ]$ invariant mass distributions for leptonic $\tilde{\chi }$ decays. The higher-order corrections, though small in general, can be sizeable near pronounced edges of the final-state distributions.

We construct efficient interpolating fields for lattice spectroscopy of mesons by applying covariant derivatives on Jacobi-smeared quark sources. These interpolators are tested in a quenched calculation of excited mesons based on the variational method. We present results for pseudoscalar, scalar, vector and pseudovector mesons.