We further pursue an approach to the sign problem of quantum chromodynamics at nonzero chemical potential, in which configurations of the lattice path integral are gathered into subsets. In the subset construction we multiply each temporal link by center elements independently and in a first step neglect the gauge action. The positivity of the subset weights—shown for $0+1$ dimensions in an earlier study—extends to larger lattices: for two sites in the temporal direction and arbitrary spatial extent we give a proof of the positivity by decomposing the subset weight in positive summands. From numerical evidence we conjecture that the positivity persists on larger lattices and that the gauge action can be reintroduced through mild reweighting. First results on the quark number obtained with this method in two dimensions are shown as well.

We extend the perturbative QCD formalism including the Glauber gluons, which has been shown to accommodate the measured $B\to \pi \pi$ and $B^0\to {\rho }^0{\rho }^0$ branching ratios simultaneously, to the analysis of the $B\to K\pi$ and $K\overline{K}$ decays. It is observed that the convolution of the universal Glauber phase factors with the transverse-momentum-dependent kaon wave function reveals weaker (stronger) Glauber effects than in the pion ($\rho$ meson) case as expected. Our predictions for the branching ratios and the direct CP asymmetries of the $B\to K\pi$ and $K\overline{K}$ modes at next-to-leading-order accuracy agree well with data. In particular, the predicted difference of the $B^{\pm }\to K^{\pm }{\pi }^0$ and $B^0\to K^{\pm }{\pi }^{\mp }$ direct CP asymmetries, $\mathrm{\Delta }{A}_{K\pi }\equiv A_{\mathrm{CP}}^{\mathrm{dir}}(K^{\pm }{\pi }^0)[0.021\pm 0.016]-A_{\mathrm{CP}}^{\mathrm{dir}}(K^{\pm }{\pi }^{\mp })[-0.081\pm 0.017]=0.102\pm 0.023$, is consistent with the measured $\mathrm{\Delta }{A}_{K\pi }=0.119\pm 0.022$ within uncertainties, and the known $B\to K\pi$ puzzle is resolved. The above $B\to \pi \pi$, $K\pi$ and $K\overline{K}$ studies confirm that the Glauber gluons associated with pseudo-Nambu-Goldstone bosons enhance the color-suppressed tree amplitude significantly, but have a small impact on other topological amplitudes.

The anomalously large experimentally measured ratios of the semitauonic decay $B\to D^{(*)}+\tau +\nu$ and the corresponding semileptonic $B\to D^{*}+l+{\overline{\nu }}_l$ disagree with the predictions of the standard $\mathrm{E}.\mathrm{W}+\mathrm{QCD}$ model (SM). We briefly comment on this disagreement and on possible new physics explanations which are rather constrained and difficult to implement.

We analyze soft and collinear gluon resummation effects at the ${\mathrm{N}}^3\mathrm{LL}$ level for Standard Model Higgs boson production via gluon fusion $gg\to H$ and the neutral scalar and pseudoscalar Higgs bosons of the minimal supersymmetric extension at the next-to-next-to-next-to-leading-log (${\mathrm{N}}^3\mathrm{LL}$) and next-to-next-to-leading-log (NNLL) level, respectively. We introduce refinements in the treatment of quark mass effects and subleading collinear gluon effects within the resummation. Soft and collinear gluon resummation effects amount to up to about 5% beyond the fixed-order results for scalar and pseudoscalar Higgs boson production.

We study the semileptonic decay of ${\mathrm{\Lambda }}_c$ to $\nu l^{+}$ and $\mathrm{\Lambda }(1405)$, where the $\mathrm{\Lambda }(1405)$ is seen in the invariant mass distribution of $\pi \mathrm{\Sigma }$. We perform the hadronization of the quarks produced in the reaction in order to have a meson baryon pair in the final state and then let these hadron pairs undergo final state interaction from where the $\mathrm{\Lambda }(1405)$ is dynamically generated. The reaction is particularly suited to study this resonance, because we show that it filters $I=0$. It is also free of tree-level $\pi \mathrm{\Sigma }$ production, which leads to a clean signal of the resonance with no background. This same feature has as a consequence that one populates the state of the $\mathrm{\Lambda }(1405)$ with higher mass around 1420 MeV, predicted by the chiral unitary approach. We make absolute predictions for the invariant mass distributions and find them within the measurable range in present facilities. The implementation of this reaction would allow us to gain insight into the existence of the predicted two $\mathrm{\Lambda }(1405)$ states and their nature as molecular states.

We constrain the Higgs boson (Yukawa) coupling to quarks in the first two generations in the $H\to ZZ$ final states. Deviation of these couplings from the Standard Model values leads to changes in the Higgs boson width and in the cross sections of relevant processes. In the Higgs boson resonance region, an increased light Yukawa coupling leads to an increased Higgs boson width, which in turn leads to a decreased cross section. In the off-shell region, increased Yukawa couplings result in an enhancement of the Higgs boson signal through $q\overline{q}$ annihilation. With the assumption of scaling one Yukawa coupling at a time, this study is conceptually simple and yields results with the same order of magnitude as the tightest in the literature. The study is based on results published by the CMS experiment at the LHC in 2014, corresponding to integrated luminosities of $5.1{\mathrm{fb}}^{-1}$ at a centre-of-mass energy $\sqrt{s}=7\mathrm{TeV}$ and $19.7{\mathrm{fb}}^{-1}$ at 8 TeV.

In this paper, we continue to pursue the question of whether gauge theories can be represented in terms of effective “scalar” degrees of freedom. We provide such a consistent representation for a free photon theory in $3+1$ dimensions. Building on results of [Phys. Rev. D 88, 125004 (2013), we construct a Lagrangian with a four-derivative kinetic term and demonstrate that, despite the seeming nonlinearity of the theory, it is equivalent to a theory of a free photon.

We present a comparison of two methods to compute the momentum spectrum and the Schwinger pair creation rate for pulsed rotating electric fields: a numerical method based upon the real-time Dirac-Heisenberg-Wigner formalism and a semiclassical approximation based on a scattering ansatz. For the semiclassical method we propose to either perform numerical calculations or an additional approximation based on an analytical solution for the constant rotating field. We find that the two numerical methods are complementary with respect to computation time as well as accuracy. The approximate method shows the same qualitative features while being computationally much faster. We additionally find that the unequal production of pairs in different spin states reported for constant rotating fields with the scattering method is in agreement with the Wigner function method.

We construct time-dependent charged black string solutions in five-dimensional Einstein-Maxwell theory. In the far region, the spacetime approaches a five-dimensional Kasner universe with an expanding three-dimensional space and a shrinking extra dimension. Near the event horizon, the spacetime is approximately static and has a smooth event horizon. We also study the motion of test particles around the black string and show the existence of quasicircular orbits. Finally, we briefly discuss the stability of this spacetime.

We find a manifestly U-duality invariant formula for the Bekenstein-Hawking entropy of the most general 4 dimensional, stationary, asymptotically flat, nonextremal STU black holes constructed recently by Chow and Compère. The expression is entirely in terms of asymptotic charges. It involves the “scalar charges” of the black hole which still need to be solved in terms of the dyonic charges and the mass. We discuss how the formula reduces to some of the known results as the Klauza-Klein black hole and the dilute gas limit of Cvetič and Larsen. We give the expected generalization to an $E_{7(7)}$ invariant in the case of maximal $\mathcal{N}=8$ supergravity.

Analytical solutions to force-free electrodynamics around black holes are fundamental for building simple models of accretion disk and jet dynamics. We present a (nonexhaustive) classification of complex highest-weight solutions to the force-free equations in the near-horizon region of the extremal Kerr black hole. Bounds on the weights of solutions are derived from the finiteness of energy and the existence of a variational principle. Two classes of real magnetically dominated solutions, respectively axisymmetric and nonaxisymmetric, are described which admit finite energy with respect to the asymptotically flat observer. Subtleties related to the velocity of light surface in the near-horizon region are discussed.

Gauge-invariant observables for quantum gravity are described, with explicit constructions given primarily to leading order in Newton’s constant, analogous to and extending constructions first given by Dirac in quantum electrodynamics. These can be thought of as operators that create a particle, together with its inseparable gravitational field, and reduce to usual field operators of quantum field theory in the weak-gravity limit; they include both Wilson-line operators and those creating a Coulombic field configuration. We also describe operators creating the field of a particle in motion; as in the electromagnetic case, these are expected to help address infrared problems. An important characteristic of the quantum theory of gravity is the algebra of its observables. We show that the commutators of the simple observables of this paper are nonlocal, with nonlocality becoming significant in strong field regions, as predicted previously on general grounds.

The recent measurements of cosmic microwave background (CMB) temperature and polarization anisotropies made by the Planck satellite have provided impressive confirmation of the $\mathrm{\Lambda }\mathrm{CDM}$ cosmological model. However interesting hints of slight deviations from $\mathrm{\Lambda }\mathrm{CDM}$ have been found, including a 95% C.L. preference for a “modified gravity” (MG) structure formation scenario. In this paper we confirm the preference for a modified gravity scenario from Planck 2015 data, find that modified gravity solves the so-called $A_{\mathrm{lens}}$ anomaly in the CMB angular spectrum, and constrains the amplitude of matter density fluctuations to ${\sigma }_8=0.815_{-0.048}^{+0.032}$, in better agreement with weak lensing constraints. Moreover, we find a lower value for the reionization optical depth of $\tau =0.059\pm 0.020$ (to be compared with the value of $\tau =0.079\pm 0.017$ obtained in the standard scenario), more consistent with recent optical and UV data. We check the stability of this result by considering possible degeneracies with other parameters, including the neutrino effective number, the running of the spectral index and the amount of primordial helium. The indication for modified gravity is still present at about 95% C.L., and could become more significant if lower values of $\tau$ were to be further confirmed by future cosmological and astrophysical data. When the CMB lensing likelihood is included in the analysis the statistical significance for MG simply vanishes, indicating also the possibility of a systematic effect for this MG signal.

We describe a method for forecasting errors in interferometric measurements of polarization of the cosmic microwave background (CMB) radiation, based on the use of the Fisher matrix calculated from the visibility covariance and relation matrices. In addition to noise and sample variance, the method can account for many kinds of systematic error by calculating an augmented Fisher matrix, including parameters that characterize the instrument along with the cosmological parameters to be estimated. The method is illustrated with examples of gain errors and errors in polarizer orientation. The augmented Fisher-matrix approach is applicable to a much wider range of problems beyond CMB interferometry.

We apply the Jansson-Farrar JF12 magnetic field model in the context of point source searches by correlating the Telescope Array ultrahigh energy cosmic ray data and the IceCube-40 neutrino candidates, as well as other magnetic field hypotheses. Our field hypotheses are: no magnetic field, the JF12 field considering only the regular component, the JF12 full magnetic field, which is a combination of regular and random field components, and the standard turbulent magnetic field used in previous correlation analyses. As expected from a neutrino sample such as IceCube-40, consistent with atmospheric neutrinos, we have found no significant correlation signal in all the cases. Therefore, this paper is mainly devoted to the comparison of the effect of the different magnetic field hypotheses on the minimum neutrino source flux strength required for a $5\sigma$ discovery and the derived 90% C.L. upper limits. We also incorporate in our comparison the cases of different power law indices $\alpha =2.2$, $\alpha =2.5$ for the neutrino point source flux. The differences in the $5\sigma$ discovery flux for our magnetic field hypotheses is $\sim 1\%–50\%$, being the maximum difference with the regular JF12 field and standard turbulent field models, being the standard turbulent higher than the regular one, while the minimum is between the no magnetic field and regular JF12 field. Considering the current flux upper limits, we find that IceCube requires a lifetime $\gtrsim 5\text{years}$ to observe neutrino-UHECR correlation signals. Our analysis for different power law indices yielded the same relative behavior between different magnetic field models.

The recent completion of Advanced LIGO suggests that gravitational waves may soon be directly observed. Past searches for gravitational-wave transients have been impacted by transient noise artifacts, known as glitches, introduced into LIGO data due to instrumental and environmental effects. In this work, we explore how waveform complexity, instead of signal-to-noise ratio, can be used to rank event candidates and distinguish short duration astrophysical signals from glitches. We test this framework using a new hierarchical pipeline that directly compares the Bayesian evidence of explicit signal and glitch models. The hierarchical pipeline is shown to perform well and, in particular, to allow high-confidence detections of a range of waveforms at a realistic signal-to-noise ratio with a two-detector network.

The ATLAS Collaboration (and also CMS) has recently reported an excess over Standard Model expectations for gauge boson pair production in the invariant mass region 1.8–2.2 TeV. In light of these results, we argue that such a signal might be the first manifestation of the production and further decay of a heavy $CP$-even Higgs resulting from a type-I two Higgs doublet model. We demonstrate that in the presence of colored vectorlike fermions, its gluon fusion production cross section is strongly enhanced, with the enhancement depending on the color representation of the new fermion states. Our findings show that barring the color triplet case, any QCD “exotic” representation can fit the ATLAS result in fairly large portions of the parameter space. We have found that if the diboson excess is confirmed and this mechanism is indeed responsible for it, then the LHC Run-2 should find (i) a $CP$-odd scalar with mass below $\sim 2.3\mathrm{TeV}$, (ii) new colored states with masses below $\sim 2\mathrm{TeV}$, (iii) no statistically significant diboson events in the $W^{\pm }Z$ channel, (iv) events in the triboson channels $W^{\pm }{W}^{\mp }Z$ and $ZZZ$ with invariant mass amounting to the mass of the $CP$-odd scalar.

We determine the continuum limit of the curvature of the pseudocritical line of QCD with $n_f=2+1$ staggered fermions at nonzero temperature and quark density. We perform Monte Carlo simulations at imaginary baryon chemical potentials with Highly Improved Staggered Quarks (HISQ), adopting the HISQ/tree action discretization as implemented in the code by the MILC Collaboration. Couplings are adjusted so as to move on a line of constant physics, as determined in Ref. [1], with the strange quark mass $m_s$ fixed at its physical value and a light-to-strange mass ratio $m_l/m_s=1/20$. The chemical potential is set at the same value for the three quark species, ${\mu }_l={\mu }_s\equiv \mu$. We attempt an extrapolation to the continuum using the results on lattices with temporal size up to $L_t=12$. Our estimate for the continuum value of the curvature $\kappa$ at zero baryon density, $\kappa =0.020(4)$, is compared with recent lattice results and with experimental determinations of the freeze-out curve.

A possible solution of the notorious sign problem preventing direct Monte Carlo calculations for systems with nonzero chemical potential is to deform the integration region in the complex plane to a Lefschetz thimble. We investigate this approach for a simple fermionic model. We introduce an easy to implement Monte Carlo algorithm to sample the dominant thimble. Our algorithm relies only on the integration of the gradient flow in the numerically stable direction, which gives it a distinct advantage over the other proposed algorithms. We demonstrate the stability and efficiency of the algorithm by applying it to an exactly solvable fermionic model and compare our results with the analytical ones. We report a very good agreement for a certain region in the parameter space where the dominant contribution comes from a single thimble, including a region where standard methods suffer from a severe sign problem. However, we find that there are also regions in the parameter space where the contribution from multiple thimbles is important, even in the continuum limit.