Generalized susceptibilities of the net quark number have been proposed to be good probes for the transitions in the QCD phase diagram and for the search of a possible critical end point. In this article we explore a new strategy for computing quark number susceptibilities from lattice QCD via an expansion in the fugacity parameter $e^{\mu \beta }$. All quark number related bulk observables are particularly easy to access in this approach, and we present results for generalized quark number susceptibilities up to fourth order. Ratios of these quantities are studied and compared with model calculations for the high- and low-temperature regions up to a chemical potential of $\mu \beta \approx 1.0$.

We calculate the form factors for $B\to \pi \ell \nu$ and $B_s\to K\ell \nu$ decay in dynamical lattice quantum chromodynamics (QCD) using domain-wall light quarks and relativistic $b$-quarks. We use the ($2+1$)-flavor gauge-field ensembles generated by the RBC and UKQCD collaborations with the domain-wall fermion action and Iwasaki gauge action. For the $b$-quarks we use the anisotropic clover action with a relativistic heavy-quark interpretation. We analyze data at two lattice spacings of $a\approx 0.11$, 0.086 fm with unitary pion masses as light as $M_{\pi }\approx 290\mathrm{MeV}$. We simultaneously extrapolate our numerical results to the physical light-quark masses and to the continuum and interpolate in the pion/kaon energy using SU(2) “hard-pion” chiral perturbation theory for heavy-light meson form factors. We provide complete systematic error budgets for the vector and scalar form factors $f_{+}(q^2)$ and $f_0(q^2)$ for both $B\to \pi \ell \nu$ and $B_s\to K\ell \nu$ at three momenta that span the $q^2$ range accessible in our numerical simulations. Next we extrapolate these results to $q^2=0$ using a model-independent $z$-parametrization based on analyticity and unitarity. We present our final results for $f_{+}(q^2)$ and $f_0(q^2)$ as the coefficients of the series in $z$ and the matrix of correlations between them; this provides a parametrization of the form factors valid over the entire allowed kinematic range. Our results agree with other three-flavor lattice-QCD determinations using staggered light quarks, and have comparable precision, thereby providing important independent cross-checks. Both $B\to \pi \ell \nu$ and $B_s\to K\ell \nu$ decays enable determinations of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{ub}|$. To illustrate this, we perform a combined $z$-fit of our numerical $B\to \pi \ell \nu$ form-factor data with the experimental measurements of the branching fraction from BABAR and Belle leaving the relative normalization as a free parameter; we obtain $|V_{ub}|=3.61(32)\times 10^{-3}$, where the error includes statistical and all systematic uncertainties. The same approach can be applied to the decay $B_s\to K\ell \nu$ to provide an alternative determination of $|V_{ub}|$ once the process has been measured experimentally. Finally, in anticipation of future experimental measurements, we make predictions for $B\to \pi \ell \nu$ and $B_s\to K\ell \nu$ differential branching fractions and forward-backward asymmetries in the Standard Model.

We present a phenomenological analysis of the $\cos \varphi$ and $\cos 2\varphi$ asymmetries in unpolarized semi-inclusive deep inelastic scattering, based on the recent multidimensional data released by the COMPASS and HERMES collaborations. In the transverse-momentum-dependent framework, valid at relatively low transverse momenta, these asymmetries arise from intrinsic transverse momentum and transverse spin effects, and from their correlations. The role of the Cahn and Boer-Mulders effects in both azimuthal moments is explored up to order $1/Q$. As the kinematics of the present experiments is dominated by the low-$Q^2$ region, higher-twist contributions turn out to be important, affecting the results of our fits.

The limitations of doublet-septet mixing models resulting from the deviations of electroweak oblique parameters $\mathrm{\Delta }S$ and $\mathrm{\Delta }T$ are studied. In the minimal model, the mixture of the septet $\eta$ and the scalar doublet in the standard model (SM) is driven by a non-Hermitian dimension-7 operator. For a smaller bare mass of the septet, $\mathrm{\Delta }S$ puts a stringent constraint on the mixing angle $\sin \beta$ between the $CP$-odd neutral parts of the SM Higgs doublet and $\eta$. In general, increasing the mass of the scalar septet $M_{\eta }$ will enhance the deviation of $T$ from the SM, whereas it decreases the magnitude of $\mathrm{\Delta }S$ for a larger bare mass within the range $M_{\eta }\lesssim 400\mathrm{GeV}$. We also examine two extended models from the ordinary doublet-septet mixture pattern. One of them is based on an inert doublet-septet mixing pattern, in which there is no vacuum expectation value for the neutral component of $\eta$ and stable dark matter could naturally exist. For a benchmark point with the inner doublet mass of $M_{\chi }=250$ and $M_{\eta }=400\mathrm{GeV}$ in this model, the mixing coefficient is found to be less than 1.8. The other extension is constructed by imposing a doubly charged scalar mixed with the doubly charged component of the septet. Apart from the contribution by the septet-doublet admixture, $\mathrm{\Delta }S$ is suppressed by a factor of $s_W^2$ and $\mathrm{\Delta }T$ has a significant constraint due to the vanishing vacuum polarization of $Z$ at the momentum transfer $p^2=0$.

Within an effective nonlinear chiral Lagrangian framework, the substructure of $f_0(1370)$ is studied. The investigation is conducted in the context of a global picture of scalar mesons in which the importance of the underlying connections among scalar mesons below and above 1 GeV is recognized and implemented. These connections are due to the mixings among various quark-antiquarks, four-quarks, and glue components and play a central role in understanding the properties of scalar mesons. Iterative Monte Carlo simulations are first performed on the 14-dimensional parameter space of the model and sets of points in this parameter space (the global sets) that give an overall agreement with all experimental data on mass spectrum, various decay widths, and decay ratios of all isosinglet scalar states below 2 GeV are determined. Then within each global set, subsets that give closest agreement for the properties of $f_0(1370)$ are studied. Unlike the properties of other isosinglet states that show a range of variation within each global set, it is found that there is a clear signal for $f_0(1370)$ to be predominantly a quark-antiquark state with a substantial $s\overline{s}$ component, together with small remnants of four-quark and glue components.

We consider a restricted type-I seesaw scenario with four texture zeros in the neutrino Yukawa matrix, in the weak basis where both the charged-lepton Yukawa matrix and the Majorana mass matrix for right-handed neutrinos are diagonal and real. Inspired by grand unified theories, we further require the neutrino Yukawa matrix to exhibit a hierarchical pattern similar to that in the up-type quark Yukawa matrix. With such a hierarchy requirement, we find that leptogenesis, which would operate in an $N_2$-dominated scenario with the asymmetry generated by the next-to-lightest right-handed neutrino $N_2$, can greatly reduce the number of allowed textures and that it disfavors the scenario that three light neutrinos are quasidegenerate. Such a quasidegenerate scenario of light neutrinos may soon be tested in upcoming neutrino experiments.

Results from an energy loss model that includes thermal fluctuations in the energy loss for heavy quarks in a strongly coupled plasma are shown to be qualitatively consistent with single particle data from both Relativistic Heavy Ion Collider and Large Hadron Collider. The model used is the first to properly include the fluctuations in heavy quark energy loss as derived in string theory and that do not obey the usual fluctuation-dissipation relations. These fluctuations are crucial for simultaneously describing both RHIC and LHC data; leading order drag results without fluctuations are falsified by current data. Including the fluctuations is nontrivial and relies on the Wong-Zakai theorem to fix the numerical Langevin implementation. The fluctuations lead to surprising results: $B$ meson anisotropy is similar to that for $D$ mesons at LHC, and the double ratio of $D$ to $B$ meson nuclear modification factors approaches unity more rapidly than even predictions from perturbative energy loss models. It is clear that future work in improving heavy quark energy loss calculations in AdS/CFT to include all energy loss channels is needed and warranted.

We investigate the possibility of estimating the mass of an isolated rapidly rotating neutron star (NS) from a continuous gravitational wave (GW) signal emitted by the NS. When the GW passes through the gravitational potential of the NS, the GW takes a slightly longer time to travel to an observer than it does in the absence of the NS. Such a time dilation effect holds also for photons and is often referred to as the gravitational time delay (or the Shapiro time delay). Correspondingly, the phase of the GW from the NS shifts due to the Coulomb-type gravitational potential of the NS, and the resulting logarithmic phase shift depends on the mass, the spin frequency of the NS, and the distance to the NS. We show that the NS mass can, in principle, be obtained by making use of the phase-shift difference between two modes of the continuous GW such as once and twice spin frequency modes induced by a freely precessing NS or a NS containing a pinned superfluid core. We estimate the measurement accuracy of the NS mass using Monte Carlo simulations and find that the mass of the NS with its spin frequency 500 Hz and its ellipticity $10^{-6}$ at 1 kpc is typically measurable with an accuracy of 20% using the Einstein Telescope.

In this paper, we consider logarithmic and exponential forms of nonlinear electrodynamics as a source and obtain magnetic brane solutions of the Lovelock gravity. Although these solutions have no curvature singularity and no horizon, they have a conic singularity with a deficit angle. We investigate the effects of nonlinear electrodynamics and the Lovelock gravity on the value of the deficit angle and find that various terms of Lovelock gravity do not affect the deficit angle. Next, we generalize our solutions to spinning cases with maximum rotating parameters in arbitrary dimensions and calculate the conserved quantities of the solutions. Finally, we consider nonlinear electrodynamics as a correction of the Maxwell theory and investigate the properties of the solutions.

We consider Horndeski cosmological models able to screen the vacuum energy coming from any field theory assuming that after this screening the space should be in a de Sitter vacuum with a particular value of the cosmological constant specified by the theory of gravity itself. The most general scalar-tensor cosmological models without higher than second order derivatives in the field equations that have a spatially flat de Sitter critical point for any kind of material content or vacuum energy are, therefore, presented. These models could allow us to understand the current accelerated expansion of the Universe as the result of a dynamical evolution towards a de Sitter attractor.

We discuss the renormalization of the Newton constant due to fields of various spin $s$. We first briefly review the cases of $s=0,1/2,1,3/2$ already discussed in the literature and notice the appearance of the well-known contact terms for the vector bosons. We then extend this discussion of the contact terms to massive vector fields, $p$-forms and to the case of spin $s=2$ particles (gravitons). We observe that, in general, the contact terms originate from the fields which mediate the interactions (such as vector gauge bosons and gravitons). We then discuss entanglement entropy and the conical entropy and their relation to the renormalized Newton constant. We address the puzzle of the nonanalytic terms due to fields of spin $s=2$ and suggest that the resolution of this puzzle comes from the nonequivalence of the orbifold and $n$-fold cover constructions which are used in the entropy calculations. Finally, we propose a mechanism by which the Bekenstein-Hawking entropy is identified with entanglement entropy in any theory which includes both matter fields and the mediators of interactions (vector gauge bosons and gravitons).

We constrain plausible dark energy models using the recently published cosmic microwave background (CMB) temperature anisotropy data from Planck together with WMAP9 low-$\ell$ polarization data and the data from low redshift surveys. To circumvent the limitations of any particular equation of state toward describing all existing dark energy models, we work with three different equations of state covering a wider class of dark energy models and hence provide more robust and generic constraints on the dark energy behavior. We show that a possible tension exists between constraints from CMB and non-CMB observations when one allows for both phantom and nonphantom behavior for the dark energy. Further, we reconstruct the equation of state of dark energy as a function of redshift using the combined CMB and non-CMB data and show that cosmological constant behavior is disallowed at the 68.3% confidence level. A fully nonphantom history is also disallowed at the 68.3% confidence level, and a considerable fine-tuning is also needed to keep it inside the 95.5% confidence limit. This result might motivate one to construct phantom models for dark energy, which may be achievable in the presence of higher derivative operators as in string theory. However, for a theoretical model that allows only nonphantom behavior, both CMB and non-CMB data sets agree on the dark energy constraint with the mean equation of state being very close to the cosmological constant.

Recent observations of high-energy neutrinos in the IceCube experiment suggests the existence of superheavy dark matter beyond the PeV scale. We identify the parent particles of neutrinos as two degenerated right-handed neutrinos, assuming the dark matter is the heaviest right-handed neutrino. The $O(V_{cb})\sim O({10}^{-2})$ flavor symmetry breaking accounts for the $O({10}^{-4})$ mass degeneracy of right-handed neutrinos, which is a sizable scale to explain the successful resonant leptogenesis at the PeV scale. At the same time, nonthermal production of the heaviest right-handed neutrino gives the right amount of dark matter for $T_{\mathrm{RH}}\sim 10\mathrm{PeV}$. The footprint of flavor symmetry is left in the degenerated mass spectra of the extra Higgs multiplet and colored Higgs multiplet, which may be testable at the LHC or future colliders.

Starting from a simple empirical parametrization of the scattering amplitude, successfully describing the dip-bump structure of elastic $pp$ scattering in $t$ at fixed values of $s$, we construct a toy model interpolating between missing energy intervals to extract the Odderon contribution from the difference between $\overline{p}p$ and $pp$ elastic and total cross sections. The model is fitted to data from $\sqrt{s}=23.5\mathrm{GeV}$ to 7 TeV and used to extract the Odderon and its ratio to the Pomeron. From our fits, a unit intercept Odderon follows, as predicted by J. Bartels, L. N. Lipatov, and G. P. Vacca, on the basis of perturbative quantum chromodynamics.

We present a simple approach to combine NNLO QCD calculations and parton showers, based on the unlops technique. We apply the method to the computation of Drell-Yan lepton-pair production at the Large Hadron Collider. We comment on possible improvements and intrinsic uncertainties.

The proposed PINGU project (Precision IceCube Next Generation Upgrade) is expected to collect $O({10}^5)$ atmospheric muon and electron neutrino events in a few years of exposure, and to probe the neutrino mass hierarchy through its imprint on the event spectra in energy and direction. In the presence of non-negligible and partly unknown shape systematics, the analysis of high-statistics spectral variations will face subtle challenges that are largely unprecedented in neutrino physics. We discuss these issues both on general grounds and in the currently envisaged PINGU configuration, where we find that possible shape uncertainties at the (few) percent level can noticeably affect the sensitivity to the hierarchy. We also discuss the interplay between the mixing angle ${\theta }_{23}$ and the PINGU sensitivity to the hierarchy. Our results suggest that more refined estimates of spectral uncertainties are needed in next-generation, large-volume atmospheric neutrino experiments.

We compute the gluon and ghost propagators of Yang-Mills theory in linear covariant gauges from the coupled system of Dyson-Schwinger equations. For small values of the gauge fixing parameter $\xi \sim 0.1$, the deviations to the Landau gauge already become clearly visible. For the ghost dressing function, this is reflected in a logarithmic infrared suppression. Also, the gluon dressing function changes—but only quantitatively—and the gluon propagator remains finite at zero momentum. From the results, a running coupling is extracted.

We study a scenario allowing a solution of the strong charge parity problem via the Peccei-Quinn mechanism, implemented in gravity with torsion. In this framework there appears a torsion-related pseudoscalar field known as the Kalb-Ramond axion. We compare it with the so-called Barbero-Immirzi axion recently proposed in the literature also in the context of the gravity with torsion. We show that they are equivalent from the viewpoint of the effective theory. The phenomenology of these torsion-descended axions is completely determined by the Planck scale without any additional model parameters. These axions are very light and very weakly interacting with ordinary matter. We briefly comment on their astrophysical and cosmological implications in view of the recent BICEP2 and Planck data.

We construct an effective QCD light-front Hamiltonian for both mesons and baryons in the chiral limit based on the generalized supercharges of a superconformal algebra. The superconformal construction is shown to be equivalent to a semiclassical approximation to light-front QCD and its embedding in anti–de Sitter space. The specific breaking of conformal invariance inside the superconformal algebra uniquely determines the effective confinement potential. The generalized supercharges connect the baryon and meson spectra to each other in a remarkable manner. In particular, the $\pi /b_1$ Regge trajectory is identified as the superpartner of the nucleon trajectory. However, the lowest-lying state on this trajectory, the $\pi$-meson, is massless in the chiral limit and has no supersymmetric partner.

Ultralight axions which couple sufficiently strongly to photons can leave imprints on the sky at diverse frequencies by mixing with cosmic light in the presence of background magnetic fields. We explore such direction dependent grey-body distortions of the cosmic microwave background spectrum, enhanced by resonant conditions in the intergalactic medium plasma. We also find that if such axions are produced in the early Universe and represent a subdominant dark radiation component today, they could convert into x-rays in supervoids and brighten them at x-ray frequencies.