Experimental tests of QCD through its predictions for the strange-quark content of the proton have been drastically restricted by our lack of knowledge of the violation of charge symmetry (CSV). We find unexpectedly tiny CSV in the proton’s electromagnetic form factors by performing the first extraction of these quantities based on an analysis of lattice QCD data. The resulting values are an order of magnitude smaller than current bounds on proton strangeness from parity-violating electron-proton scattering experiments. This result paves the way for a new generation of experimental measurements of the proton’s strange form factors to challenge the predictions of QCD.

We study the charged-current Drell–Yan process, and we evaluate the proton parton densities uncertainties on the lepton transverse momentum distribution and their impact on the determination of the $W$ boson mass. We consider the global parton density function sets CT10, MSTW2008CPdeut, NNPDF2.3, NNPDF3.0, and MMHT2014 and apply the PDF4LHC recipe to combine the individual results, obtaining an uncertainty on $m_W$ that ranges between $\pm 18$ and $\pm 24\mathrm{MeV}$, depending on the final state, collider energy, and kind. We discuss the dependence of the uncertainty on the acceptance cuts and the role of the individual parton densities in the final result. We remark that some parton density function sets predict an uncertainty on $m_W$ of $\mathcal{O}(10\mathrm{MeV})$; this encouraging result is spoiled, in the combined analysis of the different sets, by an important spread of the central values predicted by each group.

Traditional calculations in perturbative quantum chromodynamics (pQCD) are based on an order-by-order expansion in the strong coupling ${\alpha }_s$. Observables that are calculable in this way are known as “safe.” Recently, a class of unsafe observables was discovered that do not have a valid ${\alpha }_s$ expansion but are nevertheless calculable in pQCD using all-orders resummation. These observables are called “Sudakov safe” since singularities at each ${\alpha }_s$ order are regulated by an all-orders Sudakov form factor. In this paper, we give a concrete definition of Sudakov safety based on conditional probability distributions, and we study a one-parameter family of momentum sharing observables that interpolate between the safe and unsafe regimes. The boundary between these regimes is particularly interesting, as the resulting distribution can be understood as the ultraviolet fixed point of a generalized fragmentation function, yielding a leading behavior that is independent of ${\alpha }_s$.

We investigate dielectric branes in false vacua in type IIB string theory. The dielectric branes are supported against collapsing by lower energy vacua inside spherical or tubelike branes. We claim that such branes can be seeds for semiclassical (or quantum mechanical) decay of the false vacua, which makes the lifetime of the false vacua shorter. Also, we discuss a topology change of a bubble corresponding to the fuzzy monopole triggered by dissolving fundamental strings.

We analyze the $\beta$-functions of Yukawa and electromagnetic theories with Lorentz violation (LV) and propose an alternative method to find the scale dependence of the different fields that parametrize such violations. The method of solution consists of decomposing a family of parameters into their irreducible representations and thus generating a group of subfamilies that obey the same symmetries and transformation rules. The convenience of this method relies on the fact that the degree of complexity of the problem is reduced in the decoupling process. For a set of parameters describing a Lorentz-violating theory, we expect their associated $\beta$-functions to be non-negative or, otherwise, their scale dependence weak enough. These conditions are necessary because asymptotically free parameters could leave high imprints of LV at low energies, which are ruled out by observations. Besides imposing some constraints on the coefficients that describe LV, this method can be used to find the fixed points of the theory in each particular irreducible subspace.

We afford a systematic and comprehensive account of the canonical dynamics of 4D Regge calculus perturbatively expanded to linear order around a flat background. To this end, we consider the Pachner moves which generate the most basic and general simplicial evolution scheme. The linearized regime features a vertex displacement (diffeomorphism) symmetry for which we derive an Abelian constraint algebra. This permits us to identify gauge invariant lattice “gravitons” as propagating curvature degrees of freedom. The Pachner moves admit a simple method to explicitly count the gauge and graviton degrees of freedom on an evolving triangulated hypersurface, and we clarify the distinct role of each move in the dynamics. It is shown that the 1–4 move generates four “lapse and shift” variables and four conjugate vertex displacement generators; the 2–3 move generates a graviton; the 3–2 move removes one graviton and produces the only non-trivial equation of motion; and the 4–1 move removes four lapse and shift variables and trivializes the four conjugate symmetry generators. It is further shown that the Pachner moves preserve the vertex displacement generators. These results may provide new impetus for exploring ‘graviton dynamics’ in discrete quantum gravity models.

We study the $P\text{−}V$ criticality and phase transition in the extended phase space of charged anti–de Sitter black holes in canonical ensemble of ghost-free massive gravity, where the cosmological constant is viewed as a dynamical pressure of the black hole system. We give the generalized thermodynamic first law and the Smarr relation with massive gravity correction. We find that not only when the horizon topology is spherical but also in the Ricci flat or hyperbolic case, there appear the $P\text{−}V$ criticality and phase transition up to the combination $k+c_0^2{c}_2{m}^2$ in the four-dimensional case, where $k$ characterizes the horizon curvature and $c_2{m}^2$ is the coefficient of the second term of massive potential associated with the graviton mass. The positivity of such combination indicate the van der Waals–like phase transition. When the spacetime dimension is larger then four, the Maxwell charge there seems unnecessary for the appearance of critical behavior, but a infinite repulsion effect needed, which can also be realized through negative valued $c_3{m}^2$ or $c_4{m}^2$, which is third or fourth term of massive potential. When $c_3{m}^2$ is positive, a Hawking-Page–like black hole to vacuum phase transition is shown in the five-dimensional chargeless case. For the van der Waals–like phase transition in four and five spacetime dimensions, we calculate the critical exponents near the critical point and find they are the same as those in the van der Waals liquid-gas system.

In a recent publication [Ferreira et al., Phys. Rev. D 89, 083011 (2014)] we tested the consistency of current astrophysical tests of the stability of the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $\mu =m_p/m_e$ (mostly obtained in the optical/ultraviolet range) with combined measurements of $\alpha$, $\mu$ and the proton gyromagnetic ratio $g_p$ (mostly in the radio band). Given the significant observational progress made in the past year, we now revisit and update this analysis. We find that apparent inconsistencies, at about the two-sigma level, persist and are in some cases enhanced, especially for matter era measurements (corresponding to redshifts $z>1$). Although hidden systematics may be the more plausible explanation, we briefly highlight the importance of clarifying this issue, which is within the reach of state-of-the-art observational facilities such as ALMA and ESPRESSO.

I prove that general relativity admits no asymptotically well-behaved static spherically symmetric traversable wormholes supported by classical scalar fields and nonexotic matter. The theorem holds for all values of the scalar field curvature coupling parameter $\xi$, even though fields with $\xi >0$ are capable of violating the average null energy condition. Good asymptotic behavior (the effective Newton’s constant being positive and finite at both ends of the wormhole) can only be achieved by introducing additional exotic matter, which must itself violate the null energy condition over some region of nonzero volume. These results are insensitive to the number of scalar fields, the form of their potentials, and the coupling between the fields and the additional matter.

We consider the motion of classical spinning test particles in Schwarzschild and Kerr metrics and investigate innermost stable circular orbits (ISCO). The main goal of this work is to find analytically the small-spin corrections for the parameters of ISCO (radius, total angular momentum, energy, orbital angular frequency) of spinning test particles in the case of vectors of black hole spin, particle spin and orbital angular momentum being collinear to each other. We analytically derive the small-spin linear corrections for arbitrary Kerr parameter $a$. The cases of Schwarzschild, slowly rotating and extreme Kerr black hole are considered in detail. For a slowly rotating black hole, the ISCO parameters are obtained up to quadratic in $a$ and particle’s spin $s$ terms. From the formulas obtained it is seen that the spin-orbital coupling has attractive character when spin and angular momentum are parallel and repulsive when they are antiparallel. For the case of the extreme Kerr black hole with co-rotating particle we succeed to find the exact analytical solution for the limiting ISCO parameters for arbitrary spin. It has been shown that the limiting values of ISCO radius and frequency do not depend on the particle’s spin while values of energy and total angular momentum depend on it. We have also considered circular orbits of arbitrary radius and have found small-spin linear corrections for the total angular momentum, energy and frequency at given radius. System of equations for numerical calculation of ISCO parameters for arbitrary $a$ and $s$ is also explicitly written.

Very high-energy observations of blazars can be used to constrain the strength of the intergalactic magnetic field. A simplifying assumption which is often made is that of a magnetic field of constant strength composed of randomly oriented and identical cells. In this paper, we demonstrate that a more realistic description of the structure of the intergalactic magnetic field is indeed needed. If such a description is adopted, the observational bounds on the field strength are significantly affected in the limit of short field correlation lengths: in particular, they acquire a dependence on the magnetic field power spectrum. In the case of intergalactic magnetic fields which are generated causally, for which the magnetic field large-scale spectral index is $n_B\ge 2$ and even, the observational lower bound becomes more constraining by about a factor of 3. If instead $-3<n_B<-2$, the lower bound is significantly relaxed. Such magnetic fields with very red spectra can in principle be produced during inflation, but remain up to now speculative.

We have constrained the charge-mass ($ϵ-m$) phase space of millicharged particles through the simulation of the rotational evolution of neutron stars, where an extra slow-down effect due to the accretions of millicharged dark matter particles is considered. For a canonical neutron star of $M=1.4M_{\odot }$ and $R=10\mathrm{km}$ with typical magnetic field strength $B_0={10}^{12}\mathrm{G}$, we have shown an upper limit of millicharged particles, which is compatible with recently experimental and observational bounds. Meanwhile, we have also explored the influences on the $ϵ-m$ phase space of millicharged particles for different magnetic fields $B_0$ and dark matter density ${\rho }_{\mathrm{DM}}$ in the vicinity of the neutron star.

It is shown that a first-order transition associated with a jump in the strange-quark mass appears in a generalized three-flavor Nambu–Jona-Lasinio treatment of quark matter. The generalization of the Lagrangian displays the complete set of spin-0 interactions at leading and subleading orders (LO and NLO) in $\frac{1}{N_c}$ counting, including the recently derived NLO explicit chiral symmetry breaking interactions which are of the same order as the ’t Hooft flavor determinant. The parameters of the model are tightly constrained by the low-energy characteristics in both the pseudoscalar and scalar meson sectors. The transition occurs in a moderate chemical potential region ($\mu \simeq 400\mathrm{MeV}$ for zero temperature) in addition to the usual chiral transition associated with the light-quark sector. This feature has at its root the inclusion of the explicit chiral symmetry breaking interactions, which therefore can be seen to act as a catalyst in the production of strange-quark matter when compared to the conventional version of the model that takes only into account the ’t Hooft interaction in the NLO. It can be traced back to the effect of the interactions which do not violate the Okubo-Zweig-Iizuka rule, without which the empirical ordering of the scalars ($m_{K^{\star }}<m_{a_0}\approx m_{f_0}$) is not reproduced.

We present a first look at the spectroscopy of SU(4) gauge theory coupled to two flavors of Dirac fermions in the two-index antisymmetric representation, which is a real representation. We compute meson and diquark masses, the pseudoscalar and vector meson decay constants, and the masses of six-quark baryons. We make comparisons with large-$N_c$ expectations.

Light-cone string diagrams have been used to reproduce the orbifold Euler characteristic of moduli spaces of punctured Riemann surfaces at low genus and with few punctures. Nakamura studied the meromorphic differential introduced by Giddings and Wolpert to characterize light-cone diagrams and introduced a class of graphs related to this differential. These Nakamura graphs were used to parametrize the cells in a light-cone cell decomposition of moduli space. We develop links between Nakamura graphs and realizations of the worldsheet as branched covers. This leads to a development of the combinatorics of Nakamura graphs in terms of permutation tuples. For certain classes of cells, including those of the top dimension, there is a simple relation to Belyi maps, which allows us to use results from Hermitian and complex matrix models to give analytic formulas for the counting of cells at an arbitrarily high genus. For the most general cells, we develop a new equivalence relation on Hurwitz classes which organizes the cells and allows efficient enumeration of Nakamura graphs using the group theory software gap.

In this work, we have obtained Maxwell-type equations for a compressible fluid whose sources are functions of velocity and vorticity. A correlation function and the dispersion relation were analyzed as functions of the Reynolds number. A Lagrangian for the Lamb vector and the vorticity was constructed, and the equations of motion were discussed. After that, we have analyzed the case of a charged fluid dynamics. Finally, the non-Abelian generalization of some results was introduced. A basic review for non-Abelian fluids was described in Appendix B.

We investigate the shear viscosity of leptons in a strongly coupled quark gluon plasma. We find that the shear viscosity due to the lepton-quark scattering is inversely proportional to the ratio of electric conductivity of the quark gluon plasma to temperature up to the leading logarithmic order of the electromagnetic coupling. The finding implies that the thermal leptons form a more viscous fluid than the quarks by a large ratio. Using the known result for the electrical conductivity of strongly coupled plasmas obtained from gauge/gravity duality, we find that the lepton shear viscosity is suppressed compared with the one from lepton-lepton scattering. Consistently, we find an enhancement of the energy loss of hard leptons in a strongly coupled scenario compared with that in a weakly coupled plasma.

We consider the version of Hořava gravity where “detailed balance” is consistently implemented, so as to limit the huge proliferation of couplings in the full theory and obtain healthy dynamics at low energy. Since a superpotential which is third-order in spatial derivatives is not sufficient to guarantee the power-counting renormalizability of the spin-0 graviton, one needs to go an order beyond in derivatives, building a superpotential up to fourth-order spatial derivatives. Here we perturb the action to quadratic order around flat space and show that the power-counting renormalizability of the spin-0 graviton is achieved only by setting to zero a specific coupling of the theory, while the spin-2 graviton is always power-counting renormalizable for any choice of the couplings. This result raises serious doubts about the use of detailed balance.

We show that a hypothesis that spacetime is quantum with coordinate algebra $[x^i,t]={\lambda }_P{x}^i$, and spherical symmetry under rotations of the $x^i$, essentially requires in the classical limit that the spacetime metric is the Bertotti-Robinson metric, i.e., a solution of Einstein’s equations with a cosmological constant and a non-null electromagnetic field. Our arguments do not give the value of the cosmological constant or the Maxwell field strength, but they cannot both be zero. We also describe the quantum geometry and the full moduli space of metrics that can emerge as classical limits from this algebra.

Although the (varying power)-law modified gravity toy model has the attractive feature of unifying the early- and late-time expansions of the Universe, thanks to the peculiar dependence of the scalar field’s potential on the scalar curvature, the model still suffers from the fine-tuning problem when used to explain the actually observed Hubble parameter. Indeed, a more correct estimate of the mass of the scalar field needed to comply with actual observations gives an unnaturally small value. On the other hand, for a massless scalar field the potential would have no minimum and hence the field would always remain massless. What solves these issues are the radiative corrections that modify the field’s effective potential. These corrections raise the field’s effective mass, rendering the model free from fine-tuning, immune against positive fifth-force tests, and better suited to tackle the dark matter sector.