The pion electromagnetic form factor and two-pion production in electron-positron collisions are simultaneously fitted by a vector dominance model evolving to perturbative QCD at large momentum transfer. This model was previously successful in simultaneously fitting the nucleon electromagnetic form factors (spacelike region) and the electromagnetic production of nucleon-antinucleon pairs (timelike region). For this pion case dispersion relations are used to produce the analytic connection of the spacelike and timelike regions. The fit to all the data is good, especially for the newer sets of timelike data. The description of high-$q^2$ data, in the timelike region, requires one more meson with $\rho$ quantum numbers than listed in the 2014 Particle Data Group review.

In this paper we present a scenario where the stability of dark matter and the phenomenology of neutrinos are related by the spontaneous breaking of a non-Abelian flavor symmetry ($A_4$). In this scenario the breaking is done at the seesaw scale, in such a way that what remains of the flavor symmetry is a $Z_2$ symmetry, which stabilizes the dark matter. We have proposed two models based on this idea, for which we have calculated their neutrino mass matrices achieving two-zero texture in both cases. Accordingly, we have updated this two-zero texture phenomenology finding an interesting correlation between the reactor mixing angle and the sum of the light neutrino masses. We also have a correlation between the lightest neutrino mass and the neutrinoless double beta decay effective mass, obtaining a lower bound for the effective mass within the region of the nearly future experimental sensitivities.

A minimal extension of the Standard Model that provides both a dark matter candidate and a strong first-order electroweak phase transition (EWPT) consists of two additional Lorentz and gauge singlets. In this paper we work out a composite Higgs version of this scenario, based on the coset $SO(7)/SO(6)$. We show that by embedding the elementary fermions in appropriate representations of $SO(7)$, all dominant interactions are described by only three free effective parameters. Within the model dependencies of the embedding, the theory predicts one of the singlets to be stable and responsible for the observed dark matter abundance. At the same time, the second singlet introduces new $CP$-violation phases and triggers a strong first-order EWPT, making electroweak baryogenesis feasible. It turns out that this scenario does not conflict with current observations and it is promising for solving the dark matter and baryon asymmetry puzzles. The tight predictions of the model will be accessible at the forthcoming dark matter direct detection and gravitational wave experiments.

Lattice QCD calculations with chiral fermions of the $\pi \mathrm{N}$ sigma term ${\sigma }_{\pi N}$ and strangeness sigma term ${\sigma }_{sN}$ including chiral interpolation with continuum and volume corrections are provided in this work, with the excited-state contaminations subtracted properly. We calculate the scalar matrix element for the light/strange quark directly and find ${\sigma }_{\pi N}=45.9(7.4)(2.8)\mathrm{MeV}$, with the disconnected insertion part contributing 20(12)(4)%, and ${\sigma }_{sN}=40.2(11.7)(3.5)\mathrm{MeV}$, which is somewhat smaller than ${\sigma }_{\pi N}$. The ratio of the strange/light scalar matrix elements is $y=0.09(3)(1)$.

Numerical simulations of QCD-like theories in which the number of flavors is adjusted so that the beta function is very small, but confinement and chiral symmetry breaking nevertheless take place, appear to reveal the presence of a flavor-singlet scalar meson which can be as light as the pions. Because the breaking of dilatation symmetry, quantified by the beta function, is small relative to QCD, a possible explanation is that the scalar meson is a pseudo Nambu-Goldstone boson associated with the approximate dilatation symmetry. We use this observation to systematically develop a low-energy effective action that accounts for both the pions and the “dilatonic” scalar meson. In order to justify the power counting that controls the couplings of the dilatonic meson we invoke the Veneziano limit, in which the number of fundamental-representation flavors $N_f$ grows in proportion with the number of colors $N_c$, while the ratio $N_f/N_c$ is kept close to, but below, the critical value where the conformal window is entered.

Measurements are reported of the normalized differential cross sections for top quark pair production with respect to four kinematic event variables: the missing transverse energy; the scalar sum of the jet transverse momentum ($p_{\mathrm{T}}$); the scalar sum of the $p_{\mathrm{T}}$ of all objects in the event; and the $p_{\mathrm{T}}$ of leptonically decaying $W$ bosons from top quark decays. The data sample, collected using the CMS detector at the LHC, consists of $5.0{\mathrm{fb}}^{-1}$ of proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$ and $19.7{\mathrm{fb}}^{-1}$ at $\sqrt{s}=8\mathrm{TeV}$. Top quark pair events containing one electron or muon are selected. The results are presented after correcting for detector effects to allow direct comparison with theoretical predictions. No significant deviations from the predictions of several standard model event simulation generators are observed.

We propose a new scenario for baryogenesis through leptogenesis, where the $CP$ phase relevant for leptogenesis is connected directly to the Pontecorvo-Maki-Nakagawa-Sakada (PMNS) phase(s) in the light neutrino mixing matrix. The scenario is realized in the case when only one $CP$ phase appears in the full theory, originating from the complex vacuum expextation value of a standard model singlet field. In order to realize this scheme, the electroweak symmetry is required to be broken during the leptogenesis era, and a new loop diagram with an intermediate $W$ boson exchange including the low-energy neutrino mixing matrix should play the dominant contribution to the $CP$ violation for leptogenesis. In this article, we discuss the new basic mechanism, which we call type-II leptogenesis, and give an estimate for maximally reachable baryon asymmetry depending on the PMNS phases.

The moment of inertia, the spin-induced quadrupole moment, and the tidal Love number of neutron-star and quark-star models are related through some relations which depend only mildly on the stellar equation of state. These “I-Love-Q” relations have important implications for astrophysics and gravitational-wave astronomy. An interesting problem is whether similar relations hold for other compact objects and how they approach the black hole limit. To answer these questions, here we investigate the deformation properties of a large class of thin-shell gravastars, which are exotic compact objects that do not possess an event horizon nor a spacetime singularity. Working in a small-spin and small-tidal field expansion, we calculate the moment of inertia, the quadrupole moment, and the (quadrupolar electric) tidal Love number of gravastars with a polytropic thin shell. The I-Love-Q relations of a thin-shell gravastar are drastically different from those of an ordinary neutron star. The Love number and quadrupole moment for less compact models have the opposite sign relative to those of ordinary neutron stars, and the I-Love-Q relations continuously approach the black hole limit. We consider a variety of polytropic equations of state for the matter shell and find no universality in the I-Love-Q relations. However, we cannot deny the possibility that, similarly to the neutron-star case, an approximate universality might emerge for a limited class of equations of state. Finally, we discuss how a measurement of the tidal deformability from the gravitational-wave detection of a compact-binary inspiral can be used to constrain exotic compact objects like gravastars.

Causal dynamical triangulation (CDT) is a nonperturbative quantization of general relativity. Hořava-Lifshitz gravity, on the other hand, modifies general relativity to allow for perturbative quantization. Past work has given rise to the speculation that Hořava-Lifshitz gravity might correspond to the continuum limit of CDT. In this paper we add another piece to this puzzle by applying the CDT quantization prescription directly to Hořava-Lifshitz gravity in two dimensions. We derive the continuum Hamiltonian, and we show that it matches exactly the Hamiltonian derived from canonically quantizing the Hořava-Lifshitz action. Unlike the standard CDT case, here the introduction of a foliated lattice does not impose further restriction on the configuration space and, as a result, lattice quantization does not leave any imprint on continuum physics as expected.

The high degree of symmetry renders the dynamics of cosmological as well as some black hole spacetimes describable by a system of finite degrees of freedom. These systems are generally known as minisuperspace models. One of their important key features is the invariance of the corresponding reduced actions under reparametrizations of the independent variable, a fact that can be seen as the remnant of the general covariance of the full theory. In the case of a system of $n$ degrees of freedom, described by a Lagrangian quadratic in velocities, one can use the lapse by either gauge fixing it or letting it be defined by the constraint and subsequently substitute into the rest of the equations. In the first case, the system of the second-order equations of motion is solvable for all $n$ accelerations and the constraint becomes a restriction among constants of integration. In the second case, the system can be solved for only $n-1$ accelerations and the “gauge” freedom is transferred to the choice of one of the scalar degrees of freedom. In this paper, we take the second path and express all $n-1$ scalar degrees of freedom in terms of the remaining one, say $q$. By considering these $n-1$ degrees of freedom as arbitrary but given functions of $q$, we manage to extract a two-dimensional pure gauge system consisting of the lapse $N$ and the arbitrary $q$: in a way, we decouple the reparametrization invariance from the rest of the equations of motion, which are thus describing the “true” dynamics. The solution of the corresponding quantum two-dimensional system is used for the definition of a generalized probability for every configuration $f^i(q)$, be it classical or not. The main result is that, interestingly enough, this probability attains its extrema on the classical solution of the initial $n$-dimensional system.

In standard cosmology, the growth of structure becomes significant following matter-radiation equality. In nonthermal histories, where an effectively matter-dominated phase occurs due to scalar oscillations prior to big bang nucleosynthesis, a new scale at smaller wavelengths appears in the matter power spectrum. Density perturbations that enter the horizon during the early matter-dominated era (EMDE) grow linearly with the scale factor prior to the onset of radiation domination, which leads to enhanced inhomogeneity on small scales if dark matter (DM) thermally and kinetically decouples during the EMDE. The microhalos that form from these enhanced perturbations significantly boost the self-annihilation rate for dark matter. This has important implications for indirect detection experiments: the larger annihilation rate may result in observable signals from dark matter candidates that are usually deemed untestable. As a proof of principle, we consider binos in heavy supersymmetry with an intermediate extended Higgs sector and all other superpartners decoupled. We find that these isolated binos, which lie under the neutrino floor, can account for the dark matter relic density and decouple from the standard model early enough to preserve the enhanced small-scale inhomogeneity generated during the EMDE. If early forming microhalos survive as subhalos within larger microhalos, the resulting boost to the annihilation rate for bino dark matter near the pseudoscalar resonance exceeds the upper limit established by Fermi-LAT’s observations of dwarf spheroidal galaxies. These DM candidates motivate the $N$-body simulations required to eliminate uncertainties in the microhalos’ internal structure by exemplifying how an EMDE can enable Fermi-LAT to probe isolated dark matter.

We consider the impact of neutral-current (NC) nonstandard neutrino interactions (NSI) on the determination of the neutrino mass ordering. We show that in the presence of NSI there is an exact degeneracy which makes it impossible to determine the neutrino mass ordering and the octant of the solar mixing angle ${\theta }_{12}$ at oscillation experiments. The degeneracy holds at the probability level and for arbitrary matter density profiles, and hence solar, atmospheric, reactor, and accelerator neutrino experiments are affected simultaneously. The degeneracy requires order-1 corrections from NSI to the NC electron neutrino-quark interaction and can be tested in electron neutrino NC scattering experiments.

In this work we study a classically scale-invariant extension of the Standard Model in which the dark matter and electroweak scales are generated through the Coleman-Weinberg mechanism. The extra $SU(3{)}_X$ gauge factor gets completely broken by the vacuum expectation values of two scalar triplets. Out of the eight resulting massive vector bosons the three lightest are stable due to an intrinsic $Z_2\times Z_2^{\prime }$ discrete symmetry and can constitute dark matter candidates. We analyze the phenomenological viability of the predicted multi-Higgs sector imposing theoretical and experimental constraints. We perform a comprehensive analysis of the dark matter predictions of the model solving numerically the set of coupled Boltzmann equations involving all relevant dark matter processes and explore the direct detection prospects of the dark matter candidates.

We study the conjectured “insensitivity to chiral symmetry breaking” in the highly excited light baryon spectrum. While the experimental spectrum is being measured at JLab and CBELSA/TAPS, this insensitivity remains to be computed theoretically in detail. As the only existing option to have both confinement, highly excited states, and chiral symmetry, we adopt the truncated Coulomb-gauge formulation of QCD, considering a linearly confining Coulomb term. Adopting a systematic and numerically intensive variational treatment up to 12 harmonic oscillator shells we are able to access several angular and radial excitations. We compute both the excited spectra of $I=1/2$ and $I=3/2$ baryons, up to large spin $J=13/2$, and study in detail the proposed chiral multiplets. While the static-light and light-light spectra clearly show chiral symmetry restoration high in the spectrum, the realization of chiral symmetry is more complicated in the baryon spectrum than earlier expected.

In this paper we study the thermodynamics of rotating black hole solutions arising from four-dimensional gauged $\mathcal{N}=2$ supergravity. We analyze two different supergravity models, characterized by prepotentials $F=-i{X}^0{X}^1$ and $F=-2i\sqrt{X^0(X^1{)}^3}$. The black hole configurations are supported by electromagnetic charges and scalar fields with different kinds of boundary conditions. We perform our analysis in the canonical ensemble, where we find a first order phase transition for a suitable range of charges and angular momentum. We perform the thermodynamic stability check on the configurations. Using the holographic dictionary, we interpret the phase transition in terms of expectation values of operators in the dual field theory, which pertains to the class of ABJM theories living on a rotating Einstein universe. We extend the analysis to dyonic configurations as well. Lastly, we show the computation of the on shell action and mass via holographic renormalization techniques.

We construct various self-similar configurations using parallel $\delta$-function plates and show that it is possible to evaluate the Casimir interaction energy of these configurations using the idea of self-similarity alone. We restrict our analysis to interactions mediated by a scalar field, but the extension to the electromagnetic field is immediate. Our work unveils an easy and powerful method that can be easily employed to calculate the Casimir energies of a class of self-similar configurations. As a highlight, in an example, we determine the Casimir interaction energy of a stack of parallel plates constructed by positioning $\delta$-function plates at the points constituting the Cantor set, a prototype of a fractal. This, to our knowledge, is the first time that the Casimir energy of a fractal configuration has been reported. Remarkably, the Casimir energy of some of the configurations we consider turn out to be positive, and a few even have zero Casimir energy. For the case of positive Casimir energy that is monotonically decreasing as the stacking parameter increases, the interpretation is that the pressure of vacuum tends to inflate the infinite stack of plates. We further support our results, derived using the idea of self-similarity alone, by rederiving them using the Green’s function formalism. These expositions gives us insight into the connections between the regularization methods used in quantum field theories and regularized sums of divergent series in number theory.

Non-Abelian vortex strings supported in a certain four-dimensional $\mathcal{N}=2$ Yang-Mills theory with fundamental matter were shown [1] to become critical superstrings. In addition to translational moduli, the non-Abelian strings under consideration carry orientational and size moduli. Their dynamics is described by the two-dimensional sigma model whose target space is a tautological bundle over the complex projective space. For the $\mathcal{N}=2$ theory with the $U(2)$ gauge group and four fundamental hypermultiplets, there are six orientational and size moduli. After combining with four translational moduli, they form a ten-dimensional target space, which is required for a superstring to be critical. For the theory in question, the target space of the sigma model is ${\mathbb{C}}^2\times Y_6$, where $Y_6$ is a conifold. We study closed string states which emerge in four dimensions (4D) and identify them with hadrons of the 4D bulk $\mathcal{N}=2$ theory. It turns out that most of the states arising from the ten-dimensional graviton spectrum are nondynamical in 4D. We find a single dynamical massless hypermultiplet associated with the deformation of the complex structure of the conifold. We interpret this degree of freedom as a monopole-monopole baryon of the 4D theory (at strong coupling).

We present fully general-relativistic magnetohydrodynamic simulations of the merger of binary neutron star (BNS) systems. We consider BNSs producing a hypermassive neutron star (HMNS) that collapses to a spinning black hole (BH) surrounded by a magnetized accretion disk in a few tens of ms. We investigate whether such systems may launch relativistic jets and hence power short gamma-ray bursts. We study the effects of different equations of state (EOSs), different mass ratios, and different magnetic field orientations. For all cases, we present a detailed investigation of the matter dynamics and of the magnetic field evolution, with particular attention to its global structure and possible emission of relativistic jets. The main result of this work is that we observe the formation of an organized magnetic field structure. This happens independently of EOS, mass ratio, and initial magnetic field orientation. We also show that those models that produce a longer-lived HMNS lead to a stronger magnetic field before collapse to a BH. Such larger fields make it possible, for at least one of our models, to resolve the magnetorotational instability and hence further amplify the magnetic field in the disk. However, by the end of our simulations, we do not (yet) observe a magnetically dominated funnel nor a relativistic outflow. With respect to the recent simulations of Ruiz et al. [Astrophys. J. 824, L6 (2016)], we evolve models with lower and more plausible initial magnetic field strengths and (for computational reasons) we do not evolve the accretion disk for the long time scales that seem to be required in order to see a relativistic outflow. Since all our models produce a similar ordered magnetic field structure aligned with the BH spin axis, we expect that the results found by Ruiz et al. (who only considered an equal-mass system with an ideal fluid EOS) should be general and—at least from a qualitative point of view—independent of the mass ratio, magnetic field orientation, and EOS.

We study the development and saturation of the $m=1$ one-armed spiral instability in remnants of binary neutron star mergers by means of high-resolution long-term numerical relativity simulations. Our results suggest that this instability is a generic outcome of neutron star mergers in astrophysically relevant configurations, including both “stiff” and “soft” nuclear equations of state. We find that, once seeded at merger, the $m=1$ mode saturates within $\sim 10\mathrm{ms}$ and persists over secular time scales. Gravitational waves emitted by the $m=1$ instability have a peak frequency around 1–2 kHz and, if detected, they could be used to constrain the equation of state of neutron stars. We construct hybrid waveforms spanning the entire Advanced LIGO band by combining our high-resolution numerical data with state-of-the-art effective-one-body waveforms including tidal effects. We use the complete hybrid waveforms to study the detectability of the one-armed spiral instability for both Advanced LIGO and the Einstein Telescope. We conclude that the one-armed spiral instability is not an efficient gravitational wave emitter. Even under very optimistic assumptions, Advanced LIGO will only be able to detect the one-armed instability up to $\sim 3\mathrm{Mpc}$, which corresponds to an event rate of ${10}^{-7}{\mathrm{yr}}^{-1}$ to ${10}^{-4}{\mathrm{yr}}^{-1}$. Third-generation detectors or better will likely be required to observe the one-armed instability.