The center domain structure is revisited with the introduction of a quark contribution to understand the phenomenology in high-energy heavy-ion collisions. We show that the quark contribution may allow metastable states that would lead to a natural and consistent explanation for the temperature dependencies of color opacity and viscosity. We also argue the possibility of indirect observations of the center domain structure in experiments due to a topological critical temperature.

The measurement of a nonzero value of the 1–3 mixing angle has paved the way for the determination of leptonic $CP$ violation. However, the current generation long-baseline experiments T2K and $\mathrm{NO}\nu \mathrm{A}$ have limited sensitivity to ${\delta }_{CP}$. In this paper, we show, for the first time, the significance of atmospheric neutrino experiments in providing the first hint of $CP$ violation in conjunction with T2K and $\mathrm{NO}\nu \mathrm{A}$. In particular, we find that adding atmospheric neutrino data from a magnetized iron calorimeter detector at the India-Based Neutrino Observatory to T2K and $\mathrm{NO}\nu \mathrm{A}$ results in a twofold increase in the range of ${\delta }_{CP}$ values for which a $2\sigma$ hint of $CP$ violation can be obtained. In fact, in the parameter region unfavorable for the latter experiments, the first signature of $CP$ violation may well come from the inclusion of atmospheric neutrino data.

We present an extended 331 model with $T^{\prime }$ discrete flavor symmetry that simultaneously explains the need to have exactly three generations and provides acceptable quark and lepton masses and mixings. New fermionic states and gauge bosons are predicted within the reach of the LHC. We discuss the relevance to the 126 GeV scalar discovered at the LHC.

The existence of two metrics in massive gravity theories, in principle, allows solutions where there are singularities in new scalar invariants jointly constructed from them. These configurations occur when the two metrics differ substantially from each other, as in black hole and cosmological solutions. The simplest class of such singularities includes determinant singularities. We investigate whether the dynamics of bimetric massive gravity—where the second metric is allowed to evolve jointly with the spacetime metric—can avoid these singularities. We show that it is still possible to specify nonsingular initial conditions that evolve to a determinant singularity. Determinant singularities are a feature of massive gravity of both fixed and dynamical metric type.

By applying Schwinger’s variational principle to the Einstein-Cartan action for the gravitational field, we derive quantum commutation relations between the metric and torsion tensors.

We study the sensitivity of IceCube/DeepCore detector to dark matter annihilations in the Earth’s core. We focus on annihilation modes $\chi \chi \to \nu \overline{\nu }$, ${\tau }^{+}{\tau }^{-}$, $b\overline{b}$, and $W^{+}{W}^{-}$. Both track and cascade events are considered in our analysis. By fixing the dark matter annihilation cross section $⟨\sigma \upsilon ⟩$ at some nominal values, we study the sensitivity of the IceCube/DeepCore detector to dark matter spin-independent cross section ${\sigma }_p^{\mathrm{SI}}$ for $m_{\chi }$ ranging from few tens of GeV to 10 TeV. This sensitivity is compared with the existing IceCube 79-string constraint on the same cross section, which was obtained by searching for dark matter annihilations in the Sun. We compare this sensitivity to dark matter direct detection results as well, in particular the XENON100 (2012) limit and the parameter regions preferred by DAMA and CRESST-II experiments. We also present IceCube/DeepCore sensitivity to $⟨\sigma \upsilon ⟩$ as a function of $m_{\chi }$ by fixing ${\sigma }_p^{\mathrm{SI}}$ at XENON100 (2012) and XENON1T limits, respectively. This sensitivity is compared with the preferred dark matter parameter range derived from the combined fitting to PAMELA and AMS02 positron fraction data. We conclude that the search for dark matter annihilations in the Earth’s core provides competitive constraints on ${\sigma }_p^{\mathrm{SI}}$ and $⟨\sigma \upsilon ⟩$ in the case of low-mass dark matter. Particularly, the expected constraint on ${\sigma }_p^{\mathrm{SI}}$ for 5 years of data taking in IceCube/DeepCore is more stringent than the current IceCube 79-string limit mentioned above.

In this paper we present a complete and exact spectral analysis of the ($1+1$)-dimensional model that Jackiw and Rebbi considered to show that the half-integral fermion numbers are possible due to the presence of an isolated self-charge-conjugate zero mode. The model possesses the charge and particle conjugation symmetries. These symmetries mandate the reflection symmetry of the spectrum about the line $E=0$. We obtain the bound-state energies and wave functions of the fermion in this model using two different methods, analytically and exactly, for every arbitrary choice of the parameters of the kink, i.e. its value at spatial infinity (${\theta }_0$) and its scale of variations ($\mu$). Then, we plot the bound-state energies of the fermion as a function of ${\theta }_0$. This graph enables us to consider a process of building up the kink from the trivial vacuum. We can then determine the origin and evolution of the bound-state energy levels during this process. We see that the model has a dynamical mass generation process at the first quantized level and the zero-energy fermionic mode responsible for the fractional fermion number, is always present during the construction of the kink and its origin is very peculiar, indeed. We also observe that, as expected, none of the energy levels cross one another. Moreover, we obtain analytically the continuum scattering wave functions of the fermion and then calculate the phase shifts of these wave functions. Using the information contained in the graphs of the phase shifts and the bound states, we show that our phase shifts are consistent with the weak and strong forms of the Levinson theorem. Finally, using the weak form of the Levinson theorem, we confirm that the number of the zero-energy fermionic modes is exactly one.

We study the real-time dynamics of fermions coupled to scalar fields in a linear sigma model, which is often employed in the context of preheating after inflation or as a low-energy effective model for quantum chromodynamics. We find a dramatic amplification of fermion production in the presence of highly occupied bosonic quanta for weak as well as strong effective couplings. For this we consider the range of validity of different methods: lattice simulations with male/female fermions, the mode functions approach and the quantum 2PI effective action with its associated kinetic theory. For strongly coupled fermions we find a rapid approach to a Fermi-Dirac distribution with time-dependent temperature and chemical potential parameters, while the bosons are still far from equilibrium.

Integrating equations of particle-number and energy-momentum conservation and Maxwell field equations, we study the oscillation and drift of electron and positron pairs coherently with fields after these pairs are produced in external electromagnetic fields. From the electric current of oscillating pairs, we obtain the energy spectrum of electromagnetic dipole radiation. This narrow spectrum is so peculiar that the detection of such radiation can identify pair production and oscillation in strong laser fields. We also obtain the energy spectrum of gravitational quadrapole radiation from the energy-momentum tensor of oscillating pairs and fields. Thus, we discuss the generation of gravitational waves on the basis of the rapid development of strong laser fields.

Since the work of Hartle in the 1970s, and the subsequent development of the membrane paradigm approach to black hole physics it has been widely accepted that superradiant scattering of gravitational waves bears strong similarities with the phenomenon of “tidal friction” (well known from Newtonian gravity) operating in binary systems of viscous material bodies. In this paper we revisit the superradiance-tidal friction analogy within the context of ultracompact relativistic bodies. We advocate that as long as these bodies have nonzero viscosity they should undergo tidal friction that can be construed as a kind of superradiant scattering from the point of view of the dynamics of an orbiting test body. In addition we consider the presence of anisotropic matter, which is required for at least some ultracompact bodies, if they are to sustain a radius very close to the gravitational radius. We find that the tidal friction/superradiance output is enhanced with increasing anisotropy and that strongly anisotropic systems exhibit an unconventional response to tidal and centrifugal forces. Finally, we make contact with the artificial system comprising a black hole with its horizon replaced by a mirror (sometimes used as a proxy for ultracompact material bodies) and discuss superradiance and tidal friction in relation to it.

For variable gravity models the strength of gravity, as measured by Newton’s “constant” or the Planck mass, depends on the value of a scalar field, the cosmon. We discuss two simple four-parameter models with a quadratic or constant cosmon potential. They are compatible with all presently available cosmological observations, including inflation. The inflaton and the scalar field of quintessence are the same cosmon field. Dark energy constitutes a small, almost constant fraction of the energy density during the radiation- and matter-dominated epochs (early dark energy). In the present epoch we witness a transition to a new dark energy-dominated epoch. Our models are free of a big bang singularity. The stability of solutions generates an arrow of time. Our picture of the Universe is unusual, with a shrinking or static scale factor, while the masses of particles increase and the size of atoms shrinks. The evolution of the Universe can be very slow for all cosmological epochs including inflation, with typical time scale ${10}^{10}\mathrm{yr}$, and in sharp contrast to the usual big bang picture. The map to the equivalent Einstein frame with constant particle masses and expanding scale factor can be singular at the big bang.

We examine the consequences of Lorentz violation during slow-roll inflation. We consider a canonical scalar inflaton coupled, through its potential, to the divergence of a fixed-norm timelike vector field, or “aether.” The vector is described by Einstein-aether theory, a vector-tensor model of gravitational Lorentz violation. We derive and analyze the cosmological perturbation equations for the metric, inflaton, and aether. If the scale of Lorentz violation is sufficiently small compared to the Planck mass, and the strength of the scalar-aether coupling is suitably large, then the spin-0 and spin-1 perturbations grow exponentially and spoil the inflationary background. The effects of such a coupling on the cosmic microwave background (CMB) are too small to be visible to current or near-future CMB experiments; unusually, no isocurvature modes are produced at first order in a perturbative expansion around the aether norm. These results are discussed for both a general potential and a worked example, $m^2{\varphi }^2$ inflation with a quadratic scalar-aether coupling term.

We evolve a set of 32 equal-mass black-hole binaries with collinear spins (with intrinsic spin magnitudes $|{\vec{S}}_{1,2}/m_{1,2}^2|=0.8$) to study the effects of precession in the highly nonlinear plunge and merger regimes. We compare the direction of the instantaneous radiated angular momentum, ${\widehat{\delta J}}_{\mathrm{rad}}(t)$, to the directions of the total angular momentum, $\widehat{J}(t)$, and the orbital angular momentum, $\widehat{L}(t)$. We find that ${\widehat{\delta J}}_{\mathrm{rad}}(t)$ approximately follows $\widehat{L}$ throughout the evolution. During the orbital evolution and merger, we observe that the angle between $\vec{L}$ and total spin $\vec{S}$ is approximately conserved to within 1°, which allows us to propose and test models for the merger remnant’s mass and spin. For instance, we verify that the hang-up effect is the dominant effect and largely explains the observed total energy and angular momentum radiated by these precessing systems. We also verify that the total angular momentum, which significantly decreases in magnitude during the inspiral, varies in direction by less than $\sim 5^{°}$. The maximum variation in the direction of $\vec{J}$ occurs when the spins are nearly antialigned with the orbital angular momentum. Based on our results, we conjecture that transitional precession, which would lead to large variations in the direction of $\vec{J}$, is not possible for similar-mass binaries and would require a mass ratio $m_1/m_2\lesssim 1/4$.

The pion electromagnetic form factor at spacelike momentum transfer is calculated in relativistic impulse approximation using the covariant spectator theory. The same dressed quark mass function and the equation for the pion bound-state vertex function as discussed in the companion paper are used for the calculation, together with a dressed quark current that satisfies the Ward-Takahashi identity. The results obtained for the pion form factor are in agreement with experimental data, they exhibit the typical monopole behavior at high-momentum transfer, and they satisfy some remarkable scaling relations.

We formulate the covariant equations for quark-antiquark bound states in Minkowski space in the framework of the covariant spectator theory. The quark propagators are dressed with the same kernel that describes the interaction between different quarks. We show that these equations are charge-conjugation invariant, and that in the chiral limit of vanishing bare quark mass, a massless pseudoscalar bound state is produced in a Nambu–Jona-Lasinio (NJL) mechanism, which is associated with the Goldstone boson of spontaneous chiral symmetry breaking. In this introductory paper, we test the formalism by using a simplified kernel consisting of a momentum-space $\delta$ function with a vector Lorentz structure, to which one adds a mixed scalar and vector confining interaction. The scalar part of the confining interaction is not chirally invariant by itself, but decouples from the equations in the chiral limit and therefore allows the NJL mechanism to work. With this model we calculate the quark mass function, and we compare our Minkowski-space results to lattice QCD data obtained in Euclidean space. In a companion paper, we apply this formalism to a calculation of the pion form factor.

We discuss the charged pion condensation phenomenon in the linear sigma model, in the presence of an external uniform magnetic field. The critical temperature is obtained as a function of the external magnetic field, assuming the transition is of second order, by considering a dilute gas at low temperature. As a result we found magnetic catalysis for high values of the external magnetic field. This behavior confirms previous results with a single charged scalar field.

The Large Hadron Collider (LHC) has completed its run at 8 TeV with the experiments ATLAS and CMS having collected about $25{\mathrm{fb}}^{-1}$ of data each. Discovery of a light Higgs boson coupled with lack of evidence for supersymmetry at the LHC so far, has motivated studies of supersymmetry in the context of naturalness with the principal focus being the third generation squarks. In this work, we analyze the prospects of the flavor violating decay mode ${\tilde{\mathit{t}}}_1\to \mathit{c}{\chi }_1^0$ at 8 and 13 TeV center-of-mass energy at the LHC. This channel is also relevant in the dark matter context for the stop-coannihilation scenario, where the relic density depends on the mass difference between the lighter stop quark (${\tilde{t}}_1$) and the lightest neutralino (${\chi }_1^0$) states. This channel is extremely challenging to probe, especially for situations when the mass difference between the lighter stop quark and the lightest neutralino is small. Using certain kinematical properties of signal events we find that the level of backgrounds can be reduced substantially. We find that the prospect for this channel is limited due to the low production cross section for top squarks and limited luminosity at 8 TeV, but at the 13 TeV LHC with $100{\mathrm{fb}}^{-1}$ luminosity, it is possible to probe top squarks with masses up to $\sim 450\mathrm{GeV}$. We also discuss how the sensitivity could be significantly improved by tagging charm jets.

We study a class of nearest-neighbor minimally doubled actions that depend on two continuous parameters. We calculate the contributions of the three possible counterterms in perturbation theory, and we find that for each counterterm there are curves in the parameter space on which its coefficient vanishes. One can thus construct renormalized actions that contain only two counterterms, instead of the three of the standard Karsten-Wilczek or Boriçi-Creutz actions. Our investigations suggest the usefulness of analogous nonperturbative searches for values of the parameters for which the number of counterterms can be reduced. They can also be an inspiration to undertake a search for ultralocal minimally doubled actions with even better counterterm-reducing properties, including the optimal case in which all counterterms can be removed. Simulations of the latter actions will be much cheaper than the cases in which one needs to add counterterms to the bare actions, like the already conveniently inexpensive standard Karsten-Wilczek fermions. Finally, we also introduce minimally doubled fermions with next-to-nearest-neighbor interactions, which depend on four continuous parameters, as a further possibility in the search for renormalized actions with no counterterms.

Using the formalism obtained from collinear expansion, we calculate the differential cross section and azimuthal asymmetries in the semi-inclusive deeply inelastic lepton-nucleon (nucleus) scattering process $e^{-}+N(A)\to e^{-}+q+X$ with both polarized beam and polarized target up to twist-3. We derive the azimuthal asymmetries in terms of twist-3 parton correlation functions. We simplify the results by using the QCD equation of motion that leads to a set of relationships between different twist-3 functions. We further study the nuclear dependence of azimuthal asymmetries and show that they have similar suppression factors as those in the unpolarized reactions.