A variety of conditions are considered under which the cosmic dark fluid may be able to develop a future Big Rip or Little Rip singularity. Both one-component and two-component models are considered. In the latter case we present a way in which the fluid can be decomposed into two components, one nonturbulent (ideal) and one turbulent part, obeying two different equations of state. For the nonturbulent part, the thermodynamical parameter, commonly called $w$, is assumed to be less than $-1$ throughout. For the turbulent part, it turns out that it is sufficient that $w_{\mathrm{turb}}$ lies in the quintessence region in order to lead to a singularity. Both Big Rip and Little Rip behavior for dark energy are found. In the one-component case, we examine how the universe may develop from a viscous era with constant bulk viscosity into a turbulent era, the turbulence in effect protecting the universe from encountering the singularity at all. The equivalent description of the same cosmology in terms of inhomogeneous (imperfect) fluid is also presented.

The article presents the conservative dynamics of gravitationally interacting two-point-mass systems up to the eight order in the inverse power of the velocity of light, i.e., fourth post-Newtonian (4PN) order and up to quadratic order in Newton’s gravitational constant. Additionally, all logarithmic terms at the 4PN order are given as well as terms describing the test-mass limit. With the aid of the Poincaré algebra, additional terms are obtained. The dynamics is presented in the form of an autonomous Hamiltonian derived within the formalism of Arnowitt, Deser, and Misner. Out of the 57 different terms of the 4PN Hamiltonian in the center-of-mass frame, the coefficients of 45 of them are derived. Reduction of the obtained results to circular orbits is performed resulting in the 4PN-accurate formula for energy expressed in terms of angular frequency in which two coefficients are obtained for the first time.

Bosonic technicolor models accommodate fermion masses via a Higgs doublet that acquires a vacuum expectation value when technifermions condense. We point out that these models are severely constrained by vacuum stability if the Higgs boson mass is near 125 GeV, the value suggested by LHC data. The Higgs quartic coupling in bosonic technicolor is typically smaller at the weak scale than in the standard model, while the top quark Yukawa coupling is larger. We find that the running quartic coupling remains positive below a reasonably defined cutoff only in a narrow region of the model’s parameter space. This region is only slightly enlarged if one allows a metastable vacuum with a lifetime longer than the age of the universe.

We consider the ATLAS and CMS searches for dijet resonances, as well as the ATLAS search for like-sign dimuon pairs at the LHC with 7 TeV center-of-mass energy. We interpret their exclusions in terms of bounds on the supersymmetric $R$-parity–violating parameter space. For this we focus on resonant slepton production followed by the corresponding decay.

We address the issue of model dependence of partial proton decays due to exchange of a single scalar leptoquark within a minimal viable $SU(5)$ framework. The minimal setup predicts a flavor part of decay widths for $p\to {\pi }^{+}\overline{\nu }$ and $p\to K^{+}\overline{\nu }$ processes to depend solely on the known masses and mixing parameters of the quark sector and one extra phase. We accordingly establish an accurate lower limit on the mass of the scalar leptoquark in connection with the relevant experimental constraints on the matter stability. The ratio of decay widths for $p\to {\pi }^{+}\overline{\nu }$ and $p\to K^{+}\overline{\nu }$ channels turns out to be phase independent and predicts strong suppression of the former width with respect to the latter one. Our results offer a possibility to test the minimal scenario if and when proton decay is observed.

We study the potential of the $\gamma \gamma$ option of future high-energy linear $e^{+}{e}^{-}$ colliders to search for excited electrons with spin-$1/2$. We calculate single production cross sections and give the angular distributions and $f-m*$ contour plots for $\sqrt{s}=0.5\mathrm{TeV}$ and $\sqrt{s}=3\mathrm{TeV}$ both using the standard (tree-level) couplings and anomal couplings.

We determine the second Mellin moment of the isovector quark parton distribution function $⟨x{⟩}_{u-d}$ from lattice QCD with $N_f=2$ sea quark flavors, employing the nonperturbatively improved Wilson-Sheikholeslami-Wohlert action at a pseudoscalar mass $m_{\pi }=157(6)\mathrm{MeV}$. The result is converted nonperturbatively to the RI’-MOM scheme and then perturbatively to the $\overline{\mathrm{MS}}$ scheme at a scale $\mu =2\mathrm{GeV}$. As the quark mass is reduced we find the lattice prediction to approach the value extracted from experiments.

Whether the much-studied $X(3872)$ is an axial or tensor resonance makes an important difference to its interpretation. A recent paper by the BABAR Collaboration [3] raised the viable hypothesis that it might be a $J^{PC}=2^{-+}$ state based on the ${\pi }^{+}{\pi }^{-}{\pi }^0$ spectrum in the $X\to J/\psi \omega$ decays. Furthermore, the Belle Collaboration published the ${\pi }^{+}{\pi }^{-}$ invariant mass and spin-sensitive angular distributions in $X\to J/\psi \rho$ decays [2]. Starting from a general parametrization of the decay amplitudes for the axial and tensor quantum numbers of the $X$, we reanalyze the whole set of available data. The level of agreement of the two spin hypotheses with data is interpreted with a rigorous statistical approach based on Monte Carlo simulations in order to be able to combine all the distributions regardless of their different levels of sensitivity to the spin of the $X$. Our analysis returns a probability of 5.5% and 0.1% for the agreement with data of the $1^{++}$ and $2^{-+}$ hypotheses, respectively, once we combine the whole information (angular and mass distributions) from both channels. On the other hand, the separate analysis of $J/\psi \rho$ (angular and mass distributions) and $J/\psi \omega$ (mass distribution) indicates that the $2^{-+}$ assignment is excluded at the 99.9% C.L. by the former case, while the latter excludes at the same level the $1^{++}$ hypothesis. There are therefore indications that the two decay modes behave in a different way.

The light-front dynamic of the scalar field model theory is analyzed to solve the two-body bound-state problem. The light-front two-body bound-state equation is extended to the full light-front dynamic kernel including the ladder, cross-ladder, stretched-box, and particle-antiparticle creation/annihilation effects to study the contributions of higher Fock states. The light-front two-body equation is also modified by the term corresponding to the self-energy corrections and counterterms. Using the variational principle, we obtain the numerical result of the binding energy B versus the coupling constant $\alpha$ for various mass ratios of the constituent particles including the cases of nonzero exchange particle mass. We also discuss the correlation between the mass spectrum and the corresponding bound-state wave function.

In this paper, we study the three-pion $B_c$ decays $B_c^{+}\to J/\psi {\pi }^{+}{\pi }^{-}{\pi }^{+}$, ${\eta }_c{\pi }^{+}{\pi }^{-}{\pi }^{+}$ with dominance of the intermediate axial-vector meson $a_1(1260)$ and vector meson $\rho (770)$ in the ${\pi }^{+}{\pi }^{-}{\pi }^{+}$ and ${\pi }^{+}{\pi }^{-}$ invariant mass distributions, respectively, and make predictions for the branching fractions and differential decay widths. The ratio between the decays $B_c^{+}\to J/\psi {\pi }^{+}{\pi }^{-}{\pi }^{+}$ and $B_c^{+}\to J/\psi {\pi }^{+}$ is compatible with the experimental data within uncertainties; other predictions can be confronted with the experimental data in the future at the LHCb.

Accelerator neutrino oscillation experiments seek to make precision measurements of the neutrino flavor oscillations ${\stackrel{(-)}{\nu }}_{\mu }\to {\stackrel{(-)}{\nu }}_e$ in order to determine the mass hierarchy of neutrinos and to search for $CP$ violation in neutrino oscillations. These experiments are currently performed with beams of muon neutrinos at energies near 1 GeV where the charged-current quasielastic interactions ${\nu }_{\ell }n\to {\ell }^{-}p$ and ${\overline{\nu }}_{\ell }p\to {\ell }^{+}n$ dominate the signal reactions. We examine the difference between the quasielastic cross sections for muon and electron neutrinos and antineutrinos and estimate the uncertainties on these differences.

We study the physics reach of a low-energy neutrino factory (LENF) and its dependence on the chosen baseline distance, $L$, and stored-muon energy, $E_{\mu }$, in order to ascertain the configuration of the optimal LENF. In particular, we study the performance of the LENF over a range of baseline distances from 1000 km to 4000 km and stored-muon energies from 4 GeV to 25 GeV, connecting the early studies of the LENF (1300 km, 4.5 GeV) to those of the conventional, high-energy neutrino factory design (4000 km and 7000 km, 25 GeV). Three different magnetized detector options are considered: a Totally-Active Scintillator Detector (TASD) and two models of a liquid-argon detector distinguished by optimistic and conservative performance estimates. In order to compare the sensitivity of each set-up, we compute the full $\delta$-dependent discovery contours for the determination of ${\theta }_{13}\ne 0$, ${\delta }_{CP}\mathrm{\in ̸}\{0,\pi \}$ and $\mathrm{sign}(\Delta m_{13}^2)$. For large values of ${\theta }_{13}$, as recently confirmed by the Daya Bay and RENO experiments, the LENF provides a strong discovery potential over the majority of the $L\mathrm{\text{−}}{E}_{\mu }$ parameter space and is a promising candidate for the future generation of long baseline experiments aimed at discovering $CP$-violation and the mass hierarchy, and at making a precise determination of the oscillation parameters.

The radiative neutrino mass model with an inert doublet scalar has been considered as a promising candidate which can explain neutrino masses, dark matter abundance and baryon number asymmetry if dark matter is identified with the lightest neutral component of the inert doublet. We reexamine these properties by imposing all the data of the neutrino oscillation, which are recently suggested by the reactor experiments. We find that the sufficient baryon number asymmetry seems not to be easily generated in a consistent way with all the data of the neutrino masses and mixing as long as the right-handed neutrinos are kept in TeV regions. Two possible modifications of the model are examined.

We employ a top-quark mass measurement technique in the dilepton channel with in situ jet energy scale calibration. Three variables having different jet energy scale dependences are used simultaneously to extract not only the top-quark mass but also the energy scale of the jet from a single likelihood fit. Monte Carlo studies with events corresponding to an integrated luminosity of $5{\mathrm{fb}}^{-1}$ proton-proton collisions at the Large Hadron Collider $\sqrt{s}=7\mathrm{TeV}$ are performed. Our analysis suggests that the overall jet energy scale uncertainty can be significantly reduced and the top-quark mass can be determined with a precision of less than $1\mathrm{GeV}/c^2$, including jet energy scale uncertainty, at the Large Hadron Collider.

We compute the 4d superconformal index for $\mathcal{N}=1$, 2 gauge theories on $S^1\times L(p,1)$, where $L(p,1)$ is a lens space. We find that the 4d $\mathcal{N}=1$, 2 index on $S^1\times L(p,1)$ reduces to a 3d $\mathcal{N}=2$, 4 index on $S^1\times S^2$ in the large $p$ limit, and to a 3d partition function on a squashed $L(p,1)$ when the size of the temporal $S^1$ shrinks to zero. As an application of our index, we study 4d $\mathcal{N}=2$ superconformal field theories arising from the 6d $\mathcal{N}=(2,0)$ $A_1$ theory on a punctured Riemann surface $\Sigma$, and conjecture the existence of a 2d topological quantum field theory on $\Sigma$ whose correlation function coincides with the 4d $\mathcal{N}=2$ index on $S^1\times L(p,1)$.

We present a system of a self-dual Yang-Mills field and a self-dual vector-spinor field with nilpotent fermionic symmetry (but not supersymmetry) in $2+2$ dimensions, that generates supersymmetric integrable systems in lower dimensions. Our field content is $(A_{\mu }{}^I,\psi _{\mu }{}^I,{\chi }^{IJ})$, where $I$ is the adjoint index of arbitrary gauge group. The ${\chi }^{IJ}$ is a Stueckelberg field for consistency. The system has local nilpotent fermionic symmetry with the algebra $\{N_{\alpha }{}^I,N_{\beta }{}^J\}=0$. This system generates supersymmetric Kadomtsev-Petviashvili equations in $D=2+1$, and supersymmetric Korteweg–de Vries equations in $D=1+1$ after appropriate dimensional reductions. We also show that a similar self-dual system in seven dimensions generates a self-dual system in four dimensions. Based on our results we conjecture that lower-dimensional supersymmetric integral models can be generated by nonsupersymmetric self-dual systems in higher dimensions only with nilpotent fermionic symmetries.

We have investigated and verified the existence of stable uncharged Bogomol’nyi-Prasad-Sommerfeld (BPS) vortices in the framework of an Abelian Maxwell-Higgs model supplemented with $CPT$-even and Lorentz-violating (LV) terms belonging to the gauge and Higgs sectors of the standard model extension. The analysis is performed in two situations: first, by considering the Lorentz violation only in the gauge sector, and then in both gauge and Higgs sectors. In the first case, it is observed that the model supports vortices somehow equivalent to the ones appearing in a dielectric medium. The Lorentz violation controls the radial extension (core of the solution) and the magnetic field amplitude of the Abrikosov-Nielsen-Olesen vortices, yielding compactlike defects in an alternative and simpler way than that of $k$-field models. At the end, we consider the Lorentz-violating terms in the gauge and Higgs sectors. It is shown that the full model also supports compactlike uncharged BPS vortices in a modified vacuum, but this time there are two LV parameters controlling the defect structure. Moreover, an interesting novelty is introduced by the LV-Higgs sector: fractional vortex solutions.

An eternally inflating universe produces an infinite amount of spatial volume, so every possible event happens an infinite number of times, and it is impossible to define probabilities in terms of frequencies. This problem is usually addressed by means of a measure, which regulates the infinities and produces meaningful predictions. I argue that any measure should obey certain general axioms, but then give a simple toy model in which one can prove that no measure obeying the axioms exists. In certain cases of eternal inflation there are measures that obey the axioms, but all such measures appear to be unacceptable for other reasons. Thus the problem of defining sensible probabilities in eternal inflation seems not to be solved.

The width of the decay $\tau \to \pi \omega \nu$ is calculated in the framework of an extended Nambu-Jona-Lasinio model. The contributions of intermediate $\rho (770)$ and ${\rho }^{\prime }(1450)$ vector mesons are taken into account. The computed partial width and spectral function of this decay are found to be in a satisfactory agreement with experimental data.

We study the allowed parameter space of the constrained minimal supersymmetric Standard Model (cMSSM) in the light of direct searches, constraints from $B$-physics (including the recent measurement of the branching ratio for $B_s\to {\mu }^{+}{\mu }^{-}$) and the dark matter relic density. For low or moderate values of $\tan \beta$, the strongest constraints are those imposed by direct searches, and therefore, large areas of the parameter space are still allowed. In the large $\tan \beta$ limit, however, the $B$-physics constraints are more restrictive, effectively forcing the squark and gluino masses to lie close to or above a TeV. A light Higgs boson could dramatically change the allowed parameter space, but we need to know its mass precisely for this to be effective. We emphasize that it is still too early to write off the cMSSM, even in the large $\tan \beta$ limit. Finally we explore strategies to extend the LHC search for cMSSM signals beyond the present reach of the ATLAS and CMS Collaborations.