We identify the recently observed charmoniumlike structure $Z_c^{\pm }(3900)$ as the charged partner of the $X(3872)$ state. Using standard techniques of QCD sum rules, we evaluate the three-point function and extract the coupling constants of the $Z_c^{+}J/\psi {\pi }^{+}$, $Z_c^{+}{\eta }_c{\rho }^{+}$ and $Z_c^{+}{D}^{+}{\overline{D}}^{*0}$ vertices and the corresponding decay widths in these channels. The good agreement with the experimental data gives support to the tetraquark picture of this state.

After the discovery of a standard model (SM)-like Higgs boson, naturalness strongly favors the next-to-minimal supersymmetric SM. In this letter, we point out that the natural next-to-minimal supersymmetric SM usually predicts the following $CP$-even Higgs $H_i$ sector: (A) $H_2$ is the SM-like Higgs boson with mass pushed upward by a lighter $H_1$ with mass overwhelmingly within [$m_{H_2}/2$, $m_{H_2}$]; (B) $m_{H_3}\simeq 2\mu /\sin 2\beta \gtrsim 300\mathrm{GeV}$; (C) $H_3$ has a significant coupling to the top quark and can decay to $H_1{H}_2$ with a large branching ratio. Using a jet substructure we show that these three Higgs bosons can be discovered via $gg\to H_3\to H_1{H}_2\to b\overline{b}\ell \nu jj$ at the 14 TeV LHC. In particular, the LEP-LHC scenario with $H_1\simeq 98\mathrm{GeV}$ has a very good discovery potential.

The D0 collaboration has announced the observation of the like-sign dimuon charge asymmetry since 2010, which has a difference of more than $3\sigma$ from the Standard Model prediction. One of the promising explanations is considering the existence of flavor-changing $Z^{\prime }$ couplings to the $b$ and $s$ quarks which can contribute to the off-diagonal decay width in the $B_s-{\overline{B}}_s$ mixing. Model construction is highly constrained by the recent LHCb data of $1{\mathrm{fb}}^{-1}$ integrated luminosity. In this paper, we analyze the experimental constraints on constructing new physics models to explain the dimuon charge asymmetry from the $CP$ violation of the $B_s$ system. We present limits on $Z^{\prime }$ couplings and show that it is impossible to obtain the $1\sigma$ range of the dimuon charge asymmetry without the new contribution in the $B_d$ system. Even with an arbitrary contribution in the $B_d$ system, the new couplings must be in the fine-tuned region.

We present a calculation of the strangeness and charmness contents $⟨N|\overline{s}s|N⟩$ and $⟨N|\overline{c}c|N⟩$ of the nucleon from dynamical lattice QCD with $2+1$ flavors. The calculation is performed with overlap valence quarks on $2+1$-flavor domain-wall fermion gauge configurations. The configurations are generated by the RBC collaboration on a ${24}^3\times 64$ lattice with sea-quark mass $a{m}_l=0.005$, $a{m}_s=0.04$, and inverse lattice spacing $a^{-1}=1.73\mathrm{GeV}$. Both actions have chiral symmetry which is essential in avoiding contamination due to the operator mixing with other flavors. The nucleon propagator and the quark loops are both computed with stochastic grid sources, while low-mode substitution and low-mode averaging methods are used respectively which substantially improve the signal-to-noise ratio. We obtain the strangeness matrix element $f_{T_s}=m_s⟨N|\overline{s}s|N⟩/M_N=0.0334(62)$, and the charmness content $f_{T_c}=m_c⟨N|\overline{c}c|N⟩/M_N=0.094(31)$ which is resolved from zero by $3\sigma$ precision for the first time.

We argue that the deep inelastic structure function $F_2^{\gamma p}(x,Q^2)$, regarded as a cross section for virtual ${\gamma }^{*}p$ scattering, is hadronic in nature. This implies that its growth is limited by the Froissart bound at high hadronic energies, giving a ${ln}^2(1/x)$ bound on $F_2^{\gamma p}$ as Bjorken $x\to 0$. The same bound holds for the individual quark distributions. In earlier work, we obtained a very accurate global fit to the combined HERA data on $F_2^{\gamma p}$ using a fit function which respects the Froissart bound at small $x$, and is equivalent in its $x$ dependence to the function used successfully to describe all high energy hadronic cross sections, including $\gamma p$ scattering. We extrapolate that fit by a factor of $\lesssim 3$ beyond the HERA region in the natural variable $\ln (1/x)$ to the values of $x$ down to $x={10}^{-14}$ and use the results to derive the quark distributions needed for the reliable calculation of neutrino cross sections at energies up to $E_{\nu }={10}^{17}\mathrm{GeV}$. These distributions do not satisfy the Feynman “wee parton” assumption, that they all converge toward a common distribution $xq(x,Q^2)$ at small $x$ and large $Q^2$. This was used in some past calculations to express the dominant neutrino structure function $F_2^{\nu (\overline{\nu })}$ directly in terms of $F_2^{\gamma p}$. We show that the correct distributions nevertheless give results for $F_2^{\nu (\overline{\nu })}$ which differ only slightly from those obtained assuming that the wee parton limit holds. In two Appendixes, we develop simple analytic results for the effects of QCD evolution and operator-product corrections on the distribution functions at small $x$, and show that these effects amount mainly to shifting the values of $\ln (1/x)$ in the initial distributions.

In part I [M. M. Block et al., preceding article, Phys. Rev. D 88, 014006 (2013)] we argued that the structure function $F_2^{\gamma p}(x,Q^2)$ in deep inelastic $ep$ scattering, regarded as a cross section for virtual ${\gamma }^{*}p$ scattering, has a saturated Froissart-bounded form behaving as ${ln}^2(1/x)$ at small $x$. This form provides an excellent fit to the low $x$ HERA data, including the very low $Q^2$ regions, and can be extrapolated reliably to small $x$ using the natural variable $\ln (1/x)$. We used our fit to derive quark distributions for values of $x$ down to $x={10}^{-14}$. We use those distributions here to evaluate ultrahigh energy (UHE) cross sections for neutrino scattering on an isoscalar nucleon, $N=(n+p)/2$, up to laboratory neutrino energies $E_{\nu }\sim {10}^{16}–{10}^{17}\mathrm{GeV}$ where there are now limits on neutrino fluxes. We estimate that these cross sections are accurate to $\sim 2\%$ at the highest energies considered, with the major uncertainty coming from the errors in the parameters that were needed to fit $F_2^{\gamma p}(x,Q^2)$. We compare our results to recently published neutrino cross sections derived from next-to-leading order parton distribution functions, which become much larger at high energies because of the use of power-law extrapolations of quark distributions to small $x$. We argue that our calculation of the UHE $\nu N$ cross sections is the best one can make based the existing experimental deep inelastic scattering data. Further, we show that the strong interaction Froissart bound of ${ln}^2(1/x)$ on $F_2^{\gamma p}$ translates to an exact bound of ${ln}^3{E}_{\nu }$ for leading-order-weak $\nu N$ scattering. The energy dependence of $\nu N$ total cross section measurements consequently has important implications for hadronic interactions at enormous center-of-mass energies not otherwise accessible.

We investigate the prospects for reconstructing the mass, spin-independent and spin-dependent cross sections of dark matter particles with a combination of future direct detection experiments such as XENON1T, and the IceCube neutrino telescope in the 86-string configuration including the DeepCore array. We quantify the degree of complementarity between the two experiments by adopting realistic values for their exposure, energy threshold and resolution. Starting from benchmark models arising from a supersymmetric model with 25 free parameters, we show that despite the stringent constraints set by the run with 79 strings, IceCube can help break the degeneracies in the dark matter cross section parameter space, even in the unfortunate case where it fails to discover high energy neutrinos from the Sun. We also discuss how the reconstruction of the dark matter particle parameters from the combined data sets is affected by the uncertainties associated with the nuclear structure of the target material in case of spin-dependent scattering and those associated with astrophysical quantities such as the dark matter density and velocity distribution.

Neutrino oscillation experiments in the past decades have greatly improved our knowledge on neutrinos by measuring the fundamental neutrino parameters. The ongoing and upcoming neutrino oscillation experiments are intended to pin down the neutrino mass hierarchy and to discover the leptonic $CP$ violation. By means of neutrino oscillograms, we analyze the impact of nonstandard neutrino interactions on neutrino oscillations in Earth matter. The standard neutrino oscillation probabilities may be significantly changed by nonstandard interaction parameters, and, in particular, the $CP$-violating effects in the energy range $E=1–20\mathrm{GeV}$ are greatly enhanced. In addition, the event rates of muon neutrinos in the proposed huge atmospheric neutrino experiment, PINGU at the South Pole, have been estimated in the presence of nonstandard neutrino interactions. It has been found that the PINGU experiment has very good sensitivities to the nonstandard neutrino interaction parameters.

We develop a general procedure to deal with defect structures in generalized models, described by a single real scalar field, in (1, 1) spacetime dimensions. The models that we consider have the standard kinetic and potential contributions modified to include corrections that depend on single small parameters, used to control modification on the kinematics and the potential. We start with the standard model that engenders stable defect structures, and we show how to obtain new structures for the generalized models. We examine distinct aspects of the new deformed solutions, including linear stability. We work with several distinct modifications, and we show how to make the new defect structures stable, controlled by the parameters that modify the standard theory. We illustrate the procedure with examples of current interest to high energy physics.

A toy model of Einstein gravity with a Gauss-Bonnet classically “entropic” term mimicking a quantum correction is considered. The static black hole solution due to Tomozawa is found and generalized with the inclusion of nontrivial horizon topology, and its entropy is evaluated, deriving the first law by equations of motion. As a result the Bekenstein-Hawking area law turns out to be corrected by a logarithmic area term. A Misner-Sharp expression for the mass of a black hole is found. Within a Friedmann-Lemaître-Robertson-Walker cosmological setting, the model is used in order to derive modified Friedmann equations. Such new equations are shown to reproduce the first law with the same formal entropy and quasilocal energy of the static case, but here within a Friedmann-Lemaître-Robertson-Walker space-time interpreted as a dynamical cosmological black hole. A detailed analysis of cosmological solutions is presented, and it is shown that the presence of the correction term provides regular solutions and interesting phases of acceleration and deceleration, as well as, with negligible matter, exact de Sitter solutions.

The critical behavior of Myers-Perry black holes with equal angular momenta in even dimensions are studied. We include the corrections beyond the semiclassical approximation on Hawking temperature in the grand canonical ensemble. Having done so, we find that the critical behavior and critical exponents of Myers-Perry black holes correspond to those of a Van der Waals liquid-gas where this analogy holds in any dimension. Also, using Ehrenfest’s equations, we calculate the order of the phase transition in the semiclassical approximation for the canonical ensemble and beyond the semiclassical approximation for the grand canonical ensemble near the critical point. Finally, the Ruppeiner curvature formula is used to investigate the thermodynamic geometry of Myers-Perry black holes.

The Friedmann-Robertson-Walker metric with spherical topology is calculated as an effective metric at the brane in a multiple brane $D$-dimensional spacetime scenario. In this model the radius of the brane is the cosmological scale factor, and its evolution is calculated from the viewpoint of the observers on their respective branes. The cosmology of the brane-universe is analyzed in cases where the anisotropic pressure has a cosmological-constant-like state equation. The pressure values needed to distinguish the oscillating, expanding or collapsing solutions are found, and the minimum value of a brane-universe mass to prevent a collapse into a black hole is also calculated. As a result, we find solutions indicating a bouncing universe, and solutions with more than one oscillatory phase. To validate the analytical results, the equation of motion is solved numerically to show the different cosmological scenarios.

Nonlinear partially massless (PM) gravity, if it exists, is a theory of massive gravity in which the graviton has four propagating degrees of freedom. In PM gravity, a scalar gauge symmetry removes one of the five modes of the massive graviton. This symmetry ties the value of the cosmological constant to the mass of the graviton, which in turn can be kept small in a technically natural way. Thus, PM gravity could offer a compelling solution to the old cosmological constant problem. In this work we look for such a theory among the known ghost-free massive gravity models with a de Sitter reference metric. We find that despite the existence of strong supporting evidence for the existence of a PM theory of gravity, technical obstructions arise which preclude its formulation using the standard massive gravity framework.

In this paper, we investigate a unified dark fluid model with a fast transition and entropic perturbations. An effective sound speed is designated as an additional free model parameter when the entropic perturbations are included, and, if the entropic perturbations are zero, the effective sound speed will decrease to the adiabatic sound speed. In order to analyze the viability of the unified model, we calculate the squared Jeans wave number with the entropic perturbations. Furthermore, by using the Markov Chain Monte Carlo method, we perform a global fitting for the unified dark fluid model from the type Ia supernova Union 2.1, baryon acoustic oscillation, and the full information of the cosmic microwave background measurement given by the WMAP 7 yr data points. The constrained results favor a small effective sound speed. Compared to the cosmological constant and cold dark matter, it is found that the cosmic observations do not favor the phenomenon of a fast transition for the unified dark fluid model.

We used radio observations of the neighbor galaxy M31 in order to put constraints on the dark matter particle mass and annihilation cross section. Dark matter annihilation in M31 halo produces highly energetic leptons, which emit synchrotron radiation on radio frequencies in the galactic magnetic field. We predicted expected radio fluxes for the two annihilation channels: $\chi \chi \to b\overline{b}$ and $\chi \chi \to {\tau }^{+}{\tau }^{-}$. We then compared them with available data on the central radio emission of M31 as observed by four radio surveys: VLSS (74 MHz), WENSS (325 MHz), NVSS (1400 MHz), and GB6 (4850 MHz). Assuming a standard Navarro-Frenk-White dark matter density profile and a conservative magnetic field distribution inside the Andromeda galaxy, we find that the thermal relic annihilation cross section or higher $⟨\sigma v⟩\ge 3\times {10}^{-26}{\mathrm{cm}}^3/\mathrm{s}$ are only allowed for weakly interacting massive particle masses greater than $\approx 100$ and $\approx 55\mathrm{GeV}$ for annihilation into $b\overline{b}$ and ${\tau }^{+}{\tau }^{-}$, respectively. Taking into account potential uncertainties in the distributions of dark matter density and the magnetic field, the mentioned weakly interacting massive particle limiting masses can be as low as 23 GeV for both channels, and as high as 280 and 130 GeV for annihilation into $b\overline{b}$ and ${\tau }^{+}{\tau }^{-}$, respectively. These mass values exceed the best up-to-date known constraints from Fermi gamma observations: 40 and 19 GeV, respectively [A. Geringer-Sameth and S. M. Koushiappas, Phys. Rev. Lett. 107, 241303 (2011)]. Precise measurements of the magnetic field in the relevant region and better reconstruction of the dark matter density profile of M31 will be able to reduce the uncertainties of our exclusion limits.

The AMS-02 Collaboration has just published a high-precision measurement of the cosmic positron fraction $e^{+}/(e^{-}+e^{+})$, which rises with energy from $\sim 5\mathrm{GeV}$ to $\sim 350\mathrm{GeV}$. The result indicates the existence of primary electron/positron sources to account for the positron excess. In this work, we investigate the possibility that the nearby mature pulsars with ages of $O({10}^5)\mathrm{yr}$ are the primary positron sources. By fitting the data we find that the positrons from a single nearby pulsar, such as Geminga or Monogem, with the spectral index $\alpha \sim 2$ can interpret the AMS-02 result. We also investigate the possibility that high-energy positrons are generated by multiple known pulsars in the ATNF catalogue. Such a scenario can also fit the AMS-02 data well. Future precise measurements of fine structures in the positron spectrum would be a support to the pulsar scenario.

The merger of two neutron stars will in general lead to the formation of a torus surrounding a black hole whose rotational energy can be tapped to potentially power a short gamma-ray burst. We have studied the merger of equal-mass binaries with spins aligned with the orbital angular momentum to determine the maximum spin the black hole can reach. Our initial data consists of irrotational binaries to which we add various amounts of rotation to increase the total angular momentum. Although the initial data violates the constraint equations, the use of the constraint-damping conformal and covariant Z4 formulation yields evolutions with violations smaller than those with irrotational initial data and standard formulations. Interestingly, we find that a limit of $J/M^2\simeq 0.89$ exists for the dimensionless spin and that any additional angular momentum given to the binary ends up in the torus rather than in the black hole, thus providing another nontrivial example supporting the cosmic censorship hypothesis.

A monochromatic line in the cosmic neutrino spectrum would be a smoking gun signature of dark matter. It is intriguing that the IceCube experiment has recently reported two PeV neutrino events with energies that may be equal up to experimental uncertainties, and which have a probability of being a background fluctuation estimated to be less than a percent. Here we explore prospects for these events to be the first indication of a monochromatic line signal from dark matter. While measurable annihilation signatures would seem to be impossible at such energies, we discuss the dark matter quantum numbers, effective operators, and lifetimes which could lead to an appropriate signal from dark matter decays. We will show that the set of possible decay operators is rather constrained and will focus on the following viable candidates which could explain the IceCube events: R-parity violating gravitinos, hidden sector gauge bosons, and singlet fermions in an extra dimension. In essentially all cases we find that a PeV neutrino line signal from dark matter would be accompanied by a potentially observable continuum spectrum of neutrinos rising towards lower energies.

We explore the possibility that $\mathrm{SU}(3{)}_C$ was not an exact symmetry at all times in the early Universe, using minimal extensions of the standard model that contain a color triplet scalar field and perhaps other fields. We show that, for a range of temperatures, there can exist a phase in which the free energy is minimized when the color triplet scalar has a nonvanishing vacuum expectation value, spontaneously breaking color. At very high temperatures and at lower temperatures, color symmetry is restored. The breaking of color in this phase is accompanied by the spontaneous breaking of $B-L$ if the color triplet scalar Yukawa couples to quarks and/or leptons. We discuss the requirements on the minimal extensions needed for consistency of this scenario with present collider bounds on new colored scalar particles.

Models in which the Higgs sector is extended by a single electroweak scalar multiplet $X$ can possess an accidental global U(1) symmetry at the renormalizable level if $X$ has isospin $T\ge 2$. We show that all such models with an accidental U(1) symmetry are excluded by the interplay of the cosmological relic density of the lightest (neutral) component of $X$ and its direct-detection cross section via $Z$ exchange. The sole exception is the $T=2$ multiplet, whose lightest member decays on a few-day to few-year time scale via a Planck-suppressed dimension-5 operator.