We study the $\rho \pi$ and $b_1\pi$ decay modes of the $1^{-+}$ light hybrid state within the framework of light-cone QCD sum rules. We use both the tensor current $\overline{\psi }{\sigma }_{\mu \nu }\psi$ and the derivative current $\overline{\psi }{\overleftrightarrow{D}}_{\mu }{\gamma }_5\psi$ as interpolating currents to calculate the partial decay width of the $b_1\pi$ decay mode. Comparing the sum rules obtained by using different currents, we obtain $\mathrm{\Gamma }({\pi }_1\to b_1\pi )=8–23$, 32–86 and 52–151 MeV for $m_{1^{-+}}=1.6$, 1.8 and 2.0 GeV respectively, which favor the results from the flux tube models and lattice simulations. We also use the tensor current to study the $\rho \pi$ decay mode, and although an extended stability criterion is needed, our results suggest a small partial decay width.

In this paper we study the high energy behavior of electroweak Standard Model for a nonzero Weinberg angle ${\theta }_W$. We evaluate the spectrum of the electroweak Pomeron and demonstrate that the leading intercept is given by ${\alpha }_{\mathrm{e}.\mathrm{w}.}4\ln 2$ and does not depend on the mixing angle ${\theta }_W$. Due to its very small numerical value, we conclude that the high energy behavior of electroweak theory cannot be discussed without including the QCD Pomeron which, at sufficiently large energies, will dominate.

We study electron-positron pair creation by a strong and slowly varying electric field, assisted by a weaker and more rapidly changing field (e.g., in the keV regime) plus an additional high-energy (say MeV) photon. It turns out that this combination can yield a pair creation probability which is exponentially larger than in the case where one (or more) of the three ingredients is missing. Apart from a deeper understanding of these nonperturbative phenomena, this double enhancement may pave the way for an experimental verification of this fundamental prediction.

We enumerate the set of simplified models which match onto the complete set of gauge invariant effective operators up to dimension six describing interactions of a singlet-like Majorana fermion dark matter with the standard model. Tree-level matching conditions for each case are worked out in the large mediator mass limit, defining a one-to-one correspondence between the effective operator coefficients and the simplified model parameters for weakly interacting models. Utilizing such a mapping, we compute the dark matter annihilation rate in the early universe, as well as other low-energy observables like nuclear recoil rates using the effective operators, while the simplified models are used to compute the dark matter production rates at high-energy colliders like LEP, LHC and future lepton colliders. Combining all relevant constraints with a profile-likelihood analysis, we then discuss the currently allowed parameter regions and prospects for future searches in terms of the effective operator parameters, reducing the model dependence to a minimal level. In the parameter region where such a model-independent analysis is applicable, and leaving aside the special dark matter mass regions where the annihilation proceeds through an $s$-channel $Z$ or Higgs boson pole, the current constraints allow effective operator suppression scales ($\mathrm{\Lambda }$) of the order of a few hundred GeV for dark matter masses $m_{\chi }>20\mathrm{GeV}$ at 95% C.L., while the maximum allowed scale is around 3 TeV for $m_{\chi }\sim \mathcal{O}(1\mathrm{TeV})$. An estimate of the future reach of ton-scale direct detection experiments and planned electron-positron colliders show that most of the remaining regions can be probed, apart from dark matter masses near half of the $Z$-boson mass (with $500\mathrm{GeV}<\mathrm{\Lambda }<2\mathrm{TeV}$) and those beyond the kinematic reach of the future lepton colliders.

We have studied the properties of hot and dense quark matter based on the 3-flavor Nambu-Jona-Lasinio (NJL) model as well as its Polyakov-loop extension (pNJL) with scalar-isovector and vector-isovector couplings. Provided a considerable large isospin asymmetry or isospin chemical potential, isospin splittings of constituent mass, chiral phase transition boundary, and critical point for $u$ and $d$ quarks can be observed for positive isovector coupling constants but are suppressed for negative ones. The quark matter symmetry energy decreases with the increasing isovector coupling constant, and is mostly enhanced in the pNJL model than in the NJL model. A positive scalar-isovector coupling constant is more likely to lead to an unstable isospin asymmetric quark matter. The isovector coupling has been further found to affect particle fractions as well as the equation of state in hybrid stars. Possible effects on the isospin properties of quark matter have also been discussed if the strangeness sector is further broken among the flavor symmetry.

In this work we explore the consequences of considering from the very beginning the stationary and axisymmetric properties of the Kerr black hole as one attempts to derive this solution through the Kerr-Schild ansatz. The first consequence is kinematical and is based on a new stationary and axisymmetric version of the Kerr theorem that yields to the precise shear-free and geodesic null congruence of flat spacetime characterizing the Kerr solution. A straightforward advantage of this strategy is that now the parameter $a$ appears naturally as associated to the conserved angular momentum of the geodesics due to axisymmetry. The second consequence is dynamical and takes into account the circularity theorem. In fact, a stationary-axisymmetric Kerr-Schild ansatz is in general incompatible with the circularity property warranted by vacuum Einstein equations unless the remaining angular dependence in the Kerr-Schild profile appears fixed in a precise way. Thanks to these two ingredients, the integration of the Einstein equations reduces to a simple ordinary differential equation on the radial dependence, whose integration constant is precisely the mass $m$. This derivation of the Kerr solution is simple but rigorous, and it may be suitable for any textbook.

We report a study on axially and reflection symmetric dissipative fluids, just after its departure from hydrostatic and thermal equilibrium, at the smallest time scale at which the first signs of dynamic evolution appear. Such a time scale is smaller than the thermal relaxation time, the thermal adjustment time, and the hydrostatic time. It is obtained that the onset of nonequilibrium will critically depend on a single function directly related to the time derivative of the vorticity. Among all fluid variables (at the time scale under consideration), only the tetrad component of the anisotropic tensor in the subspace orthogonal to the four-velocity and the Killing vector of axial symmetry, shows signs of dynamic evolution. Also, the first step toward a dissipative regime begins with a nonvanishing time derivative of the heat flux component along the meridional direction. The magnetic part of the Weyl tensor vanishes (not so its time derivative), indicating that the emission of gravitational radiation will occur at later times. Finally, the decreasing of the effective inertial mass density, associated to thermal effects, is clearly illustrated.

As an extension of our previous work, which investigated the shadows of the Ellis wormhole surrounded by nonrotating dust, in this paper we study wormhole shadows in a rotating dust flow. First, we derive steady-state solutions of slowly rotating dust surrounding the wormhole by solving relativistic Euler equations. Solving null geodesic equations and radiation transfer equations, we investigate the images of the wormhole surrounded by dust for the above steady-state solutions. Because the Ellis wormhole spacetime possesses unstable circular orbits of photons, a bright ring appears in the image, just as in Schwarzschild spacetime. The bright ring looks distorted due to rotation. Aside from the bright ring, there appear weakly luminous complex patterns by the emission from the other side of the throat. These structure could be detected by high-resolution very-long-baseline-interferometry observations in the near future.

We derive upper and lower bounds on the mass-radius ratio of stable compact objects in extended gravity theories, in which modifications of the gravitational dynamics via-á-vis standard general relativity are described by an effective contribution to the matter energy-momentum tensor. Our results include the possibility of a variable coupling between the matter sector and the gravitational field and are valid for a large class of generalized gravity models. The generalized continuity and Tolman-Oppenheimer-Volkoff equations are expressed in terms of the effective mass, density, and pressure, given by the bare values plus additional contributions from the total energy-momentum tensor, and general theoretical limits for the maximum and minimum mass-radius ratios are explicitly obtained. As applications of the formalism developed herein, we consider compact bosonic objects, described by scalar-tensor gravitational theories with self-interacting scalar field potentials, and charged compact objects, respectively. For Higgs-type models, we find that these bounds can be expressed in terms of the value of the potential at the surface of the compact object. Minimizing the energy with respect to the radius, we obtain explicit upper and lower bounds on the mass, which admits a Chandrasekhar-type representation. For charged compact objects, we consider the effects of the Poincaré stresses on the equilibrium structure and obtain bounds on the radial and tangential stresses. As a possible astrophysical test of our results, we obtain the general bound on the gravitational redshift for compact objects in extended gravity theories and explicitly compute the redshift restrictions for objects with nonzero effective surface pressure. General implications of minimum mass bounds for the gravitational stability of fundamental particles and for the existence of holographic duality between bulk and boundary degrees of freedom are also considered.

We present results of a high-frequency all-sky search for continuous gravitational waves from isolated compact objects in LIGO’s fifth science run (S5) data, using the computing power of the Einstein@Home volunteer computing project. This is the only dedicated continuous gravitational wave search that probes this high-frequency range on S5 data. We find no significant candidate signal, so we set 90% confidence level upper limits on continuous gravitational wave strain amplitudes. At the lower end of the search frequency range, around 1250 Hz, the most constraining upper limit is $5.0\times {10}^{-24}$, while at the higher end, around 1500 Hz, it is $6.2\times {10}^{-24}$. Based on these upper limits, and assuming a fiducial value of the principal moment of inertia of ${10}^{38}\mathrm{kg}{\mathrm{m}}^2$, we can exclude objects with ellipticities higher than roughly $2.8\times {10}^{-7}$ within 100 pc of Earth with rotation periods between 1.3 and 1.6 milliseconds.

The search for weakly interacting massive particles (WIMPs) by direct detection faces an encroaching background due to coherent neutrino-nucleus scattering. For a given WIMP mass the cross section at which neutrinos constitute a dominant background is dependent on the uncertainty on the flux of each neutrino source, principally from the Sun, supernovae or atmospheric cosmic ray collisions. However there are also considerable uncertainties with regard to the astrophysical ingredients of the predicted WIMP signal. Uncertainties in the velocity of the Sun with respect to the Milky Way dark matter halo, the local density of WIMPs, and the shape of the local WIMP speed distribution all have an effect on the expected event rate in direct detection experiments and hence will change the region of the WIMP parameter space for which neutrinos are a significant background. In this work we extend the neutrino floor calculation to account for the uncertainty in the astrophysics dependence of the WIMP signal. We show the effect of uncertainties on projected discovery limits with an emphasis on low WIMP masses (less than 10 GeV) when solar neutrino backgrounds are most important. We find that accounting for astrophysical uncertainties changes the shape of the neutrino floor as a function of WIMP mass but also causes it to appear at cross sections up to an order of magnitude larger, extremely close to existing experimental limits, indicating that neutrino backgrounds will become an issue sooner than previously thought. We also explore how neutrinos hinder the estimation of WIMP parameters and how astrophysical uncertainties impact the discrimination of WIMPs and neutrinos with the use of their respective time dependencies.

The dynamical generation of a fermion mass is studied within ($2+1$)-dimensional QED with $N$ four-component fermions in the leading and next-to-leading orders of the $1/N$ expansion. The analysis is carried out in the Landau gauge, which is supposed to insure the gauge independence of the critical fermion flavor number, $N_c$. It is found that the dynamical fermion mass appears for $N<N_c$, where $N_c=3.29$, which is only about 1% larger than its value at leading order.

Based on a vector triplet model, we study a possible failure of dimension-6 operators in describing LHC Higgs kinematics. First, we illustrate that including dimension-6 contributions squared can significantly improve the agreement between the full model and the dimension-6 approximation, both in associated Higgs production and in weak-boson-fusion Higgs production. Second, we test how a simplified model with an additional heavy scalar could improve the agreement in critical LHC observables. In weak boson fusion, we find an improvement for virtuality related observables at large energies, but at the cost of sizeable deviations in interference patterns and angular correlations.

We study a simplified scenario in the next-to-minimal supersymmetric standard model with a split electroweak spectrum, in which only the singlino and Higgsinos are light and other superpartners are decoupled. Serving as a dark matter candidate, a singlino-dominated neutralino ${\tilde{\chi }}_1^0$ should have either resonant annihilation effects or sizable Higgsino components to satisfy the observed relic abundance. The sensitivities of LHC searches and dark matter detection experiments are investigated. With an integrated luminosity of $30(300){\mathrm{fb}}^{-1}$, $3l+{\cancel{E}}_{\mathrm{T}}$ and $2l+{\cancel{E}}_{\mathrm{T}}$ searches at the 13 (14) TeV LHC are expected to reach up to $m_{{\tilde{\chi }}_1^0}\sim 150(230)\mathrm{GeV}$ and $m_{{\tilde{\chi }}_2^0,{\tilde{\chi }}_1^{\pm }}\sim 320(480)\mathrm{GeV}$. Near future dark matter direct and indirect detection experiments are promising to cover the parameter regions where collider searches lose their sensitivities.

We investigate the extended Higgs sectors, specially the charged Higgs sector, in a supersymmetric $Y=0$ $SU(2)$ triplet and a Standard Model (SM) gauge singlet extension of the SM. We show that, in this model, the allowed data for the Higgs boson interaction eigenstates tend to group into separate blocks for a $SU(2)$ triplet, doublet, and singlet. A typical mass spectrum has a doublet-type Standard Model like a Higgs of 125 GeV, a tripletlike light charged Higgs boson, and a very light singletlike pseudoscalar, with the rest relatively decoupled. Later, we investigate the different decay processes allowed in a charged Higgs boson of this model. Specifically, we search for new decay modes of the charged Higgs bosons in order to distinguish between Higgs fields belonging to $SU(2)$ doublet and triplet representations, and also to show the existence of a light pseudoscalar which belong to the singlet representation. The different production modes for the light charged Higgs boson have been discussed, including the limiting case of $|{\lambda }_T|\simeq 0$. We also propose a few final state modes carrying the distinctive signatures of this model which could be investigated at the LHC and future colliders. The signatures of the singlet and/or the triplet can be explored with an earlier reach of $120{\mathrm{fb}}^{-1}$ for some final states at the LHC with 14 TeV of center of mass energy.

Construction of the pion scalar isoscalar form factor ${\mathrm{\Gamma }}_{\pi }(t)$ in the elastic region, with an emphasis on the values of the S-wave isoscalar $\pi \pi$ scattering length $a_0^0$ and the quadratic pion scalar radius $⟨r^2{⟩}_s^{\pi }$ to be in conformity with predictions of the chiral perturbation theory, is presented. It is based on a precise S-wave isoscalar $\pi \pi$ scattering phase shift generated by dispersive analysis of experimental data with and imposed crossing symmetry condition. The final result for values of the $f_0(500)$ scalar meson mass and width is $m_{\sigma }=(487\pm 31)\mathrm{MeV}$; ${\mathrm{\Gamma }}_{\sigma }=(542\pm 60)\mathrm{MeV}$ and for values of the $f_0(980)$ scalar meson mass and width is $m_{f(980)}=(988\pm 78)\mathrm{MeV}$; ${\mathrm{\Gamma }}_{f(980)}=(97\pm 29)\mathrm{MeV}$. The $f_0(500)$ scalar meson parameters are compatible with the results from dispersive analyses of the BERN and MADRID/CRACOW groups to be considered now as the most reliable values of the $f_0(500)$ scalar meson parameters, though in presented analysis another, unusual way has been applied. The $f_0(980)$ meson parameters agree well with values given by the Particle Data Group.

We study the $Y(4260)$ production mechanism in $e^{+}{e}^{-}$ annihilations in the framework of hadronic molecules and investigate the consequence of such a picture in different decay channels. In the hadronic molecule picture the $Y(4260)$ is described as a mixture state composed of a long-ranged $\overline{D}{D}_1(2420)+\mathrm{c}.\mathrm{c}.$ molecule state and a compact $c\overline{c}$ component. We show that the compositeness relation can still provide a reasonable constraint on the wave function renormalization parameter due to the dominance of the molecular component. Such a mechanism can be regarded as a natural consequence of the heavy quark spin symmetry (HQSS) breaking. This study elaborates the molecular picture for the $Y(4260)$ in the $e^{+}{e}^{-}$ annihilations and affirms that the cross section line shape of $e^{+}{e}^{-}\to \overline{D}{D}^{*}\pi +\mathrm{c}.\mathrm{c}.$ in the vicinity of the $Y(4260)$ should have a nontrivial behavior. In this framework we predict that the upper limit of the $Y(4260)$ leptonic decay width is about 500 eV. We also investigate the coupling for $D_1(2420)\to D^{*}\pi$ in the ${}^3{P}_0$ quark model and examine the possible HQSS breaking effects due to the deviation from the $|{{}^{1}P}_1⟩$ and $|{{}^{3}P}_1⟩$ ideal mixing. This in turn provides a constraint on the HQSS breaking coupling for the $Y(4260)$ to $\overline{D}{D}_1(2420)+\mathrm{c}.\mathrm{c}.$ via its $c\overline{c}$ component.

We point out that if the baryon number violating neutron-antineutron oscillation is discovered, it would impose strong limits on the departure from Einstein’s equivalence principle at a level of one part in $10^{19}$. If this departure owes its origin to the existence of long-range forces coupled to baryon number $B$ (or $B-L$), it would imply very stringent constraints on the strength of gauge bosons coupling to the baryon number current. For instance, if the force mediating baryon number has strength ${\alpha }_B$ and its range is larger than a megaparsec, we find the limit to be ${\alpha }_B\le 2\times {10}^{-57}$, which is much stronger than all other existing bounds. For smaller range for the force, we get slightly weaker, but still stringent bounds by considering the gravitational potentials of Earth and the Sun.