I point out that the excess of electronlike neutrino events recently observed by the T2K Collaboration may have a common origin with the similar excess events previously reported by the LSND and MiniBooNE experiments, and interpreted as a signal from the radiative decays of a sterile neutrino ${\nu }_h$ with the mass around 50 MeV produced in ${\nu }_{\mu }$ neutral current (NC) interactions. In this work, I assumed that the ${\nu }_h$ can also be produced in ${\nu }_{\tau }\mathrm{NC}$ reactions.

We report a search for a narrow $t\overline{t}$ resonance that decays into a $\mathrm{\text{lepton}}+\mathrm{\text{jets}}$ final state based on an integrated luminosity of $5.3{\mathrm{fb}}^{-1}$ of proton-antiproton collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected by the D0 Collaboration at the Fermilab Tevatron Collider. We set upper limits on the production cross section of such a resonance multiplied by its branching fraction to $t\overline{t}$. We exclude a leptophobic topcolor $Z^{\prime }$ at the 95% confidence level for masses below 835 GeV (940 GeV) if its width is 1.2% (3%) of its mass. We also exclude color octet vector bosons (colorons) with masses below 775 GeV.

We introduce the eikonal approximation to study the effect of the large-scale motion of cosmic fluids on their small-scale evolution. This approach consists in collecting the impact of the long-wavelength displacement field into a single or finite number of random variables, whose statistical properties can be computed from the initial conditions. For a single dark matter fluid, we show that we can recover the nonlinear propagators of renormalized perturbation theory. These are obtained with no need to assume that the displacement field follows the linear theory. Then we extend the eikonal approximation to many fluids. In particular, we study the case of two nonrelativistic components and we derive their resummed propagators in the presence of isodensity modes. Unlike the adiabatic case, where only the phase of small-scale modes is affected by the large-scale advection field, the isodensity modes change also the amplitude on small scales. We explicitly solve the case of cold dark matter-baryon mixing and find that the isodensity modes induce only very small corrections to the resummed propagators.

We construct an analytical model for two-channel, two-body scattering amplitudes, and then apply it in the description of the three-body $J/\psi \to K^{+}{K}^{-}{\pi }^0$ decay. In the construction of the partial wave amplitudes, we combine the low-energy resonance region with the Regge asymptotic behavior determined from direct two-body production. We find that resonance production in the $K\pi$ channel in $J/\psi$ decays seems to differ from that observed in direct $K\pi$ production, while the mass distribution in the $K\overline{K}$ channel may be compatible.

The $E_6\mathrm{SSM}$ extension of the minimal supersymmetric standard model allows for the solution of many of the difficulties that are usually encountered within conventional supersymmetry-breaking scenarios, e.g., the $\mu$ problem, the imposition of R-parity “by hand,” the generation of light neutrino masses and obtaining a light Higgs boson with a mass as large as $\sim 125\mathrm{GeV}$ as suggested by recent LHC measurements. In addressing these problems, such a scenario predicts the existence of additional singlet and vectorlike superfields beyond those in the minimal supersymmetric standard model as well as possibly two new neutral gauge bosons near the TeV scale. In this paper the phenomenological implications of simultaneous gauge kinetic mixing between the usual standard model hypercharge gauge field and both these new neutral gauge fields present in the $E_6\mathrm{SSM}$ scenario is explored. To this end a large class of specific toy models realizing this type of kinetic mixing is examined. In particular, we demonstrate that a significant suppression (or enhancement) of the expected event rate for $Z^{\prime }$ production in the dilepton channel at the LHC is not likely to occur in this scenario due to gauge kinetic mixing.

In the low energy effective theory describing the partially quenched extension of two light Wilson fermions, three low energy constants (LECs) appear in terms proportional to $a^2$ ($a$ being the lattice spacing). We propose methods to separately calculate these LECs, typically called $W_6^{\prime }$, $W_7^{\prime }$ and $W_8^{\prime }$. While only one linear combination of these constants enters into physical quantities, different combinations enter into the description of the spectral density and eigenvalue distributions of the lattice Dirac operator and its Hermitian counterpart. Thus it is useful to be able to determine the LECs separately. Our methods require studying certain correlation functions for either two or three pion scattering, which are accessible only in the partially quenched extension of the theory.

Using a method previously developed, based on the Mellin-Barnes transform, we reconstruct the two-point correlators in the vector, axial, scalar, and pseudoscalar channels at $\mathcal{O}({\alpha }_s^3)$ from the Taylor expansion at $q^2=0$, the threshold expansion at $q^2=4m^2$ and the high-energy expansion at $q^2\to -\infty$, where $m$ is the heavy quark mass. The reconstruction is analytic and systematic and is controlled by an error function which becomes smaller as more terms in those expansions are known.

We extend our earlier results delineating the supersymmetry reach of the CERN Large Hadron Collider operating at a center-of-mass energy $\sqrt{s}=7\mathrm{TeV}$ to integrated luminosities in the range $5–30{\mathrm{fb}}^{-1}$. Our results are presented within the paradigm minimal supergravity model or constrained minimal supersymmetric standard model. Using a six-dimensional grid of cuts for the optimization of signal to background ratio—including missing $E_T$—we find for $m_{\tilde{g}}\sim m_{\tilde{q}}$ an LHC $5\sigma$ supersymmetry discovery reach of $m_{\tilde{g}}\sim 1.3$, 1.4, 1.5, and 1.6 TeV for 5, 10, 20, and $30{\mathrm{fb}}^{-1}$, respectively. For $m_{\tilde{q}}\gg m_{\tilde{g}}$, the corresponding reach is instead $m_{\tilde{g}}\sim 0.8$, 0.9, 1.0, and 1.05 TeV, for the same integrated luminosities.

The Clausius relation between entropy change and heat flux has previously been used to derive Einstein’s field equations as an equation of state. In that derivation the entropy is proportional to the area of a local causal horizon, and the heat is the energy flux across the horizon, defined relative to an approximate boost Killing vector. We examine here whether a similar derivation can be given for extensions beyond Einstein gravity to include higher-derivative and higher-curvature terms. We review previous proposals which, in our opinion, are problematic or incomplete. Refining one of these, we assume that the horizon entropy depends on an approximate local Killing vector in a way that mimics the diffeomorphism Noether charge that yields the entropy of a stationary black hole. We show how this can be made to work if various restrictions are imposed on the nature of the horizon slices and the approximate Killing vector. Also, an integrability condition on the assumed horizon entropy density must hold. This can yield field equations of a Lagrangian constructed algebraically from the metric and Riemann tensor, but appears unlikely to allow for derivatives of curvature in the Lagrangian.

We study the particle spectrum and the unitarity of the generic $n$-dimensional Weyl-invariant quadratic curvature gravity theories around their (anti-)de Sitter and flat vacua. Weyl symmetry is spontaneously broken in (anti-)de Sitter and radiatively broken at the loop level in flat space. Save the three-dimensional theory (which is the Weyl-invariant extension of the new massive gravity), the graviton remains massless and the unitarity requires that the only viable Weyl-invariant quadratic theory is the Weyl-invariant extension of the Einstein-Gauss-Bonnet theory. The Weyl gauge field, on the other hand, becomes massive. The symmetry breaking scale fixes all the dimensionful parameters in the theory.

During the evolution of the universe there are at least two epochs during which electromagnetic waves cannot scan the universe’s internal structure to bring information to outside observers. The first epoch is when photons are in local thermodynamic equilibrium with other particles, and the second is when photon scattering by charged particles is strong. One can call these two periods of cosmological time as standard unlighted epochs. After the last scattering surface, photons become relic photons and turn into a source of information about the universe. Unlighted cosmic epochs can also appear when one considers nonminimal theories, i.e., theories in which the electromagnetic field is coupled in an intricate way with the cosmological gravitational field. By considering a cosmological model where the dark sector, i.e., the dark energy and dark matter, self-interacts via an Archimedean-type force, and taking into account a nonminimal coupling theory for the electromagnetic field, we discuss the appearance of unlighted epochs. In the framework of our nonminimal theory, a three-parameter nonminimal Einstein-Maxwell model, the curvature coupling can be formulated in terms of an effective refraction index $n(t)$. Then, taking advantage of a well-known classical analogy, namely, in a medium with $n^2<0$ electromagnetic waves do not propagate and their group velocity, i.e., energy transfer velocity, has zero value at the boundary of the corresponding zone, one can search for the unlighted epochs arising in the interacting dark fluid cosmological model. We study here, both analytically and numerically, cosmological models admitting unlighted epochs.

The detection of gravitational waves from the inspiral of a neutron star or stellar-mass black hole into an intermediate-mass black hole (IMBH) promises an entirely new look at strong-field gravitational physics. Gravitational waves from these intermediate-mass-ratio inspirals (IMRIs), systems with mass ratios from $\sim 10:1$ to $\sim 100:1$, may be detectable at rates of up to a few tens per year by Advanced LIGO/Virgo and will encode a signature of the central body’s spacetime. Direct observation of the spacetime will allow us to use the “no-hair” theorem of general relativity to determine if the IMBH is a Kerr black hole (or some more exotic object, e.g., a boson star). Using modified post-Newtonian (pN) waveforms, we explore the prospects for constraining the central body’s mass-quadrupole moment in the advanced-detector era. We use the Fisher information matrix to estimate the accuracy with which the parameters of the central body can be measured. We find that for favorable mass and spin combinations, the quadrupole moment of a non-Kerr central body can be measured to within a $\sim 15\%$ fractional error or better using 3.5 pN order waveforms; on the other hand, we find the accuracy decreases to $\sim 100\%$ fractional error using 2 pN waveforms, except for a narrow band of values of the best-fit non-Kerr quadrupole moment.

Both electric and magnetic screening masses in a nonperturbative gluonic background are investigated using operator product expansion. The magnetic screening mass is found to agree with lattice results whereas the electric screening mass is somewhat smaller than the one found on the lattice.

In extended Higgs sectors, heavy Higgs bosons can decay via cascades to a light Higgs boson plus $W$ and $Z$ bosons. We study signals of such sectors at the Tevatron and LHC that result from resonant production of a heavy $H^0$ followed by the decay $H^0\to H^{\pm }{W}^{\mp }$ with $H^{+}\to W^{+}{h}^0\to W^{+}b\overline{b}$ or $H^{+}\to t\overline{b}\to W^{+}b\overline{b}$. The final states have the same particle content as that of $t\overline{t}$ production, but with a resonant structure that can be used to distinguish signal events from background events. We propose analysis techniques and estimate the experimental sensitivity of the Tevatron and LHC experiments to these signals.

In this paper, we study instanton contributions to the correlator of the hybrid current $g\overline{q}{\sigma }_{\mu \nu }{G}_{\nu \mu }^a{T}^{a}q$. These contributions are then included in a QCD sum-rule analysis of the isoscalar $0^{++}$ hybrid mass. We find a mass at 1.83 GeV for the $(\overline{u}ug+\overline{d}dg)/\sqrt{2}$ hybrid. However, for the $\overline{s}sg$ hybrid, we find the sum rules are unstable. We also study nonzero width effects, which affect the mass prediction. The mixing effects between these two states are studied and we find QCD sum rules support the existence of a flavor singlet hybrid with mass at around 1.9 GeV. Finally, we study the mixing effects between hybrid and glueball currents. The mixing between the $(\overline{u}ug+\overline{d}dg)/\sqrt{2}(\overline{s}sg)$ and the glueball causes two states, one in the region 1.4–1.8 GeV (1.4–2.2 GeV), and the other in the range 1.8–2.2 GeV (2.2–2.6 GeV).

We develop a nonadiabatic perturbation theory for oscillations involving an arbitrary number of neutrino and antineutrino species, including the possibility of lepton-number violation which we treat as a small effect. We interpret the physics of such an approach for the one generation case by introducing the notion of adiabaticity for neutrino and antineutrino oscillations in analogy to flavor oscillations. We find that in a $CP$-odd matter environment a small lepton-number violation in vacuo can be enhanced. Eventually, we apply the perturbation theory to the two generation case and work out an example for manifestations of lepton-number violation, which can be solved both perturbatively as well as analytically thereby further clarifying the nature of the perturbation expansion.

We discuss a refined scenario of standard big bang nucleosynthesis (BBN) allowing for nonthermal nuclear reactions in the primordial plasma. These reactions are naturally triggered in the early Universe by fast particles $(n,p,t,{}^3\mathrm{He},\alpha )$ generated in the $t(d,n)\alpha$, $d(d,n){}^3\mathrm{He}$, $d(d,p)t$, and ${}^3\mathrm{He}(d,p)\alpha$ processes. We take into account the nonthermal channels for reactions between nuclei with $A⩽7$ (of the standard BBN network) and consider new processes, such as nucleon-induced breakups of fragile $d$, ${}^{6,7}\mathrm{Li}$, and ${}^7\mathrm{Be}$. It is shown that fast neutrons—the most abundant and hot nonthermal plasma species—can effectively maintain some reactions as the Universe cools. Depending on the type of an individual reaction, these neutrons can increase the reaction rate coefficient $N_{\mathrm{A}}⟨\sigma v⟩$ by a few percent (for exoergic resonant processes) and orders of magnitude (for endoergic processes, such as the breakups and some reverse reactions). However, the individual nonthermal effects prove to be insufficient to influence the whole reaction kinetics and significantly change the predictions of thermal BBN. The nonthermal corrections to element abundances are found to be 0.10% (for T), $-0.01\%$ (for ${}^3\mathrm{He}$), $-0.02\%$ (for ${}^7\mathrm{Li}$), and 0.36%–0.60% (for CNO elements).

We investigate static inhomogeneous charged planar black hole solutions of the Einstein-Maxwell system in an asymptotically anti-de Sitter spacetime. Within the framework of linear perturbations, the solutions are numerically and analytically constructed from the Reissner-Nordström-anti-de Sitter black hole solution. The perturbation analysis predicts that the Cauchy horizon always disappears for any wavelength perturbation, supporting the strong cosmic censorship conjecture. For extremal black holes, we analytically show that an observer freely falling into the black hole feels infinite tidal force at the horizon for any long wavelength perturbation, even though the Kretschmann scalar curvature invariant remains small.