We consider the Higgs boson signals from pair production at the LHC within the framework of the minimal supersymmetric standard model (MSSM) in the nondecoupling (low-$m_A$) region. In light of the recent observation of a SM-like Higgs boson, we argue that the exploration for Higgs pair production at the LHC is a crucial next step to probe the MSSM Higgs sector. We emphasize that the production of $H^{\pm }{A}^0$ and $H^{+}{H}^{-}$ depends only on the electroweak gauge couplings while all the leading Higgs production channels via gluon fusion, vector-boson fusion, and Higgsstrahlung depend on additional free Higgs sector parameters. In the nondecoupling region, the five MSSM Higgs bosons are all relatively light and pair production signals may be accessible. We find that at the 8 TeV LHC, a $5\sigma$ signal for $H^{\pm }{A}^0$, $H^{\pm }{h}^0\to {\tau }^{\pm }\nu b\overline{b}$ and $H^{+}{H}^{-}\to {\tau }^{+}\nu {\tau }^{-}\nu$ are achievable with an integrated luminosity of $7(11){\mathrm{fb}}^{-1}$ and $24(48){\mathrm{fb}}^{-1}$, respectively for $m_A=95(130)\mathrm{GeV}$. At the 14 TeV LHC, a $5\sigma$ signal for these two channels would require as little as $4(7){\mathrm{fb}}^{-1}$ and $10(19){\mathrm{fb}}^{-1}$, respectively.

We show that the Cornwall-Jackiw-Tomboulis thermodynamic potential of dynamical quark models with a quark propagator represented by complex conjugate mass poles inevitably exhibits thermodynamic instabilities. We find that the minimal coupling of the quark sector to a Polyakov loop potential can strongly suppress but not completely remove such instabilities. This general effect is explicitly demonstrated in the framework of a covariant, chirally symmetric, effective quark model.

We show that there are two reasons why the partial width for the transition ${\Gamma }_1({\rm Y}(3S)\to \gamma +{\chi }_{b1}(1P))$ is suppressed. First, the spin-averaged matrix element $\overline{I(3S|r|1P_J)}$ is small, being equal to $0.023{\mathrm{GeV}}^{-1}$ in our relativistic calculations. Secondly, the spin-orbit splittings produce relatively large contributions, giving $I(3S|r|1P_2)=0.066{\mathrm{GeV}}^{-1}$, while due to a large cancellation the matrix element $I(3S|r|1P_1)=-0.020{\mathrm{GeV}}^{-1}$ is small and negative; at the same time the magnitude of $I(3S|r|1P_0)=-0.063{\mathrm{GeV}}^{-1}$ is relatively large. These matrix elements give rise to the following partial widths: ${\Gamma }_2({\rm Y}(3S)\to \gamma +{\chi }_{b2}(1P))=212\mathrm{eV}$, ${\Gamma }_0({\rm Y}(3S)\to \gamma +{\chi }_{b0}(1P))=54\mathrm{eV}$, which are in good agreement with the CLEO and BABAR data, and also to ${\Gamma }_1({\rm Y}(3S)\to \gamma +{\chi }_{b1}(1P))=13\mathrm{eV}$, which satisfies the BABAR limit, ${\Gamma }_1(\exp )<22\mathrm{eV}$.

We study the process $\gamma \gamma \to J/\psi \omega$ using a data sample of $519.2{\mathrm{fb}}^{-1}$ recorded by the BABAR detector at SLAC at the PEP-II asymmetric-energy $e^{+}{e}^{-}$ collider at center-of-mass energies near the ${\rm Y}(nS)$ ($n=2,3,4$) resonances. We confirm the existence of the charmoniumlike resonance $X(3915)$ decaying to $J/\psi \omega$ with a significance of 7.6 standard deviations, including systematic uncertainties, and measure its mass $(3919.4\pm 2.2\pm 1.6)\mathrm{MeV}/c^2$ and width $(13\pm 6\pm 3)\mathrm{MeV}$, where the first uncertainty is statistical and the second systematic. A spin-parity analysis supports the assignment $J^P=0^{+}$ and therefore the identification of the signal as due to the ${\chi }_{c0}(2P)$ resonance. In this hypothesis we determine the product between the two-photon width and the final state branching fraction to be $(52\pm 10\pm 3)\mathrm{eV}$.

The classical description of synchrotron radiation fails at large Lorentz factors, $\gamma$, for relativistic electrons crossing strong transverse magnetic fields $B$. In the rest frame of the electron this field is comparable to the so-called critical field $B_0=4.414\times {10}^9\mathrm{T}$. For $\chi =\gamma B/B_0\simeq 1$ quantum corrections are essential for the description of synchrotron radiation to conserve energy. With electrons of energies 10–150 GeV penetrating a germanium single crystal along the $⟨110⟩$ axis, we have experimentally investigated the transition from the regime where classical synchrotron radiation is an adequate description, to the regime where the emission drastically changes character; not only in magnitude, but also in spectral shape. The spectrum can only be described by quantum synchrotron radiation formulas. Apart from being a test of strong-field quantum electrodynamics, the experimental results are also relevant for the design of future linear colliders where beamstrahlung—a closely related process—may limit the achievable luminosity.

We revisit the chiral magnetic effect (CME) using the chiral Lagrangian. We demonstrate that the electric-current formula of the CME is derived immediately from the contact part of the Wess-Zumino-Witten action. This implies that the CME could be, if observed, a signature for the local parity violation, but a direct evidence for neither quark deconfinement nor chiral restoration. We also discuss the reverse chiral magnetic Primakoff effect, i.e., the real photon production through the vertex associated with the CME, which is kinematically possible for space-time inhomogeneous configurations of magnetic fields and the strong $\theta$ angle. We make a qualitative estimate for the photon yield to find that it is comparable to the thermal photon.

Using a $478{\mathrm{pb}}^{-1}$ data sample collected with the BESIII detector operating at the Beijing Electron Positron Collider storage ring at a center-of-mass energy of $\sqrt{s}=4.009\mathrm{GeV}$, the production of $e^{+}{e}^{-}\to \eta J/\psi$ is observed for the first time with a statistical significance of greater than $10\sigma$. The Born cross section is measured to be $(32.1\pm 2.8\pm 1.3)\mathrm{pb}$, where the first error is statistical and the second systematic. Assuming the $\eta J/\psi$ signal is from a hadronic transition of the $\psi (4040)$, the fractional transition rate is determined to be $\mathcal{B}(\psi (4040)\to \eta J/\psi )=(5.2\pm 0.5\pm 0.2\pm 0.5)\times {10}^{-3}$, where the first, second, and third errors are statistical, systematic, and the uncertainty from the $\psi (4040)$ resonant parameters, respectively. The production of $e^{+}{e}^{-}\to {\pi }^{0}J/\psi$ is searched for, but no significant signal is observed, and $\mathcal{B}(\psi (4040)\to {\pi }^{0}J/\psi )<2.8\times {10}^{-4}$ is obtained at the 90% confidence level.

We compute the hadronic matrix elements of the four-quark operators needed for the study of $K^0-{\overline{K}}^0$ mixing beyond the Standard Model (SM). We use $n_f=2+1$ flavors of domain-wall fermion that exhibit good chiral-flavor symmetry. The renormalization is performed nonperturbatively through the RI-MOM scheme and our results are converted perturbatively to $\overline{\mathrm{MS}}$. The computation is performed on a single lattice spacing $a\sim 0.086$ with a lightest unitary pion mass of 290 MeV. The various systematic errors, including the discretization effects, are estimated and discussed. Our results confirm a previous quenched study, where large ratios of non-SM to SM matrix elements were obtained.

In the framework of the littlest Higgs model with $T$ parity, we study the $W_H$-pair production at the CERN Large Hadron Collider up to the QCD next-to-leading order (NLO). The kinematic distributions of final decay products and the theoretical dependence of the cross section on the factorization/renormalization scale are analyzed. We adopt the PROSPINO scheme in the QCD NLO calculations to avoid double counting and keep the convergence of the perturbative QCD description. Our numerical results show that the QCD NLO corrections significantly reduce the scale uncertainty, and enhance the leading order integrated cross section with a $K$ factor in the range of 1.10–1.22 (1.09–1.17) with the symmetry breaking scale $f$ varying from 400 GeV (400 GeV) to 1.5 TeV (1.0 TeV) at the 14 TeV (8 TeV) LHC. We find that it is possible to select the signal events of the $W_H$-pair production from the $pp\to W^{+}{W}^{-}\to e^{+}{\mu }^{-}{\nu }_e{\overline{\nu }}_{\mu }+X$ background with a high ratio of signature over background by taking proper lower limits on transverse momenta, invariant mass of the final charged leptons and the missing transverse momentum.

Results are presented from a search for the pair production of first- and second-generation scalar leptoquarks in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$. The data sample corresponds to an integrated luminosity of $5.0{\mathrm{fb}}^{-1}$, collected by the CMS detector at the LHC. The search signatures involve either two charged leptons of the same flavor (electrons or muons) and at least two jets or a single charged lepton (electron or muon), missing transverse energy, and at least two jets. If the branching fraction of the leptoquark decay into a charged lepton and a quark is assumed to be $\beta =1$, leptoquark pair production is excluded at the 95% confidence level for masses below 830 GeV and 840 GeV for the first and second generations, respectively. For $\beta =0.5$, masses below 640 GeV and 650 GeV are excluded. These limits are the most stringent to date.

We establish improved upper limits on branching fractions for $B^0$ decays to final states where the decay products are purely invisible (i.e., no observable final state particles) and for final states where the only visible product is a photon. Within the Standard Model, these decays have branching fractions that are below the current experimental sensitivity, but various models of physics beyond the Standard Model predict significant contributions for these channels. Using $471\times {10}^6$ $B\overline{B}$ pairs collected at the ${\rm Y}(4S)$ resonance by the BABAR experiment at the PEP-II $e^{+}{e}^{-}$ storage ring at the SLAC National Accelerator Laboratory, we establish upper limits at the 90% confidence level of $2.4\times {10}^{-5}$ for the branching fraction of $B^0\to \mathrm{\text{invisible}}$ and $1.7\times {10}^{-5}$ for the branching fraction of $B^0\to \mathrm{\text{invisible}}+\gamma$.

The evaluation of the determinant of the Laplacian defined on two dimensional regions of various shapes is an essential ingredient in calculating the scattering amplitudes of strings. In lightcone parameterization the regions are rectangular in shape with several slits of different length and location cut parallel to the $\tau$ axis of the rectangle. This paper offers a compendium of applications of the methods of Kac and McKean and Singer to the calculation of such worldsheet determinants. Particular attention is paid to the effect of corners on the determinants. The effect of corners joining edges with like boundary conditions is implicit in Kac’s results. We discuss the generalization to a corner joining a Dirichlet edge to a Neumann edge, and apply it to a scattering amplitude involving D-branes.

There exist two deformations of standard electrodynamics which describe Lorentz symmetry violation in the photon sector: $CPT$-odd Maxwell-Chern-Simons theory and $CPT$-even modified Maxwell theory. In this article, we focus on the parity-odd nonbirefringent sector of modified Maxwell theory. It is coupled to a standard Dirac theory of massive spin-$1/2$ fermions resulting in a modified quantum electrodynamics (QED). This theory is discussed with respect to properties such as microcausality and unitarity, where it turns out that these hold. Furthermore, a priori, the limit of the theory for vanishing Lorentz-violating parameters seems to be discontinuous. The modified photon polarization vectors are interweaved with preferred spacetime directions defined by the theory, and one vector even has a longitudinal part. That structure remains in the limit mentioned. Since it is not clear whether or not this behavior is a gauge artifact, the cross section for a physical process—modified Compton scattering—is calculated numerically. Despite the numerical instabilities occurring for scattering of unpolarized electrons off polarized photons in the second physical polarization state, it is shown that for Lorentz-violating parameters much smaller than one, the modified cross sections approach the standard QED results. Analytical investigations strengthen the numerical computations. Hence, the theory proves to be consistent, at least with regard to the investigations performed. This leads to the interesting outcome of the modification being a well-defined parity-odd extension of QED.

We present a next-to-leading-order calculation of electron mass renormalization in light-front quantum electrodynamics using old-fashioned time-ordered perturbation theory. We show that the true infrared divergences in $\delta m^2$ get canceled up to $O(e^4)$ if one uses the coherent state basis instead of the Fock basis to calculate the transition matrix elements.

We analyze the massive four-dimensional scalar multiplet in reformulated projective $N=2$ superspace (hyperspace) from both four-dimensional and six-dimensional perspectives.

Within the superfield approach, we formulate the superfield supersymmetric ether-like Lorentz-breaking models, both in three- and four-dimensional cases.

Three decades of work on the quantum field equations of pure Yang-Mills theory have distilled two families of solutions in Landau gauge. Both coincide for high (Euclidean) momentum with known perturbation theory, and both predict an infrared suppressed transverse gluon propagator, but whereas the solution known as scaling features an infrared power law for the gluon and ghost propagators, the massive solution rather describes the gluon as a vector boson that features a finite Debye screening mass. In this work we examine the gauge dependence of these solutions by adopting stochastic quantization. What we find, in four dimensions and in a rainbow approximation, is that stochastic quantization supports both solutions in Landau gauge but the scaling solution abruptly disappears when the parameter controlling the drift force is separated from zero (soft gauge-fixing), recovering only the perturbative propagators; the massive solution seems to survive the extension outside Landau gauge. These results are consistent with the scaling solution being related to the existence of a Gribov horizon, with the massive one being more general. We also examine the effective action in Faddeev-Popov quantization that generates the rainbow and we find, for a bare vertex approximation, that the massive-type solutions minimize the quantum effective action.

We study some exact and approximate solutions of Einstein’s equations that can be used to describe the gravitational field of astrophysical compact objects in the limiting case of slow rotation and slight deformation. First, we show that none of the standard models obtained by using Fock’s method can be used as an interior source for the approximate exterior Kerr solution. We then use Fock’s method to derive a generalized interior solution, and also an exterior solution that turns out to be equivalent to the exterior Hartle-Thorne approximate solution that, in turn, is equivalent to an approximate limiting case of the exact Quevedo-Mashhoon solution. As a result we obtain an analytic approximate solution that describes the interior and exterior gravitational field of a slowly rotating and slightly deformed astrophysical object.