We propose a novel scheme to measure nonlinear effects in electrodynamics arising from QED corrections. Our theoretical starting point is the Heisenberg-Euler-Schwinger effective Lagrangian which predicts that a vacuum with a strong static electromagnetic field turns birefringent. We propose to employ a pulsed laser to create Compton backscattered photons off a high energy electron beam. These photons will pass through a strong static magnetic field, which according to the QED prediction changes the state of polarization of the radiation—an effect proportional to the photon energy. This change will be measured by using an aligned single crystal, since a large difference in the pair production cross sections at high energies can be achieved with proper orientation of the crystal. As an example we will consider the machine, LHeC, under consideration at CERN as the source of these electrons, and an LHC dipole magnet as the source of the strong static magnetic field. In the proposed experimental setup the birefringence effect will be manifested in a difference in the number of pairs created in the polarizer crystal as the initial laser light has a varying state of polarization, achieved with a rotating quarter wave plate. This will be seen as a clear peak in the Fourier transform spectrum of the pair-production rate signal, which can be obtained with 3 hours of measurement. We also comment on the sensitivity of the experiment, to the existence of an axion, a hypothetical spin-0 particle that couples to two photons.

We perform detailed calculations of two-photon-exchange QED corrections to the cross section of pion electroproduction. The results are obtained with and without the soft-photon approximation; analytic expressions for the radiative corrections are derived. The relative importance of the two-photon correction is analyzed for the kinematics of several experiments at Jefferson Lab. A significant, over 20%, effect due to two-photon exchange is predicted for the backward angles of electron scattering at large transferred momenta.

We predict the neutrino-nucleon cross section at ultrahigh energies relevant in connection with the search for high-energy cosmic neutrinos. Our investigation, employing the color-dipole picture, among other things, allows us to quantitatively determine which fraction of the ultrahigh-energy neutrino-nucleon cross section stems from the saturation vs the color-transparency region. We disagree with various results in the literature that predict a strong suppression of the neutrino-nucleon cross section at neutrino energies above $E\cong {10}^9\mathrm{GeV}$. Suppression in the sense of a diminished increase of the neutrino-nucleon cross section with energy only starts to occur at neutrino energies beyond $E\cong {10}^{14}\mathrm{GeV}$.

We combine searches by the CDF and D0 Collaborations for the standard model Higgs boson with mass in the range $90–200\mathrm{GeV}/c^2$ produced in the gluon-gluon fusion, $WH$, $ZH$, $t\overline{t}H$, and vector boson fusion processes, and decaying in the $H\to b\overline{b}$, $H\to W^{+}{W}^{-}$, $H\to ZZ$, $H\to {\tau }^{+}{\tau }^{-}$, and $H\to \gamma \gamma$ modes. The data correspond to integrated luminosities of up to $10{\mathrm{fb}}^{-1}$ and were collected at the Fermilab Tevatron in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$. The searches are also interpreted in the context of fermiophobic and fourth generation models. We observe a significant excess of events in the mass range between 115 and $140\mathrm{GeV}/c^2$. The local significance corresponds to 3.0 standard deviations at $m_H=125\mathrm{GeV}/c^2$, consistent with the mass of the Higgs boson observed at the LHC, and we expect a local significance of 1.9 standard deviations. We separately combine searches for $H\to b\overline{b}$, $H\to W^{+}{W}^{-}$, $H\to {\tau }^{+}{\tau }^{-}$, and $H\to \gamma \gamma$. The observed signal strengths in all channels are consistent with the presence of a standard model Higgs boson with a mass of $125\mathrm{GeV}/c^2$.

We present a combination of searches for the standard model Higgs boson using the full CDF run II data set, which corresponds to an integrated luminosity of $9.45–10.0{\mathrm{fb}}^{-1}$ collected from $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collisions at the Fermilab Tevatron. The searches consider Higgs boson production from gluon-gluon fusion, vector-boson fusion, and associated production with either a $W$ or $Z$ boson or a $t\overline{t}$ pair. Depending on the production mode, Higgs boson decays to $W^{+}{W}^{-}$, $ZZ$, $b\overline{b}$, ${\tau }^{+}{\tau }^{-}$, and $\gamma \gamma$ are examined. We search for a Higgs boson with masses ($m_H$) in the range $90–200\mathrm{GeV}/c^2$. In the absence of a signal, we expect based on combined search sensitivity to exclude at the 95% credibility level the mass regions $90<m_H<94\mathrm{GeV}/c^2$, $96<m_H<106\mathrm{GeV}/c^2$, and $153<m_H<175\mathrm{GeV}/c^2$. The observed exclusion regions are $90<m_H<102\mathrm{GeV}/c^2$ and $149<m_H<172\mathrm{GeV}/c^2$. A moderate excess of signal-like events relative to the background expectation at the level of 2.0 standard deviations is present in the data for the $m_H=125\mathrm{GeV}/c^2$ search hypothesis. We also present interpretations of the data within the context of a fermiophobic model and an alternative standard model incorporating a fourth generation of fermions. Finally, for the hypothesis of a new particle with mass $125\mathrm{GeV}/c^2$, we constrain the coupling strengths of the new particle to $W^{\pm }$ bosons, $Z$ bosons, and fermions.

We present a search for a standard model Higgs boson decaying to two $W$ bosons that decay to leptons using the full data set collected with the CDF II detector in $\sqrt{s}=1.96\mathrm{TeV}$ $p\overline{p}$ collisions at the Fermilab Tevatron, corresponding to an integrated luminosity of $9.7{\mathrm{fb}}^{-1}$. We obtain no evidence for production of a standard model Higgs boson with mass between 110 and $200\mathrm{GeV}/c^2$, and place upper limits on the production cross section within this range. We exclude standard model Higgs boson production at the 95% confidence level in the mass range between 149 and $172\mathrm{GeV}/c^2$, while expecting to exclude, in the absence of signal, the range between 155 and $175\mathrm{GeV}/c^2$. We also interpret the search in terms of standard model Higgs boson production in the presence of a fourth generation of fermions and within the context of a fermiophobic Higgs boson model. For the specific case of a standard-model-like Higgs boson in the presence of fourth-generation fermions, we exclude at the 95% confidence level Higgs boson production in the mass range between 124 and $200\mathrm{GeV}/c^2$, while expecting to exclude, in the absence of signal, the range between 124 and $221\mathrm{GeV}/c^2$.

We perform a combination of searches for standard model Higgs boson production in $p\overline{p}$ collisions recorded by the D0 detector at the Fermilab Tevatron Collider at a center of mass energy of $\sqrt{s}=1.96\mathrm{TeV}$. The different production and decay channels have been analyzed separately, with integrated luminosities of up to $9.7{\mathrm{fb}}^{-1}$ and for Higgs boson masses $90\le M_H\le 200\mathrm{GeV}$. We combine these final states to achieve optimal sensitivity to the production of the Higgs boson. We also interpret the combination in terms of models with a fourth generation of fermions, and models with suppressed Higgs boson couplings to fermions. The result excludes a standard model Higgs boson at 95% C.L. in the ranges $90<M_H<101\mathrm{GeV}$ and $157<M_H<178\mathrm{GeV}$, with an expected exclusion of $155<M_H<175\mathrm{GeV}$. In the range $120<M_H<145\mathrm{GeV}$, the data exhibit an excess over the expected background of up to 2 standard deviations, consistent with the presence of a standard model Higgs boson of mass 125 GeV.

We present a search for the standard model Higgs boson produced in association with a $Z$ boson in $9.7{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions collected with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s}=1.96\mathrm{TeV}$. Selected events contain one reconstructed $Z\to e^{+}{e}^{-}$ or $Z\to {\mu }^{+}{\mu }^{-}$ candidate and at least two jets, including at least one jet likely to contain a $b$ quark. To validate the search procedure, we also measure the cross section for $ZZ$ production and find that it is consistent with the standard model expectation. We set upper limits at the 95% C.L. on the product of the $ZH$ production cross section and branching ratio $\mathcal{B}(H\to b\overline{b})$ for Higgs boson masses $90\le M_H\le 150\mathrm{GeV}$. The observed (expected) limit for $M_H=125\mathrm{GeV}$ is a factor of 7.1 (5.1) larger than the standard model prediction.

We present a search for Higgs bosons in multilepton final states in $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ recorded with the D0 detector at the Fermilab Tevatron Collider, using the full Run II data set with integrated luminosities of up to $9.7{\mathrm{fb}}^{-1}$. The multilepton states considered are $ee\mu$, $e\mu \mu$, $\mu {\tau }_h{\tau }_h$, and like-charge $e^{\pm }{\mu }^{\pm }$ pairs. These channels directly probe the HVV ($V=W$, $Z$) coupling of the Higgs boson in production and decay. The $\mu {\tau }_h{\tau }_h$ channel is also sensitive to $H\to {\tau }^{+}{\tau }^{-}$ decays. Upper limits at the 95% C.L on the rate of standard model Higgs boson production are derived in the mass range $100\le M_H\le 200\mathrm{GeV}$. The expected and observed limits are a factor of 6.3 and 8.4 above the predicted standard model cross section at $M_H=125\mathrm{GeV}$. We also interpret the data in a fermiophobic Higgs boson model.

We present, in detail, a search for the standard model Higgs boson, $H$, in final states with a charged lepton (electron or muon), missing energy, and two or more jets in data corresponding to $9.7{\mathrm{fb}}^{-1}$ of integrated luminosity collected at a center-of-mass energy of $\sqrt{s}=1.96\mathrm{TeV}$ with the D0 detector at the Fermilab Tevatron $p\overline{p}$ Collider. The search uses $b$-jet identification to categorize events for improved signal versus background separation and is sensitive to associated production of the $H$ with a $W$ boson, $WH\to \ell \nu b\overline{b}$; gluon fusion with the Higgs decaying to $W$-boson pairs, $H\to WW\to \ell \nu jj$; and associated production with a vector boson where the Higgs decays to $W$-boson pairs, $VH\to VWW\to \ell \nu jjjj$ production (where $V=W$ or $Z$). We observe good agreement between data and expected background. We test our method by measuring $WZ$ and $ZZ$ production with $Z\to b\overline{b}$ and find production rates consistent with the standard model prediction. For a Higgs boson mass of 125 GeV, we set a 95% C.L. upper limit on the production of a standard model Higgs boson of $5.8\times {\sigma }_{\mathrm{SM}}$, where ${\sigma }_{\mathrm{SM}}$ is the standard model Higgs boson production cross section, while the expected limit is $4.7\times {\sigma }_{\mathrm{SM}}$. We also interpret the data considering models with fourth generation fermions, or a fermiophobic Higgs boson.

We present a search for a Higgs boson decaying into a pair of photons based on $9.6{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions at $\sqrt{s}=1.96\mathrm{TeV}$ collected with the D0 detector at the Fermilab Tevatron Collider. The search employs multivariate techniques to discriminate signal from the nonresonant background and is separately optimized for a standard model and a fermiophobic Higgs boson. No significant excess of data above the background prediction is observed and upper limits on the product of the cross section and branching fraction are derived at the 95% confidence level as a function of Higgs boson mass. For a standard model Higgs boson with mass of 125 GeV, the observed (expected) upper limits are a factor of 12.8 (8.7) above the standard model prediction. The existence of a fermiophobic Higgs boson with mass in the 100–113 GeV range is excluded at the 95% confidence level.

We present a search for the Higgs boson in final states with two oppositely charged leptons and large missing transverse energy as expected in $H\to WW\to \ell \nu {\ell }^{\prime }{\nu }^{\prime }$ decays. The events are selected from the full Run II data sample of $9.7{\mathrm{fb}}^{-1}$ of $p\overline{p}$ collisions collected with the D0 detector at the Fermilab Tevatron Collider at $\sqrt{s}=1.96\mathrm{TeV}$. To validate our search methodology, we measure the nonresonant $WW$ production cross section and find ${\sigma }_{WW}=11.6\pm 0.7\mathrm{pb}$, in agreement with the standard model prediction. In the Higgs boson search, no significant excess above the background expectation is observed. Upper limits at the 95% confidence level on the Higgs boson production cross section are therefore derived. Within the standard model, the Higgs boson mass range $159<M_H<176\mathrm{GeV}$ is excluded while the expected exclusion sensitivity is $156<M_H<172\mathrm{GeV}$. For a mass hypothesis of $M_H=125\mathrm{GeV}$, we exclude Higgs boson production cross sections 4.1 times larger than the standard model expectation, which is compatible with the presence of a Higgs boson at this mass. Within a theoretical framework with a fourth generation of fermions, the mass range $125<M_H<218\mathrm{GeV}$ is excluded. The search results are also interpreted in the context of fermiophobic Higgs boson couplings, which yields an exclusion of fermiophobic Higgs boson production cross sections 3.1 times larger than the expectation for $M_H=125\mathrm{GeV}$.

We present a search for the standard model Higgs boson in final states with an electron or muon and a hadronically decaying tau lepton in association with two or more jets using $9.7{\mathrm{fb}}^{-1}$ of Run II Fermilab Tevatron Collider data collected with the D0 detector. The analysis is sensitive to Higgs boson production via gluon fusion, associated vector boson production, and vector boson fusion, followed by the Higgs boson decay to tau lepton pairs or to $W$ boson pairs. The ratios of 95% C.L. upper limits on the cross section times branching ratio to those predicted by the standard model are obtained for orthogonal subsamples that are enriched in either $H\to \tau \tau$ decays or $H\to WW$ decays, and for the combination of these subsample limits. The observed and expected limit ratios for the combined subsamples at a Higgs boson mass of 125 GeV are 11.3 and 9.0, respectively.

In this paper we discuss the (anti)BRST symmetries and $W$-algebra of higher derivative theories of relativistic particles satisfying general gauge conditions. Using this formalism, the connection between the (anti)BRST symmetries and $W$-algebra for the massless particle with rigidity is established. Incidentally, the full $W$-algebra emerges only when the anti-BRST transformations are considered in tandem with the BRST ones. Further, the BRST symmetry is made finite and coordinate dependent. We show that such finite coordinate-dependent BRST symmetry changes the BRST invariant gauge-fixing fermion within the functional integration. This is exploited to connect two different arbitrary gauge conditions.

We find coordinates, the metric tensor, the inverse metric tensor and the Laplace-Beltrami operator for the orbit space of Hamiltonian SU(2) gauge theory on a finite, rectangular lattice, with open boundary conditions. This is done using a complete axial gauge fixing.

We demonstrate that the stability of the semilocal vortex can be significantly improved by the presence of a dilatonic coupling of the form $e^{\frac{q|\Phi {|}^2}{{\eta }^2}}{F}_{\mu \nu }{F}^{\mu \nu }$ with $q>0$ where $\eta$ is the scale of symmetry breaking that gives rise to the vortex. For $q=0$ we obtain the usual embedded (semilocal) Nielsen–Olesen vortex. We find the stability region of the parameter $\beta \equiv (\frac{m_{\Phi }}{m_A}{)}^2$ ($m_{\Phi }$ and $m_A$ are the masses of the scalar and gauge fields, respectively). We show that the stability region of $\beta$ is $0<\beta <{\beta }_{\max }(q)$ where ${\beta }_{\max }(q=0)=1$ (as expected) and ${\beta }_{\max }(q)$ is an increasing function of $q$. This result may have significant implications for the stability of the electroweak vortex in the presence of a dilatonic coupling (dilatonic electroweak vortex).

We analyze the question of possible quantum corrections in the entropic scenario of emergent gravity. Using a fuzzy sphere as a natural quasiclassical approximation for the spherical holographic screen, we analyze whether it is possible to observe such corrections to Newton’s law in principle. The main outcome of our analysis is that without the complete knowledge of the quantum dynamics of the microscopic degrees of freedom, any Plank-scale correction cannot be trusted. Some perturbative corrections might produce reliable predictions well below the Plank scale.

QCD at finite isospin chemical potential ${\mu }_{\mathrm{I}}$ possesses a positively definite fermion determinant, and the lattice simulation can be successfully performed. While the two-flavor effective models may be sufficient to describe the phenomenon of pion condensation, it is interesting to study the roles of the strangeness degree of freedom and the ${\mathrm{U}}_{\mathrm{A}}(1)$ anomaly. In this paper, we present a systematic study of the three-flavor Nambu–Jona-Lasinio model with a Kobayashi-Maskawa-’t Hooft (KMT) term that mimics the ${\mathrm{U}}_{\mathrm{A}}(1)$ anomaly at finite isospin chemical potential. In the mean-field approximation, the model predicts a phase transition from the vacuum to the pion superfluid phase, which takes place at ${\mu }_{\mathrm{I}}$ equal to the pion mass $m_{\pi }$. Due to the ${\mathrm{U}}_{\mathrm{A}}(1)$ anomaly, the strangeness degree of freedom couples to the light quark degrees of freedom and the strange quark effective mass depends on the pion condensate. However, the strange quark condensate and the strange quark effective mass change slightly in the pion superfluid phase, which verifies the validity of the two-flavor models. The effective four-fermion interaction of the Kobayashi-Maskawa-’t Hooft term in the presence of the pion condensation is constructed. Due to the ${\mathrm{U}}_{\mathrm{A}}(1)$ anomaly, the pion condensation generally induces scalar-pseudoscalar interaction. The Bethe-Salpeter equation for the mesonic excitations is established, and the meson mass spectra are obtained at finite isospin chemical potential and temperature. Finally, the general expression for the topological susceptibility $\chi$ at finite isospin chemical potential ${\mu }_{\mathrm{I}}$ is derived. In contrast to the finite temperature effect which suppresses $\chi$, the isospin density effect leads to an enhancement of $\chi$.

The interpretation of the Higgs signal at $\sim 126\mathrm{GeV}$ within the Minimal Supersymmetric Standard Model (MSSM) depends crucially on the predicted properties of the other Higgs states of the model, as the mass of the charged Higgs boson, $M_{H^{\pm }}$. This mass is calculated in the Feynman diagrammatic approach within the MSSM with real parameters. The result includes the complete one-loop contributions and the two-loop contributions of $\mathcal{O}({\alpha }_t{\alpha }_s)$. The one-loop contributions lead to sizable shifts in the $M_{H^{\pm }}$ prediction, reaching up to $\sim 8\mathrm{GeV}$ for relatively small values of $M_A$. Even larger effects can occur depending on the sign and size of the $\mu$ parameter that enters the corrections affecting the relation between the bottom-quark mass and the bottom Yukawa coupling. The two-loop $\mathcal{O}({\alpha }_t{\alpha }_s)$ terms can shift $M_{H^{\pm }}$ by more than 2 GeV. The two-loop contributions amount to typically about 30% of the one-loop corrections for the examples that we have studied. These effects can be relevant for precision analyses of the charged MSSM Higgs boson.

We apply nonperturbative renormalization to bilinears composed of improved staggered fermions. We explain how to generalize the method to staggered fermions in a way that is consistent with the lattice symmetries and introduce a new type of lattice bilinear that transforms covariantly and avoids mixing. We derive the consequences of lattice symmetries for the propagator and vertices. We implement the method numerically for hypercubic-smeared (HYP-smeared) and asqtad valence fermion actions, using lattices with asqtad sea quarks generated by the MILC Collaboration. We compare the nonperturbative results so obtained to those from perturbation theory, using both scale-independent ratios of bilinears (of which we calculate 26) and the scale-dependent bilinears themselves. Overall, we find that one-loop perturbation theory provides a successful description of the results for HYP-smeared fermions if we allow for a truncation error of roughly the size of the square of the one-loop term (for ratios) or of size $\mathcal{O}(1)\times {\alpha }^2$ (for the bilinears themselves). Perturbation theory is, however, less successful at describing the nonperturbative asqtad results.