The top quark pair production cross section is measured in dilepton events with one electron or muon, and one hadronically decaying $\tau$ lepton from the decay $t\overline{t}\to (\ell {\nu }_{\ell })({\tau }_{\mathrm{h}}{\nu }_{\tau })\mathrm{b}\overline{\mathrm{b}}$, ($\ell =e,\mu$). The data sample corresponds to an integrated luminosity of $2.0{\mathrm{fb}}^{-1}$ for the electron channel and $2.2{\mathrm{fb}}^{-1}$ for the muon channel, collected by the CMS detector at the LHC. This is the first measurement of the $t\overline{t}$ cross section explicitly including $\tau$ leptons in proton-proton collisions at $\sqrt{s}=7\mathrm{TeV}$. The measured value ${\sigma }_{t\overline{t}}=143\pm 14(\mathrm{stat})\pm 22(\mathrm{syst})\pm 3(\mathrm{lumi})\mathrm{pb}$ is consistent with the standard model predictions.

We present strongly improved electroweak precision constraints on the split-UED (universal extra dimension) model. We find that the dominating effect arises from contributions to the muon decay rate by the exchange of even-numbered $W$ boson Kaluza-Klein modes at tree level, which so far have not been discussed in the context of UED models. The constraints on the split-UED parameter space are translated into bounds on the mass difference of the first Kaluza-Klein mode of fermions and the lightest Kaluza-Klein mode, which will be tested at the LHC.

We compute the energy density radiated by a quark undergoing circular motion in strongly coupled $\mathcal{N}=4$ supersymmetric Yang-Mills plasma. If it were in vacuum, this quark would radiate a beam of strongly coupled radiation whose angular distribution has been characterized and is very similar to that of synchrotron radiation produced by an electron in circular motion in electrodynamics. Here, we watch this beam of gluons getting quenched by the strongly coupled plasma. We find that a beam of gluons of momenta $\sim q\gg \pi T$ is attenuated rapidly, over a distance $\sim q^{1/3}(\pi T{)}^{-4/3}$ in a plasma with temperature $T$. As the beam propagates through the plasma at the speed of light, it sheds trailing sound waves with momenta $\lesssim \pi T$. Presumably these sound waves would thermalize in the plasma if they were not hit soon after their production by the next pulse of gluons from the lighthouselike rotating quark. At larger and larger $q$, the trailing sound wave becomes less and less prominent. The outward-going beam of gluon radiation itself shows no tendency to spread in angle or to shift toward larger wavelengths, even as it is completely attenuated. In this regard, the behavior of the beam of gluons which we analyze is reminiscent of the behavior of jets produced in heavy ion collisions at the LHC which lose a significant fraction of their energy without appreciable change in their angular distribution or their momentum distribution as they plow through the strongly coupled quark-gluon plasma produced in these collisions.

A new mechanism of baryon-antibaryon production via nonperturbative double-pair creation in intermediate mesons is proposed, and the theory contains no fitting parameters. It is shown that near-threshold resonances are responsible for enhancements in electroproduction cross sections: $\psi (4S)$ for ${\Lambda }_c^{+}{\Lambda }_c^{-}$ and ${\rm Y}(6S)$ for ${\Lambda }_b{\overline{\Lambda }}_b$. An admixture of intermediate $D$-wave resonances produces angular dependence in the differential cross section and can explain unusual behavior of the ratio $G_E/G_M$ for the proton.

Using the superfield formalism and implementing the canonical noncommutativity, the Kählerian effective superpotential is evaluated in the three-dimensional noncommutative supersymmetric Chern-Simons–matter model at the two-loop order. The computation of the Kählerian effective superpotential is enough to determine whether the model can exhibit spontaneous (super)symmetry breaking. It is shown that the model possesses a spontaneous gauge symmetry broken phase, generating masses for the scalar and gauge superfields at the two-loop order. Just as for the commutative version, in the noncommutative case, the supersymmetry cannot be broken by radiative corrections via the Coleman-Weinberg mechanism.

Five-dimensional geometries with a linearly varying dilaton background arise as gravity duals of TeV little string theories and provide a solution of the hierarchy problem through extra dimensions. The unique Kaluza-Klein (KK) graviton spectrum has a mass gap on the order of the dilaton slope followed by a closely spaced discretum of states. We study in detail the graviton phenomenology in this scenario, allowing the dilaton slope to vary from the MeV to the TeV scale. When the dilaton slope is large enough so that individual KK resonances can be resolved at the LHC, several of them can be discovered simultaneously and allow for the linear dilaton geometry to be uniquely identified. For much smaller values of the dilaton slope, the LHC signatures become similar to the five-dimensional scenario of Arkani-Hamed, Dimopoulos and Dvali while relaxing the astrophysical and experimental constraints. Because of the mass gap, the KK modes are produced on shell and decay inside the LHC detector, modifying the diphoton and dilepton spectra at large invariant mass. Finally, we perform a similar analysis for the low-curvature Randall-Sundrum geometry. We present experimental limits and calculate the ultimate reach of a 14 TeV LHC for all the above scenarios.

We study cosmological constraints on metric $f(R)$ gravity models that are designed to reproduce the $\Lambda \mathrm{CDM}$ expansion history with modifications to gravity described by a supplementary cosmological freedom, the Compton wavelength parameter $B_0$. We conduct a Markov chain Monte Carlo analysis on the parameter space, utilizing the geometrical constraints from supernovae distances, the baryon acoustic oscillation distances, and the Hubble constant, along with all of the cosmic microwave background data, including the largest scales, its correlation with galaxies, and a probe of the relation between weak gravitational lensing and galaxy flows. The strongest constraints, however, are obtained through the inclusion of data from cluster abundance. Using all of the data, we infer a bound of $B_0<1.1\times {10}^{-3}$ at the 95% C.L.

We continue the study of physical fields for the background free 4D quantum gravity based on the Riegert-Wess-Zumino action, developed in [K. Hamada, Phys. Rev. D 85, 024028 (2012).]. The background free model is formulated in terms of a certain conformal field theory on $M^4$ in which conformal symmetry arises as gauge symmetry, namely, diffeomorphism invariance. In this paper, we construct the physical field operator corresponding to any integer power of Ricci scalar curvature in the context of the Becchi-Rouet-Stora-Tyupin quantization. We also discuss how to define the correlation function and its physical meanings.

We study a massive gravity theory which is Lorentz-violating all the way from ultraviolet to infrared energy scales. At short distances the theory breaks diffeomorphism invariance and time and space scale differently. Dynamical metric fields are introduced which, upon linearization over a Minkowski background, correspond to Lorentz-violating mass terms at large distances. We perform a scalar perturbation analysis and we show that with an appropriate choice of parameters, the theory is healthy without ghosts, tachyons, strong coupling problems, and instabilities.

The gravitational-wave signal from inspiralling neutron-star–neutron-star (or black-hole–neutron-star) binaries will be influenced by tidal coupling in the system. An important science goal in the gravitational-wave detection of these systems is to obtain information about the equation of state of neutron star matter via the measurement of the tidal polarizability parameters of neutron stars. To extract this piece of information will require accurate analytical descriptions both of the motion and the radiation of tidally interacting binaries. We improve the analytical description of the late inspiral dynamics by computing the next-to-next-to-leading–order relativistic correction to the tidal interaction energy. Our calculation is based on an effective-action approach to tidal interactions and on its transcription within the effective-one-body formalism. We find that second-order relativistic effects (quadratic in the relativistic gravitational potential $u=G(m_1+m_2)/(c^{2}r)$) significantly increase the effective tidal polarizability of neutron stars by a distance-dependent amplification factor of the form $1+{\alpha }_{1}u+{\alpha }_2{u}^2+\cdots$ where, say, for an equal-mass binary, ${\alpha }_1=5/4=1.25$ (as previously known) and ${\alpha }_2=85/14\simeq 6.07143$ (as determined here for the first time). We argue that higher-order relativistic effects will lead to further amplification, and we suggest a Padé-type way of resumming them. We recommend testing our results by comparing resolution-extrapolated numerical simulations of inspiralling binary neutron stars to their effective one-body description.

In this paper, we investigate thick branes with a nonminimally coupled background scalar field, whose solution is a single-kink or a double-kink. The effects of the nonminimal coupling constant $\xi$ on the structure of the thick branes and the localization of gravity, fermions, scalars, and vectors are discussed. It is shown that each brane will split into two sub-branes as increasing the nonminimal coupling constant $\xi$. By investigating the tensor perturbation equations of gravity and the general covariant Dirac equation of fermions, we find that both the gravity zero mode and left-chiral fermion zero mode are localized at the center of the single-kink branes and localized between the two sub-branes generated by the double kink, which indicates that the constant $\xi$ does not effect the localization of these zero modes. However, the zero mode of scalars is localized on each sub-brane (for both single-kink and double-kink branes) when $\xi$ is larger than its critical value ${\xi }_0$. The effects of the nonminimal coupling constant $\xi$ on the resonances of gravity and fermions with finite lifetime on the branes are also discussed.

We study numerical stability of different approaches to the discretization of a conformal decomposition of the Z4 formulation of general relativity. We demonstrate that in the linear, constant coefficient regime a novel discretization for tensors is formally numerically stable with a method of lines time integrator. We then perform a full set of “apples with apples” tests on the nonlinear system, and thus present numerical evidence that both the new and standard discretizations are, in some sense, numerically stable in the nonlinear regime. The results of the Z4c numerical tests are compared with those of Baumgarte-Shapiro-Shibata-Nakamura-Oohara-Kojima (BSSNOK) evolutions. We typically do not employ the Z4c constraint damping scheme and find that in the robust stability and gauge wave tests the Z4c evolutions result in lower constraint violation at the same resolution as the BSSNOK evolutions. In the gauge wave tests, we find that the Z4c evolutions maintain the desired convergence factor over many more light-crossing times than the BSSNOK tests. The difference in the remaining tests is marginal.

We forecast the ability of future cosmic microwave background and galaxy lensing surveys to constrain variations of the fine structure constant. We found that lensing data, as those expected from satellite experiments as Euclid could improve the constraint from future cosmic microwave background experiments leading to a $\Delta \alpha /\alpha =8\times {10}^{-4}$ accuracy. A variation of the fine structure constant $\alpha$ is strongly degenerate with the Hubble constant $H_0$ and with inflationary parameters as the scalar spectral index $n_s$. These degeneracies may cause significant biases in the determination of cosmological parameters if a variation in $\alpha$ as large as $\sim 0.5\%$ is present at the epoch of recombination.

During de Sitter inflation massless particles of minimally coupled scalar fields acquire a mass and a decay width thereby becoming quasiparticles. For bare massless particles nonperturbative infrared radiative corrections lead to a self-consistent generation of mass, for a quartic self-interaction $M\propto {\lambda }^{1/4}H$, and for a cubic self-interaction the mass is induced by the formation of a nonperturbative condensate leading to $M\propto {\lambda }^{1/3}{H}^{2/3}$. These radiatively generated masses restore de Sitter invariance and result in anomalous scaling dimensions of superhorizon fluctuations. We introduce a generalization of the nonperturbative Wigner-Weisskopf method to obtain the time evolution of quantum states that include the self-consistent generation of mass and regulate the infrared behavior. The infrared divergences are manifest as poles in $\Delta =M^2/3H^2$ in the single particle self-energies, leading to a rearrangement of the perturbative series nonanalytic in the couplings. A set of simple rules that yield the leading order infrared contributions to the decay width are obtained and implemented. The lack of kinematic thresholds entail that all particle states acquire a decay width, dominated by the emission and absorption of superhorizon quanta $\propto (\lambda /H{)}^{4/3}[H/k_{ph}(\eta ){]}^6$; $\lambda [H/k_{ph}(\eta ){]}^6$ for cubic and quartic couplings respectively to leading order in $M/H$. The decay of single particle quantum states hastens as their wave vectors cross the Hubble radius and their width is related to the highly squeezed limit of the bi- or trispectrum of scalar fluctuations respectively.

LISA is the upcoming space-based gravitational-wave detector. LISA Pathfinder, to be launched in the coming years, will be the in-flight test of the LISA arm, with a hardware (control scheme, sensors, and actuators) identical in design to LISA. LISA Pathfinder will collect a picture of all noise disturbances possibly affecting LISA, achieving the unprecedented pureness of geodesic motion of test masses necessary for the detection of gravitational waves. The first steps of both missions will crucially depend on a very precise calibration of the key system parameters. Moreover, robust parameters estimation has a fundamental importance in the correct assessment of the residual acceleration noise between the test masses, an essential part of the data preprocessing for LISA. In this paper, we present a maximum likelihood parameter estimation technique in time domain employed for system identification, being devised for this calibration, and show its proficiency on simulated data and validation through Monte Carlo realizations of independent noise runs. We discuss its robustness to nonstandard scenarios possibly arising during the real mission. Furthermore, we apply the same technique to data produced in missionlike fashion during operational exercises with a realistic simulator provided by European Space Agency. The result of the investigation is that parameter estimation is mandatory to avoid systematic errors in the estimated differential acceleration noise.

The contribution of the $R$-parity violating minimal supersymmetric standard model at the one-loop level to the ${}^{199}\mathrm{Hg}$ atomic electric dipole moment through $P$, $CP$-odd electron-nucleon ($e-N$) interaction is calculated. We show that the current experimental data of the ${}^{199}\mathrm{Hg}$ electric dipole moment give tighter constraints on some of the imaginary parts of $R$-parity violating coupling than those currently known. We add also the analysis of the $P$, $CP$-odd 4-quark interaction generated by $R$-parity violating interactions at the one-loop level, and discuss the possibility to constrain them in future experiments.

The production and decay of a new heavy vector boson, a chromophilic $Z^{\prime }$ vector boson, is described. The chromophilic $Z^{\prime }$ couples only to two gluons, but its two-body decays are absent, leading to a dominant decay mode of $Z^{\prime }\to q\overline{q}g$. The unusual nature of the interaction predicts a cross-section which grows with $m_{Z^{\prime }}$ for a fixed coupling and an accompanying gluon with a coupling that rises with its energy. We study the $t\overline{t}g$ decay mode, proposing distinct reconstruction techniques for the observation of an excess and for the measurement of $m_{Z^{\prime }}$. We estimate the sensitivity of current experimental datasets.

We construct anomaly-free leptophobic $U(1{)}^{\prime }$ flavor models with light $Z^{\prime }(\sim 145\mathrm{GeV})$. In order to allow renormalizable Yukawa interactions for the standard model chiral fermions, new Higgs doublets with nonzero $U(1{)}^{\prime }$ charges are introduced. Then the neutral (pseudo)scalar Higgs bosons as well as $Z^{\prime }$ contribute to the $t\overline{t}$ and the same sign top pair productions [$\sigma (t\overline{t})$ and $\sigma (tt)$], and one can evade the strong constraint from $\sigma (tt)$. The top forward-backward asymmetry ($A_{\mathrm{FB}}$) and $Wjj$ excess at CDF could be accommodated by $A_{\mathrm{FB}}^{\mathrm{New}}=0.084\sim 0.12$ and $\sigma (Wjj)\lesssim O(10)\mathrm{pb}\times {sin}^{2}2\beta$.

In a recent letter [Phys. Rev. Lett. 108, 172003 (2012)] we have reported on a lattice QCD calculation of the heavy-hadron axial couplings $g_1$, $g_2$, and $g_3$. These quantities are low-energy constants of heavy-hadron chiral perturbation theory ($\mathrm{HH}\chi \mathrm{PT}$) and are related to the $B^{*}B\pi$, ${\Sigma }_b^{*}{\Sigma }_b\pi$, and ${\Sigma }_b^{(*)}{\Lambda }_b\pi$ couplings. In the following, we discuss important details of the calculation and give further results. To determine the axial couplings, we explicitly match the matrix elements of the axial current in QCD with the corresponding matrix elements in $\mathrm{HH}\chi \mathrm{PT}$. We construct the ratios of correlation functions used to calculate the matrix elements in lattice QCD, and study the contributions from excited states. We present the complete numerical results and discuss the data analysis in depth. In particular, we demonstrate the convergence of $SU(4|2)$ $\mathrm{HH}\chi \mathrm{PT}$ for the axial-current matrix elements at pion masses up to about 400 MeV and show the impact of the nonanalytic loop contributions. Finally, we present additional predictions for strong and radiative decay widths of charm and bottom baryons.

We study distances of propagation and the group velocities of muon neutrinos in the presence of mixing and oscillations assuming that Lorentz invariance holds. Oscillations lead to distortion of the ${\nu }_{\mu }$ wave packet, which, in turn, changes the group velocity and the distance ${\nu }_{\mu }$ travels. We find that the change of the distance, $d_{\mathrm{osc}}$, is proportional to the length of the wave packet, ${\sigma }_x$, and the oscillation phase, ${\varphi }_p$, acquired by neutrinos in the $\pi$- and $K$- meson decay tunnel where the neutrino wave packet is formed: $d_{\mathrm{osc}}\propto \sigma {\varphi }_p$. Although the distance $d_{\mathrm{osc}}$ may effectively correspond to the superluminal motion, the effect is too tiny ($\sim {10}^{-5}\mathrm{cm}$) to be reconciled with the OPERA result. We analyze various possibilities to increase $d_{\mathrm{osc}}$ and discuss experimental setups in which $d_{\mathrm{osc}}$ (corresponding to the superluminal motion) can reach an observable value $\sim 1\mathrm{m}$.