This paper reports results from a search for ${\nu }_{\mu }\to {\nu }_e$ transitions by the MINOS experiment based on a $7\times {10}^{20}$ protons-on-target exposure. Our observation of 54 candidate ${\nu }_e$ events in the far detector with a background of $49.1\pm 7.0(\mathrm{stat})\pm 2.7(\mathrm{syst})$ events predicted by the measurements in the near detector requires $2{sin}^2(2{\theta }_{13}){sin}^2{\theta }_{23}<0.12(0.20)$ at the 90% C.L. for the normal (inverted) mass hierarchy at ${\delta }_{CP}=0$. The experiment sets the tightest limits to date on the value of ${\theta }_{13}$ for nearly all values of ${\delta }_{CP}$ for the normal neutrino mass hierarchy and maximal ${sin}^2(2{\theta }_{23})$.

We investigate the stability of a new warped black string with nontrivial topologies in five-dimensional anti–de Sitter spacetime. After studying the linear gravitational perturbation, we find that this black string is unstable when the Kaluza-Klein mass falls in a certain range, and the instability exists for all topological spacetimes.

It seems generic to have vacua with lower dimensionality than ours. We consider the possibility that the observable universe originated in a transition from one of these vacua. Such a universe has anisotropic spatial curvature. This may be directly observable through its late-time effects on the CMB if the last period of slow-roll inflation was not too long. These affect the entire sky, leading to correlations which persist up to the highest CMB multipoles, thus allowing a conclusive detection above cosmic variance. Further, this anisotropic curvature causes different dimensions to expand at different rates. This leads to other potentially observable signals including a quadrupolar anisotropy in the CMB which limits the size of the curvature. Conversely, if isotropic curvature is observed it may be evidence that our parent vacuum was at least $3+1$ dimensional. Such signals could reveal our history of decompactification, providing evidence for the existence of vastly different vacua.

In the Randall-Sundrum scenario the compactification radius of the extra dimension is stabilized by the radion, which is a scalar field lighter than the graviton Kaluza-Klein states. It implies that the detection of the radion will be the first signature of the stabilized Randall-Sundrum model. In this paper we study the exclusive production of the radion in electromagnetic and diffractive hadron—hadron collisions at the LHC. Our results demonstrate that the diffractive production of the radion is dominant and should be feasible of study at the CERN LHC.

We investigate the behavior of light baryon masses in three inequivalent large-$N_c$ limits: ’t Hooft, ${\mathrm{QCD}}_{\mathrm{AS}}$ and Corrigan-Ramond. Our framework is a constituent quark model with relativistic-type kinetic energy, stringlike confinement, and one-gluon-exchange term, thus leading to well-defined results even for massless quarks. We analytically prove that the light baryon masses scale as $N_c$, $N_c^2$, and 1 in the ’t Hooft, ${\mathrm{QCD}}_{\mathrm{AS}}$ and Corrigan-Ramond limits, respectively. Those results confirm previous ones obtained by using either diagrammatic methods or constituent approaches, mostly valid for heavy quarks.

The prospects for the analysis of $\tau$ channels at the supersymmetry (SUSY) benchmark point SPS1a’, especially from $e^{+}{e}^{-}\to {\tilde{\tau }}_1^{+}{\tilde{\tau }}_1^{-}$ and $e^{+}{e}^{-}\to {\tilde{\tau }}_2^{+}{\tilde{\tau }}_2^{-}$, have been studied in full simulation of the ILD detector concept foreseen for the International Linear Collider. All accessible SUSY channels as well as all standard model backgrounds were generated at a center-of-mass energy $E_{\mathrm{CMS}}=500\mathrm{GeV}$, including the beam energy spectrum and beam backgrounds expected for nominal ILC beam parameters. With an integrated luminosity of $500{\mathrm{fb}}^{-1}$ delivered to the experiment, the masses of the ${\tilde{\tau }}_1$ and ${\tilde{\tau }}_2$ can be measured to ${107.73}_{-0.05}^{+0.03}\mathrm{GeV}\pm 1.1·\delta M_{{\tilde{\chi }}_1^0}$ and ${183}_{-5}^{+11}\mathrm{GeV}\pm 18·\delta M_{{\tilde{\chi }}_1^0}$, respectively, while the true values in SPS1a’ are 107.9 GeV and 194.9 GeV, respectively. This corresponds to $\delta M_{{\tilde{\tau }}_1}/M_{{\tilde{\tau }}_1}\sim 0.1\%$ and $\delta M_{{\tilde{\tau }}_2}/M_{{\tilde{\tau }}_2}\sim 3\%$ with reasonable assumptions on $\delta M_{{\tilde{\chi }}_1^0}$. The cross sections for ${\tilde{\tau }}_1$ and ${\tilde{\tau }}_2$ pair production could be obtained with a precision of 3.1% and 4.2%, respectively. Combining the mass and cross section measurement in the ${\tilde{\tau }}_2$ channel allows to determine the LSP mass with a relative error of 1.7%, assuming a known $\tilde{\tau }$ mixing angle. In ${\tilde{\tau }}_1\to \tau {\tilde{\chi }}_1^0$ decays, the $\tau$ polarization is measured to be $91\pm 9\%$ and $86\pm 5\%$ in the $\pi$ and $\rho$ decay channels of the $\tau$, respectively. The true value in the simulated SPS1a’ sample is 89.6%.

In a progress toward searching for the QCD critical point, we study the finite density phase transition of $N_f=4$ and 2 lattice QCD at finite temperature with the canonical ensemble approach. We develop a winding number expansion method to accurately project out the particle number from the fermion determinant which greatly extends the applicable range of baryon number sectors to make the study feasible. Our lattice simulation was carried out with the clover fermions and improved gauge action. For a given temperature, we calculate the baryon-chemical potential from the canonical approach to look for the mixed phase as a signal for the first-order phase transition. In the case of $N_f=4$, we observe an “S-shape” structure in the chemical potential-density plane due to the surface tension of the mixed phase in a finite volume which is a signal for the first-order phase transition. We use the Maxwell construction to determine the phase boundaries for three temperatures below $T_c$. The intersecting point of the two extrapolated boundaries turns out to be at the expected first-order transition point at $T_c$ with $\mu =0$. This serves as a check for our method of identifying the critical point. We also studied the $N_f=2$ case, but do not see a signal of the mixed phase for temperature as low as $0.83T_c$.

We calculate the scattering lengths of Nambu-Goldstone bosons interacting with $D$ mesons in a covariant formulation of chiral perturbation theory, which satisfies heavy-quark spin symmetry and analytical properties of loop amplitudes. We compare our results with previous studies performed using heavy-meson chiral perturbation theory and show that recoil corrections are sizable in most cases.

Starting from the QCD sum rules with nonlocal condensates for the pion distribution amplitude, we derive another sum rule for its derivative and its “integral derivatives”—defined in this work. We use this new sum rule to analyze the fine details of the pion distribution amplitude in the endpoint region $x\sim 0$. The results for endpoint-suppressed and flattop (or flatlike) pion distribution amplitudes are compared with those we obtained with differential sum rules by employing two different models for the distribution of vacuum-quark virtualities. We determine the range of values of the derivatives of the pion distribution amplitude and show that endpoint-suppressed distribution amplitudes lie within this range, while those with endpoint enhancement—flat-type or Chernyak-Zhitnitsky like—yield values outside this range.

We present a detailed study of the two-parton light-cone distribution amplitudes for $1{}^{3}P_2$ nonet tensor mesons. The asymptotic two-parton distribution amplitudes of twist-2 and twist-3 are given. The decay constants $f_T$ and $f_T^{\perp }$ defined by the matrices of nonlocal operators on the light-cone are estimated using the QCD sum rule techniques. We also study the decay constants for $f_2(1270)$ and $f_2^{\prime }(1525)$ based on the hypothesis of tensor meson dominance together with the data of $\Gamma (f_2\to \pi \pi )$ and $\Gamma (f_2^{\prime }\to K\overline{K})$ and find that the results are in accordance with the sum rule predictions.

Cosmological hydrogen recombination has recently been the subject of renewed attention because of its importance for predicting the power spectrum of cosmic microwave background anisotropies. It has become clear that it is necessary to account for a large number $n\gtrsim 100$ of energy shells of the hydrogen atom, separately following the angular momentum substates in order to obtain sufficiently accurate recombination histories. However, the multilevel atom codes that follow the populations of all these levels are computationally expensive, limiting recent analyses to only a few points in parameter space. In this paper, we present a new method for solving the multilevel atom recombination problem, which splits the problem into a computationally expensive atomic physics component that is independent of the cosmology and an ultrafast cosmological evolution component. The atomic physics component follows the network of bound-bound and bound-free transitions among excited states and computes the resulting effective transition rates for the small set of “interface” states radiatively connected to the ground state. The cosmological evolution component only follows the populations of the interface states. By pretabulating the effective rates, we can reduce the recurring cost of multilevel atom calculations by more than 5 orders of magnitude. The resulting code is fast enough for inclusion in Markov chain Monte Carlo parameter estimation algorithms. It does not yet include the radiative transfer or high-$n$ two-photon processes considered in some recent papers. Further work on analytic treatments for these effects will be required in order to produce a recombination code usable for Planck data analysis.

Gamma-ray bursts (GRBs) have been invoked to explain both the 511 keV emission from the Galactic bulge and the high-energy positron excess inferred from the ATIC, PAMELA, and Fermi data. While independent explanations can be responsible for these phenomena, we explore the possibility of their common GRB-related origin by modeling the GRB distribution and estimating the rates. For an expected Milky Way long GRB rate, neither of the two signals is generic; the local excess requires a 2% coincidence while the signal from the Galactic center requires a 20% coincidence with respect to the timing of the latest GRB. The simultaneous explanation requires a 0.4% coincidence. Considering the large number of statistical “trials” created by multiple searches for new physics, the coincidences of a few percent cannot be dismissed as unlikely. Alternatively, both phenomena can be explained by GRB if the Galactic rate is higher than expected. We also show that a similar result is difficult to obtain assuming a simplified short GRB distribution.

We revisit the question of whether or not one can perform reliable semiclassical QCD computations at zero temperature. We study correlation functions with no perturbative contributions, and organize the problem by means of the operator product expansion, establishing a precise criterion for the validity of a semiclassical calculation. For $N_f>N$, a systematic computation is possible; for $N_f<N$, it is not. $N_f=N$ is a borderline case. In our analysis, we see explicitly the exponential suppression of instanton effects at large $N$. As an application, we describe a test of QCD lattice gauge theory computations in the chiral limit.

We study the dynamics of isotropic and homogeneous universes in the generalized Hořava-Lifshitz gravity, and classify all possible evolutions of vacuum spacetime. In the case without the detailed balance condition, we find a variety of phase structures of vacuum spacetimes depending on the coupling constants as well as the spatial curvature $K$ and a cosmological constant $\Lambda$. A bounce universe solution is obtained for $\Lambda >0$, $K=\pm 1$ or $\Lambda =0$, $K=-1$, while an oscillation spacetime is found for $\Lambda \ge 0$, $K=1$, or $\Lambda <0$, $K=\pm 1$. We also propose a quantum tunneling scenario from an oscillating spacetime to an inflationary universe, resulting in a macroscopic cyclic universe.

The anomalous effective action describing the coupling of gravity to a non-Abelian gauge theory can be determined by a variational solution of the anomaly equation, as shown by Riegert long ago. It is given by a nonlocal expression, with the nonlocal interaction determined by the Green’s function of a conformally covariant operator of fourth order. In recent works it has been shown that this interaction is mediated by a simple pole in an expansion around a Minkowski background, coupled in the infrared in the massless fermion limit. This result relies on the local formulation of the original action in terms of two auxiliary fields, one physical scalar and one ghost, which take the role of massless composite degrees of freedom. In the gravity case, the two scalars have provided ground in favor of some recent proposals of an infrared approach to the solution of the dark energy problem, entirely based on the behavior of the vacuum energy at the QCD phase transition. As a test of this general result, we perform a complete one-loop computation of the effective action describing the coupling of a non-Abelian gauge theory to gravity. We confirm the appearance of an anomaly pole which contributes to the trace part of the $TJJ$ correlator and of extra poles in its trace-free part, in the quark and gluon sectors, describing the coupling of the energy-momentum tensor ($T$) to two non-Abelian gauge currents ($J$).

We construct the most general effective Lagrangian coupling gravity and electromagnetism up to mass dimension 6 by enumerating all possible nonminimal coupling terms respecting both diffeomorphism and gauge invariance. In all, there are only two unique terms after field redefinitions: one is known to arise from loop effects in QED, while the other is a parity-violating term which may be generated by weak interactions within the standard model of particle physics. We show that neither the cosmological propagation of light nor, contrary to earlier claims, solar system tests of general relativity are useful probes of these terms. These nonminimal couplings of gravity and electromagnetism may remain a mystery for the foreseeable future.

We present an improved prescription for the matter power spectrum in redshift space taking proper account of both nonlinear gravitational clustering and redshift distortion, which are of particular importance for accurately modeling baryon acoustic oscillations (BAOs). Contrary to the models of redshift distortion phenomenologically introduced but frequently used in the literature, the new model includes the corrections arising from the nonlinear coupling between the density and velocity fields associated with two competitive effects of redshift distortion, i.e., Kaiser and Finger-of-God effects. Based on the improved treatment of perturbation theory for gravitational clustering, we compare our model predictions with the monopole and quadrupole power spectra of $N$-body simulations, and an excellent agreement is achieved over the scales of BAOs. Potential impacts on constraining dark energy and modified gravity from the redshift-space power spectrum are also investigated based on the Fisher-matrix formalism, particularly focusing on the measurements of the Hubble parameter, angular diameter distance, and growth rate for structure formation. We find that the existing phenomenological models of redshift distortion produce a systematic error on measurements of the angular diameter distance and Hubble parameter by 1%–2% , and the growth-rate parameter by $\sim 5\%$, which would become non-negligible for future galaxy surveys. Correctly modeling redshift distortion is thus essential, and the new prescription for the redshift-space power spectrum including the nonlinear corrections can be used as an accurate theoretical template for anisotropic BAOs.

In extensions of the standard model with a heavy fourth generation, one important question is what makes the fourth-generation lepton sector, particularly the neutrinos, so different from the lighter three generations. We study this question in the context of models of electroweak symmetry breaking in warped extra dimensions, where the flavor hierarchy is generated by choosing the localization of the zero-mode fermions in the extra dimension. In this setup the Higgs sector is localized near the infrared brane, whereas the Majorana mass term is localized at the ultraviolet brane. As a result, light neutrinos are almost entirely Majorana particles, whereas the fourth-generation neutrino is mostly a Dirac fermion. We show that it is possible to obtain heavy fourth-generation leptons in regions of parameter space where the light neutrino masses and mixings are compatible with observation. We study the impact of these bounds, as well as the ones from lepton flavor violation, on the phenomenology of these models.

If nature exhibits low energy supersymmetry, discrete (non-${\mathbb{Z}}_2$) $R$ symmetries may well play an important role. In this paper, we explore such symmetries. We generalize gaugino condensation, constructing large classes of models which are classically scale invariant, and which spontaneously break discrete $R$ symmetries (but not supersymmetry). The order parameters for the breaking include chiral singlets. These simplify the construction of models with metastable dynamical supersymmetry breaking. We explain that in gauge mediation, the problem of the cosmological constant makes “retrofitting” particularly natural—almost imperative. We describe new classes of models, with interesting scales for supersymmetry breaking, and which allow simple solutions of the $\mu$ problem. We argue that models exhibiting such $R$ symmetries can readily solve not only the problem of dimension four operators and proton decay, but also dimension five operators. On the other hand, in theories of “gravity mediation,” the breaking of an $R$ symmetry is typically of order $M_p$; $R$ parity is required to suppress dimension four $B$ and $L$ violating operators, and dimension five operators remain problematic.