The azimuthal correlation between the planes formed by the vectors $({\overrightarrow{p}}_{\ell },{\overrightarrow{p}}_{X_b})$ and $({\overrightarrow{p}}_{\ell },{\overrightarrow{P}}_t)$ in the semileptonic rest frame decay of a polarized top quark $t(\uparrow )\to X_b+{\ell }^{+}+{\nu }_{\ell }$ belongs to a class of polarization observables involving the top quark which vanish at the Born term level in the standard model. We determine the next-to-leading-order QCD corrections to the aforementioned azimuthal correlation and compare the result to the corresponding contribution of a non-standard-model right-chiral quark current.

A fully differential calculation in perturbative quantum chromodynamics is presented for the production of massive photon pairs at hadron colliders. All next-to-leading order perturbative contributions from quark-antiquark, gluon-(anti)quark, and gluon-gluon subprocesses are included, as well as all-orders resummation of initial-state gluon radiation valid at next-to-next-to-leading logarithmic accuracy. The region of phase space is specified in which the calculation is most reliable. Good agreement is demonstrated with data from the Fermilab Tevatron, and predictions are made for more detailed tests with CDF and D0 data. Predictions are shown for distributions of diphoton pairs produced at the energy of the Large Hadron Collider (LHC). Distributions of the diphoton pairs from the decay of a Higgs boson are contrasted with those produced from QCD processes at the LHC, showing that enhanced sensitivity to the signal can be obtained with judicious selection of events.

We compute the contributions to continuum photon pair production at hadron colliders from processes initiated by gluon-gluon and gluon-quark scattering into two photons through a four-leg virtual quark loop. Complete two-loop cross sections in perturbative quantum chromodynamics are combined with contributions from soft parton radiation resummed to all orders in the strong coupling strength. The structure of the resummed cross section is examined in detail, including a new type of unintegrated parton distribution function affecting azimuthal angle distributions of photons in the pair’s rest frame. As a result of this analysis, we predict diphoton transverse-momentum distributions in gluon-gluon scattering in wide ranges of kinematic parameters at the Fermilab Tevatron and the CERN Large Hadron Collider.

We study the processes $e^{+}{e}^{-}\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}\gamma$, $K^{+}{K}^{-}{\pi }^0{\pi }^0\gamma$ and $K^{+}{K}^{-}{K}^{+}{K}^{-}\gamma$, where the photon is radiated from the initial state. About 34 600, 4400 and 2300 fully reconstructed events, respectively, are selected from $232{\mathrm{fb}}^{-1}$ of BABAR data. The invariant mass of the hadronic final state defines the effective $e^{+}{e}^{-}$ center-of-mass energy, so that the $K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}\gamma$ data can be compared with direct measurements of the $e^{+}{e}^{-}\to K^{+}{K}^{-}{\pi }^{+}{\pi }^{-}$ reaction; no direct measurements exist for the $e^{+}{e}^{-}\to K^{+}{K}^{-}{\pi }^0{\pi }^0$ or $e^{+}{e}^{-}\to K^{+}{K}^{-}{K}^{+}{K}^{-}$ reactions. Studying the structure of these events, we find contributions from a number of intermediate states, and we extract their cross sections where possible. In particular, we isolate the contribution from $e^{+}{e}^{-}\to \varphi (1020)f_0(980)$ and study its structure near threshold. In the charmonium region, we observe the $J/\psi$ in all three final states and several intermediate states, as well as the $\psi (2S)$ in some modes, and measure the corresponding branching fractions. We see no signal for the $Y(4260)$ and obtain an upper limit of ${\mathcal{B}}_{Y(4260)\to \varphi {\pi }^{+}{\pi }^{-}}·{\Gamma }_{ee}^Y<0.4\mathrm{eV}$ at 90% C.L.

We have studied semileptonic $B$ decay to the exclusive charmless states $\pi$, $\rho /\omega$, $\eta$ and ${\eta }^{\prime }$ using the full $15.5{\mathrm{fb}}^{-1}$ CLEO ${\rm Y}(4S)$ sample, with measurements performed in subregions of phase space to minimize dependence on a priori knowledge of the form factors involved. We find total branching fractions $\mathcal{B}(B^0\to {\pi }^{-}{\ell }^{+}\nu )=(1.37\pm {0.15}_{\mathrm{stat}}\pm {0.11}_{\mathrm{sys}})\times {10}^{-4}$ and $\mathcal{B}(B^0\to {\rho }^{-}{\ell }^{+}\nu )=(2.93\pm {0.37}_{\mathrm{stat}}\pm {0.37}_{\mathrm{sys}})\times {10}^{-4}$. We find evidence for $B^{+}\to {\eta }^{\prime }{\ell }^{+}\nu$, with $\mathcal{B}(B^{+}\to {\eta }^{\prime }{\ell }^{+}\nu )=(2.66\pm \pm {0.80}_{\mathrm{stat}}\pm {0.56}_{\mathrm{sys}})\times {10}^{-4}$ and $1.20\times {10}^{-4}<\mathcal{B}(B^{+}\to {\eta }^{\prime }{\ell }^{+}\nu )<4.46\times {10}^{-4}$ (90% CL). We also limit $\mathcal{B}(B^{+}\to \eta {\ell }^{+}\nu )<1.01\times {10}^{-4}$ (90% CL). By combining our $B\to \pi \ell \nu$ information with unquenched lattice calculations, we find $|V_{ub}|=(3.6\pm {0.4}_{\mathrm{stat}}\pm 0.2_{\mathrm{sys}-0.4\mathrm{thy}}{}^{+0.6})\times {10}^{-3}$.

The early universe is modeled through the quantization of a Friedmann-Robertson-Walker (FRW) model with positive curvature. In this model, the universe is filled by two fluids: radiation and Chaplygin gas. The quantization of these models is made by following the Wheeler-DeWitt prescriptions. Using the Schutz formalism, the time notion is recovered and the Wheeler-DeWitt equation transforms into a time dependent Schrödinger equation, which rules the dynamics of the early universe, under the action of an effective potential $V_{\mathrm{eff}}$. Using a finite differences method and the Crank-Nicholson scheme, in a code implemented in the program OCTAVE, we solve the corresponding time dependent Schrödinger equation and obtain the time evolution of an initial wave packet. This wave packet satisfies appropriate boundary conditions. The calculation of the tunneling probabilities shows that the universe may emerge from the Planck era in an inflationary phase. It also shows that the tunneling probability is a function of the mean energy of the initial wave packet and of the two parameters of the Chaplygin gas. We also show a comparison between these results and those obtained by the WKB approximation.

The Higgs-pair production process at the CERN Large Hadron Collider, which will provide a way to test the Higgs boson self-coupling, may be sensitive to new physics. In the framework of the littlest Higgs model with $T$ parity, such Higgs-pair production can proceed through additional loop diagrams, and thus the production rate can be quite different from the standard model prediction. Our calculations show that, due to the loop contributions of both $T$-even and $T$-odd quarks predicted in this model, the production rate can be significantly enhanced relative to the standard model prediction and also can be larger than the production rate in the minimal supersymmetric model. Also, we find that the $T$-odd quark contributions, which were not included in a previous study, are equally important compared with the $T$-even quark contributions.

Combining the measured $B_s$ mixing with $b\to s{\ell }^{+}{\ell }^{-}$ rate data, we find a sizable 4 generation $t^{\prime }$ quark effect is allowed, for example, with $m_{t^{\prime }}\sim 300\mathrm{GeV}$ and $V_{t^{\prime }s}^{*}{V}_{t^{\prime }b}\sim 0.025e^{\pm i70°}$, which could underlie the new physics indications in $CP$ violation studies of $b\to s\overline{q}q$ transitions. With positive phase, large and negative mixing-dependent $CP$ violation in $B_s$ system is predicted, $\sin 2{\Phi }_{B_s}\sim -0.5$ to $-0.7$. This also can be probed via width difference methods. As a corollary, the short distance generated $D^0\mathrm{\text{−}}{\overline{D}}^0$ mass difference is found to be consistent with, if not slightly higher than, recent $B$ factory measurements, while $CP$ violation is subdued with $\sin 2{\Phi }_D\sim -0.2$.

We propose a systematic procedure to study a generalized linear sigma model which can give a physical picture of possible mixing between $q\overline{q}$ and $qq\overline{q}\overline{q}$ low lying spin zero states. In the limit of zero quark masses, we derive the model independent results for the properties of the Nambu-Goldstone pseudoscalar particles. For getting information on the scalars it is necessary to make a specific choice of terms. We impose two plausible physical criteria—the modeling of the axial anomaly and the suppression of effective vertices representing too many fermion lines—for limiting the large number of terms which are allowed on general grounds. We calculate the tree-level spectrum based on the leading terms in our approach and find that it prominently exhibits a very low mass isosinglet scalar state. Finally we point out that the low energy result for scattering of pions continues to hold in the general version of the model.

We report the results of a study of neutral $B$ meson decays to the $D^0{\pi }^{+}{\pi }^{-}$ final state, where the $D^0$ is fully reconstructed. The results are obtained from an event sample containing $388\times {10}^6$ $B\overline{B}$-meson pairs collected in the Belle experiment at the KEKB $e^{+}{e}^{-}$ collider. The total branching fraction of the three-body decay $\mathcal{B}({\overline{B}}^0\to D^0{\pi }^{+}{\pi }^{-})=(8.4\pm 0.4(\mathrm{stat})\pm 0.8(\mathrm{syst}))\times {10}^{-4}$ has been measured. The intermediate resonant structure of these three-body decays has been studied. From a Dalitz plot analysis we have obtained the product of the branching fractions for $D_2^{*+}$ and $D_0^{*+}$ production: $\mathcal{B}({\overline{B}}^0\to D_2^{*+}{\pi }^{-})\times \mathcal{B}(D_2^{*+}\to D^0{\pi }^{+})=(2.15\pm 0.17(\mathrm{stat})\pm 0.29(\mathrm{syst})\pm 0.12(\mathrm{mod}))\times {10}^{-4}$, and $\mathcal{B}({\overline{B}}^0\to D_0^{*+}{\pi }^{-})\times \mathcal{B}(D_0^{*+}\to D^0{\pi }^{+})=(0.60\pm 0.13(\mathrm{stat})\pm 0.15(\mathrm{syst})\pm 0.22(\mathrm{mod}))\times {10}^{-4}$. This is the first observation of the ${\overline{B}}^0\to D_0^{*+}{\pi }^{-}$ decay. The ${\overline{B}}^0\to D^0{\rho }^0$ and $D^0{f}_2$ branching fractions are measured to be: $\mathcal{B}({\overline{B}}^0\to D^0{\rho }^0)=(3.19\pm 0.20(\mathrm{stat})\pm 0.24(\mathrm{syst})\pm 0.38(\mathrm{mod}))\times {10}^{-4}$, and $\mathcal{B}({\overline{B}}^0\to D^0{f}_2)=(1.20\pm 0.18(\mathrm{stat})\pm 0.21(\mathrm{syst})\pm 0.32(\mathrm{mod}))\times {10}^{-4}$.

We consider an expanding boost-invariant plasma at strong coupling using the AdS/CFT correspondence for $\mathcal{N}=4$ super Yang-Mills theory. We determine the relaxation time in second order viscous hydrodynamics and find that it is around 30 times shorter than weak coupling expectations. We find that the nonsingularity of the dual geometry in the string frame necessitates turning on the dilaton which leads to a nonvanishing expectation value for $\mathrm{tr}{F}^2$ behaving like ${\tau }^{-10/3}$.

We study to what extent wormholes can mimic the observational features of black holes. It is surprisingly found that many features that could be thought of as “characteristic” of a black hole (endowed with an event horizon) can be closely mimicked by a globally static wormhole, having no event horizon. This is the case for the apparently irreversible accretion of matter down a hole, no-hair properties, quasi-normal-mode ringing, and even the dissipative properties of black hole horizons, such as a finite surface resistivity equal to 377 Ohms. The only way to distinguish the two geometries on an observationally reasonable time scale would be through the detection of Hawking’s radiation, which is, however, too weak to be of practical relevance for astrophysical black holes. We point out the existence of an interesting spectrum of quantum microstates trapped in the throat of a wormhole which could be relevant for storing the information lost during a gravitational collapse.

We demonstrate the existence of spherically symmetric truly naked black holes (TNBH) for which the Kretschmann scalar is finite on the horizon but some curvature components including those responsible for tidal forces as well as the energy density $\overline{\rho }$ measured by a free-falling observer are infinite. We choose a rather generic powerlike asymptotics for the metric functions and analyze possible types of a horizon depending on the behavior of curvature components in the free-falling frame. It is also shown in a general case of distorted black holes that $\overline{\rho }$ and tidal forces are either both finite or both infinite. The general approach developed in the article includes previously found examples and, in particular, TNBHs with an infinite area of a horizon. The fact that the detection of singularity depends on a frame may be relevant for a more accurate definition of the cosmic censorship conjecture. TNBHs may be considered as a new example of so-called nonscalar singularities for which the scalar curvature invariants are finite but some components of the Riemann tensor may diverge in certain frames.

The structure of the confining string in terms of the topological charge density and the action density is studied in $SU(2)$ Yang-Mills theory on the lattice using the ${\mathrm{HP}}^1$ $\sigma$-model embedding approach. We find that the confining flux tube noticeably suppresses both the topological charge and the action densities. Beyond the string formation length the string cross section in terms of these quantities is well described by a Gaussian profile. In both cases the squared string width is found to be a logarithmic function of the string length confirming the Lüscher widening of the chromoelectric string. Characteristic string scales in terms of the topological and action densities are estimated as well.

We observe several interesting phenomena in a technicolor-like model of electroweak symmetry breaking based on the $\mathrm{D}4\mathrm{\text{−}}\mathrm{D}8\mathrm{\text{−}}\overline{\mathrm{D}8}$ system of Sakai and Sugimoto. The benefit of holographic models based on D-brane configurations is that both sides of the holographic duality are well understood. We find that the lightest technicolor resonances contribute negatively to the Peskin-Takeuchi $S$-parameter, but heavy resonances do not decouple and lead generically to large, positive values of $S$, consistent with standard estimates in QCD-like theories. We study how the $S$ parameter and the masses and decay constants of the vector and axial-vector techniresonances vary over a one-parameter family of D8-brane configurations. We discuss possibilities for the consistent truncation of the theory to the first few resonances and suggest some generic predictions of stringy holographic technicolor models.

Dirac and Majorana neutrinos can be distinguished in relativistic neutrino oscillations if new right-handed interactions exist, due to their different propagation in matter. We review how these new interactions affect neutrino oscillation experiments and discuss the size of this eventually observable effect for different oscillation channels, baselines, and neutrino energies.

For Majorana or Dirac neutrinos, using Fritzsch-like texture 4 zero mass matrices with parallel texture structures for the charged leptons and the Dirac neutrino mass matrix ($M_{\nu D}$), detailed predictions for cases pertaining to normal/inverted hierarchy as well as degenerate scenarios of neutrino masses have been carried out. The inverted hierarchy as well as degenerate scenarios seem to be ruled out at $3\sigma$ C.L. for both Majorana and Dirac neutrinos. For normal hierarchy, Jarlskog’s rephasing invariant parameter $J$, the $CP$ violating Dirac-like phase $\delta$, and the effective neutrino mass $⟨m_{ee}⟩$ have been calculated. For this case, lower limits of $m_{{\nu }_1}$ and ${\theta }_{13}$ would have implications for the nature of neutrinos.

Using $e^{+}{e}^{-}\to \mathrm{\text{hadrons}}$ data collected with the CLEO-III detector at the Cornell Electron Storage Ring, we study the inclusive production of baryons/antibaryons $(p,\Lambda )$ and mesons ($\varphi$ and $f_2(1270)$) in gluon-fragmentation and quark-fragmentation processes. We first corroborate previous per-event total particle yields in ${\rm Y}(1\mathrm{S})\to ggg$ compared with nearby continuum ($e^{+}{e}^{-}\to q\overline{q}$) indicating greater ($\sim \times 2$) per-event yields of baryons in 3-gluon fragmentation. We find similar results when we extend that comparison to include the ${\rm Y}(2\mathrm{S})$ and ${\rm Y}(3\mathrm{S})$ resonances. With higher statistics, we now also probe the momentum dependence of these per-event particle yields. Next, we compare particle production in the photon-tagged process ${\rm Y}(1\mathrm{S})\to gg\gamma$ with that in $e^{+}{e}^{-}\to q\overline{q}\gamma$ events, to allow comparison of two-parton with three-parton particle-specific fragmentation. For each particle, we determine the “enhancement” ratio, defined as the ratio of particle yields per gluon-fragmentation event compared to quark-fragmentation event. Thus defined, an enhancement of 1.0 implies equal per-event production in gluon and quark fragmentation. In the photon-tagged analysis (${\rm Y}(1\mathrm{S})\to gg\gamma$ compared to $e^{+}{e}^{-}\to q\overline{q}\gamma$), we find almost no enhancement for protons ($\sim 1.2\pm 0.1$), but a significant enhancement ($\sim 1.9\pm 0.3$) for $\Lambda$’s. This small measured proton enhancement rate is supported by a study of baryon production in ${\chi }_{b2}\to gg\to p+X$ relative to ${\chi }_{b1}\to q\overline{q}g\to p+X$. Overall, per-event baryon production in radiative two-gluon fragmentation is somewhat smaller than that observed in three-gluon decays of the ${\rm Y}(1\mathrm{S})$. Our results for baryon production are inconsistent with the predictions of the JETSET (7.3) fragmentation model.

An attempt to construct the “ground state” vacuum initial data for the gravitational field surrounding two black holes is presented. The ground state is defined as the gravitational initial data minimizing the ADM mass within the class of data for which the masses of the holes and their distance are fixed. To parametrize different geometric arrangements of the two holes (and, therefore, their distance), we use an appropriately chosen scale factor. A method for analyzing the variations of the ADM mass and the masses (areas) of the horizons in terms of gravitational degrees of freedom is proposed. The Misner initial data are analyzed in this context: it is shown that they do not minimize the ADM mass.