We propose a phenomenological Lagrangian for the decay of the $\mathrm{S}\mathrm{U}(3)$ nonets of the axial-vector mesons of $J^{PC}=1^{+-},1^{++}$ into a vector meson and a pseudoscalar constructed with tensor fields for the vector and axial-vector mesons. The formulation leads to a good reproduction of the different decay branching ratios and assuming vector meson dominance (VMD) it also leads to good results for the radiative decay of the $a_1$ into pion and photon, and in agreement with the structure proposed in the chiral tensor formulation of radiative decay of axial-vector mesons. The two $\mathrm{S}\mathrm{U}(3)$ parameters and the mixing angle of $K_{1A}$ and $K_{1B}$ needed to give the physical $K_1(1270)$ and $K_1(1400)$ resonances are also determined.

Using a sample of $14\times {10}^6$ $\psi (2S)$ events accumulated with the BES II detector, evidence for $f_0(980)f_0(980)$ production in ${\chi }_{c0}$ decays is obtained for the first time; the branching ratio is determined to be $\mathcal{B}[{\chi }_{c0}\to f_0(980)f_0(980)\to {\pi }^{+}{\pi }^{-}{\pi }^{+}{\pi }^{-}]=[7.6\pm 1.9(\mathrm{s}\mathrm{t}\mathrm{a}\mathrm{t})\pm 1.6(\mathrm{s}\mathrm{y}\mathrm{s}\mathrm{t})]\times {10}^{-4}$. The significance of the $f_0(980)$ signal is about 4.6$\sigma$.

Algebraic derivation of modified Heisenberg commutation rules for restricted Landau problem is given.

The interpretation of a family of electrovacuum stationary Taub-NUT-type fields in terms of finite charged perfect fluid disks is presented. The interpretation is made by means of an “inverse problem” approach used to obtain disk sources of known solutions of the Einstein or Einstein-Maxwell equations. The diagonalization of the energy-momentum tensor of the disks is facilitated in this case by the fact that it can be written as an upper right triangular matrix. We find that the inclusion of electromagnetic fields changes significantly the different material properties of the disks and so we can obtain, for some values of the parameters, finite charged perfect fluid disks that are in agreement with all the energy conditions.

We give a well posed initial value formulation of the Baumgarte-Shapiro-Shibata-Nakamura form of Einstein’s equations with gauge conditions given by a Bona-Massó–like slicing condition for the lapse and a frozen shift. This is achieved by introducing extra variables and recasting the evolution equations into a first order symmetric hyperbolic system. We also consider the presence of artificial boundaries and derive a set of boundary conditions that guarantee that the resulting initial-boundary value problem is well posed, though not necessarily compatible with the constraints. In the case of dynamical gauge conditions for the lapse and shift we obtain a class of evolution equations which are strongly hyperbolic and so yield well posed initial value formulations.

The use of techniques from loop quantum gravity for cosmological models may solve some difficult problems in quantum cosmology. The solutions under a number of circumstances have been well studied. We will analyze the behavior of solutions in the closed model, focusing on the behavior of a universe containing a massless scalar field. The asymptotic behavior of the solutions is examined, and is used to determine requirements of the initial conditions.

Observations exploring the contemporary cosmic acceleration have sparked interest in dark energy models possessing equations of state with $w<-1$. We review how the cosmic expansion history of a Dvali-Gabadadze-Porrati (DGP) braneworld model with a standard brane cosmological constant can mimic that of ordinary 4D gravity with $w<-1$ “phantom” dark energy for observationally relevant redshifts. We reinterpret the effective phantom nature of the dark energy as arising from dynamical-screening of the brane cosmological constant in DGP. This unusual variety of expansion history is thus possible without violating the null-energy condition, without ghosts and without any big rip, in a model which seems no more contrived than most evolving dark energy models. We indicate ways by which one may observationally test this effective $w<-1$ possibility, and differentiate it from ordinary phantom dark energy.

In the context of the brane-world scenarios with compactified extra dimensions, we study the production of brane fluctuations (branons) in hadron colliders ($p\overline{p}$, $pp$, and $e^{\pm }p$) in terms of the brane tension parameter $f$, the branon mass $M$, and the number of branons $N$. From the absence of monojet events at HERA and Tevatron (run I), we set bounds on these parameters and we also study how such bounds could be improved at Tevatron (run II) and the future LHC. The single-photon channel is also analyzed for the two last colliders.

We simulate 2-flavor lattice QCD at finite isospin chemical potential ${\mu }_I$, for temperatures close to the finite temperature transition from hadronic matter to a quark-gluon plasma. The ${\mu }_I$ dependence of the transition coupling is observed and used to estimate the decrease in the transition temperature with increasing ${\mu }_I$. These simulations are performed on an $8^3\times 4$ lattice at three different quark masses. Our estimate of the magnitude of the fluctuations of the phase of the fermion determinant at small quark-number chemical potential $\mu$, suggest that the position of the small $\mu$ and small ${\mu }_I$ transitions should be the same for ${\mu }_I=2\mu$, and we argue that the nature of these transitions should be the same. For all ${\mu }_I<m_{\pi }$ the smoothness of these transitions and the values of the Binder cumulant $B_4$, indicate that these transitions are mere crossovers, and show no sign of a critical endpoint corresponding to that expected at finite $\mu$. This suggests that this finite $\mu$ critical endpoint, if it exists, lies at $\mu >m_{\pi }/2$ over the considered range of quark masses. For ${\mu }_I>m_{\pi }$ and a small isospin ($I_3$) breaking term $\lambda$, we do find evidence of a critical endpoint which would indicate that, for $\lambda =0$, there is a tricritical point on the phase boundary where the pion condensate evaporates, where this phase transition changes from second to first-order.

We derive two coupled nonlinear evolution equations corresponding to the truncation of the Balitsky infinite hierarchy of saturation equations after inclusion of dipole-dipole correlations, i.e., one step beyond the Balitsky-Kovchegov (BK) equation. We exhibit an exact solution for maximal correlation which still satisfies the same asymptotic geometric scaling as BK but with the $S$ matrix going to $1/2$ (instead of zero) in the full saturation region.

We report on a search for $CP$ violation in the decay of $D^0$ and ${\overline{D}}^0$ to $K_S^0{\pi }^{+}{\pi }^{-}$. The data come from an integrated luminosity of $9.0{\mathrm{f}\mathrm{b}}^{-1}$ of $e^{+}{e}^{-}$ collisions at $\sqrt{s}\approx 10\mathrm{G}\mathrm{e}\mathrm{V}$ recorded with the CLEO II.V detector. The resonance substructure of this decay is well described by ten quasi-two-body decay channels plus a small nonresonant component. We observe no evidence for $CP$ violation in the amplitudes that describe the decay $D^0\to K_S^0{\pi }^{+}{\pi }^{-}$.

We present the results of a search for gravitational lensing of the cosmic microwave background (CMB) in cross-correlation with the projected density of luminous red galaxies. The CMB lensing reconstruction is performed using the first year of Wilkinson Microwave Anisotropy Probe data, and the galaxy maps are obtained using the Sloan Digital Sky Survey imaging data. We find no detection of lensing; our constraint on the galaxy bias derived from the galaxy-convergence cross-spectrum is $b_g=1.81\pm 1.92$ ($1\sigma$, statistical) as compared to the expected result of $b_g\sim 1.8$ for this sample. We discuss possible instrument-related systematic errors and show that the galactic foregrounds are not important. We do not find any evidence for point-source or thermal Sunyaev-Zel’dovich effect contamination.

Upper bounds at the weak scale are put on all ${\lambda }_{ijk}^{\prime }{\lambda }_{imn}^{\prime }$-type products of $R$-parity violating supersymmetry that may affect $K^0-{\overline{K}}^0$ and $B^0-{\overline{B}}^0$ mixing. We constrain all possible products, including some not considered before, using next-to-leading order QCD corrections to the mixing amplitudes. Constraints are obtained for both real and imaginary parts of the couplings. We also discuss briefly some correlated decay channels which should be investigated in future experiments.

In this work, we evaluate the mass spectra of baryons which consist of two heavy quarks and one light quark in the MIT bag model. The two heavy quarks constitute a heavy scalar or axial-vector diquark. Concretely, we calculate the spectra of $|q(Q{Q}^{\prime }){⟩}_{1/2}$ and $|q(Q{Q}^{\prime }){⟩}_{3/2}$ where $Q$ and $Q^{\prime }$ stand for $b$ and/or $c$ quarks. Especially, for $|q(bc){⟩}_{1/2}$ there can be a mixing between $|q(bc{)}_0{⟩}_{1/2}$ and $|q(bc{)}_1{⟩}_{1/2}$ where the subscripts 0 and 1 refer to the spin state of the diquark (bc), the mixing is not calculable in the framework of quantum mechanics as the potential model is employed, but can be evaluated by the quantum field theory. Our numerical results indicate that the mixing is sizable.

We report on a revision of our previous computation of the renormalized expectation value of the stress-energy tensor of a massless, minimally coupled scalar with a quartic self-interaction on a locally de Sitter background. This model is important because it demonstrates that quantum effects can lead to violations of the weak energy condition on cosmological scales—on average, not just in fluctuations—although the effect in this particular model is far too small to be observed. The revision consists of modifying the propagator so that dimensional regularization can be used when the dimension of the renormalized theory is not four. Although the finite part of the stress-energy tensor does not change (in $D=4$) from our previous result, the counterterms do. We also speculate that a certain, finite and separately conserved part of the stress tensor can be subsumed into a natural correction of the initial state from free Bunch-Davies vacuum.

In models with large additional dimensions, the GUT scale can be lowered to values accessible by future colliders. Because of modification of the loop corrections from particles propagating into the extra dimensions, the logarithmic running of the couplings of the Standard Model is turned into a power law. These loop corrections are divergent and the standard way to achieve finiteness is the introduction of a cutoff. The question remains, whether the results are reliable as they depend on an unphysical parameter. In this paper, we show that this running of the coupling can be calculated within a model including the existence of a minimal length scale. The minimal length acts as a natural regulator and allows us to confirm cutoff computations.

I present some general ideas about quantum entanglement in relativistic quantum field theory, especially entanglement in the physical vacuum. Here, entanglement is defined between different single particle states (or modes), parametrized either by energy-momentum together with internal degrees of freedom, or by spacetime coordinate together with the component index in the case of a vector or spinor field. In this approach, the notion of entanglement between different spacetime points can be established. Some entanglement properties are obtained as constraints from symmetries, e.g., under Lorentz transformation, space inversion, time reverse, and charge conjugation.

Unitary principal series representations of the conformal group appear in the de Sitter/conformal field theory (dS/CFT) correspondence. These are infinite-dimensional irreducible representations, without highest weights. In earlier work of Güijosa and the author it was shown for the case of two-dimensional de Sitter space, there was a natural $q$-deformation of the conformal group, with $q$ a root of unity, where the unitary principal series representations become finite-dimensional cyclic unitary representations. Formulating a version of the dS/CFT correspondence using these representations can lead to a description with a finite-dimensional Hilbert space and unitary evolution. In the present work, we generalize to the case of quantum-deformed three-dimensional de Sitter spacetime and compute the entanglement entropy of a quantum field across the cosmological horizon.

We evaluate the coordinate space dependence of the matrix elements of the commutator of the electromagnetic and gluon currents in the vicinity of the light cone but at large distances. We found within the parton model, Doushitzer-Gribov-Lipatov-Altarelli, the resummation approaches to the small $x$ behavior of deep-inelastic scattering (DIS) processes that an increase of the commutator with relative distance $py$ as $\propto (py)f(py,y^2=t^2-r^2)$, where $f$ is increasing with increase of $py$ is the generic property of QCD at small but fixed space-time interval $y^2=t^2-r^2$ in perturbative and nonperturbative QCD regimes. We explain that the factor $py$ follows within the dipole model (QCD factorization theorem) from the properties of Lorentz transformation. The increase of $f$ disappears at central impact parameters if the cross section of DIS may achieve the unitarity limit. We argue that such long-range forces are hardly consistent with thermodynamic equilibrium while a unitarity limit may signal equilibration. Possible implications of this new long-range interaction are briefly discussed.

We study the nature of the seesaw mechanism in the context of renormalizable SO(10) with Higgs fields in the 10-plets and $\overline{126}$-plet representations, paying special attention to the supersymmetric case. We discuss analytically the situation for the second and third generations of fermions ignoring any $CP$ violating phase. It is shown that $b-\tau$ unification and large atmospheric mixing angle strongly disfavor the dominance of the type I seesaw.