The study of light pseudoscalar quark-antiquark bound states in the Dyson-Schwinger approach with the effective QCD coupling enhanced by the interplay of the dimension 2 gluon condensate $⟨A^2⟩$ and dimension 4 gluon condensate $⟨F^2⟩$, is extended to the $\eta –{\eta }^{\prime }$ complex. We include the effects of the gluon axial anomaly into the Dyson-Schwinger approach to mesons. The calculated masses, mixing and two-photon decay widths of $\eta$ and ${\eta }^{\prime }$ mesons are in agreement with experiment. Also, in a model-independent way, we give the modification of the Gell-Mann–Okubo and Schwinger nonet relations due to the interplay of the gluon anomaly and SU(3) flavor symmetry breaking.

Results for Monte Carlo calculations of the electromagnetic vector and scalar form factors of the pion in a quenched simulation are presented. We work with two different lattice volumes up to a spatial size of 2.4 fm at a lattice spacing of 0.148 fm. The pion form factors in the spacelike region are determined for pion masses down to 340 MeV.

We show that, in the light-cone gauge of the proton, it is possible to derive in a very simple way the solution of the classical Yang-Mills equations for the collision between a nucleus and a proton. One important step of the calculation is the derivation of a formula that describes the propagation of a gluon in the background color field of the nucleus. This allows us to calculate observables in pA collisions in a more straightforward fashion than already proposed. We discuss also the comparison between light-cone gauge and covariant gauge in view of further investigations involving higher order corrections.

We analyze the decay $B^0\to K_S^0{\pi }^{+}{\pi }^{-}$ using a sample of $232\times {10}^6$ ${\rm Y}(4S)\to B\overline{B}$ decays collected with the BABAR detector at the SLAC PEP-II asymmetric-energy $B$ factory. A maximum likelihood fit finds the following branching fractions: $\mathcal{B}(B^0\to K^0{\pi }^{+}{\pi }^{-})=(43.0\pm 2.3\pm 2.3)\times {10}^{-6},\mathcal{B}(B^0\to f_0(\to {\pi }^{+}{\pi }^{-})K^0)=(5.5\pm 0.7\pm 0.5\pm 0.3)\times {10}^{-6}$ and $\mathcal{B}(B^0\to K^{*+}{\pi }^{-})=(11.0\pm 1.5\pm 0.5\pm 0.5)\times {10}^{-6}$. For these results, the first uncertainty is statistical, the second is systematic, and the third (if present) is due to the effect of interference from other resonances. We also measure the $CP$-violating charge asymmetry in the decay $B^0\to K^{*+}{\pi }^{-}$, ${\mathcal{A}}_{K^{*}\pi }=-0.11\pm 0.14\pm 0.05$.

Quantum inequalities have been established for various quantum fields in both flat and curved spacetimes. In particular, for spin-$3/2$ fields, Yu and Wu have explicitly derived quantum inequalities for the massive case. Employing a similar method developed by Fewster and colleagues, this paper provides an explicit formula of quantum inequalities for a massless spin-$3/2$ field in four-dimensional Minkowski spacetime.

Taking seriously the interpretation of black hole entropy as the logarithm of the number of microstates, we argue that thermal gravitons may undergo a phase transition to a kind of black hole condensate. The phase transition proceeds via nucleation of black holes at a rate governed by a saddle point configuration whose free energy is of order the inverse temperature in Planck units. Whether the universe remains in a low entropy state as opposed to the high entropy black hole condensate depends sensitively on its thermal history. Our results may clarify an old observation of Penrose regarding the very low entropy state of the universe.

It is shown by an explicit calculation that the excitations about the self-accelerating cosmological solution of the Dvali-Gabadaze-Porrati model contain a ghost mode. This raises serious doubts about viability of this solution. Our analysis reveals the similarity between the quadratic theory for the perturbations around the self-accelerating universe and an Abelian gauge model with two Stückelberg fields.

We discuss a D-term inflation scenario where a right-handed sneutrino can be an inflaton field leading to a viable inflation and leptogenesis, with a minimal form of Kähler potential. The decay of an inflaton sneutrino can nonthermally create large enough lepton asymmetry. Its entropy production is also big enough to ameliorate the gravitino problem caused by too high a reheating temperature from the decay of a symmetry breaking field.

We present Monte Carlo simulations of the Sivers effect in the polarized Drell-Yan $p{p}^{\uparrow }\to {\mu }^{+}{\mu }^{-}X$ process at the center-of-mass energy $\sqrt{s}=200\mathrm{GeV}$ reachable at the Relativistic Heavy-Ion Collider (RHIC) of BNL. We use two different parametrizations for the Sivers function, one deduced from the analysis of semi-inclusive deep-inelastic scattering (SIDIS) data at much lower energies, and another one constrained by the RHIC data for the $p{p}^{\uparrow }\to \pi X$ process at the same energy. For a given luminosity of ${10}^{32}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$, we explore the necessary conditions to reach a statistical accuracy that allows one to extract unambiguous information on the structure of the Sivers function. In particular, we consider the feasibility of the test on its predicted universality property of changing sign when switching from SIDIS to Drell-Yan processes.

We study the constraints on a minimal supersymmetric seesaw model imposed by neutrino data, charged lepton flavor violation, thermal leptogenesis, and perturbativity. We show that it is possible to constrain the three heavy Majorana neutrino masses as well as the complex Yukawa coupling matrix. Our results provide a first step towards a seesaw benchmark model for further phenomenological studies and model building.

A factorization of spacetime of the form $\mathrm{time}\times {\mathcal{M}}^3\times {\mathcal{M}}^3\times {\mathcal{M}}^3$ is considered in this paper as the closed string background in type IIA string theory. The idea behind this construction is that each ${\mathcal{M}}^3$ might give rise to one large spatial dimension of 4-dimensional spacetime in the closed string sector. In the open string sector, intersecting D6-branes can be constructed for the simple choice of an orientifolded ${\mathcal{M}}^3=T^3$ in a similar way as on the prominent $T^6=T^2\times T^2\times T^2$ using exact conformal field theory (CFT). The D6-branes then are allowed to span general 2-cycles on each $T_i^3$. The intersection 1-cycles between two stacks of branes on one $T_i^3$ can be understood as one spatial dimension of the effective 4-dimensional “spacetime“ for the massless chiral fermions charged under these two stacks. In addition to the known solutions to the Ramond-Ramond (R-R) tadpole equations conserving $(3+1)$-dimensional Poincaré invariance, this allows for solutions with globally just $(2+1)$- or $(1+1)$-Poincaré invariance. For nonsupersymmetric solutions, a string tree-level and one-loop potential for the scalar moduli (including the spacetime radii) is generated in the Neveu-Schwarz (NS-NS) sector. Here, this potential is interpreted dynamically for radii and dilaton in order to describe the global evolution of the universe. In the late time picture, $(3+1)$-dimensional global Poincaré invariance can be restored well within experimental bounds. This approach links particle properties (the chiral massless fermion spectrum) directly to the global evolution of the universe by the scalar potential, both depending on the same topological wrapping numbers. In the future, this might lead to much better falsifiable phenomenological models.

The commutator of $:\varphi (x)\star \varphi (x):$ with ${\partial }_{\mu }^y:\varphi (y)\star \varphi (y):$ fails to vanish at equal times and thus also fails to obey microcausality at spacelike separation even for the case in which ${\theta }^{0i}=0$. The failure to obey microcausality for these sample observables implies that this form of noncommutative field theory fails to obey microcausality in general. This result holds generally when there are time derivatives in the observables. We discuss possible responses to this problem.

We study the dynamics of strongly interacting gauge-theory matter (modeling quark-gluon plasma) in a boost-invariant setting using the AdS/CFT correspondence. Using Fefferman-Graham coordinates and with the help of holographic renormalization, we show that perfect fluid hydrodynamics emerges at large times as the unique nonsingular asymptotic solution of the nonlinear Einstein equations in the bulk. The gravity dual can be interpreted as a black hole moving off in the fifth dimension. Asymptotic solutions different from perfect fluid behavior can be ruled out by the appearance of curvature singularities in the dual bulk geometry. Subasymptotic deviations from perfect fluid behavior remain possible within the same framework.

We discuss the influence of the cosmological constant on the gravitational equations of motion of bodies with arbitrary masses and eventually solve the two-body problem. Observational constraints are derived from measurements of the periastron advance in stellar systems, in particular, binary pulsars and the solar system. Up to now, Earth and Mars data give the best constraint, $\Lambda \lesssim {10}^{-36}{\mathrm{km}}^{-2}$; bounds from binary pulsars are potentially competitive with limits from interplanetary measurements. If properly accounting for the gravito-magnetic effect, this upper limit on $\Lambda$ could greatly improve in the near future thanks to new data from planned or already operating space missions.

In the context of the 331 models, we consider constraints on the extra neutral boson $Z^{\prime }$ predicted by the model, where three different quark family assignments are identified. Using the ansatz of Matsuda as an specific texture for the quark mass matrices, we obtain allowed regions associated with the $Z\mathrm{\text{−}}{Z}^{\prime }$ mixing angle, the mass of the $Z^{\prime }$ boson and the parameter $\beta$ which determines different 331 models. The $Z_1$ and $Z_2$ decays with and without flavor changing are also considered. The flavor changing decays of the $Z_1$ boson into quarks at tree level are highly suppressed by the $Z\mathrm{\text{−}}{Z}^{\prime }$ mixing angle, obtaining the same order of magnitude as the standard model prediction at one-loop level. The $Z_2$ decay widths are calculated with and without flavor changing, where oblique radiative corrections at one loop accounts for about $1\%–4\%$ deviations.

Supersymmetry combined with little Higgs can render the Higgs vacuum expectation value super-little, providing models of electroweak symmetry breaking free from fine-tunings. We discuss the difficulties that arise in implementing this idea and propose one simple successful model. Thanks to appropriately chosen Higgs representations, $D$-terms give a negligible tree-level mass term to the Goldstone. The fermion representations are anomaly free, generation independent, and embeddable into an SU(6) grand unified theory. A simple mechanism provides the large top quark mass.

We describe the extension of the improvement program for bilinear operators composed of Wilson fermions to nondegenerate dynamical quarks. We consider two, three and four flavors, and both flavor nonsinglet and singlet operators. We find that there are many more improvement coefficients than with degenerate quarks, but that, for three or four flavors, nearly all can be determined by enforcing vector and axial Ward identities. The situation is worse for two flavors, where many more coefficients remain undetermined.

In this paper we deal with the issue of Lorentz symmetry breaking in quantum field theories formulated in a noncommutative space-time. We show that, unlike in some recent analysis of quantum gravity effects, supersymmetry does not protect the theory from the large Lorentz-violating effects arising from the loop corrections. We take advantage of the noncommutative Wess-Zumino model to illustrate this point.