One-loop gg\to b\bar{b} effects in the main irreducible background to exclusive H\to b\bar{b} production at the LHC

We calculate the amplitude of $gg\to b\bar{b}$ production for the colour singlet, J _z =0, di-gluon state at $\mathcal{O}(\alpha_{\mathrm{S}}^{2})$ order. We consider the cancellation and a realistic cut-off, of the infrared divergent terms. We show that the one-loop radiative QCD contributions effectively reduce the Born level result for the central exclusive $b\bar{b}$ cross section at the LHC. This process is essentially the only irreducible QCD background to the exclusive $H\to b\bar{b}$ signal.     

CP violation and the widthZ→b \bar b

We discuss the effect of CP-violatingZb $\bar b$ Zb $\bar b$ G andZb $\bar b$ γ couplings on the width Γ(Z→b $\bar b$ X). The presence of such couplings leads in a natural way to an increase of this width relative to the prediction of the standard model. Various strategies of a direct search for such CP-violating couplings by using CP-odd observables are outlined. The number ofZ bosons required to obtain significant information on the couplings in this way is well within the reach of present LEP experiments.     

Scattering length expansion of the coupled channels\bar pp \to \bar \Lambda \Lambda and\bar \Lambda \Lambda \to \bar \Lambda \Lambda near theΛ production threshold

We fit the scattering lengths in the triplets-,p- andd- waves for the two channels \(\bar pp \to \bar \Lambda \Lambda\) and \(\bar \Lambda \Lambda \to \bar \Lambda \Lambda\) near theΛ production threshold to the differential cross section \(\frac{{d\sigma }}{{d\Omega }}(\bar pp \to \bar \Lambda \Lambda )\) and to the polarization P.     

$$Q\bar{Q}$$ ($$Q\in \{b,c\}$$Q∈{b,c}) spectroscopy using the Cornell potential

The mass spectra and decay properties of heavy quarkonia are computed in nonrelativistic quark-antiquark Cornell potential model. We have employed the numerical solution of Schrödinger equation to obtain their mass spectra using only four parameters namely quark mass (\(m_c\), \(m_b\)) and confinement strength (\(A_{c\bar{c}}\), \(A_{b\bar{b}}\)). The spin hyperfine, spin-orbit and tensor components of the one gluon exchange interaction are computed perturbatively to determine the mass spectra of excited S, P, D and F states. Digamma, digluon and dilepton decays of these mesons are computed using the model parameters and numerical wave functions. The predicted spectroscopy and decay properties for quarkonia are found to be consistent with available data from experiments, lattice QCD and other theoretical approaches. We also compute mass spectra and life time of the \(B_c\) meson without additional parameters. The computed electromagnetic transition widths of heavy quarkonia and \(B_c\) mesons are in tune with available experimental data and other theoretical approaches.     

The Z → c \bar c → γγ*, Z → b \bar b → γγ* triangle diagrams and the Z → γψ, Z → γϒ decays

The approach to the Z → γψ and Z → γ? decay study is presented in detail, based on the sum rules for the Z → c $ \bar c $ → γγ* and Z → b $ \bar b $ → γγ* amplitudes and their derivatives. The branching ratios of the Z → γψ and Z → γ? decays are calculated for different hypotheses on saturation of the sum rules. The lower bounds of Σ _ψ BR(Z → γψ) = 1.95 × 10^?7 and Σ_υ BR(Z → γ?) = 7.23 × 10^?7 are found. Deviations from the lower bounds are discussed, including the possibility of BR(Z → γJ/ψ(1S)) ～ BR(Z → γ?(1S)) ～ 10^?6, that could be probably measured in LHC. The angular distributions in the Z → γψ and Z → γ? decays are also calculated.     

The set of mapsF_{a,b} :x \mapsto x + a + \tfrac{b}{{2\pi }} sin(2πx) with any given rotation interval is contractiblewith any given rotation interval is contractible

Consider the two-parameter family of real analytic maps $F_{a,b} :x \mapsto x + a + \tfrac{b}{{2\pi }}$ sin(2πx) which are lifts of degree one endomorphisms of the circle. The purpose of this paper is to provide a proof that for any closed intervalI, the set of mapsF _a,b whose rotation interval isI, form a contractible set.     

Constraints on low energy QCD parameters from $$\eta \rightarrow 3\pi $$ and $$\pi \pi $$ππ scattering

The \(\eta \,\rightarrow \,3\pi \) decays are a valuable source of information on low energy QCD. Yet they were not used for an extraction of the three flavor chiral symmetry breaking order parameters until now. We use a Bayesian approach in the framework of resummed chiral perturbation theory to obtain constraints on the quark condensate and pseudoscalar decay constant in the chiral limit. We compare our results with recent CHPT and lattice QCD fits and find some tension, as the \(\eta \,\rightarrow \,3\pi \) data seem to prefer a larger ratio of the chiral order parameters. The results also disfavor a very large value of the pseudoscalar decay constant in the chiral limit, which was found by some recent work. In addition, we present results of a combined analysis including \(\eta \,\rightarrow \,3\pi \) decays and \(\pi \pi \) scattering and though the picture does not changed appreciably, we find some tension between the data we use. We also try to extract information on the mass difference of the light quarks, but the uncertainties prove to be large.     

Inclusive decays χ b0,2 → ψD \bar D + X and duality relation

The three-body decays χ _b0,2 → J/ ψc $\bar c$ and the decays x _bJ → J/ ψD $\bar D$ related to them are studied. The differential widths with respect to these decays are calculated analytically, and their total widths are evaluated numerically. The duality relation between these decays and the two-body decays x _b0,2 → J/ ψ(c $\bar c$ ) is verified. The possibility of observing these decays at the LHC and Tevatron colliders is discussed.     

Predictions for $$\Xi _b^- \rightarrow \pi ^- (D_s^- ) \ \Xi _c^0 (2790) \left( \Xi _c^0 (2815) \right) $$ and $$\Xi _b^- \rightarrow \bar{\nu }_l l \ \Xi _c^0 (2790) \left( \Xi _c^0 (2815) \right) $$Ξb-→ν¯llΞc0(2790)Ξc0(2815)

We have performed calculations for the nonleptonic \(\Xi _b^- \rightarrow \pi ^- \ \Xi _c^0 (2790) \left( J=\frac{1}{2}\right) \) and \(\Xi _b^- \rightarrow \pi ^- \ \Xi _c^0 (2815) \left( J=\frac{3}{2}\right) \) decays and the same reactions replacing the \(\pi ^-\) by a \(D_s^-\). At the same time we have also evaluated the semileptonic rates for \(\Xi _b^- \rightarrow \bar{\nu }_l l \ \Xi _c^0 (2790)\) and \(\Xi _b^- \rightarrow \bar{\nu }_l l \ \Xi _c^0 (2815)\). We look at the reactions from the perspective that the \(\Xi _c^0 (2790)\) and \(\Xi _c^0 (2815)\) resonances are dynamically generated from the pseudoscalar–baryon and vector–baryon interactions. We evaluate ratios of the rates of these reactions and make predictions that can be tested in future experiments. We also find that the results are rather sensitive to the coupling of the \(\Xi _c^*\) resonances to the \(D^* \Sigma \) and \(D^* \Lambda \) components.     

How does anticommutator\left\{ {Q_\alpha \bar Q_\beta } \right\} realize energy-momentumP μ in quantum supergravity?

It is investigated to what extent the well-known algebra \(\left\{ {Q^S ,\bar Q^S } \right\} = \gamma ^\mu P_\mu \) in the rigid supersymmetry theory holds in quantum supergravity: The anti-commutator \(\left\{ {Q_\alpha ^S ,\bar Q_\beta ^S } \right\} = \gamma ^m \tilde P_m \) defines an “internal” translation generator \(\tilde P_m \) , quite another from the “external” translation generatorP _μ. It is, however, shown that those two operators give the same matrix elements between any two physical states aside from a proportional factor. Such a “miracle” is caused by some particular properties of global gauge transformation charge universal in gauge theories. These properties are fully clarified in a general manner.     

$\Lambda$ resonances studied in $K^-p\rightarrow \Sigma^0\pi^0$ in a chiral quark model

A chiral quark-model approach is extended to the study of the $\bar{K}N$ scattering at low energies. The process of $K^-p\rightarrow \Sigma^0\pi^0$ at $P_K\lesssim 800$ MeV/c (i.e. the center mass energy $W\lesssim 1.7$ GeV) is investigated. The $\Lambda(1405)S_{01}$ dominates the reactions over the energy region considered here. Around $P_K\simeq 400$ MeV/c, the $\Lambda(1520)D_{03}$ is responsible for a strong resonant peak in the cross section. Our analysis suggests that there exist configuration mixings within the $\Lambda(1405)S_{01}$ and $\Lambda(1670)S_{01}$ as admixtures of the $[\textbf{70},^2\textbf{1},1/2]$ and $[\textbf{70},^2\textbf{8},1/2]$ configurations. The $\Lambda(1405)S_{01}$ is dominated by $[\textbf{70},^2\textbf{1},1/2]$, and $\Lambda(1670)S_{01}$ by $[\textbf{70},^2\textbf{8},1/2]$. The non-resonant background contributions, i.e. $u$-channel and $t$-channel, also play important roles in the explanation of the angular distributions due to amplitude interferences.     

Analysis of the vertexes \Xi_{Q}^{*}′QV , \Sigma_{Q}^{*} \Sigma_{Q}^{}V and radiative decays \Xi_{Q}^{*} \rightarrow ′Q \gamma , \Sigma_{Q}^{*} \rightarrow \Sigma_{Q}^{} \gamma

In this article, we study the vertexes $ \Xi_{Q}^{*}$ ′_Q V and $ \Sigma_{Q}^{*}$ $ \Sigma_{Q}^{}$ V with the light-cone QCD sum rules, then assume the vector meson dominance of the intermediate $ \phi$ (1020) , $ \rho$ (770) and $ \omega$ (782) , and calculate the radiative decays $ \Xi_{Q}^{*}$ $ \rightarrow$ ′_Q $ \gamma$ and $ \Sigma_{Q}^{*}$ $ \rightarrow$ $ \Sigma_{Q}^{}$ $ \gamma$ .     

The Green Function in the n μ $$n_\mu \dot A_\mu = 0{\text{ AND }}\partial _\mu \dot A_\mu = 0 $$ Gauges

A straightforward method for calculating the quantum-field functions in terms of the Yang–Mills gauge theory is proposed. The Green functions of a free gluon in the n _μ $n_\mu \dot A_\mu = 0{\text{ }}and{\text{ }}\partial _\mu \dot A_\mu = 0$ gauges are calculated using the method. New formulas are derived that have no analogy in the literature.     

Are $B\rightarrow\pi K$ CP-asymmetries quantized?

A search for patterns in the numerous B-decay modes now available is necessary in order to test the Cabibbo-Kobayashi-Maskawa theory of CP-violation. In particular, the well-structured pattern of branching ratios may lead to a quantized spectrum for direct CP-asymmetries, providing in this way a rather unique opportunity to discriminate between hadronic final state interaction models.Arrival of the final proofs: 25 June 2003     

Can a non-symmetric metric mimic NCQFT in $e^ + e^- \to \gamma \gamma$?

In the non-symmetric gravitational theory (NGT) the space-time metric departs from the flat-space Minkowski form in such a way that it is no longer symmetric, i.e. . We find that in the most conservative such scenario coupled to quantum field theory, which we call minimally non-symmetric quantum field theory (MNQFT), there are experimentally measurable consequences similar to those from non-commutative quantum field theory (NCQFT). This can be expected from the Seiberg-Witten map which has recently been interpreted as equating gauge theories on non-commutative space-times with those in a field-dependent gravitational background. In particular, in scattering processes such as the pair annihilation , both theories make the same striking prediction that the azimuthal cross section oscillates in . However the predicted number of oscillations differs in the two theories: MNQFT predicts between one and four, whereas NCQFT has no such restriction.Received: 17 May 2004, Revised: 10 September 2004, Published online: 18 November 2004This work was supported by the Department of Physics at Tsinghua University and the Chinese Academy of Sciences.     

O(G μ 2 m t 4 ) electroweak radiative corrections to theZb \bar b vertex

The leading heavy-top two-loop corrections to theZb \(\bar b\) vertex are determined from a direct evaluation of the corresponding Feynman diagrams in the largem _t limit. The leading one-loop top-mass effect is enhanced by \([{{1 + G_\mu m_t^2 ({{9 - \pi ^2 } \mathord{\left/ {\vphantom {{9 - \pi ^2 } 3}} \right. \kern-0em} 3})} \mathord{\left/ {\vphantom {{1 + G_\mu m_t^2 ({{9 - \pi ^2 } \mathord{\left/ {\vphantom {{9 - \pi ^2 } 3}} \right. \kern-0em} 3})} {(8\pi ^2 \sqrt 2 )}}} \right. \kern-0em} {(8\pi ^2 \sqrt 2 )}}]\) . Our calculation confirms a recent result of Barbieri et al..