The 4PI effective action for $\phi^4$ theory

In the symplectic Lagrangian framework we in a new fashion embed an irreducible massive vector-tensor theory into a gauge invariant system, which has become reducible, by extending the configuration space to include an additional pair of scalar and vector fields, which give the desired Wess-Zumino action. A comparison with the BFT Hamiltonian embedding approach is also given.Received: 13 January 2004, Published online: 16 March 2004     

Spectra and decays of $\pi \pi$ and $\pi K$ atoms

We describe the spectra and decays of and atoms within a non-relativistic effective field theory. The evaluations of the energy shifts and widths are performed at next-to-leading order in isospin symmetry breaking. We provide general formulae for all S-states, and discuss the states with angular momentum one in some detail. The prediction for the lifetime of the atom in its ground state yields s.Received: 9 May 2004, Published online: 23 July 2004     

The $\beta$-function in duality-covariant non-commutative $\phi^4$-theory

We compute the one-loop -functions describing the renormalisation of the coupling constant and the frequency parameter for the real four-dimensional duality-covariant non-commutative -model, which is renormalisable to all orders. The contribution from the one-loop four-point function is reduced by the one-loop wavefunction renormalisation, but the -function remains non-negative. Both and vanish at the one-loop level for the duality-invariant model characterised by . Moreover, also vanishes in the limit , which defines the standard non-commutative -quantum field theory. Thus, the limit exists at least at the one-loop level.Received: 19 March 2004, Published online: 5 May 2004     

Neutralino pair production in a $\gamma \gamma $ collider

We present a complete one-loop study of the process and the predicted cross section in a Linear Collider. A suitable numerical code, PLATONlc, valid for any set of real MSSM parameters, is released. This study and code are complementary to those suitable for dark matter detection through the inverse process describing neutralino-neutralino annihilation at rest, which were presented previously. If SUSY is realized in nature, both codes should be very helpful in future astrophysical and collider studies of the neutralino sector.Received: 6 November 2003, Published online: 9 January 2004Programme dActions Intégrées Franco-Hellenique, Platon 04100 UM.     

Effect of top quark spin on the unparticle couplings in $\gamma\gamma \to t\bar{t}$

We investigate the potential of γ γ collisions to probe scalar unparticle couplings via top–antitop quark pair production. We find 95% confidence level limits on the unparticle couplings with an integrated luminosity of 500 fb⁻¹ and an energy of  TeV. We investigate the effect of the top quark spin polarization on the unparticle couplings. It is shown that spin polarization of the top quark leads to a significant improvement in the sensitivity limits.     

Different effect of the hyperons $\Lambda$ and $\Xi$ on the nuclear core

We demonstrate the different effect of strange impurities ( and ) on the static properties of nuclei within the framework of the relativistic mean-field model. Systematic calculations show that the glue-like role of the -hyperon is universal for all -hypernuclei considered. However, the -hyperon has a glue-like role only for the protons distribution in nuclei, while for the neutrons distribution it plays a repulsive role. On the other hand, the -hyperon attracts the surrounding neutrons and reveals a repulsive force to the protons. Possible explanations of the above observation are discussed.Received: 10 March 2003, Revised: 6 November 2003, Published online: 5 May 2004PACS: 21.80. + a Hypernuclei - 24.10.Cn Many-body theory     

Towards a model-independent determination of the $\phi\to \gamma f_0$ coupling

A guide to the composition of the enigmatic f ₀(980) and a ₀(980) states is their formation in -radiative decays. Precision data are becoming available from the KLOE experiment at the DA NE machine at Frascati, as well as results from SND and CMD-2 at VEPP-2M at Novosibirsk. We show how the coupling of the f ₀(980) to this channel can be extracted from these, independently of the background provided by production. To do this we use the fact that the behaviour of both the f ₀(980) and cannot be determined by these data alone, but is strongly constrained by experimental results from other hadronic processes as required by unitarity. We find that the resulting coupling for the is GeV with a background that is quite unlike that assumed if unitarity is neglected. This provides an object lesson in how unitarity teaches us to add resonances. Not surprisingly the result is crucially dependent on the pole position of the f ₀(980), for which there are still sizeable uncertainties. At present this leads to an uncertainty in the branching ratio which can only be fixed by further precision data on the f ₀(980). Nevertheless, the is now the same order of magnitude as the experimental .Received: 25 March 2003, Published online: 5 September 2003     

QCD saturation and $\gamma^{*}$-$\gamma^{*}$ scattering

Two photon collisions at high energy have an important theoretical advantage: the simplicity of the initial state, which gives us a unique opportunity to calculate these processes for large virtualities of both photons in the perturbative QCD approach. In this paper we study QCD saturation in two photon collisions in the framework of the Glauber-Mueller approach. The Glauber-Mueller formula is derived emphasising the impact parameter dependence (b_t) of the dipole-dipole amplitude. It is shown that non-perturbative QCD contributions are needed to describe the large b _t behaviour, and the way how to deal with them is suggested. Our approach can be viewed as the model for the saturation in which the entire impact parameter dependence is determined by the initial conditions. The unitarity bound for the total cross section, its energy dependence as well as predictions for future experiments are discussed. It is argued that the total cross section increases faster than any power of in a wide range of energy or x, namely -, where reflects the x dependence of the gluon density and is the pion mass. Received: 22 November 2002 / Revised version: 27 January 2003 / Published online: 5 May 2003 RID="a" ID="a" e-mail: kozlov@post.tau.ac.il RID="b" ID="b" e-mail: leving@post.tau.ac.il and levin@mail.desy.de     

Partial wave analysis of $\bar pp \to \bar \Lambda \Lambda$

A partial wave analysis of PS185 data for is presented. A ³ S ₁ cusp is identified in the inverse process at threshold, using detailed balance to deduce cross sections from . Partial wave amplitudes for ³ P ₀, ³ F ₃, ³ D ₃ and ³ G ₃ exhibit a behaviour very similar to resonances observed in Crystal Barrel data. With this identification, the data then provide evidence for a new I = 0, J ^PC = 1^- resonance with mass MeV, MeV, coupling to both ³ S ₁ and ³ D ₁.Received: 4 June 2004, Published online: 9 July 2004     

The $\gamma \gamma \rightarrow H^0 H^0$ decay in non-commutative quantum electrodynamics

We study the possibility of detecting non-commutative QED through neutral Higgs boson pair production at a collider. This is based on the assumption that H⁰ interacts directly with the photon as suggested by symmetry considerations. The sensitivity of the cross-section to the non-commutative scale and the Higgs mass is investigated. Received: 28 August 2002 / Revised version: 15 November 2002 / Published online: 19 February 2003     

Search for resonant $\tilde\nu$ production at $\sqrt{s} = $ 183 to 208 GeV

Searches for resonant production in e ⁺ e ^- collisions under the assumption that R-parity is not conserved and that the dominant R-parity violating coupling is or used data recorded by DELPHI in 1997 to 2000 at centre-of-mass energies of 183 to 208 GeV. No deviation from the Standard Model was observed. Upper limits are given for the and couplings as a function of the sneutrino mass and total width. The limits are especially stringent for sneutrino masses equal to the centre-of-mass energies with the highest integrated luminosities recorded. Received: 14 January 2003 / Published online: 14 March 2003     

Three-body baryonic $\overline B\to \Lambda \bar p \pi$ decays and such

We study the decay rates and spectra of , , , , and modes in the factorization approach. The baryon pairs are produced through vector, axial vector, scalar and pseudoscalar operators. Previous predictions, including ours, are an order of magnitude too small compared to experiment. By incorporating QCD counting rules and studying the asymptotic behavior, we find an earlier relation between the pseudoscalar and axial vector form factors to be too restrictive. Instead, the pseudoscalar and scalar form factors are related asymptotically. Following this approach, the measured rate () and spectrum can be understood, and should be dominantly left-hand polarized, while we expect . These results and other predictions can be checked soon. Received: 27 February 2003 / Published online: 5 May 2003     

Gauge theories on the $\kappa$-Minkowski spacetime

This study of gauge field theories on -deformed Minkowski spacetime extends previous work on field theories on this example of a non-commutative spacetime. We construct deformed gauge theories for arbitrary compact Lie groups using the concept of enveloping algebra-valued gauge transformations and the Seiberg-Witten formalism. Derivative-valued gauge fields lead to field strength tensors as the sum of curvature- and torsion-like terms. We construct the Lagrangians explicitly to first order in the deformation parameter. This is the first example of a gauge theory that possesses a deformed Lorentz covariance.Received: 17 December 2003, Revised: 6 May 2004, Published online: 23 June 2004     

Process $$\gamma \gamma \to \nu \bar \nu$$ in a strong magnetic field

The three-vertex loop amplitude in a strong magnetic field are analyzed in a general form by using the asymptotic behavior of the electron propagator in an external field. The process \(\gamma \gamma \to \nu \bar \nu\) is studied in terms of the scalar-vector-vector (SVV), pseudoscalar-vector-vector (PVV), vector-vector-vector (VVV), and axial-vector-vector-vector (AVV) combinations of couplings. It is shown that only in the case of the SVV combination does the amplitude grow linearly with increasing magnetic-field strength, the amplitudes evaluated with the other combinations of couplings (PVV, VVV, and AVV) featuring no linearly increasing terms. The process \(\gamma \gamma \to \nu \bar \nu\) is also studied within the left-right model, which is an extension of the Standard Model of electroweak interactions and which may involve an effective scalar ννee coupling. Possible astrophysical manifestations of this process are discussed.     

Diffractive $\gamma \gamma$ production at hadron colliders

We compute the cross section for exclusive double-diffractive production at the Tevatron, , and the LHC. We evaluate both the gg and -channel exchange contributions to the process. The observation of exclusive production at the Tevatron will provide a check on the model predictions and offer an opportunity to confirm the expectations for exclusive double-diffractive Higgs production at the LHC.Received: 10 September 2004, Revised: 8 October 2004, Published online: 1 December 2004     

High-statistics measurement of the $\beta$ -delayed $\alpha$ spectrum of 20Na

The European Physical Journal A - A measurement of the 20Na $ \beta$ -delayed alpha spectrum with a high-granularity setup has allowed the decay scheme to be revised on several points. Three new...     

Application of large deviation theory to the mean-field $\boldsymbol{\varphi}^\mathsf{4}$-model

A large deviation technique is used to calculate the microcanonical entropy function s(v,m) of the mean-field ϕ⁴-model as a function of the potential energy v and the magnetization m. As in the canonical ensemble, a continuous phase transition is found. An analytical expression is obtained for the critical energy v_c(J) as a function of the coupling parameter J.