arXiv subjects
Publications and source records attributed to G. P. Vacca.
We study the collapse of a self-gravitating and radiating shell. Matter constituting the shell is quantized and the construction is viewed as a semiclassical model of possible black hole formation. It is shown that the shell internal degrees of freedom are excited by the quantum non-adiabaticity of the collapse and, consequently, on coupling them to a massless scalar field, the collapsing matter emits a burst of coherent (thermal) radiation.
A review on how the Odderon idea does appear in QCD is given. In the last years it has been developed a non-perturbative QCD approach based on the stochastic vacuum model and a perturbative one based on resummation techniques in the small x QCD region. Last developments on the perturbative analysis are shown in some details, in particular in application to diffractive eta_c production.
Using a set of new odderon states, we calculate their contribution to the diffractive eta_c photo- and electroproduction process. Compared to previous simple 3-gluon exchange calculations we find an enhancement of about one order of magnitude in the cross section. The t-dependence of the cross section exhibits a dip structure in the small t region.
Our aim is to show how the reggeization of the gluon, encoded in the bootstrap property of the BFKL kernel, permits to calculate the interaction kernel in the octet colour channel in the forward and non forward direction, for the quark contribution, starting from the known gluon trajectory up to 2nd order. To this end an ansatz to solve the bootstrap equation is used. The obtained result, for what regard the quark contribution, has been verified by direct Feynman diagram calculations.
We present and discuss a new bound state solution of the three gluon system in perturbative QCD. It carries the quantum numbers of the odderon, has intercept at one and couples to the impact factor $γ^* \to η_c$.
Using the results recently obtained for the non-forward quark and gluon impact factors, it is shown that their form in the gluon colour channel is consistent with the ``third bootstrap condition'', namely, that they should be proportional to the gluon wave function. The gluon wave function found from this assumption is used to write the full bootstrap condition for the gluonic potential in the next-to-leading order.
We study chaotic inflation driven by a real, massive, homogeneous minimally coupled scalar field in a flat Robertson-Walker spacetime. The semiclassical limit for gravity is considered, whereas the scalar field is treated quantum mechanically by the technique of invariants in order to also investigate the dynamics of the system for non-classical states of the latter. An inflationary stage is found to be possible for a large set of initial quantum states, obviously including the coherent ones. States associated with a vanishing mean value of the field (such as the vacuum and the thermal) can also lead to inflation, however for such states we cannot make a definitive prediction due to the importance of higher order corrections during inflation. The results for the above coupled system are described and their corrections evaluated perturbatively.
The semi-classical collapse, including lowest order back-reaction, of a thin shell of self-gravitating quantized matter is illustrated. The conditions for which self-gravitating matter forms a thin shell are first discussed and an effective Lagrangian for such matter is obtained. The matter-gravity system is then quantized, the semi-classical limit for gravitation is taken and the method of adiabatic invariants is applied to the resulting time dependent matter Hamiltonian. The governing equations are integrated numerically, for suitable initial conditions, in order to illustrate the effect of back-reaction, due to the creation of matter, in slowing down the collapse near the horizon.
The Regge limit in perturbative QCD for processes as DIS (low x) and photon or onia-particles scattering is considered. In the first part a phenomenological approach for the inclusion of the running coupling, preserving the gluon reggeization property, is analyzed. In particular the spectrum of the hard pomeron equation and the asymptotic form of the solution are used to study scattering processes with also inclusive jet production. The singlet part of the proton structure function is evolved towards the low x region according to the full equation. In the second part the problem of unitarity in the QCD is considered. Following the general Bartels approach the four reggeized gluon system is studied in the large number of colours limit. The interplay between double pomeron exchange and triple pomeron vertex contributions is studied. The conformal invariance of the three pomeron vertex is shown in terms of a building block function, and the coupling to pomerons has been considered to make contact with the colour dipole picture which presents a similar triple pomeron interaction. It is also shown that in the A.H. Mueller approach his equation for higher order colour dipole densities leads to solutions which can be represented as fan diagrams with only triple pomeron vertices. Finally we draw some conclusion and open problems.
In the hard pomeron theory with the number of colours Nc in the infinity limit the diffractive amplitude obtained in [3] is compared with the results found for Nc=3 in [1] and in the dipole approach in [5]. It is shown that the double pomeron exchange contribution can be substituted by an equivalent triple pomeron interaction term. After such a substitution the triple pomeron vertices in [1,3,5] essentially coincide. It is demonstrated that, in any form, the triple pomeron vertex is conformal invariant. It is also shown that higher order densities in the dipole approach do not involve 1 to k pomeron verteces with k>2 but are rather given by a set of pomeron fan diagrams with only a triple pomeron coupling.
The identification of the particle creation and distruction operators is discussed.