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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 by Fadin et al..

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 ηc production.

The next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet jets production in hadronic collisions and for the forward jet cross section in lepton-hadron collisions are presented in the context of a k t factorizazion formula which resums the leading and next-toleading logarithms of the energy. Both the quark-and gluon-initiated contribution are now computed. This completes the framework for a full phenomenological analysis of Mueller-Navelet jets in NL log(s) approximation. Forward jets phenomenology still requires the NL photon impact factor.

The next-to-leading corrections to the jet vertex which is relevant for the Mueller-Navelet jets production in hadronic collisions and for the forward jet cross section in lepton-hadron collisions are presented in the context of a k t factorizazion formula which resums the leading and next-to-leading logarithms of the energy.

A review of some theoretical aspects of small x QCD physics is given, with a particular emphasis to the relation between the BFKL and the colour dipole approaches. The nonlinear evolution equations one may construct, as a better approximation beyond the linear analysis, are discussed together with their relation to a possible saturation regime.

The relation between the two approaches is discussed both in the linear and nonlinear regimes. It is connected to the gauge invariance and Möbius symmetry in LL perturbative QCD. First corrections beyond the large Nc approximation are discussed for the nonlinear case.

DIS on a two nucleon system in the regge limit is considered. In this framework a review is given of a pQCD approach for the computation of the corrections to the inclusive one jet production cross section at finite number of colors and discuss the general results.

A novel perturbative analysis for the 2 + 1 local supercritical field theory of pomerons is developed. It is based on the PT symmetry of the model which allows to study a similar Hamiltonian with the same real perturbative spectrum. In the lowest non trivial order of perturbation theory the pomeron interactions are shown to lead to the renormalization of the slope. The appearance of a non local interaction for two pomeron states is such that at small coupling only scattering states are present and the spectrum of two particle states is not affected.

In the hard pomeron theory with the number of colours N c → ∞ the diffractive amplitude obtained in [3] is compared with the results found for N c = 3 in [1] and in the dipole approach in . 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.

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.

A general relation between families of (n+1) gluon and n gluon eigenstates of the BKP evolution kernels in the multicolour limit of QCD is derived. It allows to construct an (n + 1) gluon eigenstate if an n gluon eigenstate is known; this solution is Bose symmetric and thus physical for even n. A recently found family of odderon solutions corresponds to the particular case n = 2.

There seems to be a common prejudice that asymptotic safety is either incompatible with, or at best unrelated to, the other topics in the title. This is not the case. In fact, we show that 1) the existence of a fixed point with suitable properties is a promising way of deriving emergent properties of gravity, and 2) there is a sense in which asymptotic safety implies a minimal length. In so doing we also discuss possible signatures of asymptotic safety in scattering experiments.

Within the functional renormalization group approach we study the effective QFT of Einstein gravity and one self-interacting scalar coupled to N f Dirac fermions. We include in our analysis the matter anomalous dimensions induced by all the interactions and analyze the highly non linear beta functions determining the renormalization flow. We find the existence of a non trivial fixed point structure both for the gravity and the matter sector, besides the usual gaussian matter one. This suggest that asymptotic safety could be realized in the gravitational sector and in the standard model. Non triviality in the Higgs sector might involve gravitational interactions.

Starting from the basic path integral in phase space we reconsider the functional approach to the RG flow of the one particle irreducible effective average action. On employing a balanced coarse-graining procedure for the canonical variables we obtain a functional integral with a non trivial measure which leads to a modified flow equation. We first address quantum mechanics for boson and fermion degrees of freedom and we then extend the construction to quantum field theories. For this modified flow equation we discuss the reconstruction of the bare action and the implications on the computation of the vacuum energy density. * [email protected] † [email protected]

In an inflationary regime driven by a free massive inflaton we consider a class of observers which sees an inhomogeneous and isotropic Universe and derive within a genuinely gauge invariant approach the backreaction effects due to long wavelength scalar fluctuations on the associated effective Hubble factor and equation of state. We find that, for such so-called isotropic observers, contrary to what happens for the observables defined by free-falling observers, there is an effect to leading order in the slow-roll parameter in the direction of slowing down the measured rate of expansion and of having an effective equation of state less de Sitter like. From a general point of view the isotropic observers result has to be considered complementary to other cases (observers) in helping to characterize the physical properties of the models under investigation.

After a brief review of the definition and properties of the quantum effective Hamiltonian action we describe its renormalization flow by a functional RG equation. This equation can be used for a non-perturbative quantization and study also of theories with bare Hamiltonians which are not quadratic in the momenta. As an example the vacuum energy and gap of quantum mechanical models are computed. Extensions of this framework to quantum field theories are discussed. In particular one possible Lorentz covariant approach for simple scalar field theories is developed. Fermionic degrees of freedom, being naturally described by a first order formulation, can be easily accommodated in this approach. * [email protected] † [email protected]

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.