International Journal of Modern Physics A

After a short introduction on the importance of the soft and of the diffractive studies in the understanding of minimum bias events, the main results obtained at LHC are discussed. This overview includes identified particle and inclusive measurements, minimum bias and underlying events, all of them shedding light on the soft process production mechanisms. The results of the inelastic cross-section measurements obtained by the LHC experiments and their compatibility are discussed together with the models used to extrapolate the data at low diffractive masses. A review of the most recent diffraction results is presented, showing the different approaches used by the LHC experiments, relying on different experimental techniques. The combination of the results obtained by ALICE, ATLAS, CMS, LHCb and TOTEM provides a wide sample of informations, covering an unprecedented pseudorapidity range. A detailed comparison between the obtained results is shown, followed by a critical discussion on the still existing discrepancies between the experimental data and the Monte Carlo used at LHC to simulate soft and diffractive physics.

We start from the Maurer–Cartan (MC) equations of the superalgebras satisfied by the left-invariant superforms realized on supercoset manifolds of the corresponding supergroups and we derive some new pure spinor constraints. They are obtained by "ghostifying" the MC forms and extending the differential d to a BRST differential. From the superalgebras we single out different subalgebras associated with the different cosets : each choice of ℍ leads to a different weakening of the pure spinor constraints. In each case, the number of parameter is counted and we show that in the cases of Osp(6|4)/U(3)×SO(1, 3), Osp(4|4)/SO(3) ×SO(1, 3) and finally Osp(4|4)/U(2) ×SO(1, 3) the bosonic and fermionic degrees of freedom match in order to provide a c = 0 superconformal field theory. We construct both the Green–Schwarz and the pure spinor sigma model for the case Osp(6|4)/U(3)×SO(1, 3) corresponding to AdS₄ ×ℙ³. The pure spinor sigma model can be consistently quantized.

We propose to include gravity in quantum field theory nonperturbatively, by modifying the propagators so that each virtual particle in a Feynman graph move in the space–time determined by the four-momenta of the other particles in the same graph. By making additional working assumptions, we are able to put this idea at work in a simplified context, and obtain a modified Feynman propagator for the massless neutral scalar field. Our expression shows a suppression at high momentum, strong enough to entail finite results, to all loop orders, for processes involving at least two virtual particles.

We examine the impact of electromagnetic properties of neutrinos on the annihilation of relic neutrinos with ultrahigh energy cosmic neutrinos for the process. For this process, photon–neutrino decoupling temperature is calculated via effective Lagrangian model beyond the standard model. We find that photon–neutrino decoupling temperature can be importantly reduced below the QCD phase transition with the model independent analysis defining electromagnetic properties of neutrinos.

Magnetic moment of electron at finite temperature is directly related to the modified electron mass in the background heat bath. Magnetic moment of electron gets modified at finite temperature also, when it couples with the magnetic field, through its temperature-dependent physical mass. We show that the second-order corrections to the magnetic moment of electron is a complicated function of temperature. We calculate the self-mass induced thermal contributions to the magnetic moment of electron, up to the two-loop level, for temperatures valid around the era of primordial nucleosynthesis. A comparison of thermal behavior of the magnetic moment is also quantitatively studied in detail, around the temperatures below and above the nucleosynthesis temperature.

Starting from a generic second-order Lagrangian density (that describes the dynamics of an Abelian tensor gauge field of degree two and depends on two arbitrary real constants) we first perform the Dirac analysis. This procedure reveals seven distinct situations (dictated by the values of the real parameters that label the second-order Lagrangian density) in each of them one determines the number of degrees of freedom and also a generating set of gauge transformations. Second, with the help of some auxiliary gauge/matter tensor gauge fields of degree three, in each of the seven situations aforementioned, we construct the first-order Lagrangian density corresponding to the second-order one.