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Olmo, G. J. (2011). Palatini actions and quantum gravity phenomenology. J. Cosmol. Astropart. Phys., 10(10), 018–15pp.
Abstract: We show that an invariant an universal length scale can be consistently introduced in a generally covariant theory through the gravitational sector using the Palatini approach. The resulting theory is able to capture different aspects of quantum gravity phenomenology in a single framework. In particular, it is found that in this theory field excitations propagating with different energy-densities perceive different background metrics, which is a fundamental characteristic of the DSR and Rainbow Gravity approaches. We illustrate these properties with a particular gravitational model and explicitly show how the soccer ball problem is avoided in this framework. The isotropic and anisotropic cosmologies of this model also avoid the big bang singularity by means of a big bounce.
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Olmo, G. J. (2011). Palatini approach to modified gravity: f(R) theories and beyond. Int. J. Mod. Phys. D, 20(4), 413–462.
Abstract: We review the recent literature on modified theories of gravity in the Palatini approach. After discussing the motivations that lead to consider alternatives to Einstein's theory and to treat the metric and the connection as independent objects, we review several topics that have been recently studied within this framework. In particular, we provide an in-depth analysis of the cosmic speed-up problem, laboratory and solar system tests, the structure of stellar objects, the Cauchy problem, and bouncing cosmologies. We also discuss the importance of going beyond the f(R) models to capture other phenomenological aspects related with dark matter/energy and quantum gravity.
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Hidalgo-Duque, C., & Llanes-Estrada, F. J. (2015). Soft interactions in jet quenching. Int. J. Mod. Phys. A, 30(13), 1550067–25pp.
Abstract: We study the collisional aspects of jet quenching in a high-energy nuclear collision, especially in the final state pion gas. The jet has a large energy, and acquires momentum transverse to its axis more effectively by multiple soft collisions than by few hard scatterings (as known from analogous systems such as J/psi production at Hera). Such regime of large E and small momentum transfer corresponds to Regge kinematics and is characteristically dominated by the pomeron. From this insight we estimate the jet quenching parameter in the hadron medium (largely a pion gas) at the end of the collision, which is naturally small and increases with temperature in line with the gas density and compare it to the jet quenching parameter obtained within the quark-gluon plasma (QGP) phase in widely known perturbative approximations. The physics in the quark-gluon plasma/liquid phase is less obvious, and here we revisit a couple of simple estimates that suggest indeed that the pomeron-mediated interactions are very relevant and should be included in analysis of the jet quenching parameter. Finally, since the occasional hard collisions produce features characteristic of a Levy flight in the q(perpendicular to)(2) plane perpendicular to the jet axis, we suggest one- and two-particle q perpendicular to correlations as interesting experimental probes sensitive to the nature (softness versus hardness) of the interactions of a jet inside the QGP.
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Ghosh, P., Lara, I., Lopez-Fogliani, D. E., Muñoz, C., & Ruiz de Austri, R. (2018). Searching for left sneutrino LSP at the LHC. Int. J. Mod. Phys. A, 33(18-19), 1850110–62pp.
Abstract: We analyze relevant signals expected at the LHC for a left sneutrino as the lightest supersymmetric particle (LSP). The discussion is carried out in the “mu from nu” supersymmetric standard model (mu nu SSM), where the presence of R-parity breaking couplings involving right-handed neutrinos solves the μproblem and reproduces neutrino data. The sneutrinos are pair produced via a virtual W, Z or gamma in the s channel. From the prompt decay of a pair of left sneutrinos LSPs of any family, a significant diphoton signal plus missing transverse energy (MET) from neutrinos can be present in the mass range 118-132 GeV, with 13 TeV center-of-mass energy and an integrated luminosity of 100 fb(-1). In addition, in the case of a pair of tau left sneutrinos LSPs, given the large value of the tau Yukawa coupling diphoton plus leptons and/or multileptons can appear. We find that the number of expected events for the multilepton signal, together with properly adopted search strategies, is sufficient to give a significant evidence for a sneutrino of mass in the range 130-310 GeV, even with the integrated luminosity of 20 fb(-1). In the case of the signal producing diphoton plus leptons, an integrated luminosity of 100 fb(-1) is needed to give a significant evidence in the mass range 95-145 GeV. Finally, we discuss briefly the presence of displaced vertices and the associated range of masses.
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Bordes, J., Hong-Mo, C., & Tsun, T. S. (2018). The Z boson in the framed standard model. Int. J. Mod. Phys. A, 33(32), 1850190–19pp.
Abstract: The framed standard model (FSM), constructed initially for explaining the existence of three fermion generations and the hierarchical mass and mixing patterns of quarks and leptons,(1,2) suggests also a “hidden sector” of particles(3) including some dark matter candidates. It predicts in addition a new vector boson G, with mass of order TeV, which mixes with the gamma and Z of the standard model yielding deviations from the standard mixing scheme, all calculable in terms of a single unknown parameter mG. Given that standard mixing has been tested already to great accuracy by experiment, this could lead to contradictions, but it is shown here that for the three crucial and testable cases so far studied (i) m(Z) – m(W), (ii) Gamma(Z -> l(+)l(-)), (iii) Gamma(Z -> hadrons), the deviations are all within the present stringent experimental bounds provided m(G) > 1 TeV, but should soon be detectable if experimental accuracy improves. This comes about because of some subtle cancellations, which might have a deeper reason that is not yet understood. By virtue of mixing, G can be produced at the LHC and appear as a l(+)l(-) anomaly. If found, it will be of interest not only for its own sake but serve also as a window on to the “hidden sector” into which it will mostly decay, with dark matter candidates as most likely products.
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