https://hdl.handle.net/20.500.12008/38538 2026-02-15T01:59:03Z https://hdl.handle.net/20.500.12008/49471 Título: Spherically symmetric loop quantum gravity: Schwarzschild spacetimes with a cosmological constant. Autor: Mato, Esteban; Olmedo, Javier; Saini, Sahil Resumen: We provide a quantization of the Schwarzschild spacetime in the presence of a cosmological constant, based on midisuperspace methods developed in the spherically symmetric sector of loop quantum gravity, using in particular the 'improved dynamics' scheme. We include both the de Sitter and anti-de Sitter cases. We find that the quantization puts a Planckian positive upper limit on the possible values of the cosmological constant similar to the bounds obtained earlier from studies of homogeneous spacetimes. This means that, for negative cosmological constant, no negative bound is found. Moreover, using semiclassical physical states, we obtain the effective metric and demonstrate the causal structure for various cases. Quantum gravity modifications ensure that the singularity is replaced by a transition surface in all the cases, where the curvature invariants approach mass-independent Planckian bounds. Analysis of the effective stress-energy tensor shows that the null energy condition is strongly violated in the vicinity of the transition surface. Moreover, it shows a weaker asymptotic fall off for a nonvanishing cosmological constant, which could have interesting phenomenological implications. 2024-01-01T00:00:00Z https://hdl.handle.net/20.500.12008/49469 Título: Unitarization of the one-loop graviton-graviton scattering amplitudes and study of the graviball. Autor: Oller, J.A.; Peláez, Marcela Resumen: From the graviton-graviton scattering amplitudes calculated perturbatively in quantum gravity to the oneloop order, we develop further a formalism that allows one to calculate infrared-finite partial-wave amplitudes fulfilling perturbative unitarity. As a result of this process a parameter dubbed ln𝑎 emerges that separate between infrared and typical external momenta. The resulting partial-wave amplitudes are next unitarized by employing the Inverse Amplitude Method and the algebraic-𝑁∕𝐷 method. Then, the graviball resonance, with a similar pole position, is confirmed in the 𝑆-wave partial-wave amplitude for all unitarization methods, also with respect to the unitarization of only the leading-order amplitude. Although the spectrum of the theory is independent of the specific value of ln𝑎, the requirement for a well-behaved unitarized effective field theory of gravity identifies the optimal range of ln𝑎 for our next-to-leading-order calculations as 0.5 ≲ ln𝑎≲1.7. Briefly, we discuss the 𝐷-wave scattering that is weaker than the 𝑆-wave scattering, repulsive and non-resonant for ln𝑎 ≈1. 2025-01-01T00:00:00Z https://hdl.handle.net/20.500.12008/49467 Título: The EFT of large spin mesons. Autor: Cuomo, Gabriel; Dubovsky, Sergei; Hernández-Chifflet, Guzmán; Monin, Alexander; Zare, Shahrzad Resumen: We use effective string theory to study mesons with large spin J in large Nc QCD as rotating open strings. In the first part of this work, we formulate a consistent effective field theory (EFT) for open spinning strings with light quarks. Our EFT provides a consistent treatment of the endpoints' singularities that arise in the massless limit. We obtain results, in a systematic 1/J expansion, for the spectrum of the leading and daughter Regge trajectories. Interestingly, we find that the redshift factor associated with the quarks' acceleration implies that the applicability regime of the EFT is narrower compared to that of static flux tubes. In the second part of this work, we discuss several extensions of phenomenological interests, including mesons with heavy quarks, the quarks' spin and the daughter Regge trajectories associated with the worldsheet axion, a massive string mode identified in lattice simulations of 4d flux tubes. We compare our predictions with 4d QCD spectroscopy data, and suggest potential stringy interpretations of the observed mesons. We finally comment on the relation between the EFT spectrum and the Axionic String Ansatz, a recently proposed characterization of the spectrum of Yang-Mills glueballs. 2024-01-01T00:00:00Z https://hdl.handle.net/20.500.12008/44910 Título: Nonperturbative gluon exchange in pp elastic scattering at TeV energies. Autor: Bopsin, G.B.; Luna, E. G. S.; Natale, A.A.; Peláez, Marcela Resumen: We investigate the two-gluon-exchange model of the Pomeron using nonperturbative gluon propagators characterized by a dynamical mass scale. We present the results for an analysis of the available pp differential cross section data at TeV energies which accounts for dynamical gluon masses obtained from a non-linear version of the Schwinger-Dyson equations. We show that our two-gluon exchange model gives an excellent description of the LHC data, provided we demand the Reggeization of the scattering amplitude and make a suitable choice for the convolution of proton wave functions. 2023-01-01T00:00:00Z