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Alfaro, J., Rubio, C., & San Martin, M. (2023). Cosmological Fluctuations in Delta Gravity. Universe, 9(7), 315.
Abstract: About 70% of the Universe is Dark Energy, but the physics community still does not know what it is. Delta gravity (DG) is an alternative theory of gravitation that could solve this cosmological problem. Previously, we studied the Universe's accelerated expansion, where DG was able to explain the SNeIa data successfully. In this work, we computed the cosmological fluctuations in DG that give rise to the CMB through a hydrodynamic approximation. We calculated the gauge transformations for the metric and the perfect fluid to present the equations of the evolution of cosmological fluctuations. This provided the necessary equations to solve the scalar TT power spectrum in a semianalytical way. These equations are useful for comparing the DG theory with astronomical observations and thus being able to constrain the DG cosmology.

Nastase, H., Rojas, F., & Rubio, C. (2022). Celestial IR divergences in general mostsubleadingcolor gluon and gravity amplitudes. J. High Energy Phys., (1), 136.
Abstract: Gluon amplitudes at mostsubleading order in the 1/N expansion share a remarkable simplicity with graviton amplitudes: collinear divergences are completely absent in both and, as a consequence, their full IR behavior arises from soft gluon/graviton exchange among the external states. In this paper we study the effect of allloop IR divergences of celestial mostsubleading color gluon amplitudes and their similarities with the celestial gravity case. In particular, a simple celestial exponentiation formula for the dipole part can be written. We also analize how this exponentiation is modified by nondipole contributions. Finally we also show that, in the Regge limit, the soft factor satisfies the KnizhnikZamolodchikov equation hinting at the possibility that, in this limit, an effective WessZuminoWitten model would describe the dynamics of the infrared sector.
Keywords: Scattering Amplitudes; Conformal Field Theory

Rubio, C. A., Asenjo, F. A., & Hojman, S. A. (2019). Quantum Cosmologies Under Geometrical Unification of Gravity and Dark Energy. Symmetry, 11(7).
Abstract: A FriedmannRobertsonWalker Universe was studied with a dark energy component represented by a quintessence field. The Lagrangian for this system, hereafter called the FriedmannRobertsonWalkerquintessence (FRWq) system, was presented. It was shown that the classical Lagrangian reproduces the usual two (second order) dynamical equations for the radius of the Universe and for the quintessence scalar field, as well as a (first order) constraint equation. Our approach naturally unified gravity and dark energy, as it was obtained that the Lagrangian and the equations of motion are those of a relativistic particle moving on a twodimensional, conformally flat spacetime. The conformal metric factor was related to the dark energy scalar field potential. We proceeded to quantize the system in three different schemes. First, we assumed the Universe was a spinless particle (as it is common in literature), obtaining a quantum theory for a Universe described by the KleinGordon equation. Second, we pushed the quantization scheme further, assuming the Universe as a Dirac particle, and therefore constructing its corresponding Dirac and Majorana theories. With the different theories, we calculated the expected values for the scale factor of the Universe. They depend on the type of quantization scheme used. The differences between the Dirac and Majorana schemes are highlighted here. The implications of the different quantization procedures are discussed. Finally, the possible consequences for a multiverse theory of the Dirac and Majorana quantized Universe are briefly considered.
