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Barenboim, G., Ternes, C. A., & Tortola, M. (2020). CPT and CP, an entangled couple. J. High Energy Phys., 07(7), 155–12pp.
Abstract: Even though it is undoubtedly very appealing to interpret the latest T2K results as evidence of CP violation, this claim assumes CPT conservation in the neutrino sector to an extent that has not been tested yet. As we will show, T2K results are not robust against a CPT-violating explanation. On the contrary, a CPT-violating CP-conserving scenario is in perfect agreement with current neutrino oscillation data. Therefore, to elucidate whether T2K results imply CP or CPT violation is of utter importance. We show that, even after combining with data from NO nu A and from reactor experiments, no claims about CP violation can be made. Finally, we update the bounds on CPT violation in the neutrino sector.
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Pich, A., Rosell, I., & Sanz-Cillero, J. J. (2020). Bottom-up approach within the electroweak effective theory: Constraining heavy resonances. Phys. Rev. D, 102(3), 035012–12pp.
Abstract: The LHC has confirmed the existence of a mass gap between the known particles and possible new states. Effective field theory is then the appropriate tool to search for low-energy signals of physics beyond the Standard Model. We adopt the general formalism of the electroweak effective theory, with a nonlinear realization of the electroweak symmetry breaking, where the Higgs is a singlet with independent couplings. At higher energies we consider a generic resonance Lagrangian which follows the above-mentioned nonlinear realization and couples the light particles to bosonic heavy resonances with J(P) = 0(+/-) and J(P) = 1(+/-). Integrating out the resonances and assuming a proper short-distance behavior, it is possible to determine or to constrain most of the bosonic low-energy constants in terms of resonance masses. Therefore, the current experimental bounds on these bosonic low-energy constants allow us to constrain the resonance masses above the TeV scale, by following a typical bottom-up approach, i.e., the fit of the low-energy constants to precise experimental data enables us to learn about the high-energy scales, the underlying theory behind the Standard Model.
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Delhom, A. (2020). Minimal coupling in presence of non-metricity and torsion. Eur. Phys. J. C, 80(8), 728–17pp.
Abstract: We deal with the question of what it means to define a minimal coupling prescription in presence of torsion and/or non-metricity, carefully explaining while the naive substitution partial derivative -> del introduces extra couplings between the matter fields and the connection that can be regarded as non-minimal in presence of torsion and/or non-metricity. We will also investigate whether minimal coupling prescriptions at the level of the action (MCPL) or at the level of field equations (MCPF) lead to different dynamics. To that end, we will first write the Euler-Lagrange equations for matter fields in terms of the covariant derivatives of a general non-Riemannian space, and derivate the form of the associated Noether currents and charges. Then we will see that if the minimal coupling prescriptions is applied as we discuss, for spin 0 and 1 fields the results of MCPL and MCPF are equivalent, while for spin 1/2 fields there is a difference if one applies the MCPF or the MCPL, since the former leads to charge violation.
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Ferreiro, A., & Navarro-Salas, J. (2020). Running gravitational couplings, decoupling, and curved spacetime renormalization. Phys. Rev. D, 102(4), 045021–6pp.
Abstract: We propose to slightly generalize the DeWitt-Schwinger adiabatic renormalization subtractions in curved space to include an arbitrary renornialization mass scale mu. The new predicted running for the gravitational couplings are fully consistent with decoupling of heavy massive fields. This is a somewhat improvement with respect to the more standard treatment of minimal (DeWitt-Schwinger) subtractions via dimensional regularization. We also show how the vacuum metamorphosis model emerges from the running couplings.
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Bernabeu, J. (2020). Symmetries and Their Breaking in the Fundamental Laws of Physics. Symmetry-Basel, 12(8), 1316–27pp.
Abstract: Symmetries in the Physical Laws of Nature lead to observable effects. Beyond the regularities and conserved magnitudes, the last few decades in particle physics have seen the identification of symmetries, and their well-defined breaking, as the guiding principle for the elementary constituents of matter and their interactions. Flavour SU(3) symmetry of hadrons led to the Quark Model and the antisymmetric requirement under exchange of identical fermions led to the colour degree of freedom. Colour became the generating charge for flavour-independent strong interactions of quarks and gluons in the exact colour SU(3) local gauge symmetry. Parity Violation in weak interactions led us to consider the chiral fields of fermions as the objects with definite transformation properties under the weak isospin SU(2) gauge group of the Unifying Electro-Weak SU(2) x U(1) symmetry, which predicted novel weak neutral current interactions. CP-Violation led to three families of quarks opening the field of Flavour Physics. Time-reversal violation has recently been observed with entangled neutral mesons, compatible with CPT-invariance. The cancellation of gauge anomalies, which would invalidate the gauge symmetry of the quantum field theory, led to Quark-Lepton Symmetry. Neutrinos were postulated in order to save the conservation laws of energy and angular momentum in nuclear beta decay. After the ups and downs of their mass, neutrino oscillations were discovered in 1998, opening a new era about their origin of mass, mixing, discrete symmetries and the possibility of global lepton-number violation through Majorana mass terms and Leptogenesis as the source of the matter-antimatter asymmetry in the universe. The experimental discovery of quarks and leptons and the mediators of their interactions, with physical observables in spectacular agreement with this Standard Theory, is the triumph of Symmetries. The gauge symmetry is exact only when the particles are massless. One needs a subtle breaking of the symmetry, providing the origin of mass without affecting the excellent description of the interactions. This is the Brout-Englert-Higgs Mechanism, which produces the Higgs Boson as a remnant, discovered at CERN in 2012. Open present problems are addressed with by searching the New Physics Beyond-the-Standard-Model.
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