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Adolf, P., Hirsch, M., Krieg, S., Pas, H., & Tabet, M. (2024). Fitting the DESI BAO data with dark energy driven by the Cohen-Kaplan-Nelson bound. J. Cosmol. Astropart. Phys., 08(8), 048–18pp.
Abstract: Gravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet (UV) and infrared (IR) cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the IR cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a time-dependent dark energy density. In this paper we confront this idea with recent data from DESI BAO, Hubble and supernova measurements. We find that the CKN model provides a better fit to the data than the Lambda CDM model and can compete with other models of time-dependent dark energy that have been studied so far.
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Albertus, C., Hernandez, E., & Nieves, J. (2010). Hyperfine mixing in electromagnetic decay of doubly heavy bc baryons. Phys. Lett. B, 690(3), 265–271.
Abstract: We investigate the role of hyperfine mixing in the electromagnetic decay of ground state doubly heavy bc baryons. As in the case of a previous calculation on b -> c semileptonic decays of doubly heavy baryons, we find large corrections to the electromagnetic decay widths due to this mixing. Contrary to the weak case just mentioned, we find here that one cannot use electromagnetic width relations obtained in the infinite heavy quark mass limit to experimentally extract information on the admixtures in a model independent way.
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Arbelaez, C., Helo, J. C., Hirsch, M., & Ota, T. (2026). n → Kℓ and the baryon asymmetry of the universe. J. High Energy Phys., 09(9), 099–21pp.
Abstract: The observed baryon asymmetry (BAU) of the universe puts strong constraints on any (B – L)-violating interaction. An observation of a (B – L)-violating nucleon decay channel would therefore have profound implications for our understanding of the BAU. Here we point out that the observation of the final state with a kaon and a charged lepton in a future nucleon decay experiment would hint at (B – L) violation even if the charge of the lepton is not determined experimentally. In SMEFT, this follows from the fact that n -> K + & ell; – arises already at dimension seven, while the (B – L)-conserving decay n -> K – & ell; + requires dimension-ten operators that, in addition, would be accompanied by lower-dimensional (B + L)-violating decay modes. An observation of n -> K & ell; in the absence of other modes such as p -> pi 0 & ell; +, would then strongly suggest that (B – L) is violated.
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Ardu, M., Queiroz, D., & Vives, O. (2025). Asymmetric dark matter in SUSY with approximate R-symmetry. J. Cosmol. Astropart. Phys., 08(8), 013–28pp.
Abstract: We implement the asymmetric dark matter framework, linking the ordinary and dark matter abundances, within a supersymmetric context. We consider a supersymmetric model that respects an approximate U(1)R symmetry, which is broken in such a way that at high temperature the R breaking sector mediate processes in equilibrium, but at the SUSY mass scale, the sparticles asymmetry is frozen. In this framework, the gravitino serves as the dark matter candidate, and its mass is predicted to be similar to 10 GeV to match the observed relic abundance. We identify several realistic spectra; however, the requirement for the Next-to-Lightest Supersymmetric Particle (NLSP) to decay into the gravitino before Big Bang Nucleosynthesis constrains the viable spectrum to masses above 2 TeV.
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Aristizabal Sierra, D., Tortola, M., Valle, J. W. F., & Vicente, A. (2014). Leptogenesis with a dynamical seesaw scale. J. Cosmol. Astropart. Phys., 07(7), 052–20pp.
Abstract: In the simplest type-I seesaw leptogenesis scenario right-handed neutrino annihilation processes are absent. However, in the presence of new interactions these processes are possible and can affect the resulting B – L asymmetry in an important way. A prominent example is provided by models with spontaneous lepton number violation, where the existence of new dynamical degrees of freedom can play a crucial role. In this context, we provide a model-independent discussion of the effects of right-handed neutrino annihilations. We show that in the weak washout regime, as long as the scattering processes remain slow compared with the Hubble expansion rate throughout the relevant temperature range, the efficiency can be largely enhanced, reaching in some cases maximal values. Moreover, the B – L asymmetry yield turns out to be independent upon initial conditions, in contrast to the “standard” case. On the other hand, when the annihilation processes are fast, the right-handed neutrino distribution tends to a thermal one down to low temperatures, implying a drastic suppression of the efficiency which in some cases can render the B – L generation mechanism inoperative.
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Barenboim, G., Fernandez-Martinez, E., Mena, O., & Verde, L. (2010). The dark side of curvature. J. Cosmol. Astropart. Phys., 03(3), 008–17pp.
Abstract: Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d(A)(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Omega(k) in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d(A)(z) up to sufficiently high redshifts z similar to 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z) – Omega(k) degeneracy.
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Bas i Beneito, A., Fajfer, S., & Petrov, A. A. (2026). New avenues for |△B|=2 processes beyond neutron-antineutron oscillations. J. High Energy Phys., 03(3), 124–35pp.
Abstract: We explore baryon-number-violating (|∆B| = 2) processes beyond the well-known neutron-antineutron (n−n‾) oscillations, focusing on the Λ−Λ‾ system. The presence of a strange quark in the Λ baryon introduces a new set of six-quark operators roughly of the form (uds)2, which are different from the (udd)2 operators responsible for n−n‾ oscillations. Using the Standard Model Effective Field Theory (SMEFT), we classify all dimension-9 operators that cause |∆B| = 2 transitions and study their UV completions mediated by exotic scalar fields with trilinear interactions. We demonstrate that in these models, Λ−Λ‾ oscillations can occur at tree level, with n−n‾ mixing potentially appearing at higher loop levels. We employ a chiral effective theory to constrain the effective mass mixing δmΛΛ, deriving bounds from current experimental limits on n−n‾ oscillations and dinucleon decays such as pp → K+K+. These bounds indicate that Λ−Λ‾ oscillations probe a complementary parameter space, sensitive to baryon-number violation at scales up to 10^2 − 10^3 TeV. We show that the existing indirect bounds make it challenging to provide a competitive bound on δmΛΛ at BESIII.
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Bas i Beneito, A., Gargalionis, J., Herrero-Garcia, J., Santamaria, A., & Schmidt, M. A. (2024). An EFT approach to baryon number violation: lower limits on the new physics scale and correlations between nucleon decay modes. J. High Energy Phys., 07(7), 004–37pp.
Abstract: Baryon number is an accidental symmetry of the Standard Model at the Lagrangian level. Its violation is arguably one of the most compelling phenomena predicted by physics beyond the Standard Model. Furthermore, there is a large experimental effort to search for it including the Hyper-K, DUNE, JUNO, and THEIA experiments. Therefore, an agnostic, model-independent, analysis of baryon number violation using the power of Effective Field Theory is very timely. In particular, in this work we study the contribution of dimension six and seven effective operators to |triangle(B – L)| = 0, 2 nucleon decays taking into account the effects of Renormalisation Group Evolution. We obtain lower limits on the energy scale of each operator and study the correlations between different decay modes. We find that for some operators the effect of running is very significant.
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Bas i Beneito, A., Gargalionis, J., Herrero-Garcia, J., & Schmidt, M. A. (2025). Squeezing proton decay and neutrino masses: upper bounds on standard model extensions. J. High Energy Phys., 10(10), 083–40pp.
Abstract: Baryon and lepton number are excellent low-energy symmetries of the Standard Model (SM) that tightly constrain the form of its extensions. In this paper we investigate the possibility that these accidental symmetries are violated in the deep UV, in such a way that one multiplet necessary for their violation lives at an intermediate energy scale M above the electroweak scale. We write down the simplest effective operators containing each multiplet that may couple linearly to the SM at the renormalisable level and estimate the dominant contribution of the underlying UV model to the pertinent operators in the SMEFT: the dimension-5 Weinberg operator and the baryon-number-violating operators up to dimension 7. Our results are upper bounds on the scale M for each multiplet-operator pair, derived from neutrino-oscillation data as well as prospective nucleon-decay searches. We also analyse the possibility that both processes are simultaneously explained within a natural UV model. In addition, we advocate that our framework provides a convenient and digestible way of organising the space of UV models that violate these symmetries.
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Bas i Beneito, A., Palavric, A., & Sainaghi, A. (2026). EFT pathways to |△B|=2: chiral constructions and phenomenology. J. High Energy Phys., 09(9), 091–64pp.
Abstract: We develop a systematic effective field theory framework for studying |triangle B| = 2 interactions across energy scales. Using chiral symmetry, we construct the complete and non-redundant set of operators governing these interactions at low energies and establish their connection to the corresponding operators in the Standard Model effective field theory, as well as to their realizations in baryon chiral perturbation theory. The framework is then applied to the phenomenology of baryon-antibaryon oscillations and dinucleon decay. While oscillations probe only a limited subset of operator structures, dinucleon decay is sensitive to a significantly broader class, including transitions that are otherwise inaccessible. In addition, we identify previously unexplored dinucleon decay channels, which can probe these unconstrained regions of parameter space. More generally, this formalism makes explicit the complementarity of different probes and provides a consistent way to trace baryon-number-violating effects from their ultraviolet origin to low-energy hadronic observables, thereby providing a basis for systematic studies of ultraviolet models generating such interactions.
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