Abstract
In the near future, the Deep Underground Neutrino Experiment and the European Spallation Source aim to reach unprecedented sensitivity in the search for neutron-antineutron (n- overline{n} ) oscillations, whose observation would directly imply |∆B| = 2 violation and hence might hint towards a close link to the mechanism behind the observed baryon asymmetry of the Universe. In this work, we explore the consequences of such a discovery for baryogenesis first within a model-independent effective field theory approach. We then refine our analysis by including a source of CP violation and different hierarchies between the scales of new physics using a simplified model. We analyse the implication for baryogenesis in different scenarios and confront our results with complementary experimental constraints from dinucleon decay, LHC, and meson oscillations. We find that for a small mass hierarchy between the new degrees of freedom, an observable rate for n- overline{n} oscillation would imply that the washout processes are too strong to generate any sizeable baryon asymmetry, even if the CP violation is maximal. On the other hand, for a large hierarchy between the new degrees of freedom, our analysis shows that successful baryogenesis can occur over a large part of the parameter space, opening the window to be probed by current and future colliders and upcoming n- overline{n} oscillation searches.
Highlights
Well motivated ultraviolet (UV) extensions, e.g. grand unified theories (GUTs) naturally violate B, given the fact that quarks andleptons are often placed in the same representation(s) of the Grand Unified Theory (GUT) gauge group
Our findings suggest that in the low-scale baryogenesis scenario, even for the case of maximal CP violation, successful baryogenesis can only occur when the mass scales mXdd ∼ mXud are sufficiently heavier (at least O(108) GeV) than the electroweak scale such that the washout processes remain largely subdominant as compared to the baryon asymmetry generation through Xdd decays
In case the CP-violating parameter would be given by eq (5.1) rather than being fixed to the maximum value as in figure 20, we find that the entire parameter space of the low-scale baryogenesis scenario cannot reach the observed baryon asymmetry of the Universe
Summary
Since the relevant latest hadronic matrix elements are readily available in an SU(3)C × U(1)EM invariant chiral basis with a SU(2)L ⊗ SU(2)R symmetry [17], we find It convenient to work with it for the numerical evaluation of the n-noscillation rates. We first compute the relevant Wilson coefficients corresponding to a given operator in eq (2.7) at the scale where the heavy NP is integrated out and identify the operator with one of the four independent hadronic matrix elements, which are subject to running effects between the scale where the lattice-QCD nucleon matrix elements are available in the MS scheme and the heavy NP scale where the effective Lagrangian is defined, as discussed in the following subsection. For the NNBAR experiment with an expected improved future sensitivity by an order of magnitude τnN-Nn BAR ≥ 3 × 109 s we find the limit Λ1 ≥ 1.02 × 106 GeV
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