An EFT approach to baryon number violation: lower limits on the new physics scale and correlations between nucleon decay modes

Baryon number violation is our most sensitive probe of physics beyond the Standard Model, especially through the study of nucleon decays. Angular momentum conservation requires a lepton in the final state of such decays, kinematically restricted to electrons, muons, or neutrinos. We show that operators involving taus, which are at first sight too heavy to play a role in nucleon decays, still lead to clean nucleon decay channels with tau neutrinos. While many of them are already constrained from existing two-body searches such as p → π+ν, other operators induce many-body decays such as $$ p\to {\eta \pi}^{+}{\overline{\nu}}_{\tau } $$ p → ηπ + ν ¯ τ and n → K+π−ντ that have never been searched for.

Baryon number violation involving tau leptons

Heeck,

Watkins

2024

Baryon-number-violating nucleon decays in ALP effective field theories

Li,

Schmidt,

Yao

2024

The search for baryon-number-violating (BNV) nucleon decay is an intriguing probe of new physics beyond the SM in future neutrino experiments with enhanced sensitivity. The dark sector states such as an axion or axion-like particle (ALP) can induce nucleon decays with distinct signature and kinematics from the conventional nucleon decays. In this work, we study the ALP effective field theories (EFTs) with baryon number violation and the impact of light ALP on BNV nucleon decays. We revisit the dimension-8 BNV operators in the extended EFTs with an ALP field a respecting shift symmetry. The low-energy EFT operators with |∆(B – L)| = 2 and |∆(B – L)| = 0 are matched to the baryon chiral perturbation theory. We obtain the effective chiral Lagrangian and the BNV interactions between ALP and baryons/mesons. The ALP interactions lead to two-body baryon decays B → ℓ (or ν) a and three-body nucleon decays N → M ℓ (or ν) a. We obtain the constraints on the UV scale from the invisible Λ0 decay search at BESIII, the invisible neutron decay search at KamLAND and proton decay search at Super-K. We also show the projections of some other baryon/nucleon decays and present the distinct distributions of kinematic observable.

Indirect constraints on third generation baryon number violation

Beneke,

Finauri,

Petrov

2024

The non-observation of baryon number violation suggests that the scale of baryon-number violating interactions at zero temperature is comparable to the GUT scale. However, the pertinent measurements involve hadrons made of the first-generation quarks, such as protons and neutrons. One may therefore entertain the idea that new flavour physics breaks baryon number at a much lower scale, but only in the coupling to a third generation quark, leading to observable baryon-number violating b-hadron decay rates. In this paper we show that indirect constraints on the new physics scale ΛBNV from the existing bounds on the proton lifetime do not allow for this possibility. For this purpose we consider the three dominant proton decay channels p → $$ {\ell}^{+}{\nu}_{\ell}\overline{\nu} $$ ℓ + ν ℓ ν ¯ , p → $$ {\pi}^{+}\overline{\nu} $$ π + ν ¯ and p → π0ℓ+ mediated by a virtual bottom quark.