Baryon Number Violation Research Articles

Muon-induced baryon number violation

The search for charged-lepton flavor violation in muon capture on nuclei is a powerful probe of heavy new physics. A smoking gun signal for μ→e conversion is a monochromatic electron with energy almost equal to the muon mass. We show that light new physics can mimic this signature and that it can also lead to electrons above the μ→e signal peak. A concrete example of such light new physics is μ−-nucleon annihilation into a light dark sector, which can produce an energetic e− as well as e+e− by-products. Due to the size of the muon mass, the exotic muon capture process can be kinematically allowed, while the otherwise stringent constraints, e.g., from proton decay, are kinematically forbidden. We also discuss other relevant constraints, including those from the stability of nuclei and muon capture in the interior of neutron stars. Published by the American Physical Society 2024

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

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.

Baryon number violation involving tau leptons

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→ηπ+ν¯τ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ p\ o {\\eta \\pi}^{+}{\\overline{\ u}}_{\ au } $$\\end{document} and n → K+π−ντ that have never been searched for.

Λb→Pℓ factorization in QCD

We calculate the form factors for the baryon number violation processes of a heavy-flavor baryon decaying into a pseudoscalar meson and a lepton. In the framework of the Standard Model effective field theory, the leptoquark operators at the bottom quark scale, whose matrix elements define the form factors, are derived by integrating out the high energy physics. Under the quantum chromodynamics (QCD) factorization approach, the form factors of the baryon number violation processes at leading power can be factorized into the convolution of the long-distance hadron wave functions as well as the short-distance hard and jet functions representing the hard scale and hard-collinear scale effects, separately. Based on measurements of the baryon number violation processes by LHCb, we further impose constraints on the new physics constants of leptoquark operators. Published by the American Physical Society 2024

Assisted baryon number violation in 4k+2 dimensions

Proton decay in six-dimensions orbifolded on square T2/Z2 is highly suppressed at tree level. This is because baryon number violating (BNV) operators containing only the zero mode of bulk fermions must satisfy the selection rule 32ΔB±12ΔL=0 mod 4. In this article, we show that the above relation does not prohibit mass dimension-six BNV operators containing Kaluza-Klein partners of the bulk fermions. Together with a “spinless” adjoint scalar partner of hypercharge gauge boson (the dark matter candidate), these novel operators generate dark matter assisted proton decay at mass dimension eight. Here, with explicit examples of scalar and vector baryon number violating interactions, we discuss the importance of such ΔB=1=ΔL and ΔB=2=ΔL operators and derive the limit on new physics. Published by the American Physical Society 2024

Pulsar timing anomalies: a window into baryon number violation

We investigate the influence of a specific class of slow Baryon Number Violation (BNV)—one that induces quasi-equilibrium evolution — on pulsar spin characteristics. This work reveals how BNV can potentially alter observable parameters, including spin-down rates, the second derivative of spin frequency, and braking indices of pulsars. Moreover, we demonstrate that BNV could lead to anomalies in pulsar timing, along with a wide array of braking indices, both positive and negative. In addition, we examine the possibility of pulsar spin-up due to BNV, which may result in a novel mechanism for the revival of “dead” pulsars. We conclude by assessing the sensitivity required for future pulsar timing efforts to detect such BNV effects, thus highlighting the potential for pulsars to serve as laboratories for testing fundamental physics.

(Assisted) baryon number violation

(Assisted) baryon number violation

Gravitational wave signatures of a PBH-generated baryon-dark matter coincidence

We propose a new way of probing non-thermal origin of baryon asymmetry of universe (BAU) and dark matter (DM) from evaporating primordial black holes (PBH) via stochastic gravitational waves (GW) emitted due to PBH density fluctuations. We adopt a baryogenesis setup where CP violating out-of-equilibrium decays of a coloured scalar, produced non-thermally at late epochs from PBH evaporation, lead to the generation of BAU. The same PBH evaporation is also responsible for non-thermal origin of superheavy DM. Unlike the case of baryogenesis {\it via leptogeneis} that necessarily corners the PBH mass to $\sim\mathcal{O}(1)$ g, here we can have PBH mass as large as $\sim\mathcal{O}(10^7)$ g due to the possibility of producing BAU directly below sphaleron decoupling temperature. Due to the larger allowed PBH mass we can also have observable GW with mHz-kHz frequencies originating from PBH density fluctuations keeping the model constrained and verifiable at ongoing as well as near future GW experiments like LIGO, BBO, DECIGO, CE, ET etc. Due to the presence of new coloured particles and baryon number violation, the model also has complementary detection prospects at laboratory experiments.

Electroweak sphaleron in a magnetic field

Using lattice simulations we calculate the rate of baryon number violating processes, the sphaleron rate, in the Standard Model with an external (hyper)magnetic field for temperatures across the electroweak cross-over, focusing on the broken phase. Additionally, we compute the Higgs expectation value and the pseudocritical temperature. The electroweak cross-over shifts to lower temperatures with increasing external magnetic field, bringing the onset of the suppression of the baryon number violation with it. When the hypermagnetic field reaches the magitude $B_Y \approx 2 T^2$ the cross-over temperature is reduced from $160$ GeV to $145$ GeV. In the broken phase for small magnetic fields the rate behaves quadratically as a function of the magnetic flux. For stronger magnetic fields the rate reaches a linear regime which lasts until the field gets strong enough to restore the electroweak symmetry where the symmetric phase rate is reached.

Baryon number violation from confining new physics

The detection of neutron-antineutron oscillation will be a discovery of fundamental importance in particle physics and cosmology. In models discussed widely in literature, the process is generated through heavy new physics with weak, perturbative coupling at the scale of the experiment. Acknowledging the fact that nature has been quite evasive regarding the strength and scale of new physics, we discuss a new mechanism, generated by confining new physics, at $\ensuremath{\sim}2\text{ }\text{ }\mathrm{GeV}$, resulting in low-energy baryon number violating effects. The mechanism predicts baryon number violating processes like neutron disappearance, neutron-neutron annihilation and neutron-antineutron oscillation generated through the condensation of the linear moose.

Lepton- and baryon-number violation in nuclear effective field theory

Lepton and baryon numbers are accidental symmetries in the effective field theory (EFT) of the Standard Model. Their violation would lead to spectacular nuclear decays which can be described with nuclear EFTs. I discuss ways in which two such decays — the neutrinoless double-beta decay of heavy nuclei and the disappearance of the deuteron — provide complementary information to processes that take place outside the nuclear environment — neutrino masses, nucleon decay, and neutron-antineutron oscillations.

Dimension-five baryon-number violation in low-scale Pati-Salam models

The gauge bosons of Pati-Salam do not mediate proton decay at the renormalisable level, and for this reason it is possible to construct scenarios in which $SU(4) \otimes SU(2)_{R}$ is broken at relatively low scales. In this Letter we show that such low-scale models generate dimension-5 operators that can give rise to nucleon decays at unacceptably large rates, even if the operators are suppressed by the Planck scale. We find an interesting complementarity between the nucleon-decay limits and the usual meson-decay constraints. Furthermore, we argue that these operators are generically present when the model is embedded into $SO(10)$, lowering the suppression scale. Under reasonable assumptions, the lower limit on the breaking scale can be constrained to be as high as $\mathcal{O}(10^{8})$ GeV.

Callan-Rubakov effect and higher charge monopoles

In this paper we study the interaction between magnetic monopoles and massless fermions. In the low energy limit, the monopole’s magnetic field polarizes the fermions into purely in-going and out-going modes. Consistency requires that the UV fermion-monopole interaction leads to non-trivial IR boundary conditions that relate the in-going to out-going modes. These non-trivial boundary conditions lead to what is known as the Callan-Rubakov effect. Here we derive the effective boundary condition by explicitly integrating out the UV degrees of freedom for the general class of spherically symmetric SU(N) monopoles coupled to massless fermions of arbitrary representation. We then show that the boundary conditions preserve symmetries without ABJ-type anomalies. As an application we explicitly derive the boundary conditions for the stable, spherically symmetric monopoles associated to the SU(5) Georgi-Glashow model and comment on the relation to baryon number violation.

Baryon number violation from confining New Physics

The detection of neutron-antineutron oscillation will be a discovery of fundamental importance in particle physics and cosmology. Models predicting them, usually, assume weak couplings at the scale of the experiment, although Nature has been quite evasive regarding the issue. Acknowledging this, we discuss a new non-perturbative mechanism, generated by confining New Physics in a linear moose, resulting in low-energy baryon number violating effects within the reach of current terrestrial and Neutron Star measurements.

New Opportunities for the Study of Baryon Number Violation at Low-Energy Accelerators

I motivate new searches for baryon-number violation and consider, particularly, the prospects for detecting baryon number violation by two units at low-energy accelerators with intense electron beams, using ARIEL as a particular example.

Seesaw mechanism in the R-parity-violating supersymmetric standard model with the gauged flavor U(1)X symmetry

Abstract We study the seesaw mechanism in the supersymmetric standard model (SSM) with the ${\mathbb {Z}}_3$ symmetry called matter triality (M3). The Abelian discrete symmetry prohibits the baryon number violation operators at the (non-)renormalizable level, which ensures proton longevity. The cubic coupling by right-handed neutrinos generates the Majorana mass term after the right-handed sneutrinos develop into the vacuum expectation values. Due to the R-parity violation, the active neutrino masses can be generated not only from the mixings with the right-handed neutrinos but also from those with the minimal SSM neutralinos. We propose a model where M3 is embedded in the gauged flavor symmetry. The flavor charges are constrained by the anomaly cancellation conditions and the requirements to realize the fermion masses and mixing angles in the quark and lepton sectors. We analyze the assignments of the flavor charge, and show that the sterile neutrino mass is allowed to be below the soft supersymmetry-breaking scale, which is constrained by the half-lifetime of the neutrinoless double beta decay.

Light cone sum rules and form factors for p → e+γ

Proton decay is a baryon number violating process, and hence is forbidden in the Standard Model (SM) of particle physics. Baryon number violation is expected to be an important criteria to explain the matter-anti-matter asymmetry of the universe. Any detection of the proton decay will be a direct evidence of physics beyond the SM. In SMEFT, proton decay is possible via baryon number violating dimension-6 operators. In this work, we pay attention to the decay channel p → e+γ which is expected to be an experimentally cleaner channel due to less nuclear absorption. The gauge invariant amplitude of this process involves two form factors. We calculate these form factors in the framework of light cone sum rules (LCSR) using photon DAs upto two particle twist-3 accuracy as well as proton DAs of twist-3 accuracy. We find that the form factors calculated using photon DAs are more reliable.

Searches for baryon and lepton number Violations at BESIII

Based on the data samples of (1310.6 ± 7.0) × 106 J/ψ events at the center-of-mass energy of √ s = 3.097 GeV and 2.93 fb−1 at √ s = 3.773 GeV, BESIII has searched for baryon number violation (BNV) and lepton number violation (LNV) processes in J/ψ, Σ −, and D decays, respectively. No signal events are observed, and the corresponding upper limits on the branching fraction are determined. The Λ-Λ¯ oscillation is also investigated in J/ψ decays, and the upper limits on the oscillation rate and oscillation parameter are extracted.

Proton decay matrix elements on the lattice at physical pion mass

Proton decay is a major prediction of grand-unified theories (GUT) and its observation would indicate baryon number violation that is required for baryogenesis. Many decades of searching for proton decay have constrained its rate and ruled out some of the simplest GUT models. Apart from the baryon number-violating interactions, this rate also depends on transition amplitudes between the protons and mesons or leptons produced in the decay, which are matrix elements of three-quark operators. We report the nonperturbative calculation of these matrix elements for the most studied two-body decay channels into a meson and antilepton done on a lattice with physical light and strange quark masses and lattice spacings $a\ensuremath{\approx}0.14\text{ }\text{ }\mathrm{fm}$ and 0.20 fm. We perform nonperturbative renormalization and excited state analysis to control associated systematic effects. Our results largely agree with previous lattice calculations done with heavier quark masses and thus remove ambiguity in ruling out some simple GUT theories due to quark mass dependence of hadron structure.

Neutron Stars with Baryon Number Violation, Probing Dark Sectors

The neutron lifetime anomaly has been used to motivate the introduction of new physics with hidden-sector particles coupled to baryon number, and on which neutron stars provide powerful constraints. Although the neutron lifetime anomaly may eventually prove to be of mundane origin, we use it as motivation for a broader review of the ways that baryon number violation, be it real or apparent, and dark sectors can intertwine and how neutron star observables, both present and future, can constrain them.