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Verifiable type-III seesaw and dark matter in a gauged $\boldsymbol{U(1)_{\rm B-L}}$ symmetric model

Satyabrata Mahapatra, Partha Kumar Paul, Narendra Sahu, Prashant Shukla

TL;DR

This work develops a gauged $U(1)_{B-L}$ extension of the Standard Model incorporating the type-III seesaw to explain neutrino masses and to provide a natural dark matter candidate. Anomaly cancellation necessitates additional chiral fermions, which form a Dirac DM stabilized by a residual symmetry, and the model features a rich scalar sector enabling SM–B-L portal interactions through a new $Z_{BL}$ gauge boson and a mixed scalar $h_2$. The authors analyze DM relic density, direct and indirect detection bounds, collider signatures including enhanced triplet-fermion production and disappearing tracks, and a complementary gravitational-wave signal from a first-order $B-L$ phase transition, highlighting strong multi-observable correlations between neutrino parameters, DM, collider phenomenology, and GW probes. Overall, the framework offers testable predictions across particle physics and cosmology, with current and upcoming experiments capable of probing significant portions of its parameter space. The study thus provides a tightly interconnected picture linking neutrino mass generation, dark matter, collider signatures, and stochastic gravitational waves as concurrent tests of new physics beyond the Standard Model.

Abstract

We propose a new extension of the Standard Model that incorporates a gauged \( U(1)_{\rm B-L} \) symmetry and the type-III seesaw mechanism to explain neutrino mass generation and provide a viable dark matter (DM) candidate. Unlike the type-I seesaw, the type-III seesaw extension under \( U(1)_{\rm B-L} \) is not automatically anomaly-free. We show that these anomalies can be canceled by introducing additional chiral fermions, which naturally emerge as DM candidates in the model. We thoroughly analyze the DM phenomenology, including relic density, direct and indirect detection prospects, and constraints from current experimental data. Furthermore, we explore the collider signatures of the model, highlighting the enhanced production cross-section of the triplet fermions mediated by the \( \rm B-L \) gauge boson, as well as the potential disappearing track signatures. Additionally, we investigate the gravitational wave signals arising from the first-order phase transition during \( \rm B-L \) symmetry breaking, offering a complementary cosmological probe of the framework.

Verifiable type-III seesaw and dark matter in a gauged $\boldsymbol{U(1)_{\rm B-L}}$ symmetric model

TL;DR

This work develops a gauged extension of the Standard Model incorporating the type-III seesaw to explain neutrino masses and to provide a natural dark matter candidate. Anomaly cancellation necessitates additional chiral fermions, which form a Dirac DM stabilized by a residual symmetry, and the model features a rich scalar sector enabling SM–B-L portal interactions through a new gauge boson and a mixed scalar . The authors analyze DM relic density, direct and indirect detection bounds, collider signatures including enhanced triplet-fermion production and disappearing tracks, and a complementary gravitational-wave signal from a first-order phase transition, highlighting strong multi-observable correlations between neutrino parameters, DM, collider phenomenology, and GW probes. Overall, the framework offers testable predictions across particle physics and cosmology, with current and upcoming experiments capable of probing significant portions of its parameter space. The study thus provides a tightly interconnected picture linking neutrino mass generation, dark matter, collider signatures, and stochastic gravitational waves as concurrent tests of new physics beyond the Standard Model.

Abstract

We propose a new extension of the Standard Model that incorporates a gauged \( U(1)_{\rm B-L} \) symmetry and the type-III seesaw mechanism to explain neutrino mass generation and provide a viable dark matter (DM) candidate. Unlike the type-I seesaw, the type-III seesaw extension under \( U(1)_{\rm B-L} \) is not automatically anomaly-free. We show that these anomalies can be canceled by introducing additional chiral fermions, which naturally emerge as DM candidates in the model. We thoroughly analyze the DM phenomenology, including relic density, direct and indirect detection prospects, and constraints from current experimental data. Furthermore, we explore the collider signatures of the model, highlighting the enhanced production cross-section of the triplet fermions mediated by the gauge boson, as well as the potential disappearing track signatures. Additionally, we investigate the gravitational wave signals arising from the first-order phase transition during symmetry breaking, offering a complementary cosmological probe of the framework.

Paper Structure

This paper contains 16 sections, 83 equations, 16 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Model
  3. Neutrino mass
  4. Dark matter
  5. Parameter Space Scan
  6. Case-I: $M_{h_2}=500$ GeV
  7. Case-II: $M_{h_2}\in[1,10^4]$ GeV
  8. Detection Prospects
  9. Direct Detection
  10. Indirect Detection
  11. Collider Search
  12. Stochastic Gravitational Waves from first-order phase transition
  13. Conclusion
  14. Triplet fermion decay modes
  15. First-order phase transition
  16. ...and 1 more sections

Figures (16)

  • Figure 1: Relic density as a function of DM mass, with the color bar indicating variations in Yukawa coupling $y_\chi$. Other free parameters are kept fixed as mentioned in the inset of the figure.
  • Figure 2: Dependence of relic density on DM mass. Free parameters are varied as mentioned.
  • Figure 3: left: Case-I: correct relic points in the plane of $\sin\theta_{h\phi}$ and $M_{\rm DM}$ for fixed $\phi$ mass at 500 GeV. right: Case-II: correct relic points in the plane of $\sin\theta_{h\phi}$ and $M_{\rm DM}$.
  • Figure 4: Case-I (left), Case-II (right): Spin-independent direct detection cross-section as a function of DM mass. The present constraints and future sensitivities from the different direct detection experiments are shown with different colored lines as mentioned in the legend, see text for details.
  • Figure 5: [left]: Scalar mediated DM-N scattering, [right]: $Z_{\rm BL}$ mediated DM-N scattering
  • ...and 11 more figures