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UV-Complete Models for a Light Axial Gauge Boson

Bhaskar Dutta, Aparajitha Karthikeyan, Rabindra N. Mohapatra

Abstract

We present new anomaly free gauge models where the gauge field only has axial vector couplings to both quarks and leptons. We use the left-right symmetric universal seesaw models as the basis for this construction with an extra $U(1)_a$ as the axial gauge group. We present three main versions of the model, denoted as models A, B and C (and their variations), with different properties depending on the way the gauge anomaly is canceled. We show how the models can accommodate small neutrino masses. The models allow for a new Dirac fermion coupled via the $U(1)_a$ gauge portal to the SM fields which can be the dark matter. The models A and its variation have the novel property that there is an upper limit on the $U(1)_a$ gauge coupling $g_a$, due to the fact that the standard model Higgs doublet shares the $U(1)_a$ quantum number. For models B and C, we discuss the phenomenological constraints on the gauge coupling $g_a$ and gauge boson mass $m_{\cal A}$ from current low energy observations where, unlike in models A, $g_a$ depends on $m_{\mathcal{A}}$ through a single vacuum expectation value.

UV-Complete Models for a Light Axial Gauge Boson

Abstract

We present new anomaly free gauge models where the gauge field only has axial vector couplings to both quarks and leptons. We use the left-right symmetric universal seesaw models as the basis for this construction with an extra as the axial gauge group. We present three main versions of the model, denoted as models A, B and C (and their variations), with different properties depending on the way the gauge anomaly is canceled. We show how the models can accommodate small neutrino masses. The models allow for a new Dirac fermion coupled via the gauge portal to the SM fields which can be the dark matter. The models A and its variation have the novel property that there is an upper limit on the gauge coupling , due to the fact that the standard model Higgs doublet shares the quantum number. For models B and C, we discuss the phenomenological constraints on the gauge coupling and gauge boson mass from current low energy observations where, unlike in models A, depends on through a single vacuum expectation value.

Paper Structure

This paper contains 25 sections, 43 equations, 4 figures, 4 tables.

Table of Contents

  1. Introduction
  2. The Models
  3. Model A
  4. Model $A'$, a variation of model A without gauge singlet fermions:
  5. Model B
  6. Model C
  7. Fermion masses and strong CP
  8. Neutrino mass
  9. Model A
  10. Model $A'$
  11. Model B
  12. Model C
  13. Dark matter
  14. Symmetry breaking and interactions
  15. ${\cal A}$ boson couplings
  16. ...and 10 more sections

Figures (4)

  • Figure 1: One-loop Feynman diagram contributing to neutrino mass.
  • Figure 2: (a) Variation of eigenvalues of the neutral gauge boson mass matrix as $g_a$ is increased. Note the level crossings for different values of $g_a$. The tuples ($v_R$, $v_\eta$) denote the choice of VEVs. The vertical lines denote the values of $g_a$ where the level crossing occurs giving the upper limits on $g_a$. This feature does not apply to model B and C where ${\cal A}$ does not mix with $Z$ and $Z_R$. (b) Variation of mixing angles of the $Z$ as $g_a$ is increased. The vertical lines denote the values of $g_a$ where the mixing of $Z$ changes drastically, giving the upper limits on $g_a$.
  • Figure 3: Bounds on (a) universal invisibly decaying and (b) universal visibly decaying $B-L$ axial gauge boson (model B).
  • Figure 4: Bounds on (a) an invisibly decaying and (b) a visibly decaying $B-3L_{\tau}$ (model C) axial gauge boson.