arXiv subjects
Publications and source records attributed to Ernest Ma.
Flavor alignment and mass hierarchy in quarks are shown to be achievable together in a renormalizable theory using the dark sector, while keeping only the one Higgs doublet of the standard model.
In the conventional gauged ${B-L}$ extension of the standard model, the $B-L$ charge of the singlet scalar $\chi$, responsible for the breaking of $U(1)_{B-L}$ symmetry, is taken to be 2 such that it can anchor type-I seesaw by giving Majorana masses to the right-handed neutrinos, $\nu_R$. In this paper, we consider instead the cases $\chi \sim 3$ or 4 under $B-L$, so that $\nu_R$ may not acquire any Majorana mass and neutrinos are Dirac fermions. We then consider a vector-like fermion $S$ with 2 units of $B-L$ charge, which becomes a good candidate for dark matter, either Dirac for $\chi \sim 3$ or Majorana for $\chi \sim 4$. In both cases, spontaneous $B-L$ breaking can induce a strong first-order phase transition, producing stochastic gravitational waves (GW) which can be tested at GW experiments. Moreover, the presence of light $\nu_R$s gives rise to an additional contribution to the effective number of relativistic degrees of freedom, $\Delta{N}_{\rm eff}$, providing complementary constraints from current and upcoming CMB observations.
In the canonical type-I seesaw mechanism for neutrino masses, a residual symmetry known as lepton parity: $(-1)^L$, remains preserved. Introducing a Majorana fermion $S$ with even lepton parity renders it naturally stable, making it a viable dark matter (DM) candidate. The addition of a lepton parity odd singlet scalar $\sigma$ allows for the coupling $N S \sigma$, where $N$ is the right-handed neutrino. If $S$ is not thermalized, then DM relic can be produced in two distinct ways: (i) for reheating temperature, $T_{\rm rh}>m_{N}$, dominantly through the decay of $N$ ($N\rightarrow S\sigma$), and (ii) for $T_{\rm EW}<T_{\rm rh}\ll m_{N}$, via standard model Higgs ($h$) decay ($h\rightarrow SS$ at one loop). If the $\sigma-h$ quartic coupling is large, then it can lead to a strong first-order electroweak phase transition even if $\langle\sigma\rangle=0$. Alternatively, if $\sigma-h$ coupling is small, then $\sigma$ can freeze out with a larger abundance, and hence its decay ($\sigma\rightarrow S\nu$) at late epochs can give rise to additional relativistic degrees of freedom ($\Delta{N}_{\rm eff}$). Thus, the framework gives a viable DM with mass range varying from MeV to TeV and leaves observable imprints, via gravitational waves and $\Delta{N}_{\rm eff}$, which offer complementary probes, potentially detectable in future gravitational wave and CMB experiments.
We propose a simple and predictive setup that connects neutrino masses, dark matter (DM), and gravitational waves. A minimal lepton parity DM scenario is considered where the residual symmetry $(-1)^L$ from the type I seesaw acts as the dark parity $D=(-1)^{L+2j}$, ensuring DM stability without imposing any new symmetry. A singlet Majorana fermion $S$ with even lepton parity serves as the DM candidate, interacting via a real scalar $\sigma$ which is also even lepton parity. The scalar potential possesses an accidental $\mathcal{Z}_2$ symmetry, whose spontaneous breaking gives rise to unstable domain walls (DW) in the presence of explicit $\mathcal{Z}_2$ breaking terms allowed by the lepton parity. The subsequent DW annihilation generates a stochastic gravitational wave (GW) background potentially observable at different GW experiments.
Flavor symmetry and other ideas beyond the standard model (SM) may be achieved in a renormalizable theory using the dark sector, while keeping only the one SM Higgs doublet.
Implementing the Peccei-Quinn mechanism to enforce CP conservation in strong interactions with heavy dark quarks, a scotogenic model of quark masses with $Z_3 \times Z_3$ symmetry is discussed where there is only one Higgs doublet. A natural extension to the lepton sector using $A_4 \times A_4$ is also presented.
Preserving the unique role of the one Higgs doublet of the standard model, it is proposed that quark and lepton mass patterns, often ascribed to the Froggatt-Nielsen mechanism using nonrenormalizable higher-dimensional terms, may be enforced in a renormalizable theory of just one Higgs doublet by the scotogenic mechanism with soft symmetry breaking in the dark sector. A revised version of the original $A_4$ model of charged leptons and neutrinos is discussed.
Dark matter is postulated as a light fermion in two natural scenarios as the outcome of a softly broken discrete symmetry. It is produced from the naturally suppressed decay of the standard-model Higgs boson through the freeze-in mechanism.
The addition of a Higgs quadruplet to the standard model (SM) of quarks and leptons would shift the $W$ boson mass upward. It could also facilitate the production of dark matter through the conventional thermal freeze-out scenario via Yukawa interaction with the Higgs quadruplet or freeze-in production from the decay of SM Higgs. We investigate the same-sign lepton smoking gun signature of the double-charged scalar component of the Quadruplet Higgs at the LHC.
It is pointed out that every renormalizable supersymmetric field theory has a symmetry which is hidden in plain sight, but is usually broken by soft terms which obey supersymmetry. On the other hand, the terms which break supersymmetry softly may or may not break this symmetry. Implications for the minimal supersymmetric standard model (MSSM) are discussed.
If dark matter is light, it may be due to a seesaw mechanism just as neutrinos are. It is postulated that both originate from the same type of heavy fermion anchors, either singlets or triplets. In the latter case, a shift of the $W$ mass is predicted, as suggested by the $CDF$ precision measurement. A spontaneously broken dark $U(1)$ gauge symmetry is assumed, resulting in freeze-in long-lived light dark matter.
It is pointed out that every renormalizable field theory has a symmetry which is hidden in plain sight. In all practical cases, it is also broken softly, either explicitly or spontaneously. The soft explicit breaking mass terms may be assumed naturally small compared to the scalar mass-squared terms. Implications for extensions of the standard model are discussed. New left-right model of two-loop radiative Dirac neutrino mass is proposed.
The dark sector is postulated to be invariant under an $SU(2)$ gauge symmetry, spontaneously broken by a Higgs quadruplet to a conserved residual $Z_3 \times Z_2$ symmetry. The resulting dark matter phenomenology is studied.
Dark matter is postulated to transform under the non-Abelian $SU(2)_D$ gauge symmetry. Its connection to Dirac neutrino masses is explored.
In the framework of seesaw neutrino masses from heavy fermion triplets $(Σ^+,Σ^0,Σ^-)$, the addition of a light fermion singlet $N$ and a heavy scalar triplet $(ρ^+,ρ^0,ρ^-)$ has some important consequences. The new particles are assumed to be odd under a new $Z_2$ symmetry which is only broken softly, both explicitly and spontaneously. With $N-Σ^0$ mixing, freeze-in long-lived dark matter through Higgs decay becomes possible. At the same time, the $W$ mass is shifted slightly upward, as suggested by a recent precision measurement.
The scotogenic model of neutrino mass is modified so that the dark Majorana fermion singlet $S$ which makes the neutrino massive is itself generated in one loop. This is accomplished by having $Z_6$ lepton symmetry softly broken to $Z_2$ in the scalar sector by a unique quadratic term. It is shown that $S$ is a viable freeze-in dark-matter candidate through Higgs decay.
Dark matter is postulated to be a neutral Dirac fermion, charged under a dark $U(1)_D$ gauge symmetry. Scalar partners of the quarks and leptons are also charged under $U(1)_D$. The dark gauge boson $Z_D$ and the dark Higgs boson $h_D$ enable either freeze-out or freeze-in mechanisms to account for the correct dark matter relic abundance. Dark number $D$ is connected to baryon number $B$ and lepton number $L$ through $D=3B+L-(2j)_{[mod~2]}$ where $j$ is the intrinsic spin of the particle.
Radiative Dirac neutrino masses and their mixing are linked to dark matter through the non-Abelian discrete symmetry $A_5$ of the 4-dimensional pentatope, softly broken to $A_4$ of the 3-dimensional tetrahedron. This unifying understanding of neutrino family structure from dark matter is made possible through the interplay of gauge symmetry, renormalizable Lagrangian field theory, and softly broken discrete symmetries. Dark neutral fermions are produced through Higgs decay.