Dark matter assisted Dirac leptogenesis and neutrino mass

We propose a minimal extension of the standard model with U(1)_{B-L} \times Z_{2} symmetry. In this model by assuming that the neutrinos are Dirac (i.e. $B-L$ is an exact symmetry), we found a simultaneous solution for non zero neutrino masses and dark matter content of the universe. The observed baryon asymmetry of the universe is also explained using Dirac Leptogenesis, which is assisted by a dark sector, gauged under a U(1)_D symmetry. The latter symmetry of the dark sector is broken at a TeV scale and thereby giving mass to a neutral gauge boson Z_D. The standard model Z-boson mixes with the gauge boson Z_D at one loop level and thus paves a way to detect the dark matter through spin independent elastic scattering at terrestrial laboratories.Comment: 12 pages, 10 figures. Accepted for publication in Nuclear Physics

Baryogenesis via leptogenesis from asymmetric dark matter and radiatively generated neutrino mass

We propose an extension of the standard model (SM) by including a dark sector comprised of three generations of heavy right-handed neutrinos, a singlet scalar, and a singlet Dirac fermion, where the latter two particles are stable and are viable candidates of dark matter (DM). In the early Universe, the CP-violating out-of-equilibrium decay of heavy right-handed neutrinos to a singlet Dirac fermion and scalar in the dark sector generates a net DM asymmetry. The latter is then transported to the visible sector via a dimension-eight operator which conserves B - L symmetry and is in thermal equilibrium above the sphaleron decoupling temperature. An additional light singlet scalar is introduced which mixes with the SM Higgs and paves a path for annihilating the symmetric components of the DM candidates. We discuss the constraints on singlet-doublet Higgs mixing from invisible Higgs decay, signal strength at the LHC, and the direct search of DM at terrestrial laboratories. At tree level, the neutrinos are shown to be massless since the symmetry of the dark sector forbids the interaction of right-handed neutrinos with SM particles. However, at the one-loop level, the neutrinos acquire sub-eV masses as required by the oscillation experiments

Leptogenesis and eV scale sterile neutrino

We consider the minimal extended seesaw model which can accommodate an eV scale sterile neutrino. The scenario also includes three heavy right handed neutrinos in addition to the light sterile neutrino. In this model, the active-sterile mixing act as non-unitary parameters. If the values of these mixing angles are of $\mathcal{O}(0.1)$, the model introduces deviation of the PMNS matrix from unitarity to this order. We find that the oscillation data from various experiments imposes an upper bound on the lightest heavy neutrino mass scale as $\sim 10^{11}$ GeV in the context of this model. We study {\it vanilla} leptogenesis in this scheme, where the decay of the heavy right handed neutrinos in the early universe can give rise to the observed baryon asymmetry. Here, even though the eV scale sterile neutrino does not participate directly in leptogenesis, its effect is manifested through the non-unitary effects. We find that the parameter space that can give rise to successful leptogenesis is constrained by the bounds on the active-sterile mixing as obtained from the global analysis.Comment: 20 pages, 8 figures, Accepted for publication in PR

Dark matter to baryon ratio from scalar triplets decay in type-II seesaw

We propose a minimal model for the cosmic coincidence problem $\Omega_{\rm DM}/\Omega_B \sim 5$ and neutrino mass in a type-II seesaw scenario. We extend the standard model of particle physics with a $\rm SU(2)$ singlet leptonic Dirac fermion $\chi$, which represents the candidate of dark matter (DM), and two triplet scalars $\Delta_{1,2}$ with hierarchical masses. In the early Universe, the CP violating out-of-equilibrium decay of lightest $\Delta$ generates a net $B-L$ asymmetry in the visible sector (comprising of SM fields), where $B$ and $L$ represents the total baryon and lepton number respectively. A part of this asymmetry gets transferred to the dark sector (comprising of DM $\chi$) through a dimension eight operator which conserves $B-L$. Above the electroweak phase transition, the $B-L$ asymmetry of the visible sector gets converted to a net $B$-asymmetry by the $B+L$ violating sphalerons, while the $B-L$ asymmetry of the dark sector remains untouched which we see today as relics of DM. We show that the observed DM abundance can be explained for a DM mass about 8 GeV. We then introduce an additional singlet scalar field $\phi$ which mixes with the SM-Higgs to annihilate the symmetric component of the DM resonantly which requires the singlet scalar mass to be twice the DM mass, {\it i.e.} around 16 GeV, which can be searched at collider experiments. In our model, the active neutrinos also get small masses by the induced vacuum expectation value (vev) of the triplet scalars $\Delta_{1,2}$. In the later part of the paper we discuss all the constraints on model parameters coming from invisible Higgs decay, Higgs signal strength, DM direct detection and relic density of DM.Comment: 22 pages, 11 figures. Change in title, added text and figures, matches accepted versio

Dark matter to baryon ratio from scalar triplets decay in type-II seesaw

We propose a minimal model for the cosmic coincidence problem $$\Omega _\mathrm{DM}/\Omega _B \sim 5$$ and neutrino mass in a type-II seesaw scenario. We extend the standard model of particle physics with a $$\mathrm SU(2)$$ singlet leptonic Dirac fermion $$\chi$$, which represents the candidate of dark matter (DM), and two triplet scalars $$\Delta _{1,2}$$ with hierarchical masses. In the early Universe, the CP violating out-of-equilibrium decay of lightest $$\Delta$$ generates a net $$B-L$$ asymmetry in the visible sector (comprising of SM fields), where B and L represents the total baryon and lepton number respectively. A part of this asymmetry gets transferred to the dark sector (comprising of DM $$\chi$$) through a dimension eight operator which conserves $$B-L$$. Above the electroweak phase transition, the $$B-L$$ asymmetry of the visible sector gets converted to a net B-asymmetry by the $$B+L$$ violating sphalerons, while the $$B-L$$ asymmetry of the dark sector remains untouched which we see today as relics of DM. We show that the observed DM abundance can be explained for a DM mass about 8 GeV. We then introduce an additional singlet scalar field $$\phi$$ which mixes with the SM-Higgs to annihilate the symmetric component of the DM resonantly which requires the singlet scalar mass to be twice the DM mass, i.e. around 16 GeV, which can be searched at collider experiments. In our model, the active neutrinos also get small masses by the induced vacuum expectation value (vev) of the triplet scalars $$\Delta _{1,2}$$. In the later part of the paper we discuss all the constraints on model parameters coming from invisible Higgs decay, Higgs signal strength, DM direct detection and relic density of DM

VERIFIABLE TYPE-II SEESAW AND DARK MATTER IN A GAUGED U(1)B−L MODEL

We propose a gauged U(1)B−L extension of the standard model (SM) to explain simultaneously the light neutrino masses and dark matter (DM). The generation of neutrino masses occurs through a variant of type-II seesaw mechanism in which one of the scalar triplets lies at the TeV scale yet have a large dilepton coupling, which paves a path for probing this model at colliders. The gauging of U(1)B−L symmetry in a type-II seesaw framework introduces B − L anomalies. Therefore we invoke three right handed neutrinos νRi (i=1,2,3) with B − L charges -4,-4,+5 to cancel the anomalies. We further show that the lightest one among the three right handed neutrinos can be a viable DM candidate. The stability of DM can be owed to a remnant Z2 symmetry under which the right handed neutrinos are odd while all other particles are even. We then discuss the constraints on the model parameters from observed DM abundance and the search at direct detection experiments

Asymmetric Dark Matter From Triplet Scalar Leptogenesis

In this article we extend the standard model with a SU(2) singlet leptonic Dirac fermion χ, which represents the candidate of dark matter, and a triplet scalar ∆. In the early Universe, the CP violating out of equilibrium decay of ∆ generates a net B − L asymmetry in the SM sector, where B and L represents the total baryon and lepton number respectively. A part of this asymmetry gets transferred to the dark sector through a higher dimensional operator which conserve B − L, while the B + L violating sphalerons keeps converting B − L asymmetry to the observed B asymmetry. In addition, we introduce a singlet scalar field φ which mixes with the SM-Higgs to give a resonance channel to annihilate the symmetric component of DM and also gives direct detection signal. In our model, the active neutrinos get small masses by the induced vacuum expectation value (vev) of the triplet scalar ∆. In the later part of the paper we discuss all the constraints coming from invisible Higgs decay, Higgs signal strength, DM direct detection and relic density of DM