We present a minimal extension of the left-right symmetric model based on the gauge group $SU(3)_{c} \times SU(2)_{L} \times SU(2)_{R} \times U(1)_{B-L} \times U(1)_{X}$, in which a vector-like fermion pair ($ζ_L$ and $ζ_R$) charged under the $U(1)_{B-L} \times U(1)_X$ symmetry is introduced. Associated with the symmetry breaking of the gauge group $SU(2)_{R} \times U(1)_{B-L} \times U(1)_{X}$ down to the Standard Model (SM) hypercharge $U(1)_Y$, Majorana masses for $ζ_{L, R}$ are generated and the lightest mass eigenstate plays a role of the dark matter (DM) in our universe by its communication with the SM particles through a new neutral gauge boson "$X$". We consider various phenomenological constraints of this DM scenario, such as the observed DM relic density, the LHC Run-2 constraints from the search for a narrow resonance, and the perturbativity of the gauge couplings below the Planck scale. Combining all constraints, we identify the allowed parameter region which turns out to be very narrow. A significant portion of the currently allowed parameter region will be tested by the High-Luminosity LHC experiments.
A minimal extension of the left-right symmetric model for neutrino masses that includes a vector-like singlet fermion dark matter (DM) is presented with the DM connected to the visible sector via a gauged U(1) portal. We discuss the symmetry breaking in this model and calculate the mass and mixings of the extra heavy neutral gauge boson at the TeV scale. The extra gauge boson can decay to both standard model particles as well to dark matter. We calculate the relic density of the singlet fermion dark matter and its direct detection cross section and use these constraints to obtain the allowed p…
We introduce a mirror copy of the ordinary fermions and Higgs scalars for embedding the $SU(2)_L\times U(1)_Y$ electroweak gauge symmetry into an $SU(2)_L\times SU(2)_R\times U(1)_{B-L}$ left-right gauge symmetry. We then show the spontaneous left-right symmetry breaking can automatically break the parity symmetry motivated by solving the strong CP problem. Through the $SU(2)_R$ gauge interactions, a mirror Majorana neutrino can decay into a mirror charged lepton and two mirror quarks. Consequently we can obtain a lepton asymmetry stored in the mirror charged leptons. The Yukawa couplings of t…
Dirac Vs. Majorana Neutrino Masses From a TeV Interval
我们研究了在[0，πR]区间内紧致化的超对称五维模型中左手中微子质量的性质（Dirac vs. Majorana）和大小，其中夸克和轻子局域在边界上，而规范和希格斯扇区在第五维的大部分中传播.超对称性被Scherk-Schwarz边界条件破缺，电弱破缺通过辐射修正进行。右手中微子在体中传播，并具有一般的五维质量M，它将零模定位在其中一个边界和任意边界项上。我们发现，对于一般边界项，左手中微子具有马约拉纳质量。然而，对于特定的边界配置，左手中微子是狄拉克费米子，因为理论具有守恒的整体U（1）对称性，这防止了轻子数的破坏。中微子质量的大小取决于右手中微子零模的局域化和/或五维中微子汤川耦合的大小。亚电子伏特范围内的左手中微子需要MR~10或汤川耦合~10^{-3}R，这使得五维理论在自然截止之前是微扰的。
Dynamical Mass Generations and Collective Excitations in the (Supersymmetric-)Nambu$-$Jona-Lasinio Model and a Gauge Theory with Left-Right-Asymmetric Majorana Mass Terms
In the context of the minimal left-right symmetric model, we study the interplay between current and future neutrinoless double beta ($0νββ$) decay experiments, long-lived particle searches at the LHC main detectors ATLAS/CMS, and the proposed far detector MATHUSLA. The heavy Majorana neutrino can be produced in association with an electron from the decay of $W$ boson for a non-zero left-right mixing and subsequently decays into another electron with the same charge and jets. Owing to the suppression of large right-handed charged gauge boson $W_R$ mass, the heavy neutrinos could be long-lived.…
Collider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson $Δ$, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At $Δ$ masses below the opening of the $VV$ decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion $gg \to Δ\to NN$ and pair production of triplets from…
In a residual $\mathbb{Z}_2 \times \mathbb{Z}_2$ symmetry approach, we investigate minimally perturbed Majorana neutrino mass matrices. Constraint relations among the low energy neutrino parameters are obtained. Baryogenesis is realized through flavored leptogenesis mechanism with quasi-degenerate right handed (RH) heavy neutrinos.
We revisit the neutrino magnetic moments (MMs) in the left-right model with non-manifest symmetry. After deriving an expression in terms of the Dirac and Majorana phases, we analyze the sensitivity of neutrino MMs to these $CP$-violating phases in two scenarios: 1) a maximal right mixing in which left- and right-handed neutrinos are mixed by the same matrix; and 2) a right-handed neutrino mixing whose off-diagonal entries are much smaller than the elements in the diagonal, but where the $CP$ phases remain general. Our results show that, even though certain values of the Majorana phases can eli…
We propose a simple left-right symmetric theory where the neutrino masses are generated at the quantum level. In this context the neutrinos are Majorana fermions and the model has the minimal degrees of freedom in the scalar sector needed for symmetry breaking and mass generation. We discuss the lepton number violating signatures with two charged leptons of different flavor and missing energy at the Large Hadron Collider in order to understand the testability of the theory.
In collaboration with Jogesh Pati, Abdus Salam challenged the chiral gauge nature of the Standard Model by paving the road towards the Left-Right symmetric electro-weak theory. I describe here the logical and historical construction of this theory, by emphasising the pioneering and key role it played for neutrino mass. I show that it is a self-contained and predictive model with the Higgs origin of Majorana neutrino mass, in complete analogy with the SM situation regarding charged fermions.
In the simplest left-right extension of the Standard Model of particle interactions with one scalar bidoublet and one $SU(2)_R$ triplet for seesaw Majorana neutrino masses, the addition of a variety of fermion and scalar multiplets automatically makes them stable (predestined) dark matter candidates. We discuss the interplay of this dark ensemble in relic abundance and direct searches.
In the canonical seesaw mechanism we require the relevant neutrino mass terms to be invariant under the $S^{}_3$ charge-conjugation transformations of left- and right-handed neutrino fields. Then both the Dirac mass matrix $M^{}_{\rm D}$ and the right-handed neutrino mass matrix $M^{}_{\rm R}$ are well constrained, so is the effective light Majorana neutrino mass matrix $M^{}_ν$ via the seesaw formula. We find that these mass matrices can be classified into 22 categories, among which some textures respect the well-known $μ$-$τ$ permutation or reflection symmetry and flavor democracy. It is als…
We present a class of left-right symmetric models where Dirac as well as Majorana mass terms of neutrinos can arise at one-loop level in a scotogenic fashion: with dark matter particles going inside the loop. We show the possibility of naturally light right handed neutrinos that can have interesting implications at neutrinoless double beta decay experiments as well as cosmology. Apart from a stable dark matter candidate stabilised by a remnant $Z_2$ symmetry, one can also have a long lived keV sterile neutrino dark matter in these models. This class of models can have very different collider s…
We investigate the predictions for lepton flavour number violating processes in the context of a simple left-right symmetric theory. In this context neutrinos are Majorana fermions and their masses are generated at the quantum level through the Zee mechanism using the simplest Higgs sector. We show that the right handed neutrinos are generically light and can give rise to large lepton number violating contributions to rare processes. We discuss the correlation between the collider constrains and the predictions for lepton number violating processes. We find that using the predictions for mu to…
In this paper, we indicate a possibility of utilizing the intense chromium source ($\sim 370 PBq$) in probing the neutrino nature in low energy neutrino experiments with the ultra-low threshold and background real-time Borexino detector located near the source ($\sim 8 m$). We analyze the elastic scattering of electron neutrinos (Dirac or Majorana, respectively) on the unpolarized electrons in the relativistic neutrino limit. We assume that the incoming neutrino beam is the superposition of left-right chiral states. Left chiral neutrinos may be detected by the standard $V A$ and non-standard s…
In 2002, two neutrino mixing ansatze having trimaximally-mixed middle ($ν_2$) columns, namely tri-chi-maximal mixing ($\text{T}χ\text{M}$) and tri-phi-maximal mixing ($\text{T}ϕ\text{M}$), were proposed. In 2012, it was shown that $\text{T}χ\text{M}$ with $χ=\pm \fracπ{16}$ as well as $\text{T}ϕ\text{M}$ with $ϕ= \pm \fracπ{16}$ leads to the solution, $\sin^2 θ_{13} = \frac{2}{3} \sin^2 \fracπ{16}$, consistent with the latest measurements of the reactor mixing angle, $θ_{13}$. To obtain $\text{T}χ\text{M}_{(χ=\pm \fracπ{16})}$ and $\text{T}ϕ\text{M}_{(ϕ=\pm \fracπ{16})}$, the type~I see-saw fr…
We consider the low scale ($10$ - $100$ TeV) left-right symmetric model with "naturally" small neutrino masses generated through the inverse seesaw mechanism. The Dirac neutrino mass terms are taken to be similar to the masses of charged leptons and quarks in order to satisfy the quark-lepton similarity condition. The inverse seesaw implies the existence of fermion singlets $S$ with Majorana mass terms as well as the "left" and "right" Higgs doublets. These doublets provide the portal for $S$ and break the left-right symmetry. The inverse seesaw allows to realize a scenario in which the large …
We propose the left-right models based on SU(3)_C\otimes SU(M)_L \otimes SU(N)_R \otimes U(1)_X gauge symmetry for (M,N)=(3,3), (2,3), and (3,2) that address the 750 GeV diphoton excess recently reported by the LHC. The fermion contents are minimally introduced, and the generation number must match the fundamental color number to cancel anomalies and ensure QCD asymptotic freedom. The diphoton excess arises from the field that breaks the left-right symmetry spontaneously in the first model, while for the last models it emerges as an explicit violation of the left-right symmetry. The neutrino m…
We propose an effective left-right-right-left model with a parity breaking scale around a few TeV. One of the main achievements of the model is that the mirror fermions as well as the mirror gauge sector simultaneously could be at TeV scale. It is shown that the most dangerous quadratic divergence of the SM Higgs boson involving the top quark in the loop is naturally suppressed, and begins at three loop. The model postpones the fine-tuning of the mass of the SM Higgs boson up to a sufficiently high scale. The model explains the smallness of the neutrino masses whether they are Dirac or Majoran…
