Search

We consider a $U(1)_{B-L}$ model with a $Z^\prime$ portal Dirac fermion dark matter (DM) $\chi$ of low mass which couples very weakly to the $B - L$ gauge boson $Z^\prime$. An arbitrary $B-L$ charge $Q\neq \pm1, \pm 3$ of the DM $\chi$ ensures its stability. Motivated by the sensitivity reach of forthcoming "Lifetime Frontier" experiments, we focus on the $Z^\prime$ mass, $m_{Z^\prime}$, in the sub-GeV to few GeV range. To evaluate the DM relic abundance, we examine both the freeze-out and freeze-in DM scenarios. For the freeze-out scenario, we show that the observed DM abundance is reproduced near the $Z^\prime$ resonance, $m_\chi \simeq m_{Z^\prime}/2$, where $m_\chi$ is the DM mass. For the freeze-in scenario, we focus on $m_\chi \ll m_{Z^\prime}$. We show that for a fixed value of $m_{Z^\prime}$, $g_{BL}$ values roughly scale as $1/Q$ to reproduce the observed DM abundance. For various $Q$ values in the range between $10^{-6}$ and $10^2$, we show that the gauge coupling values $g_{BL}$ needed to reproduce the observed DM abundance lie in the search reach of future planned and/or proposed experiments such as FASER, Belle-II, LDMX, and SHiP. In the freeze-in case, the $Q$ values to realize observable $g_{BL}$ values are found to be much smaller than that in the freeze-out case., Comment: 14 pages, 3 figures, revised section III with new Figure 1

Whether the neutrino mass ordering is normal or inverted remains an experimentally open issue in neutrino physics. The knowledge of neutrino mass ordering has great importance for neutrinoless double-beta ($ 0\nu\beta\beta$) decay experiments, which can establish the nature of massive neutrinos, i.e., whether they are Dirac or Majorana fermions. Recently, the KamLAND-Zen 800 measurement has reached for the first time the parameter space of the inverted ordering with a vanishing lightest neutrino mass. By assuming the inverted ordering, we attempt to derive the physical information of the neutrino nature and Majorana CP phases from a negative or positive observation of $ 0\nu\beta\beta$ decays in the near future. Moreover, the possibility of extracting the nuclear matrix element in the case of a positive observation is also examined. To avoid the ambiguity from unknown priors of neutrino masses, we adopt the maximum likelihood method instead of the Bayesian approach usually considered in previous works., Comment: 13 pages, 7 figures, version published in EPJC

Whether the neutrino mass ordering is normal or inverted remains an experimentally open issue in neutrino physics. The knowledge of neutrino mass ordering has great importance for neutrinoless double-beta ( $$ 0\nu \beta \beta $$ 0 ν β β ) decay experiments, which can establish the nature of massive neutrinos, i.e., whether they are Dirac or Majorana fermions. Recently, the KamLAND-Zen 800 measurement has reached for the first time the parameter space of the inverted ordering with a vanishing lightest neutrino mass. By assuming the inverted ordering, we attempt to derive the physical information of the neutrino nature and Majorana CP phases from a negative or positive observation of $$ 0\nu \beta \beta $$ 0 ν β β decays in the near future. Moreover, the possibility of extracting the nuclear matrix element in the case of a positive observation is also examined.To avoid the ambiguity from unknown priors of neutrino masses, we adopt the maximum likelihood method instead of the Bayesian approach usually considered in previous works.

We make an attempt to study the impact of renormalization-group-equation-(RGE-) induced μ−τ reflection symmetry breaking on the effective Majorana neutrino mass |⟨m⟩ee| in neutrinoless double beta (0νββ) decay. At present, the 0νββ decay serves as a unique process to address the Majorana nature of massive neutrinos. The rate of such a decay process depends on |⟨m⟩ee|. On the other hand, μ−τ reflection symmetry predicts θ23=45° and δ=±90° together with trivial values of the Majorana CP-phases (ρ, σ). Moreover, based on the recent global best-fit values which prefer a higher octant of θ23 and third quadrant of δ, it is hard to believe the exactness of such symmetry. Also, any nontrivial values of ρ, σ may have some significant impact on |⟨m⟩ee|. In this context, we study the spontaneous breaking of the symmetry via one-loop RGE running from a superhigh energy scale (Λμτ) down to the electroweak scale (ΛEW). Given the broken symmetry, we perform some systematic analysis for |⟨m⟩ee| in substantial detail. Further, we also extend this analysis for other lepton-number violating effective Majorana masses.

We embed $μ-τ$ reflection symmetry into the minimal seesaw formalism, where two right-handed neutrinos are added to the Standard Model of particle physics. Assuming that both the left- and right-handed neutrino fields transform under $μ-τ$ reflection symmetry, we obtain the required forms of the neutrino Dirac mass matrix and the Majorana mass matrix for the right-handed neutrinos. To investigate the neutrino phenomenology at low energies, we first consider the breaking of $μ-τ$ reflection symmetry due to the renormalization group running, and then systematically study various breaking schemes by introducing explicit breaking terms at high energies., 35 pages, 7 figures, 4 tables, Version accepted for publication in Eur. Phys. J. C

We consider minimal type-I seesaw framework to realize $ ��-��$ reflection symmetry in the low-energy neutrino mass matrix, $ M_�� $. Considering DUNE experiment, we scrutinize its potential to measure the precision of 2-3 mixing angle, $ ��_{23} $ and the Dirac CP-phase, $ ��$ for the given symmetry. Later, we examine the precision of these two parameters considering NuFit-3.2 data as one of the important true points. To study the low-energy phenomenology, we further discuss various breaking patterns of such an exact symmetry. Moreover, for each breaking scenario we perform the capability test of DUNE for the determination of $ ��_{23} $ and to establish the phenomenon of CP violation considering the true benchmark point arising from the breaking of $ ��-��$ reflection symmetry. We also make remarks on the potential of DUNE to rule out maximal CP-violation or CP-conservation hypothesis at a certain confidence level for different scenarios., 28 pages, 6 figures, 11 tables, minor changes in the text, Version accepted for publication in Phys. Rev. D

The minimal seesaw framework, embroiling the Dirac neutrino mass matrix $ M_D $ and the Majorana neutrino mass matrix $ M_R $, is quite successful to explain the current global-fit results of neutrino oscillation data. In this context, we consider most predictive forms of $ M_D $ and $ M_R $ with two simple parameters, respectively. Considering these matrices, we obtain the low energy neutrino mass matrix under type-I seesaw formalism which obeys $ ��-��$ reflection symmetry and predicts $ ��_{23} = ��/4$ and $ ��= \pm ��/2 $. In the given set-up, we also evaluate the Baryon Asymmetry of the Universe (BAU) through successful leptogenesis and find that perturbation of $ \mathcal{O}(10^{-2}) $ leads to the observed BAU and breaks exactness of the symmetry. Moreover, we also perform various correlation studies among different parameters in the framework of broken symmetry., 13 pages, 4 figures, some more discussion added. Version accepted for publication in MPLA

We discuss the implications of the latest NO$ ��$A results on the measurement of $��_��- ��_e$ conversions. From a combined analysis of the disappearance and appearance data, the preferred solutions reported by NO$ ��$A are normal hierarchy (NH) with two degenerate best-fit points one in the lower octant (LO) and $ ��_{CP} = 1.48��$ whereas the other in the higher octant (HO) with $ ��_{CP} = 0.74��$. There is also another solution with inverted hierarchy (IH) which is $0.46 ��$ away from the best-fit. We discuss and quantify the possibility of resolving these degeneracies by inclusion of NO$ ��$A antineutrino runs. We show that if the true solution corresponds to (NH, LO, $\sim 1.48��$) then future data from NO$ ��$A comprising of 3 years of neutrino and 3 years of antineutrino run will be able to resolve the degenerate solutions at 95.45\% C.L. However, if the true solution corresponds to (NH, HO, $\sim 0.74��$), a wrong hierarchy-wrong $ ��_{CP} $ solution remains unresolved even at 68\% C.L. with the full $3��+3\bar��$ projected run of NO$ ��$A. Same is the case if the IH solution turns out to be the true solution. We further show that DUNE (10 kton) will be able to resolve these degenerate solutions at 99.73\% C.L. with only 1 year of neutrino and one year of antineutrino run [1+1] while 5+5 years of DUNE data can resolve the degeneracies at 99.99\% C.L., 8 pages, 6 figures, 2 tables