Search

We perform a comprehensive analysis of neutrinoless double beta decay and its interplay with low-energy flavor observables in a radiative neutrino mass model with scalar leptoquarks $S_1(\bar{3},1,1/3)$ and $\widetilde{R}_2(3,2,1/6)$. We carve out the parameter region consistent with constraints from neutrino mass and mixing, from collider searches, as well as from measurements of several flavor observables, including muon and electron anomalous magnetic moments, charged lepton flavor violation and rare (semi)leptonic kaon and $B$-meson decays. We perform a global analysis to all existing constraints and show the (anti)correlations between all relevant Yukawa couplings satisfying these restrictions. We find that the most stringent constraint on the parameter space comes from $\mu \to e$ conversion in nuclei. We also point out a tension between the $R_{D^{(*)}}$ and muon $(g-2)$ anomalies in this context. Taking benchmark points from these combined allowed regions, we study the implications for neutrinoless double beta decay including the canonical light neutrino and the leptoquark contributions. We find that for normal ordering of neutrino masses, the leptoquark contribution removes the cancellation region that occurs for the canonical case. The effective mass in presence of leptoquarks can lie in the desert region between the standard normal and inverted ordering cases, and this can be probed in future ton-scale experiments like LEGEND-1000 and nEXO. Taking suitable representative values of Yukawa couplings, we also obtain stringent constraints on leptoquark masses from different observables., Comment: 38 pages, 8 figures and 6 tables

The framework of three-flavor neutrino oscillation is a well-established phenomenon, but results from the short-baseline experiments, such as the Liquid Scintillator Neutrino Detector (LSND) and MiniBooster Neutrino Experiment (MiniBooNE), hint at the potential existence of an additional light neutrino state characterized by a mass-squared difference of approximately $1\,\rm eV^2$. The new neutrino state is devoid of all Standard Model (SM) interactions, commonly referred to as a 'sterile' state. In addition, a sterile neutrino with a mass-squared difference of $10^{-2}$ $\rm eV^2$ has been proposed to improve the tension between the results obtained from the Tokai to Kamioka (T2K) and the NuMI Off-axis $\nu_e$ Appearance (NO$\nu$A) experiments. Further, the non-observation of the predicted upturn in the solar neutrino spectra below 8 MeV can be explained by postulating an extra light sterile neutrino state with a mass-squared difference around $10^{-5} \rm eV^2$. The hypothesis of an additional light sterile neutrino state introduces four distinct mass spectra depending on the sign of the mass-squared difference. In this paper, we discuss the implications of the above scenarios on the observables that depend on the absolute mass of the neutrinos, namely the sum of the light neutrino masses $(\Sigma)$ from cosmology, the effective mass of the electron neutrino from beta decay $(m_{\beta})$, and the effective Majorana mass $( m_{\beta\beta})$ from neutrinoless double beta decay. We show that some scenarios can be disfavored by the current constraints of the above variables. The implications for projected sensitivity of Karlsruhe Tritium Neutrino Experiment (KATRIN) and future experiments like Project-8, next Enriched Xenon Observatory (nEXO) have been discussed., Comment: 32 pages (with appendix), 45 figures and 10 tables

Investigation of conservation/violation of CP symmetry in the leptonic sector is very essential in understanding the evolution of the universe. Lorentz invariance and CPT are fundamental symmetries of nature. The violation of Lorentz invariance can also lead to CPT violations. The standard three flavour neutrino oscillation framework presents a scenario to observe the signature of Lorentz invariance and CP violations. This work focuses on the effect of Lorentz invariance violating (LIV) parameters on the sensitivity to CP violation. We investigate the sensitivity in two proposed configurations of the upcoming T2HK experiment: (i) one detector each placed at 295 km and 1100 km, and (ii) two identical detectors at 295 km. This study probes the effect of CPT violating parameters $a_{e\mu},a_{e\tau},a_{\mu\tau}$., Comment: 10 pages, 11 figures

Results from experiments like LSND and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations. In particular, it can give rise to additional degeneracies due to additional sterile parameters. For an eV scale sterile neutrino, the cosmological constraints dictate that the sterile state is heavier than the three active states. However, for lower masses of sterile neutrinos, it can be lighter than one and/or more of the three states. In such cases, the mass ordering of the sterile neutrinos also becomes unknown along with the mass ordering of the active states. In this paper, we explore the mass ordering sensitivity in the presence of a sterile neutrino assuming the mass squared difference $|\Delta_{41}|$ to be in the range $10^{-4} - 1$ eV$^2$. We study (i) how the ordering of the active states, i.e. the determination of the sign of $\Delta_{31}$ gets affected by the presence of a sterile neutrino in the above mass range, (ii) the possible determination of the sign of $\Delta_{41}$ for $\Delta_{41}$ in the range $10^{-4} - 0.1$ eV$^2$. This analysis is done in the context of a liquid argon detector using both beam neutrinos traveling a distance of 1300 km and atmospheric neutrinos which propagates through a distance ranging from 10 - 10000 km allowing resonant matter effects. Apart from presenting separate results from these sources, we also do a combined study and probe the synergy between these two in giving an enhanced sensitivity., Comment: 14 pages, 19 figures

In this paper, we study the implications of the Dark Large Mixing Angle (DLMA) solutions of $\theta_{12}$ in the context of the IceCube data. We study the consequences in the measurement of the neutrino oscillation parameters namely $\theta_{23}$ and $\delta_{\rm CP}$ in light of both Large Mixing Angle (LMA) and DLMA solutions of $\theta_{12}$. We find that it will be impossible for IceCube to determine the $\delta_{\rm CP}$ and the true nature of $\theta_{12}$ i.e., LMA or DLMA at the same time. This is because of the existence of an intrinsic degeneracy at the Hamiltonian level between these parameters. Apart from that, we also identify a new degeneracy between $\theta_{23}$ and two solutions of $\theta_{12}$ for a fixed value of $\delta_{\rm CP}$. We perform a chi-square fit using three different astrophysical sources, i.e., $\mu$ source, $\pi$ source, and $n$ source to find that both $\mu$ source and $\pi$ source are allowed within $1 \sigma$ whereas the $n$ source is excluded at $2 \sigma$. It is difficult to make any conclusion regarding the measurement of $\theta_{23}$, $\delta_{\rm CP}$ for $\mu$ source. However, The $\pi$ ($n$) source prefers higher (lower) octant of $\theta_{23}$ for both LMA and DLMA solution of $\theta_{12}$. The best-fit value of $\delta_{\rm CP}$ is around $180^\circ$ ($0^\circ/360^\circ$) for LMA (DLMA) solution of $\theta_{12}$ whereas for DLMA (LMA) solution of $\theta_{12}$, the best-fit value is around $0^\circ/360^\circ$ ($180^\circ$) for $\pi$ ($n$) source. If we assume the current best-fit values of $\theta_{23}$ and $\delta_{\rm CP}$ to be true, then the $\mu$ and $\pi$ source prefer the LMA solution of $\theta_{12}$ whereas the $n$ source prefers the DLMA solution of $\theta_{12}$., Comment: 10 pages, 6 figures, 3 tables. Version accepted for publication in Universe

The gender imbalance in physics higher education and advanced professions is a global problem, and India is not an exception. Although the issue has been acknowledged widely, discrimination needs to be recognized as the driving force. The past three years have witnessed initiatives by different gender groups as well as the Government of India in addressing these lacunae. We report various activities, describe interventions, and present statistics indicating improvements achieved. The Gender in Physics Working Group has brought about significant gender reforms in the Indian Physics Association. The working group organized an open discussion on the issue of sexual harassment in physics professions for the first time in 2018. Subsequently, in 2019, GIPWG organized the first-ever national conference on gender issues, Pressing for Progress. The deliberations of the conference culminated in the Hyderabad Charter, a roadmap towards gender equity in India. The Working Group for Gender Equity constituted under the Astronomical Society of India, also played an impactful role. At the government level, notable new initiatives include Gender Advancement through Transforming Institutions and the proposed Science and Technology Innovation Policy for mainstreaming equity and inclusion., Comment: 3 pages, 1 figure

Results from the experiments like LSND, and MiniBooNE hint towards the possible presence of an extra eV scale sterile neutrino. The addition of such a neutrino will significantly impact the standard three flavour neutrino oscillations; in particular, it can give rise to additional degeneracies due to new sterile parameters. In our work, we investigate how the sensitivity to determine the octant of the neutrino mixing angle $\theta_{23}$ is affected by introducing a sterile neutrino to the standard neutrino oscillation framework. We compute the oscillation probabilities in presence of a sterile neutrino, analytically, using the approximation that $\Delta_{21}$, the smallest mass squared difference, is zero. We use these probabilities to understand the degeneracies analytically at different baselines. We present our results of the sensitivity to octant of $\theta_{23}$ for beam neutrinos using a liquid argon time projection chamber (LArTPC). We also obtain octant sensitivity using atmospheric neutrinos using the same LArTPC detector without any charge identification capability. In addition, we include the charge tagging capability of muon capture in argon which allows one to differentiate between muon neutrino and antineutrino events. The combined sensitivity of beam and atmospheric neutrinos in a similar experimental setup is also delineated. We observe that by combining simulated data from the beam and atmospheric neutrinos (including charge-id for muons), the sensitivity to the octant of $\theta_{23}$ for true values of $\theta_{23}=41^\circ(49^\circ)$ exceeds $4\sigma(3\sigma)$ for more than $50\%$ values of true $\delta_{13}$., Comment: 25 pages, 18 figures

In this paper, we consider the possibility of generating the observed baryon asymmetry of the Universe via leptogenesis in the context of triplet fermion mediated type-III seesaw model of neutrino mass. With a hierarchical spectrum of the additional fermions, the lower bound on the lightest triplet mass is $\sim 10^{10} {\rm~GeV}$ for successful leptogenesis, a couple of orders higher than that of the type-I case. We investigate the possibility of lowering this bound in the framework of two-Higgs-doublet models. We find that the bounds can be lowered down to $10^7$ GeV for a hierarchical spectrum. If we include the flavor effects, then a further lowering by one order of magnitude is possible. We also discuss if such lowering can be compatible with the naturalness bounds on the triplet mass., Comment: 9 pages, 7 figures; v2: Published version

The pair annihilation of neutrinos $(\nu\overline{\nu}\rightarrow e^+e^-)$ can energize violent stellar explosions such as gamma ray bursts (GRBs). The energy in this neutrino heating mechanism can be further enhanced by modifying the background spacetime over that of Newtonian spacetime. However, one cannot attain the maximum GRB energy $(\sim 10^{52}~\rm{erg})$ in either the Newtonian background or Schwarzschild and Hartle-Thorne background. On the other hand, using modified gravity theories or the Quintessence field as background geometries, the maximum GRB energy can be reached. In this paper, we consider extending the standard model by an extra $U(1)_{\rm{B-L}}$ gauge group and augmenting the energy deposition by neutrino pair annihilation process including contributions mediated by the $Z^\prime$ gauge boson belonging to this model. From the observed energy of GRB, we obtain constraints on $U(1)_{\rm{B-L}}$ gauge coupling in different background spacetimes. We find that the bounds on gauge coupling in modified gravity theories and quintessence background are stronger than those coming from the neutrino-electron scattering experiments in the limit of small gauge boson masses. Future GRB observations with better accuracy can further strengthen these bounds., Comment: 35 pages, 22 figures, 2 tables

We present compact analytic expressions for 3-flavor neutrino oscillation probabilities with invisible neutrino decay, where matter effects have been explicitly included. We take into account the possibility that the oscillation and decay components of the effective Hamiltonian do not commute. This is achieved by employing the techniques of inverse Baker-Campbell-Hausdorff (BCH) expansion and the Cayley-Hamilton theorem applied in the 3-flavor framework. If only the vacuum mass eigenstate $\nu_3$ decays, we show that the treatment of neutrino propagation may be reduced to an effective 2-flavor analysis in the One Mass Scale Dominance (OMSD) approximation. The oscillation probabilities for $P_{\mu\mu}$, $P_{ee}$, $P_{e\mu}$ and $P_{\mu e}$ -- relevant for reactor, long baseline and atmospheric neutrino experiments -- are obtained as perturbative expansions for the case of only $\nu_3$ decay, as well as for the more general scenario where all components of the decay matrix are non-zero. The analytic results thus obtained match the exact numerical results for constant density matter to a high precision and provide physical insights into possible effects of the decay of neutrinos as they propagate through Earth matter. We find that the effects of neutrino decay are most likely to be observable in $P_{\mu\mu}$. We also point out that at any long baseline, the oscillation dips in $P_{\mu\mu}$ can show higher survival probabilities in the case with decay than without decay, and explain this feature using our analytic approximations., Comment: 35 pages, 6 figures, references updated in v2 (no other changes)

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential., Comment: 429 pages, contribution to Snowmass 2021

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 PRD

We point out that the Hermitian and anti-Hermitian components of the effective Hamiltonian for decaying neutrinos cannot be simultaneously diagonalized by unitary transformations for all matter densities. We develop a formalism for the two-flavor neutrino propagation through matter of uniform density, for neutrino decay to invisible states. Employing a resummation of the Zassenhaus expansion, we obtain compact analytic expressions for neutrino survival and conversion probabilities, to first and second order in the "mismatch parameter" $\bar{\gamma}$., Comment: 5 pages, 1 figure

The neutrino-electron scattering process is a powerful tool to explore new physics beyond the standard model. Recently the possibility of DUNE Near Detector (ND) to constrain various new physics scenarios using this process have been highlighted in the literature. In this work, we consider the most general U(1) model and probe the constraints on the mass and coupling strength of the additional $Z'$ from $\nu-e$ scattering at DUNE ND. The presence of the $Z^\prime$ gives rise to extra interference effects. In the context of the general U(1) model, the destructive interference can occur in either neutrino or anti-neutrino channel or for both or none. This opens up the possibilities of getting four different type of signal in the neutrino and ant-neutrino runs of DUNE. We perform the analysis using both the total rate and binned events spectrum. Our results show that in a bin by bin analysis the effect of destructive interference is less compared to the analysis using total rate. We present the bounds on the $ m_{Z^\prime} - g_X$ plane from $\nu-e$ scattering measurements at DUNE ND and compare these with those obtained from other $\nu-e$ scattering, COHERENT, and beam dump experiments. We show that the DUNE ND can give the best bound for certain mass ranges of $Z^\prime$., Comment: 21 pages, 6 figures, 2 tables, matches accepted version in JHEP

We consider a general, anomaly free U$(1)^\prime$ extension of the Standard Model (SM) where the neutrino mass is generated at the tree level via the inverse seesaw mechanism. The model contains three right handed neutrinos, three additional singlet fermions, one extra complex scalar and a neutral gauge boson $(Z^\prime)$. Instead of resorting to a specific $U(1)$ extension, we consider a class of models by taking the $U(1)^\prime$ charges of the scalars to be free parameters. Here, we assign one pair of the pseudo-Dirac degenerate sterile neutrinos as Dark Matter (DM) candidates which are produced by the freeze-in mechanism. Considering different mass regimes of the DM, $Z^\prime$ and reheating temperature, we obtain constraints on the $U(1)^\prime$ charges giving the correct relic abundance. We have also obtained constraints on $Z^\prime$ mass and coupling from consideration of relic density as well as high energy collider experiments like ATLAS in case of heavy $Z^\prime$ or in intensity and lifetime frontier experiments like DUNE, FASERs, and ILC beam dump which are looking for light $Z^\prime$. Additionally, in this model, the decay of pseudo-Dirac DM into active neutrinos can explain the 511 keV line observed by the INTEGRAL satellite., Comment: 35 pages, 19 figures, 2 tables, matched with the journal version

In this work we have re-investigated two different kinds of texture zero ansatz of the low energy neutrino mass matrix in view of the Dark-Large-Mixing-Angle (DLMA) solution of the solar neutrino problem which can arise in the presence of non-standard interactions. In particular we revisit the cases of (i) one zero mass matrices when the lowest neutrino mass is zero and (ii) one zero texture with a vanishing minor. In our study we find that for most of the cases, the texture zero conditions which are allowed for the LMA solution, are also allowed for the DLMA solution. However, we found two textures belonging to the case of one zero texture with a vanishing minor where LMA solution does not give a viable solution whereas DLMA solution does. We analyze all the possible texture zero cases belonging to these two kinds of texture zero structures in detail and present correlations between different parameters. We also present the predictions for the effective neutrino mass governing neutrino-less double beta decay for the allowed textures., Comment: 18 pages, 5 figures. To appear in Nucl. Phys. B

We study the physics potential of the long-baseline experiments T2HK, T2HKK and ESS$\nu$SB in the context of invisible neutrino decay. We consider normal mass ordering and assume that the state $\nu_{3}$ as unstable, decaying into sterile states during the flight and obtain constraints on the neutrino decay lifetime ($\tau_3$). We find that T2HK, T2HKK and ESS$\nu$SB are sensitive to the decay-rate of $\nu_{3}$ for $\tau_{3}/m_{3} \leq 2.72\times10^{-11}$s/eV, $\tau_{3}/m_{3} \leq 4.36\times10^{-11}$s/eV and $\tau_{3}/m_{3} \leq 2.43\times10^{-11}$s/eV respectively at 3$\sigma$ C.L. We compare and contrast the sensitivities of the three experiments and specially investigate the role played by the mixing angle $\theta_{23}$. It is seen that for experiments with flux peak near the second oscillation maxima, the poorer sensitivity to $\theta_{23}$ results in weaker constraints on the decay lifetime. Although, T2HKK has one detector close to the second oscillation maxima, having another detector at the first oscillation maxima results in superior sensitivity to decay. In addition, we find a synergy between the two baselines of the T2HKK experiment which helps in giving a better sensitivity for $\theta_{23}$ in the higher octant. We discuss the octant sensitivity in presence of decay and show that there is an enhancement in sensitivity which occurs due to the contribution from the survival probability $P_{\mu\mu}$ which is more pronounced for the experiments at the second oscillation maxima. We also obtain the combined sensitivity of T2HK+ESS$\nu$SB and T2HKK+ESS$\nu$SB as $\tau_{3}/m_{3} \leq 4.36\times10^{-11}$s/eV and $\tau_{3}/m_{3} \leq 5.53\times10^{-11}$s/eV respectively at 3$\sigma$ C.L., Comment: 12 figure, 4 tables

We have studied the correlations among the three absolute neutrino mass observables - the effective Majorana mass ($m_{ee}$) which can be obtained from neutrinoless double beta decay, the electron neutrino mass ($m_{\beta}$) which is measured in single beta decay experiments and the sum of the light neutrino masses ($\Sigma$) which is constrained from cosmological observations, in the context of minimal left-right symmetric model. Two phenomenologically interesting cases of type-I seesaw dominance as well as type-II seesaw dominance have been considered. We have taken into account the independent constraints coming from lepton flavor violation, single $\beta$ decay, cosmology and neutrinoless double beta decay and have determined the combined allowed parameter space that can be probed in the future experiments. We have also analyzed the correlations and tensions between the different mass variables. In addition, the constraints on the masses of the heavy particles coming from lepton flavor violation and the bounds on three absolute neutrino mass observables are also determined. We show that these constraints can rule out some of the parameter space which are not probed by the collider experiments., Comment: 22 pages, 10 multi-panel figures, new references added, made minor corrections, matches the published version

In this work we investigate the usefulness of nuSTORM as a probe of two new-physics scenarios which are sterile neutrinos and non-unitarity of the neutrino mixing matrix. For the sterile neutrino we show the importance of the neutral current events when combined with the charged current events to constrain the effective mixing angle, $\theta_{\mu \mu}$, and the sterile mixing angles $\theta_{14}$ and $\theta_{24}$. We also study the role nuSTORM will play in the study of neutrino oscillation physics if the three generation neutrino mixing matrix is non-unitary. In this context we elucidate the role of nuSTORM, considering both charged current and neutral current events, in constraining the various non-unitarity parameters such as $\alpha_{11}$, $|\alpha_{21}|$ and $\alpha_{22}$., Comment: 26 pages, 7 figures, 1 new figure added, New references added, Updated to the version accepted in PRD

We construct a neutrino mass model based on the flavour symmetry group $A_4\times C_4 \times C_6 \times C_2$ which accommodates a light sterile neutrino in the minimal extended seesaw (MES) scheme. Besides the flavour symmetry, we introduce a $U(1)$ gauge symmetry in the sterile sector and also impose CP symmetry. The vacuum alignments of the scalar fields in the model spontaneously break these symmetries and lead to the construction of the fermion mass matrices. With the help of the MES formulas, we extract the light neutrino masses and the mixing observables. In the active neutrino sector, we obtain the $\text{TM}_2$ mixing pattern with non-zero reactor angle and broken $\mu$-$\tau$ reflection symmetry. We express all the active and the sterile oscillation observables in terms of only four real model parameters. Using this highly constrained scenario we predict $\sin^2 \theta_{23} =0.545^{+0.003}_{-0.004}$, $\sin \delta = -0.911^{+0.006}_{-0.005}$, $|U_{e4}|^2 = 0.029^{+0.009}_{-0.008}$, $|U_{\mu4}|^2 = 0.010^{+0.003}_{-0.003}$ and $|U_{\tau4}|^2 = 0.006^{+0.002}_{-0.002}$ which are consistent with the current data., Comment: 26 pages, 5 figures, version published in JHEP

We analyze the effect of the Dark-large mixing angle (DLMA) solution on the effective Majorana mass ($m_{\beta\beta}$) governing neutrino-less double beta decay ($0\nu\beta\beta$) in the presence of a sterile neutrino. We consider the 3+1 picture, comprising of one additional sterile neutrino. We have checked that the MSW resonance in the sun can take place in the DLMA parameter space in this scenario. Next we investigate how the values of the solar mixing angle $\theta_{12}$ corresponding to the DLMA region alter the predictions of $m_{\beta\beta}$ including a sterile neutrino in the analysis. We also compare our results with three generation cases for both standard large mixing angle (LMA) and DLMA. Additionally, we evaluate the discovery sensitivity of the future ${}^{136}Xe$ experiments in this context., Comment: 23 pages, 6 figures, 3 tables, Accepted to PRD

We consider a class of gauged $U(1)$ extensions of the Standard Model (SM), where the light neutrino masses are generated by an inverse seesaw mechanism. In addition to the three right handed neutrinos, we add three singlet fermions and demand an extra $Z_2$ symmetry under which, the third generations of both of the neutral fermions are odd, which in turn gives us a stable dark matter candidate. We express the $U(1)$ charges of all the fermions in terms of the U(1) charges of the standard model Higgs and the new complex scalar. We study the bounds on the parameters of the model from vacuum stability, perturbative unitarity, dark matter relic density and direct detection constraints. We also obtain the collider constraints on the $Z'$ mass and the $U(1)'$ gauge coupling. Finally we compare all the bounds on the $Z'$ mass versus the $U(1)'$ gauge coupling plane., Comment: typos fixed, references added, results unchanged

We investigate the consequences of $\mu-\tau$ reflection symmetry in presence of a light sterile neutrino for the $3+1$ neutrino mixing scheme. We discuss the implications of total $\mu-\tau$ reflection symmetry as well partial $\mu-\tau$ reflection symmetry. For the total $\mu-\tau$ reflection symmetry we find values of $\theta_{23}$ and $\delta$ remains confined near $\pi/4$ and $\pm \pi/2$ respectively. The current allowed region for $\theta_{23}$ and $\delta$ in case of inverted hierarchy lies outside the area preferred by the total $\mu-\tau$ reflection symmetry. However, interesting predictions on the neutrino mixing angles and Dirac CP violating phases are obtained considering partial $\mu-\tau$ reflection symmetry. We obtain predictive correlations between the neutrino mixing angle $\theta_{23}$ and Dirac CP phase $\delta$ and study the testability of these correlations at the future long baseline experiment DUNE. We find that while the imposition of $\mu-\tau$ reflection symmetry in the first column admit both normal and inverted neutrino mass hierarchy, demanding $\mu-\tau$ reflection symmetry for the second column excludes the inverted hierarchy. Interestingly, the sterile mixing angle $\theta_{34}$ gets tightly constrained considering the $\mu-\tau$ reflection symmetry in the fourth column. We also study consequences of $\mu-\tau$ reflection symmetry for the Majorana phases and neutrinoless double beta decay., Comment: 8 figures, Version accepted in PRD

The main aim of the ESS$\nu$SB proposal is the discovery of the leptonic CP phase $\delta_{CP}$ with a high significance ($5\sigma$ for 50% values of $\delta_{CP}$) by utilizing the physics at the second oscillation maxima of the $P_{\mu e}$ channel. It can achieve $3\sigma$ sensitivity to hierarchy for all values of $\delta_{CP}$. In this work, we concentrate on the hierarchy and octant sensitivity of the ESS$\nu$SB experiment. We show that combining the ESS$\nu$SB experiment with the atmospheric neutrino data from the proposed India-based Neutrino Observatory(INO) experiment can result in an increased sensitivity to mass hierarchy. In addition, we also combine the results from the ongoing experiments T2K and NO$\nu$A assuming their full runtime and present the combined sensitivity of ESS$\nu$SB + ICAL@INO + T2K + NO$\nu$A. We show that while by itself ESS$\nu$SB can have up to $3\sigma$ hierarchy sensitivity, the combination of all the experiments can give up to $5\sigma$ sensitivity depending on the true hierarchy-octant combination. The octant sensitivity of ESS$\nu$SB is low by itself. However the combined sensitivity of all the above experiments can give up to $3\sigma$ sensitivity depending on the choice of true hierarchy and octant. We discuss the various degeneracies and the synergies that lead to the enhanced sensitivity when combining different experimental data., Comment: 7 figures, 4 tables, minor typos corrected, updated to the published version

We study the implications of the Dark-LMA solution to the solar neutrino problem for neutrino-less double beta decay ($0\nu\beta\beta$ ). We show that while the predictions for the effective mass governing $0\nu\beta\beta$ remains unchanged for the inverted mass scheme, that for normal ordering becomes higher for the Dark-LMA parameter space and moves into the "desert region" between the two. This sets a new goal for sensitvity reach for the next generation experiments if no signal is found for the inverted ordering by the future search programmes., Comment: Matches with the published version

We study the minimal type-III seesaw model in which we extend the SM by adding two $SU(2)_L$ triplet fermions with zero hypercharge to explain the origin of the non-zero neutrino masses. We show that the naturalness conditions and the limits from lepton flavor violating decays provide very stringent bounds on the model parameters along with the constraints from the stability/metastability of the electroweak vacuum. We perform a detailed analysis of the model parameter space including all the constraints for both normal as well as inverted hierarchies of the light neutrino masses. We find that most of the region that are allowed by lepton flavor violating decays and naturalness fall in the stable/metastable region depending on the values of the standard model parameters., Comment: Title modified, added new plots, matches with the published version

We study origin, consequences and testability of a hypothesis of `partial $\mu$-$\tau$' reflection symmetry. This symmetry predicts $ |U_{\mu i}|=|U_{\tau i}|~(i=1,2,3) $ for a single column of the leptonic mixing matrix $U$. Depending on whether this symmetry holds for the first or second column of $U$ different correlations between $\theta_{23}$ and $ \delta_{CP} $ can be obtained. This symmetry can be obtained using discrete flavour symmetries. In particular, all the subgroups of SU(3) with 3-dimensional irreducible representation which are classified as class C or D can lead to partial $\mu$-$\tau$ reflection symmetry. We show how the predictions of this symmetry compare with the allowed area in the $\sin^2\theta_{23} - \delta_{CP}$ plane as obtained from the global analysis of neutrino oscillation data. Furthermore, we study the possibility of testing these symmetries at the proposed DUNE and Hyper-Kamiokande (HK) experiments (T2HK, T2HKK), by incorporating the correlations between $\theta_{23}$ and $ \delta_{CP}$ predicted by the symmetries. We find that when simulated data of DUNE and HK is fitted with the symmetry predictions, the $\theta_{23}-\delta_{CP}$ parameter space gets largely restricted near the CP conserving values of $ \delta_{CP} $. Finally, we illustrate the capability of these experiments to distinguish between the two cases leading to partial $\mu-\tau$ symmetry namely $|U_{\mu1}| = |U_{\tau 1}|$ and $|U_{\mu 2}| = |U_{\tau 2}|$., Comment: 10 pages, 17 figures, Updated to the published version

Neutrino oscillation physics has entered the precision era and the potential forthcoming experiments Hyper-Kamiokande and Deep Under-ground Neutrino Experiment (DUNE) are expected to lead this endeavor. In this paper we perform a comprehensive study of the octant, mass hierarchy and CP discovery sensitivities of DUNE, T2HK & T2HKK in their individual capacity and investigate the synergies of the aforementioned experiments with the on going T2K and NO$\nu$A experiments. We present a comparative account of the probabilities at the three baselines and explore in detail the physics issues which can cause the discrepancies in the sensitivities among the different experiments. We also find out the optimal exposure required by these experiments for achieving $5\sigma$ hierarchy and octant sensitivity and to discover CP violation at $3\sigma$ for 60\% values of $\delta_{CP}$. In addition we vary the neutrino-antineutrino runtime ratios for T2HK & T2HKK and check if the sensitivities are affected significantly due to this.

One of the primary objectives of Deep Underground Neutrino Experiment (DUNE) is to discover the leptonic CP violation and to identify it's source. In this context, we study the impact of non-standard neutrino interactions (NSIs) on observing the CP violation signal at DUNE. We explore the impact of various parameter degeneracies introduced by non-zero NSI and identify which of these can influence the CP violation sensitivity and CP precision of DUNE, by considering NSI both in data and in theory. In particular, we study how the CP sensitivity of DUNE is affected because of the intrinsic hierarchy degeneracy which occurs when the diagonal NSI parameter $\epsilon_{ee}=-1$ and $\delta_{CP}= \pm 90^{\circ}$.

Sensitivity of the magnetised Iron CALorimeter (ICAL) detector at the proposed India-based Neutrino Observatory (INO) to invisible decay of the mass eigenstate $\nu_3$ using atmospheric neutrinos is explored. A full three-generation analysis including earth matter effects is performed in a framework with both decay and oscillations. The wide energy range and baselines offered by atmospheric neutrinos are shown to be excellent for constraining the $\nu_3$ lifetime. We find that with an exposure of 500 kton-yr the ICAL atmospheric experiment could constrain the $\nu_3$ lifetime to $\tau_3/m_3>1.51\times10^{-10}$ s/eV at the 90\% C.L. This is two orders of magnitude tighter than the bound from MINOS. The effect of invisible decay on the precision measurement of $\theta_{23}$ and $|\Delta{m^2_{32}}|$ is also studied.

We consider singlet extensions of the standard model, both in the fermion and the scalar sector, to account for the generation of neutrino mass at the TeV scale and the existence of dark matter respectively. For the neutrino sector we consider models with extra singlet fermions which can generate neutrino mass via the so called inverse or linear seesaw mechanism whereas a singlet scalar is introduced as the candidate for dark matter. We show that although these two sectors are disconnected at low energy, the coupling constants of both the sectors get correlated at high energy scale by the constraints coming from the perturbativity and stability/metastability of the electroweak vacuum. The singlet fermions try to destabilize the electroweak vacuum while the singlet scalar aids the stability. As an upshot, the electroweak vacuum may attain absolute stability even upto the Planck scale for suitable values of the parameters. We delineate the parameter space for the singlet fermion and the scalar couplings for which the electroweak vacuum remains stable/metastable and at the same time giving the correct relic density and neutrino masses and mixing angles as observed., Comment: 35 pages, 15 figures

We study the consequences of invisible decay of neutrinos in the context of the DUNE experiment. We assume that the third mass eigenstate is unstable and decays to a light sterile neutrino and a scalar or a pseudo-scalar. We consider DUNE running in 5 years neutrino and 5 years antineutrino mode and a detector volume of 40 kt. We obtain the bounds on the rest frame life time $\tau_3$ normalized to the mass $m_3$ as $\tau_3/m_3 > 4.50\times 10^{-11}$ s/eV at 90\% C.L. for a normal hierarchical mass spectrum. We also find that DUNE can discover neutrino decay for $\tau_3/m_3 > 4.27\times 10^{-11}$ s/eV at 90\% C.L. In addition, for an unstable $\nu_3$ with an illustrative value of $\tau_3/m_3$ = $1.2 \times 10^{-11}$ s/eV, the no decay case gets disfavoured at the $3\sigma$ C.L. At 90\% C.L. the allowed range for this true value is obtained as $1.71 \times 10^{-11} > \tau_3/m_3 > 9.29\times 10^{-12}$ in units of s/eV. We also study the correlation between a non-zero $\tau_3/m_3$ and standard oscillation parameters and find an interesting correlation in the appearance channel probability with the mixing angle $\theta_{23}$. This alters the octant sensitvity of DUNE, favorably (unfavorably) for true $\theta_{23}$ in the lower (higher) octant. The effect of a decaying neutrino does not alter the hierarchy or CP discovery sensitivity of DUNE in a discernible way., Comment: accepted and published in JHEP with additional figures and few references

We discuss the implications of the latest NO$ \nu $A results on the measurement of $\nu_\mu - \nu_e$ conversions. From a combined analysis of the disappearance and appearance data, the preferred solutions reported by NO$ \nu $A are normal hierarchy (NH) with two degenerate best-fit points one in the lower octant (LO) and $ \delta_{CP} = 1.48\pi$ whereas the other in the higher octant (HO) with $ \delta_{CP} = 0.74\pi$. There is also another solution with inverted hierarchy (IH) which is $0.46 \sigma$ away from the best-fit. We discuss and quantify the possibility of resolving these degeneracies by inclusion of NO$ \nu $A antineutrino runs. We show that if the true solution corresponds to (NH, LO, $\sim 1.48\pi$) then future data from NO$ \nu $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, $\sim 0.74\pi$), a wrong hierarchy-wrong $ \delta_{CP} $ solution remains unresolved even at 68\% C.L. with the full $3\nu+3\bar{\nu}$ projected run of NO$ \nu $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., Comment: 8 pages, 6 figures, 2 tables

We discuss a comprehensive way to study the parameter degeneracies in the form of a generalized degeneracy in the neutrino oscillation experiments. First we describe the various degeneracies by considering only neutrino run of the long baseline experiment (LBL), NO$ \nu $A. Then we discuss the role of antineutrinos. Later, we present the combined role of T2K (LBL experiment) and ICAL@INO (atmospheric experiment) to resolve these degeneracies. We also discuss the affect of new physics like non-standards interactions (NSI) on the determination of neutrino mass hierarchy in DUNE., Comment: 3 pages, 2 figures, Contribution to the proceedings of XXII DAE-BRNS High Energy Physics Symposium, University of Delhi, India, Dec. 12-16, 2016

We study the effect of non-standard interactions (NSIs) on the propagation of neutrinos through the Earth matter and how it affects the hierarchy sensitivity of the DUNE experiment. We emphasize on the special case when the diagonal NSI parameter $\epsilon_{ee} = -1$, nullifying the standard matter effect. We show that, if in addition, CP violation is maximal then this gives rise to an exact intrinsic hierarchy degeneracy in the appearance channel, irrespective of the baseline and energy. Introduction of off-diagonal NSI parameter, $\epsilon_{e \tau}$, shifts the position of this degeneracy to a different $\epsilon_{ee}$. Moreover the unknown magnitude and phases of the off-diagonal NSI parameters can give rise to additional degeneracies. Overall, given the current model independent limits on NSI parameters, the hierarchy sensitivity of DUNE can get seriously impacted. However, a more precise knowledge on the NSI parameters, specially $\epsilon_{ee}$, can give rise to an improved sensitivity. Alternatively, if NSI exists in nature, and still DUNE shows hierarchy sensitivity, certain ranges of the NSI parameters can be excluded. Additionally, we briefly discussed the implications of $\epsilon_{ee} = -1$ (in the Earth) on MSW effect in the Sun., Comment: 6 pages, 4 figures

We study the efficiency of DUNE, a next generation long baseline oscillation experiment to resolve two major unknowns in neutrino oscillation physics. These are, octant of $\theta_{23}$ (i.e. if $\theta_{23}$ is $< 45^\circ$ or $>45^\circ$) and Dirac CP phase $\delta_{CP}$. We mainly focus on the role of antineutrinos when they travel 1300 km baseline of DUNE. We observe that for DUNE, the antineutrino runs help to remove parameter degeneracies even in the parameter space where the antineutrino probability suffers from various degeneracies. We study these points in detail and find that, due to enhanced matter effect longer baseline experiments create an increased tension between the neutrino and the antineutrino probabilities which helps to increase total sensitivity in case of combined runs. We also find that, antineutrino run increases overall CP sensitivity due to its ability to abolish octant-$\delta_{CP}$ degeneracy., Comment: 4 pages, 3 figures, Contribution to the proceedings of the 38th International Conference on High Energy Physics (ICHEP 2016), Chicago, Aug. 3-10, 2016

The right-handed neutrinos within the type-I seesaw mechanism can induce large radiative corrections to the Higgs mass, and naturalness arguments can then be used to set limits on their mass scale and Yukawa couplings. Driven by minimality, we consider the presence of two degenerate right-handed neutrinos. We compare the limits from naturalness with the ones from the stability of the electroweak vacuum and from lepton flavor violation. Implications from neutrinoless double beta decay are also discussed and renormalization effects for the light neutrino parameters are presented. Adding small perturbations to the degenerate heavy neutrino spectrum allows for successful leptogenesis., Comment: 22 pages, 11 figures; minor changes; version to appear in Phys. Rev. D

We study the zero textures of the Yukawa matrices in the minimal extended type-I seesaw (MES) model which can give rise to $\sim$ eV scale sterile neutrinos. In this model, three right handed neutrinos and one extra singlet $S$ are added to generate a light sterile neutrino. The light neutrino mass matrix for the active neutrinos, $ m_{\nu}$, depends on the Dirac neutrino mass matrix ($ M_{D} $), Majorana neutrino mass matrix ($ M_{R} $) and the mass matrix ($ M_{S} $) coupling the right handed neutrinos and the singlet. The model predicts one of the light neutrino masses to vanish. We systematically investigate the zero textures in $ M_{D} $ and observe that maximum five zeros in $ M_{D} $ can lead to viable zero textures in $ m_{\nu} $. For this study we consider four different forms for $ M_R $ (one diagonal and three off diagonal) and two different forms of $(M_{S})$ containing one zero. Remarkably we obtain only two allowed forms of $ m_{\nu} $ ($m_{e\tau} = 0 $ and $m_{\tau\tau}=0$) having inverted hierarchical mass spectrum. We re-analyze the phenomenological implications of these two allowed textures of $m_\nu$ in the light of recent neutrino oscillation data. In the context of the MES model, we also express the low energy mass matrix, the mass of the sterile neutrino and the active-sterile mixing in terms of the parameters of the allowed Yukawa matrices. The MES model leads to some extra correlations which disallow some of the Yukawa textures obtained earlier, even though they give allowed one-zero forms of $m_\nu$. We show that the allowed textures in our study can be realized in a simple way in a model based on MES mechanism with a discrete Abelian flavor symmetry group $Z_8 \times Z_2$., Comment: 29 pages, 6 figures and 7 tables, Version accepted for publication in JHEP