Search

We revisit the phenomenology of neutrinoless double beta ($0\nu\beta\beta$) decay mediated by non-interfering exchange of light and heavy Majorana neutrinos, in the context of current and prospective ton-scale experimental searches, as well as of recent calculations of nuclear matrix elements (NME) in different nuclear models. We derive joint upper bounds on the light and heavy contributions to $0\nu\beta\beta$ decay, for different sets of NME, through separate and combined data coming from the following experiments (and isotopes): KamLAND-Zen and EXO (Xe), GERDA, and MAJORANA (Ge) and CUORE (Te). We further consider three proposed projects that could provide, within current bounds, possible $0\nu\beta\beta$ decay signals at $>\!3\sigma$ level with an exposure of 10 ton years: nEXO (Xe), LEGEND (Ge) and CUPID (Mo). Separate and combined (Xe, Ge, Mo) signals are studied for different representative cases and NME sets, and the conditions leading to (non)degenerate light and heavy neutrino mechanisms are discussed. In particular, the role of heavy-to-light NME ratios in different isotopes is highlighted through appropriate graphical representations. By using different sets of ``true'' and ``test'' NME as a proxy for nuclear uncertainties, it is shown that the relative contributions of light and heavy neutrino exchange to $0\nu\beta\beta$ signals may be significantly biased in some cases. Implications for theoretical models connecting light and heavy Majorana neutrino masses are also briefly illustrated. These results provide further motivations to improve NME calculations, so as to better exploit the physics potential of future multi-isotope $0\nu\beta\beta$ searches at the ton scale., Comment: 20 pages, 9 figures

There are several unanswered questions regarding neutrinos which pave the way for physics beyond the standard model (SM) of particle physics. Generalized interactions of neutrinos provide a way to characterize these effects in a manner which is even more general than the oft-studied non-standard neutrino interactions. These interactions are described by higher dimensional operators maintaining the SM gauge symmetries. On the other hand cosmic neutrino background, although yet to be detected directly, is a robust prediction of the SM and the standard cosmology. We perform a global analysis of the relevant generalized neutrino interactions which are expressly relevant for the proposed cosmic neutrino detector PTOLEMY. The electron spectrum due to the capture of cosmic neutrinos on radioactive tritium gets modified due to the presence of these generalized interactions. We also show how the differential electron spectrum is sensitive to the finite experimental resolution, mass of the lightest neutrino eigenstate, the strength of these interactions and the ordering of neutrino mass., 24 pages, 5 figures, 5 tables; references added, discussions modified

We revisit the phenomenology of neutrinoless double beta ($0νββ$) decay mediated by non-interfering exchange of light and heavy Majorana neutrinos, in the context of current and prospective ton-scale experimental searches, as well as of recent calculations of nuclear matrix elements (NME) in different nuclear models. We derive joint upper bounds on the light and heavy contributions to $0νββ$ decay, for different sets of NME, through separate and combined data coming from the following experiments (and isotopes): KamLAND-Zen and EXO (Xe), GERDA, and MAJORANA (Ge) and CUORE (Te). We further consider three proposed projects that could provide, within current bounds, possible $0νββ$ decay signals at $>\!3σ$ level with an exposure of 10 ton years: nEXO (Xe), LEGEND (Ge) and CUPID (Mo). Separate and combined (Xe, Ge, Mo) signals are studied for different representative cases and NME sets, and the conditions leading to (non)degenerate light and heavy neutrino mechanisms are discussed. In particular, the role of heavy-to-light NME ratios in different isotopes is highlighted through appropriate graphical representations. By using different sets of ``true'' and ``test'' NME as a proxy for nuclear uncertainties, it is shown that the relative contributions of light and heavy neutrino exchange to $0νββ$ signals may be significantly biased in some cases. Implications for theoretical models connecting light and heavy Majorana neutrino masses are also briefly illustrated. These results provide further motivations to improve NME calculations, so as to better exploit the physics potential of future multi-isotope $0νββ$ searches at the ton scale., 20 pages, 9 figures

Solar nuclear reactions can occasionally produce sub-MeV elusive beyond the Standard Model particles that escape the solar interior without further interactions. This study focuses on massive spin-one particles. We construct the general theoretical framework and identify two crucial mixing sources involving the photon, which facilitate communication between the hidden and visible sectors: kinetic mixing with the photon, and plasma-induced mixing due to thermal electron loops. For both cases, we focus on the second stage of the solar proton-proton chain and evaluate the fluxes of monochromatic 5.49~MeV hidden vectors produced by the $p(d, ^3{\rm He})\gamma^\prime$ nuclear reaction. We then investigate their terrestrial detection via Compton-like scatterings. The incoming fluxes are polarized, and we evaluate the cross sections for Compton-like scatterings for transverse and longitudinal vectors. Finally, we apply this framework to a concrete case by investigating the sensitivity of the forthcoming Jiangmen Underground Neutrino Observatory (JUNO) experiment and identifying parameter space where current terrestrial bounds will be improved., Comment: 40 pages, 9 figures; v2: numerical mistake in the analysis corrected, updated results and discussion

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.

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 ($ 0νββ$) 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 $ 0νββ$ 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., 13 pages, 7 figures, version published in EPJC

We explore the neutrinoless double beta ($0\nu \beta\beta$) decay induced by an ultralight dark matter field coupled to neutrinos. The effect on $0\nu\beta\beta$ decay is significant if the coupling violates the lepton number, for which the $\Delta L=2$ transition is directly driven by the dark matter field without further suppression of small neutrino masses. As the ultralight dark matter can be well described by a classical field, the effect features a periodic modulation pattern in decay events. However, we find that in the early Universe such coupling will be very likely to alter the standard cosmological results. In particular, the requirement of neutrino free-streaming before the matter-radiation equality severely constrains the parameter space, such that the future $0\nu \beta\beta$ decay experiments can hardly see any signal even with a meV sensitivity to the effective neutrino mass., Comment: 10 pages, 5 figures, v2: matching the published version

We explore the neutrinoless double beta ($0νββ$) decay induced by an ultralight dark matter field coupled to neutrinos. The effect on $0νββ$ decay is significant if the coupling violates the lepton number, for which the $ΔL=2$ transition is directly driven by the dark matter field without further suppression of small neutrino masses. As the ultralight dark matter can be well described by a classical field, the effect features a periodic modulation pattern in decay events. However, we find that in the early Universe such coupling will be very likely to alter the standard cosmological results. In particular, the requirement of neutrino free-streaming before the matter-radiation equality severely constrains the parameter space, such that the future $0νββ$ decay experiments can hardly see any signal even with a meV sensitivity to the effective neutrino mass., 10 pages, 5 figures, v2: matching the published version

We explore the possibility of having a fermionic dark matter candidate within $U(1)'$ models for CE$��$NS experiments in light of the latest COHERENT data and the current and future dark matter direct detection experiments. A vector-like fermionic dark matter has been introduced which is charged under $U(1)'$ symmetry, naturally stable after spontaneous symmetry breaking. We perform a complementary investigation using CE$��$NS experiments and dark matter direct detection searches to explore dark matter as well as $Z^{\prime}$ boson parameter space. Depending on numerous other constraints arising from the beam dump, LHCb, BABAR, and the forthcoming reactor experiment proposed by the SBC collaboration, we explore the allowed region of $Z^{\prime}$ portal dark matter., Matches published version. 21 pages, 5 figures, 2 tables

The T2K collaboration has recently reported their results, which gives the best-fit values of the atmospheric mixing angle $\sin^2 ��_{23} = 0.53$ and the Dirac CP-violating phase $��= -1.89$ for normal neutrino mass ordering. We give a possible theoretical origin of such values based on the $��$-$��$ reflection symmetry. It has been found that the breaking of such symmetry using one-loop renormalization-group equations (RGEs) in the framework of minimal supersymmetric standard model can fit well with the latest T2K results and the recent global fits. To make a quantitative analysis, we have included for the first time the complete dataset of oscillation, beta decay, neutrinoless double-beta decay and cosmological observations in comparing the theory to experiments. We also further examine the importance of such breaking patterns for neutrinoless double-beta decay experiments., 12 pages, 3 figures, accepted for publication in EPJC

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 make an attempt to study the impact of renormalization-group equations (RGE) induced $\mu-\tau$ reflection symmetry breaking on the effective Majorana neutrino mass $ |\langle m\rangle_{ee} | $ in neutrinoless double beta ($ 0\nu\beta \beta $) decay. At present, the $ 0\nu\beta \beta $ decay serves as a unique process to address the Majorana nature of massive neutrinos. The rate of such decay process depends on $ |\langle m\rangle_{ee} | $. On the other hand, $\mu-\tau$ reflection symmetry predicts $ \theta_{23} = 45^\circ$ and $ \delta = \pm 90^\circ $ together with trivial values of the Majorana CP-phases ($ \rho, \sigma $). Moreover, based on the recent global best-fit values which prefer higher octant of $ \theta_{23} $ and third quadrant of $ \delta $, it is hard to believe the exactness of such symmetry. Also, any non-trivial values of $ \rho, \sigma $ may have some significant impact on $ |\langle m\rangle_{ee} | $. In this context, we study the spontaneous breaking of the symmetry via one-loop RGE-running from a superhigh energy scale ($\Lambda_{\mu \tau} $) down to the electroweak scale ($ \Lambda_{\rm EW} $). Given the broken symmetry, we perform some systematic analysis for $ |\langle m\rangle_{ee} | $ in substantial detail. Further, we also extend this analysis for other lepton-number violating effective Majorana masses., Comment: v2: 12 pages, 4 figures, 1 table, LaTex format changed. Some more discussion added in section IV-A, conclusion is unchanged. Version accepted for publication in Phys. Rev. D

We study origin, consequences and testability of a hypothesis of `partial $��$-$��$' reflection symmetry. This symmetry predicts $ |U_{��i}|=|U_{��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 $��_{23}$ and $ ��_{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 $��$-$��$ reflection symmetry. We show how the predictions of this symmetry compare with the allowed area in the $\sin^2��_{23} - ��_{CP}$ 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 $��_{23}$ and $ ��_{CP}$ predicted by the symmetries. We find that when simulated data of DUNE and HK is fitted with the symmetry predictions, the $��_{23}-��_{CP}$ parameter space gets largely restricted near the CP conserving values of $ ��_{CP} $. Finally, we illustrate the capability of these experiments to distinguish between the two cases leading to partial $��-��$ symmetry namely $|U_{\mu1}| = |U_{��1}|$ and $|U_{��2}| = |U_{��2}|$., 10 pages, 17 figures, Updated to the published version

In the traditional neutrinophilic two-Higgs doublet model ($��$2HDM), there is no non-standard neutrino interaction (NSI) as the interactions between the Standard Model fermions with neutrinos are negligibly small due to the tiny mixing of the two scalar doublets. In this work, we propose that if $��$2HDM is modified by considering the right-handed electron, $e_R$ is negatively charged under a global $U(1)$-symmetry then one can generate significant amount of NSI along with the tiny Dirac neutrino mass. Depending on different constraints from the LEP experiment, tree level lepton flavor violating processes, big-bang neucleosynthesis etc., we observe that this model significantly restricts the range of permissible NSI parameters, putting a strict upper bound on different NSIs. Furthermore, considering these model-dependent NSIs, we study their impact on the next-generation superbeam experiment, DUNE. We present a detailed discussion on the mass hierarchy sensitivity and the CP-violation discovery study considering the impact of both diagonal as well as off-diagonal NSIs., 28 pages, 6 figures, minor changes in the text; fixed typos; updated reference list; this matches published version

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$ \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

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 $��_{ee}=-1$ and $��_{CP}= \pm 90^{\circ}$.

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

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 $��_{23}$ (i.e. if $��_{23}$ is $< 45^\circ$ or $>45^\circ$) and Dirac CP phase $��_{CP}$. 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-$��_{CP}$ degeneracy., 4 pages, 3 figures, Contribution to the proceedings of the 38th International Conference on High Energy Physics (ICHEP 2016), Chicago, Aug. 3-10, 2016

At present the three major unknowns in neutrino oscillation parameters are the mass hierarchy, the octant of $\theta_{23}$ and the CP phase $\delta_{CP}$. It is well known that the presence of hierarchy$-\delta_{CP}$ and octant degeneracies affects the unambiguous determination of these parameters. In this paper we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy-$\theta_{23}$ - $\delta_{CP}$ degeneracy. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of $\delta_{CP}$. These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if $\theta_{13}$ is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of $\delta_{CP}$. We identify which of these eight different degenerate solutions can occur in the test ($\theta_{23} - \delta_{CP}$) parameter space, taking the long-baseline experiment NO$\nu$A running in the neutrino mode as an example. The inclusion of the NO$\nu$A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy -- right octant solutions to a large extent. The remaining wrong hierarchy solutions can be removed by combining NO$\nu$A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the $2\sigma$ level by the combined data set, for the true parameter space considered in the study., Comment: 32 pages, 6 figures, 4 tables, version accepted for publication in Phys. Rev. D

The octant of $��_{23}$ and $��_{CP}$ are the two major unknowns in neutrino oscillation physics. The precise determination of octant and $��_{CP}$ is interlinked through the octant-$��_{CP}$ degeneracy. In this paper we study the proficiency of the DUNE experiment to determine these parameters, in particular, the role played by the antineutrinos, the broadband nature of the beam and the matter effect. For $P_{��e}$ and $P_{\bar�� \bar{e}}$ the octant-$��_{CP}$ degeneracy occurs at different values of $��_{CP}$, combination of neutrino and antineutrino runs help to resolve this. However, in regions where neutrinos do not have octant degeneracy adding antineutrino data is expected to decrease the sensitivity because of the degeneracy and reduced statistics. However we find that in case of DUNE baseline, the antineutrino runs help even in parameter space where the antineutrino probabilities suffer from degeneracies. We explore this point in detail and point out that this happens because of the (i) broad-band nature of the beam so that even if there is degeneracy at a particular energy bin, over the whole spectrum the degeneracy may not be there; (ii) the enhanced matter effect due to the comparatively longer baseline which creates an increased tension between the neutrino and the antineutrino probabilities which raises the overall $��^2$ in case of combined runs. This feature is more prominent for IH since the antineutrino probabilities in this case are much higher than the neutrino probabilities due to matter effects. The main role of antineutrinos in enhancing CP sensitivity is their ability to remove the octant-$��_{CP}$ degeneracy. However even if one assumes octant to be known the addition of antineutrinos can give enhanced CP sensitivity in some parameter regions due to the tension between the neutrino and antineutrino $��^2$s., 18 pages, 12 figures, 4 tables, Version accepted for publication in Nucl. Phys. B

At present the three major unknowns in neutrino oscillation parameters are the mass hierarchy, the octant of $��_{23}$ and the CP phase $��_{CP}$. It is well known that the presence of hierarchy$-��_{CP}$ and octant degeneracies affects the unambiguous determination of these parameters. In this paper we show that a comprehensive way to study the remaining parameter degeneracies is in the form of a generalized hierarchy-$��_{23}$ - $��_{CP}$ degeneracy. We show that the wrong-hierarchy and/or wrong-octant solutions can be further classified into eight different solutions depending on whether they occur with the wrong or right value of $��_{CP}$. These eight solutions are different from the original eightfold degenerate solutions and can exist, in principle, even if $��_{13}$ is known. These multiple solutions, apart from affecting the determination of the true hierarchy and octant, also affect the accurate estimation of $��_{CP}$. We identify which of these eight different degenerate solutions can occur in the test ($��_{23} - ��_{CP}$) parameter space, taking the long-baseline experiment NO$��$A running in the neutrino mode as an example. The inclusion of the NO$��$A antineutrino run removes the wrong-octant solutions appearing with both right and wrong hierarchy. Adding T2K data to this resolves the wrong hierarchy -- right octant solutions to a large extent. The remaining wrong hierarchy solutions can be removed by combining NO$��$A + T2K with atmospheric neutrino data. We demonstrate this using ICAL@INO as the prototype atmospheric neutrino detector. We find that the degeneracies can be resolved at the $2��$ level by the combined data set, for the true parameter space considered in the study., 32 pages, 6 figures, 4 tables, version accepted for publication in Phys. Rev. D