arXiv subjects

Newton Nath

Publications and source records attributed to Newton Nath.

At least 19 recordsLinked to original sources

arXiv2026

Precision Tests of SM and new physics with the COHERENT Ge-mini and TEXONO data

A comprehensive numerical analysis of the latest germanium based CE$\nu$NS data from the COHERENT Ge-mini and TEXONO experiments has been conducted to test the Standard Model (SM) and search for new physics. By combining CE$\nu$NS and E$\nu$NS signals with a consistent treatment of detector effects and systematic uncertainties, we obtain a low energy determination of the weak mixing angle from COHERENT Ge-mini, in agreement with the SM prediction. We derive novel constraints on neutrino electromagnetic properties, including the magnetic moment, millicharge, charge radius, and anapole moment, with TEXONO providing particularly competitive bounds. Inclusion of E$\nu$NS, significantly improves the sensitivity to the neutrino millicharge by up to three orders of magnitude. We also investigated light scalar and vector mediators, finding striking complementarity between reactor and stopped pion sources across different mediator mass regimes. Finally, we put bounds on sterile neutral leptons production through transition dipole, scalar, and vector portals, probing masses from the sub MeV to tens of MeV scale. Our results demonstrate that current germanium based CE$\nu$NS experiments provide a powerful low energy laboratory for precision electroweak tests and complementary probes of a broad class of physics beyond the SM.

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arXiv2026

Solar Axions from Nuclear Transitions

We investigate the possibility of detecting 14.4 keV and 9.4 keV solar axions and axion-like particles that could be produced in the M1 nuclear transitions of $^{57}$Fe and $^{83}$Kr, respectively. To do so, we used data from soft X-ray observations of the quiet Sun collected by the Solar X-ray Monitor (XSM) on board India's Chandrayaan-2 lunar mission. We observe that although the effective axion-nucleon couplings for $^{83}$Kr and $^{57}$Fe differ only slightly, their fluxes differ by nearly three orders of magnitude. Consequently, the limit on $|g_{aN}^{\rm eff} \times g_{a\gamma\gamma}|$ and only $g_{a\gamma\gamma}$ vs. $m_a$ provide more than an order-of-magnitude stronger constraint for Fe than for Kr.

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arXiv2025

Zooming in on `bi-large' neutrino mixing with the first JUNO results

The leptonic mixing matrix is examined within bi-large mixing patterns and confronted with the latest results announced by the Jiangmen Underground Neutrino Observatory (JUNO). We analyze the viability of bi large mixing schemes and assess JUNO's ability to test neutrino mixing and discriminate among different bi-large mixing patterns, some of which are strongly disfavored when compared with neutrino oscillation global-fit results. Specific octant and CP predictions emerge. Finally, we comment on the implications of JUNO's findings for neutrinoless double beta decay.

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arXiv2025

Dirac Scoto Inverse-Seesaw from $A_4$ Flavor Symmetry

We present a Dirac scotogenic-like one loop radiative model where the stability of dark matter is intricately linked to the breaking of $A_4$ flavor symmetry. This breaking induces a $Z_2$ dark symmetry, stabilizing the dark matter candidate. The breaking of $A_4 \to Z_2$ leads to cutting the loop and facilitating a "scoto inverse-seesaw" mass mechanism responsible for neutrino mass generation. This elucidates the explicit explanation of two mass-squared differences, $\Delta m^2_{\rm{atm}}$ and $\Delta m^2_{\rm{sol}}$ observed in neutrino oscillations. Our model accounts for normal and inverted ordering of neutrino masses, revealing sharp correlations between $\sum m_i$ and $\langle m_{\beta} \rangle$. It also shows strong compatibility with current data in the $\delta_{CP}$-$\theta_{23}$ plane. Moreover, stringent constraints on scalar masses narrow down the viable dark matter mass regions, accommodating $SU(2)_L$ singlet and doublet scalar dark matter as well as fermionic dark matter. Additionally, our model presents a viable avenue for addressing lepton flavor violating decays while remaining consistent with current experimental constraints.

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arXiv2024

Majorana CP Violation Insights from Decaying Neutrinos

It is well-known that within the standard three flavor neutrino oscillation formalism, the Majorana phases appearing in the neutrino mixing matrix cannot have any effect on neutrino oscillation probabilities thereby evading testability at neutrino oscillation experiments. We consider an effective non-Hermitian Hamiltonian describing three flavor neutrino oscillations with the possibility of neutrino decay and demonstrate that the two Majorana phases can entangle with the off-diagonal decay terms and appear at the level of oscillation probabilities. Using the Cayley-Hamilton theorem, we derive approximate analytical expressions for three flavor neutrino oscillation probabilities in the presence of neutrino decay, taking into account matter effects. In the context of a long baseline neutrino experiment, we then analyse the impact of Majorana phases on the oscillation probabilities for different channels as well as on observables related to CP violation effects in neutrino oscillations. Finally, we discuss the effect of Majorana phases on the parameter degeneracies in the neutrino oscillation framework.

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arXiv2024

QCD axion, colour-mediated neutrino masses, and $B^+\to K^+ + E_{\text{miss}}$ anomaly

Motivated by the recent Belle II result indicating a $2.7\,\sigma$ excess of $B^+\to K^+ + E_{\text{miss}}$ events compared to the Standard Model (SM) prediction for $B^+ \to K^+ \nu\bar{\nu}$, we explore an explanation to this anomaly based on a KSVZ-type QCD axion model featuring a Peccei-Quinn (PQ) symmetry breaking at high-scale, that can provide a solution to the strong CP problem with dark matter relic abundance. The model contains a PQ-charged scalar} leptoquark which can interact with the SM quarks only via mass-mixing of the latter with vector-like quarks. The mixing between SM and vector-like quarks is determined by the PQ mass scales and can explain the excess $B^+\to K^+ + E_{\text{miss}}$ events while respecting other flavour constraints. The same PQ-charged scalar leptoquarks and vector-like quarks also mediate the two-loop radiative neutrino masses.

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arXiv2024

Cutting the Scotogenic loop: Adding flavor to Dark Matter

We introduce a framework for hybrid neutrino mass generation, wherein scotogenic dark sector particles, including dark matter, are charged non-trivially under the $A_4$ flavor symmetry. The spontaneous breaking of the $A_4$ group to residual $\mathcal{Z}_2$ subgroup results in the ``cutting" of the radiative loop. As a consequence the neutrinos acquire mass through the hybrid ``scoto-seesaw" mass mechanism, combining aspects of both the tree-level seesaw and one-loop scotogenic mechanisms, with the residual $\mathcal{Z}_2$ subgroup ensuring the stability of the dark matter. The flavor symmetry also leads to several predictions including the normal ordering of neutrino masses and ``generalized $\mu-\tau$ reflection symmetry" in leptonic mixing. Additionally, it gives testable predictions for neutrinoless double beta decay and a lower limit on the lightest neutrino mass. Finally, $A_4 \to \mathcal{Z}_2$ breaking also leaves its imprint on the dark sector and ties it with the neutrino masses and mixing. The model allows only scalar dark matter, whose mass has a theoretical upper limit of $\lesssim$ 600 GeV, with viable parameter space satisfying all dark matter constraints, available only up to about 80 GeV. Conversely, fermionic dark matter is excluded due to constraints from the neutrino sector. Various aspects of this highly predictive framework can be tested in both current and upcoming neutrino and dark matter experiments.

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arXiv2024

PTOLEMY's test of generalized neutrino interactions: unveiling challenges and constraints

Unanswered questions surrounding neutrinos have motivated investigations into physics beyond the standard model (SM) of particle physics. In particular, generalized neutrino interactions (GNI) provide a broader framework for studying these effects compared to the commonly studied non-standard neutrino interactions. These interactions are described by higher dimensional operators while maintaining the gauge symmetries of the SM. Furthermore, the cosmic neutrino background, a predicted component of the SM and standard cosmology, has yet to be directly detected. To shed light on this elusive phenomenon, we conduct a comprehensive analysis of the relevant GNI, specifically focusing on their implications for the proposed cosmic neutrino detector PTOLEMY. We make an attempt to see the capabilities and the limitations of PTOLEMY in sensing GNI while remaining optimistic regarding PTOLEMY's experimental resolution. These interactions play a significant role in modifying the electron spectrum resulting from the capture of cosmic neutrinos on radioactive tritium. This work also explores how the presence of these interactions influences the differential electron spectrum, taking into account factors such as finite experimental resolution, the mass of the lightest neutrino eigenstate, the strength of the interactions, and the ordering of neutrino mass.

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arXiv2023

Terrestrial detection of hidden vectors produced by solar nuclear reactions

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 $p(d, ^3{\rm He})γ^\prime$ 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.

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arXiv2023

Interplay between non-interfering neutrino exchange mechanisms and nuclear matrix elements in $0νββ$ decay

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.

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arXiv2022

Inference of neutrino nature and Majorana CP phases from $0νββ$ decays with inverted mass ordering

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.

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arXiv2022

Probing high-energy solar axion flux with a large scintillation neutrino detector

We investigate the 5.49 MeV solar axions flux produced in the $p(d,\, ^{3}{\rm He})a$ reaction and analyze the potential to detect it with the forthcoming large underground neutrino oscillation experiment Jiangmen Underground Neutrino Observatory (JUNO). The JUNO detector could reveal axions through various processes such as Compton and inverse Primakoff conversion, as well as through their decay into two photons or electron-positron pairs inside the detector. We perform a detailed numerical analysis in order to forecast the sensitivity on different combinations of the axion-electron ($ g_{ae} $), axion-photon ($g_{aγ}$), and isovector axion-nucleon ($ g_{3aN} $) couplings, using the expected JUNO data for different benchmark values of axion mass in a model-independent way. We find that JUNO would improve by approximately one order of magnitude current bounds by Borexino and it has the best sensitivity among neutrino experiments.

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arXiv2022

Light $Z^\prime$ and Dirac fermion dark matter in the $B-L$ model

We consider a $U(1)_{B-L}$ model with a $Z^\prime$ portal Dirac fermion dark matter (DM) $χ$ 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 $χ$ 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, $m_χ\simeq m_{Z^\prime}/2$, where $m_χ$ is the DM mass. For the freeze-in scenario, we focus on $m_χ\ll m_{Z^\prime}$. 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.

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arXiv2022

Neutrino meets ultralight dark matter: $\boldsymbol{0νββ}$ decay and cosmology

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.

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arXiv2022

CE$ν$NS as a probe of flavored generalized neutrino interactions

We examine the potential to probe generalized neutrino interactions (GNI), exotic effective couplings due to new physics interactions beyond the Standard Model, in the coherent-elastic neutrino-nucleus scattering experiments in light of the latest COHERENT-CsI, and -LAr data. Our analysis focuses on scalar, vector and tensor flavored-GNI parameters. A combined analysis has been made to constrain these exotic couplings for the CsI and LAr detector. We further add the projected forthcoming reactor-based Scintillating Bubble Chamber detector to examine these couplings. It has been observed that the addition of reactor data strongly constrained electron flavor GNI.

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arXiv2021

Complementarity between dark matter direct searches and CE$ν$NS experiments in $U(1)'$ models

We explore the possibility of having a fermionic dark matter candidate within $U(1)'$ models for CE$ν$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$ν$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.

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arXiv2021

Charged Higgs effects in IceCube: PeV events and NSIs

Extensions of the Standard Model with charged Higgs, having a non-negligible coupling with neutrinos, can have interesting implications vis-à-vis neutrino experiments. Such models can leave their footprints in the ultra-high energy neutrino detectors like IceCube in the form of neutrino non-standard interactions (NSIs) which can also be probed in lower energy neutrino experiments. We consider a model based on the neutrinophilic two-Higgs doublets and study its imprints in the recently reported excess neutrino events in the PeV energy bins at the IceCube. An additional signature of the model is that it also leads to sizeable NSIs. We perform a combined study of the latest IceCube data along with various other constraints arising from neutrino experiments e.g., Borexino, TEXONO, COHERENT, DUNE, and T2HK, together with the limits set by the LEP experiment, and explore the parameter space which can lead to a sizeable NSI.

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arXiv2021

Flavored axion in the UV-complete Froggatt-Nielsen models

We propose UV-completions of Froggatt-Nielsen-Peccei-Quinn models of fermion masses and mixings with flavored axions, by incorporating heavy fields. Here, the $U(1)$ Froggatt-Nielsen symmetry is identified with the Peccei-Quinn symmetry to solve the strong CP problem along with the mass hierarchies of the Standard Model fermions. We take into account leading order contributions to the fermion mass matrices giving rise to Nearest-Neighbour-Interaction structure in the quark sector and $A_2$ texture in the neutrino sector. A comprehensive numerical analysis has been performed for the fermion mass matrices. Subsequently, we investigate the resulting axion flavor violating couplings and the axion-photon coupling arising from the model.

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