arXiv subjects

Dibyakrupa Sahoo

Publications and source records attributed to Dibyakrupa Sahoo.

At least 19 recordsLinked to original sources

arXiv2026

Comments on Exploring Quantum Statistics for Dirac and Majorana Neutrinos using Spinor-Helicity technique (arXiv:2507.07180 [hep-ph])

We give our comments on Ref. [1](arXiv:2507.07180) which critiques our idea of exploring quantum statistics to distinguish between Dirac and Majorana neutrinos proposed in some of our earlier works [2-4]. The ad-hoc symmetrization of the Dirac case amplitude square advocated in Eqs. (16) and (35) of [1] has no physical basis and it leads to violation of lepton number in the the standard model for Dirac neutrinos. Therefore, this symmetrization by hand is in principle incorrect.

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arXiv2026

Implications of the evidence for direct $\mathbf{CP}$ violation in $D\to π^+π^-$ decays

The observation of $CP$ violation in the difference of $CP$ asymmetries between $D\to K^+K^-$ and $D\to π^+π^-$ has raised a debate whether the observed asymmetries can be regarded as a signal of physics beyond the standard model (SM). In this paper we obtain all the topological amplitudes and isospin amplitudes directly from measured observables for $D\to ππ$. These results unambiguously imply a very large penguin contribution, having a central value $4.74$ times the magnitude of the amplitude for $D^0\toπ^+ π^-$. This fitted central value differs from a reasonable SM estimate of $10\%$ with a significance greater than $3.3σ$. In contrast to previous studies, we present model-independent arguments based only on unitarity of re-scattering amplitudes to show that large penguins cannot arise from re-scattering alone and likely indicate physics beyond the SM. In a model-independent approach we show how a very small contribution from physics beyond the SM with a large weak phase alleviates the problem.

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arXiv2024

Searching for signatures of new physics in $B \to K \, ν\, \overlineν$ to distinguish between Dirac and Majorana neutrinos

We conduct a model-independent analysis of the distinct signatures of various generic new physics possibilities in the decay $B \to K \, ν\, \overlineν$ by analyzing the branching ratio as well as the missing mass-square distribution. Considering the final neutrinos to be of the same flavor with non-zero mass, we discuss the new physics contributions for both Dirac and Majorana neutrino possibilities. In our study, we utilize the analytical relations among form factors in semi-leptonic $B \to K$ transitions, which are consistent with current lattice QCD predictions to a very high numerical accuracy. We provide constraints on different new physics parameters, taking into account the recent measurement of $B^+ \to K^+ \, ν\, \overlineν$ branching ratio by the Belle-II collaboration. In future, if the missing mass-square distribution for $B^+ \to K^+ \, ν\, \overlineν$ decay gets reported by Belle-II with analysis of more events than their present data set, one can not only investigate possible new physics effects in these decays, but also probe the Dirac/Majorana nature of the neutrinos using quantum statistics, since a difference between the two cases is known to exist in the presence of non-standard neutrino interactions.

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arXiv2024

Exploring CP violation in $H \to τ^+ τ^- γ$

We propose a method of measuring the CP-odd part of the Yukawa interaction of Higgs boson and $τ$ leptons by observing the forward-backward asymmetry in the decay $H \to τ^+ \, τ^- \, γ$. The source of such asymmetry is the interference of the CP-even loop-level contribution coming from $H \to Z \, γ\to τ^+ \, τ^- \, γ$ decay channel with the contribution from tree-level CP-odd Yukawa interaction. We find that the CP violating effect is maximum when the invariant mass of the $τ^+ \, τ^-$ pair is equal to the mass of the $Z$ boson. We propose and utilise various Dalitz plot asymmetries to quantify the maximal size of the asymmetry and perform Monte Carlo simulations to study the feasibility of measuring it in the high luminosity phase of the Large Hadron Collider (HL-LHC).

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arXiv2024

Comments on "On the Dirac-Majorana neutrinos distinction in four-body decays" (arXiv:2305.14140 [hep-ph], Phys. Rev. D 109, no.3, 033005 (2024))

In arXiv:2305.14140 [hep-ph] the authors analyze the radiative leptonic decay $\ell^- \to ν_\ell \, \overlineν_{\ell'} \, \ell^{\prime -} \, γ$ to distinguish between Dirac and Majorana nature of neutrinos. They utilize the back-to-back kinematics for this purpose, a special kinematic configuration which we first proposed in our paper arXiv:2106.11785 [hep-ph]. Here we point out how and why their analysis of the back-to-back configuration is incorrect. This makes their conclusion and comments invalid and untenable.

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arXiv2024

Comments on "Can quantum statistics help distinguish Dirac from Majorana neutrinos?" (arXiv:2402.05172 [hep-ph])

In a recent article arXiv:2402.05172 [hep-ph], the authors discuss the question "whether quantum statistics can help distinguish between Dirac and Majorana neutrinos." The paper contains, among other things, an unsubstantiated critique of the results derived in our papers arXiv:2106.11785 [hep-ph] and arXiv:2307.05654 [hep-ph]. One of the criticisms is related to our expression for differential decay rate for the back-to-back neutrino-antineutrino configuration in the decay $B^0 \to μ^- \, μ^+ \, ν_μ\, \overlineν_μ$. We show that the claim is wrong and point out how the correct result was obtained. The second criticism is related to the implementation of the anti-symmetrization as dictated by quantum statistics for Majorana neutrinos and antineutrinos (which are identical, by definition). Any direct observation of the neutrinos, as done in Ref. \cite{Akhmedov:2024}, would project the neutrinos into distinguishable helicity states, thus nullifying all observable effects of quantum statistics. They have missed the point that our procedure holds when the neutrino and antineutrino remain undetected by the detector. In the back-to-back kinematic configuration, one can infer the neutrino energies without directly detecting their identities. This smartly ensures that the quantum statistical effects are not erased. Their overriding assertion that our papers arXiv:2106.11785 [hep-ph] and arXiv:2307.05654 [hep-ph] are incorrect fails to recognize that in both arXiv:2106.11785 [hep-ph] and arXiv:2307.05654 [hep-ph] we also point out generic conditions under which the practical Dirac-Majorana confusion theorem holds. "Clearly there is no confusion over confusion theorem."

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arXiv2023

Probing the non-standard neutrino interactions using quantum statistics

Using the well established principles of Lorentz invariance, CP and CPT symmetry, and quantum statistics we do a model-independent study of effects of possible non-standard couplings of (Dirac and Majorana) neutrinos. The study is sensitive to the different quantum statistical properties of the Dirac and Majorana neutrinos which, contrary to neutrino-mediated processes of lepton number violation, could lead to observable effects not suppressed by the small ratios of neutrino and heavier particle masses. For processes with a neutrino-antineutrino pair of the same flavor in the final state, we formulate the ``Dirac Majorana confusion theorem (DMCT)'' showing why it is normally very difficult to observe the different behaviour of both kinds of neutrinos in experiments if they have only the standard model (SM)-like left-handed vector couplings to gauge bosons. We discuss deviations from the confusion theorem in the presence of non-standard neutrino interactions, allowing to discover or constrain such novel couplings. We illustrate the general results with two chosen examples of neutral current processes, $Z \to ν\, \overlineν$ and $\mathcal{P}_i \to \mathcal{P}_f \, ν\, \overlineν$ (with $\mathcal{P}_{i,f}$ denoting pseudoscalar mesons, such as $B,K,π$). Our analysis shows that using 3-body decays the presence of non-standard interactions can not only be constrained but one can also distinguish between Dirac and Majorana neutrino possibilities.

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arXiv2022

Inferring the nature of active neutrinos: Dirac or Majorana?

The nature of a neutrino, whether it is a Dirac type or Majorana type, may be comprehensively probed using their quantum statistical properties. If the neutrino is a Majorana fermion, then by definition it is identical and indistinguishable from the corresponding antineutrino. When a Majorana neutrino and antineutrino are pair produced, the corresponding state has to obey the Pauli principle unlike in the Dirac case. We use this property to distinguish between the two cases using the process $B^0 \to μ^-\,μ^+\,ν_μ\,\barν_μ$. We show that the two cases differ dramatically in a special kinematic scenario where, in the rest frame of the parent $B$ meson, the muons fly away back-to-back (i.e. fly with 3-momenta of equal magnitudes but opposite directions), and so do the neutrino and antineutrino. Unlike any other scenario, we know the energies and magnitudes of $3$-momenta of both the neutrino and the antineutrino in this back-to-back configuration without even directly measuring them. This provides a way of avoiding the constraint imposed by the `practical Dirac-Majorana confusion theorem', as one need not fully integrate over neutrino and antineutrino in this case. As a true signature of the universal principle of quantum statistics which does not depend on the size of the mass of the particle but its spin, the difference between Dirac and Majorana cases in this special kinematic configuration does survive independent of the neutrino mass as long as neutrino mass is nonzero. The analysis presented here is applicable immediately to several other processes with the same final state as in the case of $B^0$ decay without any major change.

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arXiv2021

Methodology to determine the spin-parity of muon-philic $X$ boson in $J/ψ\rightarrow μ^- μ^+ X$ decay

The present anomaly in muon anaomalous magnetic moment can be explained by the presence of a muon-philic $X$ boson which could be a scalar particle or a vector particle with mass less than twice the mass of muon. The muon-philic $X$ boson could interestingly not be a parity eigenstate as well. If there exists such a boson, irrespective of its parity, it can be directly observed in the decay $J/ψ\to μ^- μ^+ X$ where $X$ remains invisible. We show that by using the angular distribution or the distribution of events in the square Dalitz plot, along with two well defined dimensionless ratios, one can clearly distinguish among the various spin-parity possibilities. This would constitute an important probe of both the existence and the nature of this new physics possibility.

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arXiv2020

Probing sterile neutrino in $B$ ($D$) meson decays at Belle II (BESIII)

We present, how a systematic study of $B \to D\ell N$ ($D \to K \ell N$) decays with $\ell=μ,τ$, at Belle II (BESIII) can provide unambiguous signature of a heavy neutrino $N$ and/or constrain its mixing with active neutrinos $ν_\ell$, which is parameterized by $|U_{\ell N}|^2$. Our constraint on $|U_{μN}|^2$ that can be achieved from the full Belle II data is comparable with what can be obtained from the much larger data set of the upgraded LHCb. Additionally, our method offers better constraint on $|U_{μN}|^2$ for mass of sterile neutrino $m_N < 2$ GeV. We can also probe the Dirac and Majorana nature of $N$ by observing the sequential decay of $N$, including suppression from observation of a displaced vertex as well as helicity flip, for Majorana $N$.

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arXiv2020

Probing new physics scenarios of muon $g-2$ via $J/ψ$ decay at BESIII

The disagreement between the standard model prediction and the experimental measurement of muon anomalous magnetic moment can be alleviated by invoking an additional particle which is either a vector boson ($X_1$) or a scalar ($X_0$). This new particle, with the mass $m_X \lesssim 2 m_μ$, can be searched for in the decay $J/ψ\to μ^- μ^+ X$, where $X$ is missing. Our numerical study shows that the search is quite feasible at the BESIII experiment in the parameter space allowed by muon $g-2$ measurements.

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arXiv2018

Angular distribution as an effective probe of new physics in semi-hadronic three-body meson decays

We analyze, in a fully model-independent manner, the effects of new physics on a few semi-hadronic three-body meson decays of the type $P_i \to P_f f_1 f_2$, where $P_i$, $P_f$ are well chosen pseudo-scalar mesons and $f_{1,2}$ denote fermions out of which at least one gets detected in experiments. We find that the angular distribution of events of these decays can probe many interesting new physics, such as the nature of the intermediate particle that can cause lepton-flavor violation, or presence of heavy sterile neutrino, or new intermediate particles, or new interactions. We also provide angular asymmetries which can quantify the effects of new physics in these decays. We illustrate the effectiveness of our proposed methodology with a few well chosen decay modes showing effects of certain new physics possibilities without any hadronic uncertainties.

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arXiv2018

Constraints on a sub-eV scale sterile neutrino from non-oscillation measurements

Anomalies in several short-baseline neutrino oscillation experiments suggest the possible existence of sterile neutrinos at about eV scale having appreciable mixing with the already known three neutrinos. We find that if such a light sterile neutrino exists, through a combined study of the leptonic decays of $μ^-$, $τ^-$, $π^-$ and $K^-$, some semi-leptonic decays of $τ^-$ and the invisible decay width of the $Z$ boson, it is possible to constrain the relevant mixing matrix elements. Furthermore, we compare the constraints, derived by using the method presented here, with the experimental results obtained from short-baseline neutrino oscillation experiments. We find that a single light sterile neutrino cannot satisfy the existing short-baseline neutrino oscillation constraints and explain the anomalies mentioned above. Along the way we provide a number of experimentally clean observables which can be used to directly study the light sterile neutrino independently of the neutrino oscillation experiments.

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arXiv2017

Prediction of the $CP$ asymmetry $C_{00}$ in $B^0 \to D^0\overline{D^0}$ decay

Of all $B \to D \overline{D}$ decays, the $B^0 \to D^0 \overline{D^0}$ decay has the smallest observed branching ratio as it takes place primarily via the suppressed $W$-exchange diagram. The $CP$ asymmetry for this mode is yet to be measured experimentally. By exploiting the relationship among the decay amplitudes of $B \to D\overline{D}$ decays (using isospin and topological amplitudes) we are able to relate the $CP$ asymmetries and branching ratios by a simple expression. This enables us to predict the $CP$ asymmetry $C_{00}$ in $B^0 \to D^0 \overline{D^0}$. While the predicted central values of $C_{00}$ are outside the physically allowed region, they are currently associated with large uncertainties owing to the large errors in the measurements of the $B^0 \to D^0 \overline{D^0}$ branching ratio ($B_{00}$), the other $CP$ asymmetries $C_{+-}$ (of $B^0 \to D^+ D^-$) and $A_{\text{CP}}$ (of $B^+ \to D^+ \overline{D^0}$). With a precise determination of $B_{00}$, $C_{+-}$ and $A_{\text{CP}}$, one can use our analytical result to predict $C_{00}$ with a reduced error and compare it with the experimental measurement when it becomes available. The correlation between $B_{00}$ and $C_{00}$ is an interesting aspect that can be probed in ongoing and future particle physics experiments such as LHCb and Belle II.

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arXiv2017

Deciphering Majorana nature of sub-eV neutrinos by using their quantum statistical property

Neutrinos are the only known elementary fermions that can exhibit Majorana nature. As per the "practical Dirac-Majorana confusion theorem" it is impossible to distinguish between Dirac and Majorana neutrinos via any kinematic tests when their masses are very small. However, it is also well known that Majorana neutrino and anti-neutrino present in the final state must obey the Fermi-Dirac statistics, irrespective of how small the mass of neutrino is. We propose a new method to search for Majorana neutrinos by exploiting their quantum statistical property. We analyse `effective' three-body decays of the kind $X \to Y ν\overlineν$ (e.g.\ $X \left[ B^0 \right] \to π^+ \big( \to μ^+ ν_μ \big) μ^- \overlineν_μ \equiv Y \left[ μ^+ μ^-\right] ν_μ \overlineν_μ$), with 4-momenta of $X$ and $Y$ experimentally known, such that the 4-momenta of both neutrino and anti-neutrino can be deduced. For Majorana neutrinos the distribution of events in the `effective' Dalitz plot for such a well chosen process would be fully symmetric under exchange of the neutrino and anti-neutrino. Unlike the neutrinoless double-beta decay or other lepton-number violating modes, this distinction between Majorana and Dirac neutrinos survives even in the almost massless neutrino limit due to the quantum statistical property.

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arXiv2017

Discovering intermediate mass sterile neutrinos through $τ^- \to π^- μ^- e^+ ν$ (or $\barν$) decay

Distinguishing the Dirac and Majorana nature of neutrinos remains one of the most important tasks in neutrino physics. By assuming that the $τ^- \to π^- μ^- e^+ ν$ (or $\barν$) decay is resonantly enhanced by the exchange of an intermediate mass sterile neutrino $N$, we show that the energy spectrum of emitted pions and muons can be used to easily distinguish between the Dirac and Majorana nature of $N$. This method takes advantage of the fact that the flavor of light neutrinos is not identified in the tau decay under consideration. We find that it is particularly advantageous, because of no competing background events, to search for $N$ in the mass range $m_e + m_μ \leqslant m_N \leqslant m_μ + m_π$, where $m_X$ denotes the mass of particle $X \in \{ e, μ, π, N \}$.

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arXiv2017

Probing new physics in $B \to D \ell^+ \ell^-$ decays by using angular asymmetries

We present the fully general, model independent study of a few rare semileptonic $B$ decays that get dominant contributions from $W$-annihilation and $W$-exchange diagrams, in particular $B^0 \to \bar{D}^0 \ell^+\ell^-$, where $\ell = e,μ$. We consider the most general Lagrangian for the decay, and define three angular asymmetries in the Gottfried-Jackson frame, which are sensitive to new physics. We show how these angular asymmetries can be easily extracted from the distribution of events in the Dalitz plot for $B \to D \ell^+ \ell^-$ decays. Especially a non-zero forward-backward asymmetry within the frame would give the very first hint of possible new physics. These observations are also true for related decay modes, such as $B^+ \to D^+ \ell^+ \ell^-$ and $B^0 \to D^0 \ell^+ \ell^-$. Moreover, these asymmetry signatures are not affected by either $B^0$-$\bar{B}^0$ or $D^0$-$\bar{D}^0$ mixings. Then, this implies that both $B^0 \to \bar{D}^0 \ell^+ \ell^-$ and $B^0 \to D^0 \ell^+ \ell^-$ as well as their CP conjugate modes can all be considered together in our search for signature of new physics. Hence, it would be of great importance to look for and study these decays in the laboratory, LHCb and Belle II in particular.

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arXiv2015

Disentangling the Spin-Parity of a Resonance via the Gold-Plated Decay Mode

Searching for new resonances and finding out their properties is an essential part of any existing or future particle physics experiment. The nature of a new resonance is characterized by its spin, charge conjugation, parity, and its couplings with the existing particles of the Standard Model. If a new resonance is found in the four lepton final state produced via two intermediate $Z$ bosons, the resonance could be a new heavy scalar or a $Z'$ boson or even a higher spin particle. In such cases the step by step methodology as enunciated in this paper can be followed to determine the spin, parity and the coupling to two $Z$ bosons of the parent particles, in a fully model-independent way. In our approach we show how three uni-angular distributions and few experimentally measurable observables can conclusively tell us about the spin, parity as well as the couplings of the new resonance to two $Z$ bosons. We have performed a numerical analysis to validate our approach and showed how the uniangular observables can be used to disentangle the spin parity as well as coupling of the resonance.

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