<p>Coherence, which represents the superposition of orthogonal states, is a fundamental concept in quantum mechanics and can also be precisely defined within quantum resource theory. Thus exploring quantum coherence in neutrino oscillations can not only help in examining the intrinsic quantum nature but can also explore their potential applications in quantum information technologies. Previous studies on quantum coherence have focused on neutrino flavor oscillations (FO). However, FO imply that neutrinos have mass, and this can lead to the generation of a tiny but finite magnetic dipole moment of neutrinos through quantum loop diagrams at higher orders of perturbative expansion of the interaction. This electromagnetic property of neutrinos can induce spin flavor oscillations (SFO) in the presence of an external magnetic field and hence is expected to enrich the study of coherence. In this work, we investigate quantum coherence in neutrino SFO with three flavor mixing within the interstellar as well as intergalactic magnetic fields, quantified by the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>l</mi><mn>1</mn></msub></math> norm and the relative entropy of coherence, and express these measures in terms of neutrino SFO probabilities. For FO, coherence measures can sustain higher values (say, within 50% of the maximum) over distances of several kilometers, which are relevant for terrestrial experiments like reactor and accelerator neutrinos. However, for SFO, we find that the coherence scale can extend to astrophysical distances, spanning from kiloparsecs to gigaparsecs.</p>

India

Ashutosh Kumar Alok

Trambak Jyoti Chall

Neetu Raj Singh Chundawat

Shireen Gangal

Italy

Gaetano Lambiase

Quantum coherence in neutrino spin-flavor oscillations

We conduct a comprehensive investigation into the flavor phenomenology and collider signatures of flavon of <math><msub><mi>Z</mi><mi>N</mi></msub><mo>×</mo><msub><mi>Z</mi><mi>M</mi></msub></math> flavor symmetries for the soft symmetry-breaking scenario and a new symmetry-conserving mechanism at the high-luminosity LHC, high-energy LHC, and a 100 TeV hadron collider. The flavor physics of quark and leptonic observables places different bounds on the parameter space of flavons of <math><msub><mi>Z</mi><mi>N</mi></msub><mo>×</mo><msub><mi>Z</mi><mi>M</mi></msub></math> flavor symmetries. On the collider side, the decay <math><mi>t</mi><mo>→</mo><mi>c</mi><mi>a</mi></math> can be probed by the high-luminosity LHC, high-energy LHC, and a 100 TeV hadron collider for the <math><msub><mi>Z</mi><mn>8</mn></msub><mo>×</mo><msub><mi>Z</mi><mn>22</mn></msub></math> flavor symmetry. The inclusive production signatures can be used to probe the flavon of all the <math><msub><mi>Z</mi><mi>N</mi></msub><mo>×</mo><msub><mi>Z</mi><mi>M</mi></msub></math> flavor symmetries for the soft symmetry-breaking scenario for a heavy flavon at a 100 TeV collider. Flavons of all the <math><msub><mi>Z</mi><mi>N</mi></msub><mo>×</mo><msub><mi>Z</mi><mi>M</mi></msub></math> flavor symmetries can be probed at high-energy LHC and a 100 TeV collider for a low mass in the case of soft symmetry breaking. The diflavon production is within reach of the high-luminosity LHC, high-energy LHC, and a 100 TeV collider only for a light flavon. The 14 TeV high-luminosity LHC can probe only the <math><msub><mi>Z</mi><mn>2</mn></msub><mo>×</mo><msub><mi>Z</mi><mn>5</mn></msub></math> and <math><msub><mi>Z</mi><mn>8</mn></msub><mo>×</mo><msub><mi>Z</mi><mn>22</mn></msub></math> flavor symmetries for a few specific inclusive signatures. The symmetry-conserving scenario remains beyond the detection capabilities of any collider.

Gauhar Abbas

Najimuddin Khan

Neelam Singh

Finding flavons at colliders

It was previously shown that unlike the ratios <math><msubsup><mi>R</mi><mi>K</mi><mrow><mi>μ</mi><mi>e</mi></mrow></msubsup><mo>≡</mo><msub><mi>R</mi><mi>K</mi></msub><mo>≡</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><mi>K</mi><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup><mo>)</mo><mo>/</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><mi>K</mi><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo>)</mo></math> and <math><msubsup><mi>R</mi><msup><mi>K</mi><mo>*</mo></msup><mrow><mi>μ</mi><mi>e</mi></mrow></msubsup><mo>≡</mo><msub><mi>R</mi><msup><mi>K</mi><mo>*</mo></msup></msub><mo>≡</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><msup><mi>μ</mi><mo>+</mo></msup><msup><mi>μ</mi><mo>−</mo></msup><mo>)</mo><mo>/</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><msup><mi>e</mi><mo>+</mo></msup><msup><mi>e</mi><mo>−</mo></msup><mo>)</mo></math>, the ratios <math><msubsup><mi>R</mi><mi>K</mi><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> and <math><msubsup><mi>R</mi><msup><mi>K</mi><mo>*</mo></msup><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> can deviate from their Standard Model (SM) predictions even with universal new physics couplings. This observation highlights the critical need to identify and establish genuine lepton flavor universality violating (LFUV) observables in the <math><mi>τ</mi><mo>−</mo><mi>μ</mi></math> sector. This work embarks on establishing genuine LFUV ratio observables in <math><mi>B</mi><mo>→</mo><mi>K</mi><mo>ℓ</mo><mo>ℓ</mo></math> and <math><mi>B</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><mo>ℓ</mo><mo>ℓ</mo></math> decays through comprehensive analysis of their angular distributions. We find that like <math><msubsup><mi>R</mi><msup><mi>K</mi><mo>*</mo></msup><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math>, the ratios <math><msubsup><mi>R</mi><msub><mi>A</mi><mrow><mi>F</mi><mi>B</mi></mrow></msub><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> and <math><msubsup><mi>R</mi><msub><mi>f</mi><mi>L</mi></msub><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> do not qualify as genuine LFUV observables, whereas the ratios of all optimized observables in <math><mi>B</mi><mo>→</mo><msup><mi>K</mi><mo>*</mo></msup><mo>ℓ</mo><mo>ℓ</mo></math> decays within the <math><mi>τ</mi><mo>−</mo><mi>μ</mi></math> sector definitively do. In the case of <math><mi>B</mi><mo>→</mo><mi>K</mi><mo>ℓ</mo><mo>ℓ</mo></math> decays, similar to <math><msubsup><mi>R</mi><mi>K</mi><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math>, the ratio <math><msub><mi>R</mi><msub><mi>F</mi><mi>H</mi></msub></msub></math> is influenced by mass effects and therefore cannot be considered a genuine LFUV observable in the <math><mi>τ</mi><mo>−</mo><mi>μ</mi></math> sector. However, the ratio <math><msub><mi>Γ</mi><mi>τ</mi></msub><mo>(</mo><mn>1</mn><mo>−</mo><msubsup><mi>F</mi><mi>H</mi><mi>τ</mi></msubsup><mo>)</mo><mo>/</mo><msub><mi>Γ</mi><mi>μ</mi></msub><mo>(</mo><mn>1</mn><mo>−</mo><msubsup><mi>F</mi><mi>H</mi><mi>μ</mi></msubsup><mo>)</mo></math> stands as the sole genuine LFUV observable in <math><mi>B</mi><mo>→</mo><mi>K</mi><mo>ℓ</mo><mo>ℓ</mo></math> decays. Furthermore, by making use of new physics Lorentz structures which provide a better fit to the current <math><mi>b</mi><mo>→</mo><mi>s</mi><mo>ℓ</mo><mo>ℓ</mo></math> data as compared to the SM, we demonstrate how the nongenuine LFUV ratios <math><msubsup><mi>R</mi><msub><mi>A</mi><mrow><mi>F</mi><mi>B</mi></mrow></msub><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> and <math><msubsup><mi>R</mi><msub><mi>f</mi><mi>L</mi></msub><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> can be employed to distinguish between framework with solely universal lepton couplings and those with both universal and nonuniversal couplings.

Jitendra Kumar

Arindam Mandal

Umberto Tamponi

Genuine lepton-flavor-universality-violating observables in the <math><mrow><mi>τ</mi><mo>−</mo><mi>μ</mi></mrow></math> sector of <math><mrow><mi>B</mi><mo>→</mo><mo>(</mo><mi>K</mi><mo>,</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>*</mo></mrow></msup><mo>)</mo><mo>ℓ</mo><mo>ℓ</mo></mrow></math> decays

The neutrino magnetic moment operator clasps a tiny but nonzero value within the standard model (SM) of particle physics and rather enhanced values in various new physics models. This generation of the magnetic moment (<math><mrow><msub><mrow><mi>μ</mi></mrow><mrow><mi>ν</mi></mrow></msub></mrow></math>) is through quantum loop corrections which can exhibit spin-flavor oscillations in the presence of an external magnetic field. Also, several studies predict the existence of a primordial magnetic field (PMF) in the early Universe, extending back to the era of Big Bang nucleosynthesis (BBN) and before. The recent North American Nanohertz Observatory for Gravitational Waves measurement can be considered as a strong indication of the presence of these PMFs. In this work, we consider the effect of the PMF on the flux of relic neutrinos. For Dirac neutrinos, we show that half of the active relic neutrinos can become sterile due to spin-flavor oscillations well before becoming nonrelativistic owing to the expansion of the Universe and also before the timeline of the formation of galaxies and hence intergalactic fields, subject to the constraints on the combined value of <math><msub><mi>μ</mi><mi>ν</mi></msub></math> and the cosmic magnetic field at the time of neutrino decoupling. For the upper limit of PMF allowed by the BBN, this can be true even if the experimental bounds on <math><msub><mi>μ</mi><mi>ν</mi></msub></math> approach a few times its SM value.

Spin-flavor oscillations of relic neutrinos in primordial magnetic field

The measurements of the Cabibbo-Kobayashi-Maskawa (CKM) elements can be contaminated by new-physics effects. We point out that purely leptonic operators at the high scale can influence semileptonic <math><mi>K</mi></math> decays and nuclear beta decay through renormalization group (RG) running, and hence can influence the measurements of <math><msub><mi>V</mi><mrow><mi>u</mi><mi>s</mi></mrow></msub></math>. Interestingly, through this mechanism, a single six-dimensional effective operator <math><msub><mi>O</mi><mrow><mo>ℓ</mo><mo>ℓ</mo></mrow></msub></math> at the high scale can alleviate the tension due to the Cabibbo angle anomaly, by generating the desired operators at the low scale through RG running. When generated as a result of a <math><msup><mi>Z</mi><mo>′</mo></msup></math> model, the nonuniversal leptonic couplings of this operator can also contribute to the lepton flavor universality violating ratios such as <math><msub><mi>R</mi><msup><mi>K</mi><mrow><mo>(</mo><mo>*</mo><mo>)</mo></mrow></msup></msub></math>, which would act as stringent constraints on such scenarios. By performing a global fit of the <math><msup><mi>Z</mi><mo>′</mo></msup></math> model, we find that it is essential to have nonuniversal couplings of such a <math><msup><mi>Z</mi><mo>′</mo></msup></math> boson to all three generations of leptons.

Amol Dighe

France

Germany

Jacky Kumar

Leptonic operators for the Cabbibo angle anomaly with SMEFT RG evolution

In this work we study the potential of the lepton flavor ratios <math><msubsup><mrow><mi>R</mi></mrow><mrow><mi>K</mi></mrow><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup><mo>≡</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><mi>K</mi><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>)</mo><mo>/</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><mi>K</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>)</mo></math> and <math><msubsup><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></mrow><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup><mo>≡</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>τ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>)</mo><mo>/</mo><mi>Γ</mi><mo>(</mo><mi>B</mi><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup><mo>)</mo></math> to probe lepton flavor universality (LFU) violation in <math><mi>τ</mi><mo>−</mo><mi>μ</mi></math> sector. We show that these ratios can deviate from their SM values even if the new physics couplings are universal in nature, i.e., having equal couplings to e, μ and τ leptons. Therefore in order to utilize these observables to probe LFU violation, we need to compare the allowed range of <math><msubsup><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>(</mo><mo>⁎</mo><mo>)</mo></mrow></msup></mrow><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> for class of solutions with only universal couplings to leptons and solutions having both universal and non-universal components. For the current <math><mi>b</mi><mo>→</mo><mi>s</mi><mi>ℓ</mi><mi>ℓ</mi></math> (<math><mi>ℓ</mi><mo>=</mo><mi>e</mi><mo>,</mo><mspace width="0.2em"></mspace><mi>μ</mi></math>) data, we find that these two class of solutions can be discriminated provided the measured value of <math><msubsup><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></mrow><mrow><mi>τ</mi><mi>μ</mi></mrow></msubsup></math> is greater than the SM prediction.

Investigating the potential of To Probe Lepton Flavor Universality Violation

In this work we study the impact of new physics, stimulated by flavor anomalies, on neutrino oscillations through dense dark matter halo. Inspired by a model where a Majorana dark matter fermion and two new scalar fields contribute to <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> transition at the one loop level, we study the impact of neutrino-dark matter interaction on the oscillation patterns of ultra-high energy cosmic neutrinos passing through this muonphilic halo located near the center of Milky Way. We find that due to this interaction, the flavor ratios of neutrinos reaching earth would be different from that of vacuum oscillations. We also consider a <math><msup><mrow><mi>Z</mi></mrow><mrow><mo>′</mo></mrow></msup></math> model driven by <math><msub><mrow><mi>L</mi></mrow><mrow><mi>μ</mi></mrow></msub><mo>−</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>τ</mi></mrow></msub></math> symmetry and containing a vector-like fermion as a dark matter candidate. It was previously shown that for such a model, the three flavors of neutrinos decouple from each other. This will render a flavor ratio similar to that of vacuum oscillations. Therefore, the interaction of neutrinos with dense dark matter halo can serve as an important tool to discriminate between flavor models with a dark connection.

Imprints of flavor anomalies on neutrino oscillations through dark matter halo

The ultra high energy (UHE) cosmic neutrinos are expected to play a pivotal role in the disquisition of physics beyond the standard model of particle physics as well as serve as an ideal cosmic messengers. This epitomizes the selling point of several currently running or planned neutrino telescopes. The UHE cosmic neutrinos usually perambulate gargantuan scales in the extragalactic universe having a magnetic field. If neutrinos have a finite magnetic moment (<math><msub><mrow><mi>μ</mi></mrow><mrow><mi>ν</mi></mrow></msub></math>) owing to quantum loop corrections, this may result in spin-flavor oscillations, which can affect the cosmic neutrino flux. Using the current limit and assuming neutrinos to be Dirac particles, we show that the flux of cosmic neutrinos will reduce by half if they traverse few Mpcs through the intergalactic magnetic field, in the range of μG to nG. Moreover, one can safely neglect the effect of <math><msub><mrow><mi>μ</mi></mrow><mrow><mi>ν</mi></mrow></msub></math> if the current upper bound is improved by a few orders of magnitude even if the neutrinos travel through the size of the visible universe.

Cosmic neutrino flux and spin flavor oscillations in intergalactic medium

The tension among measurements of <math><msub><mrow><mi>V</mi></mrow><mrow><mi>u</mi><mi>s</mi></mrow></msub></math> from different channels, the so-called Cabibbo Angle Anomaly, can be interpreted as a signal of lepton flavor universality (LFU) violation in the W boson couplings. We investigate this issue in the framework of effective field theory, keeping the gauge structure of the Standard Model (SM) unchanged. We introduce gauge-invariant dimension-6 effective operators that couple the Higgs doublet to leptons, thereby giving non-universal tree-level contributions to the couplings of electroweak gauge bosons. Due to the <math><mi>S</mi><mi>U</mi><msub><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow><mrow><mi>L</mi></mrow></msub></math> gauge symmetry, a tension arises between the <math><msub><mrow><mi>V</mi></mrow><mrow><mi>u</mi><mi>s</mi></mrow></msub></math> measurements that are affected by new W couplings, and the electroweak precision measurements, which are also affected by the new Z couplings. We show that this tension can be alleviated by allowing additional sources of gauge-invariant couplings of Z boson to left- or right-handed leptons, and find the optimal regions indicated by the current data in the Wilson-coefficient space. We illustrate our model-independent results with the examples of minimal extensions of the SM involving the vector-like lepton (VLL) models. We point out that dimension-6 operators coupling the Higgs doublet to leptons can affect the rate of <math><mi>h</mi><mo>→</mo><mi>τ</mi><mi>τ</mi></math> decay significantly in general, however this effect is restricted to less than a per cent level for the minimal VLL models.

Canada

The role of non-universal Couplings in Explaining the Anomaly

The lepton universality violating flavor ratios <math><msub><mrow><mi>R</mi></mrow><mrow><mi>K</mi></mrow></msub><mo>/</mo><msub><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></mrow></msub></math> indicate new physics either in <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>μ</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>μ</mi></mrow><mrow><mo>−</mo></mrow></msup></math> or in <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> or in both. If the new physics is only <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> transition, the corresponding new physics operators, in principle, can have any Lorentz structure. In this work, we perform a model independent analysis of new physics only in <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> decay by considering effective operators either one at a time or two similar operators at a time. We include all the measurements in <math><mi>b</mi><mo>→</mo><mi>s</mi><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> sector along with <math><msub><mrow><mi>R</mi></mrow><mrow><mi>K</mi></mrow></msub><mo>/</mo><msub><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></mrow></msub></math> in our analysis. We show that various new physics scenarios with vector/axial-vector operators can account for <math><msub><mrow><mi>R</mi></mrow><mrow><mi>K</mi></mrow></msub><mo>/</mo><msub><mrow><mi>R</mi></mrow><mrow><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup></mrow></msub></math> data but those with scalar/pseudoscalar operators and with tensor operators can not. We also show that the azimuthal angular observable <math><msub><mrow><mi>P</mi></mrow><mrow><mn>1</mn></mrow></msub></math> in <math><mi>B</mi><mo>→</mo><msup><mrow><mi>K</mi></mrow><mrow><mo>⁎</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>+</mo></mrow></msup><msup><mrow><mi>e</mi></mrow><mrow><mo>−</mo></mrow></msup></math> decay is most suited to discriminate between the different allowed solutions.