Mixing Angle Research Articles

95 GeV light Higgs in the top-pair-associated diphoton channel at the LHC in the minimal dilaton model* *Supported by the National Natural Science Foundation of China (12275066, 11605123)

Motivated by experimental hints and theoretical frameworks indicating the existence of an extended Higgs sector, we explore the feasibility of detecting a 95 GeV light Higgs boson decaying into a diphoton within the minimal dilaton model at the 14 TeV LHC. Initially, we identify the correlations between the production cross section, decay branching ratios, and model parameters, e.g., the scalar mixing angle . Subsequently, we utilize Monte Carlo simulations to generate the signal of the light Higgs boson via the process, along with the corresponding backgrounds. To effectively separate the signal from the dominant backgrounds , we employ a meticulous cut-based selection process. Ultimately, we find that with an integrated luminosity of , the regions of can be covered over the level.

The flavor puzzle: Textures and symmetries

We discuss aspects of a promising top-down origin of flavor symmetries in particle physics. Modular transformations originating from string theory dualities are shown to play a crucial role. We introduce the notion of an “eclectic” flavor scheme that unifies traditional flavor symmetries, modular symmetries and [Formula: see text]-transformations. It exhibits the phenomenon of “Local Flavor Unification” with enhanced flavor symmetries at fixed points or lines in moduli space. Successful fits of masses and mixing angles of quarks and leptons are found in the vicinity of these points and lines.

Updated analysis of D→PP,VP , and VV decays: Implications for KS0−KL0 asymmetries and D0−D¯0 mixing

An updated analysis of the two-body D→PP,VP, and VV decays within the framework of the topological diagram approach is performed. A global fit to the Cabibbo-favored (CF) modes in the VP sector gives many solutions with similarly small local minima in χ2. The solution degeneracy is lifted once we use them to predict for the singly-Cabibbo-suppressed modes. Topological amplitudes are extracted for the η−η′ mixing angles ϕ=40.4° and 43.5°. The KS0−KL0 asymmetries in D→KS,L0M decays denoted by R(D,M) are studied. While the predicted R(D0,P) for P=π0,η and η′ agree with experiment, the calculated R(D+,π+), R(Ds+,K+), R(D0,ω), and R(D0,ϕ) deviate from the data. We conjecture that the relative phase between the topological amplitudes (C+A) and (T+C) should be slightly smaller than 90° in order to explain the first two discrepancies and that additional singlet contributions due to the SU(3)-singlet nature of ω and ϕ are needed to account for the last two. For doubly-Cabibbo-suppressed (DCS) D→VP decays, their topological amplitudes (double primed) cannot be all the same as the corresponding ones in the CF modes. The assumption of EV,P′′=EV,P for the W-exchange amplitude leads to some inconsistencies with the experiment. Through the measured relative phases between CF and DCS channels, the relations of EV,P′′ with EV,P are determined. Long-distance contributions to the D0−D¯0 mixing parameter y are evaluated in the exclusive approach. In particular, we focus on D→PP and VP decays where y can be reliably estimated. We conclude that yPP∼(0.110±0.011)% and the lower bound on yVP is (0.220±0.071)%. It is thus conceivable that at least half of the mixing parameter y can be accounted for by the two-body PP and VP modes. The main uncertainties arise from the yet-to-be-measured DCS channels and their phases relative to the CF ones. Published by the American Physical Society 2024

Sensitivity of octant of θ23, CP violation and mass hierarchy in NOνA with multinucleon and detector effects

In this work, we investigate how multinucleon enhancement and RPA (Random Phase Approximation) suppression can affect the measurement of three unknown neutrino oscillation parameters — the CP-violating phase δCP, the octant of the atmospheric mixing angle θ23, and the determination of the mass hierarchy, in the appearance channel of the NOνA experiment. We include the presence of the detector effect as well in the analysis, which is crucial for capturing realistic experimental scenarios. We also conducted a comparison between the nuclear model Effective Spectral Function (calculated within the RFG model) with and without Transverse Enhancement in terms of sensitivity analysis. It is found that the analysis using our comprehensive model QE(+RPA)+2p2h along with Effective Spectral Function+Transverse Enhancement exhibits significantly enhanced sensitivity compared to the pure QE interaction process, in all the cases. Also, the higher octant of θ23, the lower half plane of δCP, and the normal mass hierarchy (HO-LHP-NH) exhibit improved sensitivity, enabling a more precise determination of the corresponding parameters. Furthermore, it is also noted that improving the performance of the detector also improves the results. Thus, including multinucleon effects and improving detector efficiency have the potential to enhance the capabilities of the NOνA (and other long baseline) experiment in conducting precise parameter studies.

Study on the mixing of Ξc and Ξc′ by the transition Ξb→Ξc(′)

Recently, the LHCb Collaboration has observed the decays Ξb0→Ξc+Ds− and Ξb−→Ξc0Ds−. They measured the relative branching fractions times the ratio of beauty-baryon production cross sections R(Ξb0Λb)≡σ(Ξb0)σ(Λb0)×B(Ξb0→Ξc+Ds−)B(Λb0→Λc+Ds−) and R(Ξb−Λb)≡σ(Ξb−)σ(Λb0)×B(Ξb−→Ξc0Ds−)B(Λb0→Λc+Ds−). Once the ratio σ(Ξb0)σ(Λb0) or σ(Ξb−)σ(Λb0) is known, one can determine the relative branching fractions which can be used to exam the mixing of Ξc and Ξc′. In previous literature, Ξc and Ξc′ were assumed to belong to SU(3)F antitriple and sextet, respectively. However, recent experimental measurements, such as the ratio Γ(Ξcc→Ξcπ+)/Γ(Ξcc→Ξc′π+), indicate the spin-flavor structures of Ξc and Ξc′ are a mixture of Ξc3¯ and Ξc6. The exact value of mixing angle θ is still under debate. In theoretical models, the mixing angle was fitted to be about 16.27°±2.30° or 85.54°±2.30° based on decay channels Ξcc→Ξc(′). While in lattice calculation, a small angle (1.2°±0.1°) is preferred. To address such discrepancy and test the mixing of Ξc and Ξc′, here we propose the analysis of semileptonic and nonleptonic decays of Ξb→Ξc and Ξb→Ξc′. We calculate the decay rate of Ξb→Ξc and Ξb→Ξc′ based on the light-front quark model and study the effect of the mixing angle on the ratios of weak decays Ξb→Ξc and Ξb→Ξc′. In particular, we find the transition Ξb→Ξc′ can be an ideal channel to verify the mixing and extract the mixing angle because in theory, the decay rate would be extremely tiny without mixing. Our calculation suggests a measurement of Ξb→Ξc′ can be feasible in the near future, which will help to test flavor mixing angle θ and elucidate the mechanism of decay of heavy baryons. Published by the American Physical Society 2024

Fast exact algorithm for neutrino oscillation in constant matter density

A recently published method [1,2] for solving the neutrino evolution equation with constant matter density is further refined and used to lay out an exact algorithm for computing oscillation probabilities, which is moderately faster than previous methods when looping through neutrinos of different energies. In particular, the three examples of ν(−)e survival, ν(−)μ survival and ν(−)e appearance probabilities are written in terms of mixing angles, mass differences and matter electron density. A program based on this new method is found to be roughly twice as fast as, and in agreement with, the leading GLoBES package. Furthermore, the behaviour of all relevant effective parameters is sketched out in terms of a range of neutrino energies, or matter electron densities. For instance, the ν(−)e survival probability in constant matter density is found to have no dependence on the mixing angle θ23 or the CP-violating phase δ13.

Using the effective weak mixing angle as an input parameter in SMEFT

We implement electroweak renormalisation schemes involving the effective weak mixing angle to NLO in Standard Model Effective Field Theory (SMEFT). After developing the necessary theoretical machinery, we analyse a select set of electroweak precision observables in such input schemes. An attractive feature is that large corrections from top-quark loops appearing in other schemes are absorbed into the definition of the effective weak mixing angle. On the other hand, the renormalisation condition which achieves this involves a large number of flavour-specific SMEFT couplings between the Z boson and charged leptons, motivating simple flavour assumptions such as minimal flavour violation for practical applications. The results of this paper provide a valuable new component for estimating systematic uncertainties in SMEFT fits by performing analyses in multiple input schemes.

Anomalous interactions between mesons with nonzero spin and glueballs

Topologically nontrivial fluctuations control the anomalous interactions for the η and η′ pseudoscalar mesons. We consider the anomalous interactions for mesons with higher spin, the heterochiral nonets with JPC=1+− and 2−+. Under the approximation of a dilute gas of instantons, the mixing angle between nonstrange and strange mesons decreases strongly as J increases, and oscillates in sign. Anomalous interactions also open up new, rare decay channels. For glueballs, anomalous interactions indicate that the X(2600) state is primarily gluonic. Published by the American Physical Society 2024

Constraints on metastable superheavy dark matter coupled to sterile neutrinos with the Pierre Auger Observatory

Dark matter particles could be superheavy, provided their lifetime is much longer than the age of the Universe. Using the sensitivity of the Pierre Auger Observatory to ultrahigh energy neutrinos and photons, we constrain a specific extension of the Standard Model of particle physics that meets the lifetime requirement for a superheavy particle by coupling it to a sector of ultralight sterile neutrinos. Our results show that, for a typical dark coupling constant of 0.1, the mixing angle θm between active and sterile neutrinos must satisfy, roughly, θm≲1.5×10−6(MX/109 GeV)−2 for a mass MX of the dark-matter particle between 108 GeV and 1011 GeV. Published by the American Physical Society 2024

Stimulated Emission of Signal Photons from Dark Matter Waves.

The manipulation of quantum states of light has resulted in significant advancements in both dark matter searches and gravitational wave detectors. Current dark matter searches operating in the microwave frequency range use nearly quantum-limited amplifiers. Future high frequency searches will use photon counting techniques to evade the standard quantum limit. We present a signal enhancement technique that utilizes a superconducting qubit to prepare a superconducting microwave cavity in a nonclassical Fock state and stimulate the emission of a photon from a dark matter wave. By initializing the cavity in an |n=4⟩ Fock state, we demonstrate a quantum enhancement technique that increases the signal photon rate and hence also the dark matter scan rate each by a factor of 2.78. Using this technique, we conduct a dark photon search in a band around 5.965GHz (24.67 μeV), where the kinetic mixing angle ε≥4.35×10^{-13} is excluded at the 90% confidence level.

Exploiting polarization dependence in two-dimensional coherent spectroscopy: Examples of Ce2Zr2O7 and Nd2Zr2O7

Two-dimensional coherent spectroscopy (2DCS) probes the nonlinear optical response of correlated systems. An interesting application is the study of fractionalized excitations, which are challenging to distinguish unambiguously in linear response. Here we demonstrate how the sensitivity of optical matrix elements to variations in the photon polarization allows one to probe different aspects of low-lying excitations in models of the candidate fractionalized materials Ce2Zr2O7 and Nd2Zr2O7, which host effective one-dimensional spin chains when subjected to a [110] magnetic field. We show how both fractionalized spinon excitations or conventional magnons can be picked out in the 2DCS response and how the response from polarized spin chains can be used to probe the dipolar-octupolar mixing angle θ through the relative intensity of one- and two-magnon signals. Further, we find that a [001] polarization of the probe field is particularly sensitive to lower band edge of the spinon continuum and can be used as a measure of the proximity of a quantum critical point in Ce2Zr2O7. 2DCS can thus be employed to provide invaluable and detailed information both on the constituent degrees of freedom of a quantum material and on their collective behavior. Published by the American Physical Society 2024

θ23 Octant sensitivity in presence of light sterile and active ν and [formula omitted] oscillations using beamline experiments

We examine the octant sensitivity of the long-baseline neutrino oscillation experiments in view of light sterile neutrino flavors with masses in the 1 eV range. Considering the active-sterile mixing, we explore the possible preferred running modes either neutrino or anti-neutrino for a long-baseline experiment to avoid the octant degeneracy and will show the θ23 sensitivity for different values of active and sterile neutrino phase angles. We simulated different Long baseline experiments for the different possible combinations of mixing angles and phases and will show whether an experiment can probe the right octant in presence of sterile neutrino by choosing the suitable beam either in neutrino or antineutrino running mode.

Predicting the XRISM dark matter decay signal in the Milky Way halo

ABSTRACT Dark matter may be detected in X-ray decay, including from the decay of the dark matter particles that make up the Milky Way (MW) halo. We use a range of density profiles to compute X-ray line intensity profiles, with a focus on the resonantly produced sterile neutrino dark matter candidate. Compared to the Navarro–Frenk–White density profile, we show that using an adiabatically contracted halo profile suppresses the line intensity in the halo outskirts and enhances it in the Galactic Centre (GC), although this enhancement is eliminated by the likely presence of a core within 3 kpc. Comparing our results to MW halo observations, other X-ray observations, and structure formation constraints implies a sterile neutrino mixing angle parameter s11 ≡ sin 2(2θ) × 1011 ∼ [3, 4] (particle lifetime $\tau _{28}\equiv \tau /(10^{28}\rm {s})\sim [1.0,1.3]$), which is nevertheless is strong tension with some reported non-detections. We make predictions for the likely decay flux that the X-Ray Imaging and Spectroscopy Mission (XRISM) satellite would measure in the GC, plus the Virgo and Perseus clusters, and outline further steps to determine whether the dark matter is indeed resonantly produced sterile neutrinos as detected in X-ray decay.

Neutrino mass matrices with generalized CP symmetries and texture zeros

We investigate the properties of neutrino mass matrices that incorporate texture zeros and generalized CP symmetries associated with tribimaximal mixing. By combining these approaches, we derive predictive neutrino mass matrices and explore their implications for mass hierarchies, mixing angles, and CP-violating phases. We find that the three angles defining the generalized CP symmetries have narrow allowed ranges. We also obtain distinct correlations between the three mixing angles and the CP-violating phases that distinguish the various texture patterns from one another. Moreover, we compute the effective neutrino mass for neutrinoless double beta decay and the sum of neutrino masses. Our results highlight the predictability and testability of neutrino mass matrices with generalized CP symmetry.

Probing charged Higgs bosons in the two-Higgs-doublet model type II with vectorlike quarks

We study the phenomenology of charged Higgs bosons (H±) and vectorlike quarks (VLQs), denoted as T, the latter possessing a charge identical to the top quark one, within the framework of the two-Higgs-doublet model type II (2HDM-II). Upon examining two scenarios, one featuring a singlet (T) [2HDM−II+(T)] and another a doublet (TB) [2HDM−II+(TB)], we discover that the presence of VLQs has a significant effect on the (pseudo)scalar sector of the 2HDM-II. In particular, this leads to a reduction in the strict constraint on the mass of the charged Higgs boson, which is imposed by B-physics observables, specifically B→Xsγ. The observed reduction stems from modifications in the charged Higgs couplings to the Standard Model top and bottom quarks. Notably, the degree of this reduction varies distinctly between the singlet 2HDM+(T) and doublet 2HDM+(TB) scenarios. Additionally, our investigation extends to constraints imposed by the oblique parameters S and T on the VLQ mixing angles. Furthermore, to facilitate efficient exploration of the “2HDM−II+VLQ” parameter space, we present results on pair production of VLQs T (pp→TT¯), followed by T→H±b and H±→tb decays, yielding a distinctive 2t4b final state. This investigation thus provides valuable insights guiding the search for extended Higgs and quark sectors at the Large Hadron Collider (LHC) at CERN. Published by the American Physical Society 2024

Neutrino mixing phenomenology: A4 discrete flavor symmetry with type-I seesaw mechanism

We study a neutrino mass model with [Formula: see text] discrete flavor symmetry using a type-I seesaw mechanism. The inclusion of extra flavons in our model leads to deviations from the exact tribimaximal mixing pattern resulting in a nonzero [Formula: see text] consistent with the recent experimental results and a sum rule for light neutrino masses is also obtained. In this framework, a connection is established among the neutrino mixing angles-reactor mixing angle ([Formula: see text]), solar mixing angle ([Formula: see text]), and atmospheric mixing angle ([Formula: see text]). This model also allows us a prediction of Dirac CP-phase and Jarlskog parameter [Formula: see text]. The octant of the atmospheric mixing angle [Formula: see text] occupies the lower octant. Our model prefers Normal Hierarchy (NH) than Inverted Hierarchy (IH). We use the parameter space of our model of neutrino masses to study the neutrinoless double beta decay parameter [Formula: see text].

Radiative Majorana neutrino masses in a parity solution to the strong CP problem

The strong CP problem is solved in Parity symmetric theories, with the electroweak gauge group containing SU(2)L × SU(2)R broken by the minimal set of Higgs fields. Neutrino masses may be explained by adding the same number of gauge singlet fermions as the number of generations. The neutrino masses vanish at tree-level and are only radiatively generated, leading to larger couplings of right-handed neutrinos to Standard Model particles than with the tree-level seesaw mechanism. We compute these radiative corrections and the mixing angles between left- and right-handed neutrinos. We discuss sensitivities to these right-handed neutrinos from a variety of future experiments that search for heavy neutral leptons with masses from tens of MeV to the multi-TeV scale.

Smallness of matter effects in long-baseline muon neutrino disappearance

Current long-baseline accelerator experiments, NOvA and T2K, are making excellent measurements of neutrino oscillations and the next generation of experiments, DUNE and HK, will make measurements at the O(1%) level of precision. These measurements are a combination of the appearance channel which is more challenging experimentally but depends on many oscillation parameters, and the disappearance channel which is somewhat easier and allows for precision measurements of the atmospheric mass splitting and the atmospheric mixing angle. It is widely recognized that the matter effect plays a key role in the appearance probability, yet the effect on the disappearance probability is surprisingly small for these experiments. Here we investigate both exactly how small the effect is and show that it just begins to become relevant in the high statistics regime of DUNE. Published by the American Physical Society 2024

B − L model with D 4 × Z 4 × Z 2 symmetry for fermion mass hierarchies and mixings* *This research was funded by Tay Nguyen University under grant number T2023-45CBTÐ

We constructed a gauge model with symmetry to explain the quark and lepton mass hierarchies and their mixings with realistic CP phases via the type-I seesaw mechanism. Six quark mases, three quark mixing angles, and the CP phase in the quark sector take the central values whereas Yukawa couplings in the quark sector are diluted in a range of difference of three orders of magnitude by the perturbation theory at the first order. Concerning the neutrino sector, a small neutrino mass is achieved by the type-I seesaw mechanism. Both inverted and normal neutrino mass hierarchies are consistent with the experimental data. The predicted sum of neutrino masses for normal and inverted hierarchies, the effective neutrino masses, and the Dirac CP phase are also consistent with recently reported limits.

Improved method to determine the Ξc−Ξc′ mixing

We develop an improved method to explore the Ξc−Ξc′ mixing, which arises from the flavor SU(3) and heavy quark symmetry breaking. In this method, the flavor eigenstates under the SU(3) symmetry are at first constructed, and the corresponding masses can be nonperturbatively determined. Matrix elements of the mass operators, which break the flavor SU(3) symmetry sandwiched by the flavor eigenstates, are then calculated. Diagonalizing the corresponding matrix of Hamiltonian gives the mass eigenstates of the full Hamiltonian and determines the mixing. Following the previous lattice QCD calculation of Ξc and Ξc′, and estimating an off diagonal matrix element, we extract the mixing angle between the Ξc and Ξc′. Preliminary numerical results for the mixing angle confirm the previous observation that such mixing is incapable to explain the large SU(3) symmetry breaking in semileptonic decays of charmed baryons. Published by the American Physical Society 2024