Axial Coupling Research Articles

New Physics in {varvec{b rightarrow s ell ^+ ell ^-}} confronts new data on lepton universality

In light of the very recent updates on the R_K and R_{K^*} measurements from the LHCb and Belle collaborations, we systematically explore here imprints of New Physics in b rightarrow s ell ^+ ell ^- transitions using the language of effective field theories. We focus on effects that violate Lepton Flavour Universality both in the Weak Effective Theory and in the Standard Model Effective Field Theory. In the Weak Effective Theory we find a preference for scenarios with the simultaneous presence of two operators, a left-handed quark current with vector muon coupling and a right-handed quark current with axial muon coupling, irrespective of the treatment of hadronic uncertainties. In the Standard Model Effective Field Theory we select different scenarios according to the treatment of hadronic effects: while an aggressive estimate of hadronic uncertainties points to the simultaneous presence of two operators, one with left-handed quark and muon couplings and one with left-handed quark and right-handed muon couplings, a more conservative treatment of hadronic matrix elements leaves room for a broader set of scenarios, including the one involving only the purely left-handed operator with muon coupling.

Muon-capture strength functions in intermediate nuclei of 0νββ decays

Capture rates of ordinary muon capture (OMC) to the intermediate nuclei of neutrinoless double beta ($0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$) decays of current experimental interest are computed. The corresponding OMC (capture-rate) strength functions have been analyzed in terms of multipole decompositions. The computed low-energy OMC-rate distribution to $^{76}\mathrm{As}$ is compared with the available data of Zinatulina et al. [Phys. Rev. C 99, 024327 (2019)]. The present OMC computations are performed using the Morita-Fujii formalism by extending the original formalism beyond the leading order. The participant nuclear wave functions are obtained in extended no-core single-particle model spaces using the spherical version of proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange $G$ matrix. The Hamiltonian parameters are taken from our earlier work [Jokiniemi et al., Phys. Rev. C 98, 024608 (2018)], except for $A=82$ nuclei for which the parameters were determined in this work. Both the OMC and $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ decays involve momentum exchanges of the order of 100 MeV and thus future measurements of the OMC strength functions for $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$ daughter nuclei help trace the in-medium renormalization of the weak axial couplings with the aim to improve the accuracy of the $0\ensuremath{\nu}\ensuremath{\beta}\ensuremath{\beta}$-decay nuclear matrix elements.

Renormalization of the Gamow-Teller operator within the realistic shell model

In nuclear structure calculations, the choice of a limited model space, due to computational needs, leads to the necessity to renormalize the Hamiltonian as well as any transition operator. Here, we present a study of the renormalization procedure and effects of the Gamow-Teller operator within the framework of the realistic shell model. Our effective shell-model operators are obtained, starting from a realistic nucleon-nucleon potential, by way of the many-body perturbation theory in order to take into account the degrees of freedom that are not explicitly included in the chosen model space. The theoretical effective shell-model Hamiltonian and transition operators are then employed in shell-model calculations, whose results are compared with data of Gamow-Teller transition strengths and double-beta half-lives for nuclei which are currently of interest for the detection of the neutrinoless double-beta decay process, in a mass interval ranging from A=48 up to A=136. We show that effective operators are able to reproduce quantitatively the spectroscopic and decay properties without resorting to an empirical quenching neither of the axial coupling constant gA, nor of the spin and orbital gyromagnetic factors. This should assess the reliability of applying present theoretical tools to this problematic.

Effect of Injection Current on the Normalized Gain Amplitude, Normalized Detuning Coefficient and the Output Power of Axial Distributed Coupling Coefficient Distributed Feedback Laser Diode (ADCC-DFB-LD)

An axial distributed coupling coefficient (ADCC) distributed feedback (DFB) laser diode (LD) in which the coupling coefficient (K) has been distributed axially on both sides of the phase shift region. The effects of injection current on the normalized gain amplitude, normalized detuning coefficient and the output power are investigated using transfer matrix method. The results show that the ADCC DFB laser exhibits high single mode stability at different injection currents above threshold and the main mode operates close to Bragg wavelength at high injected current. For different injection currents the optical output power has been increased with decreased the coupling coefficient.

Pinning down the strength function for ordinary muon capture on 100Mo

Ordinary muon capture (OMC) on 100Mo is studied both experimentally and theoretically in order to access the weak responses in wide energy and momentum regions. The OMC populates states in 100Nb up to some 50 MeV in excitation energy. For the first time the associated OMC strength function has been computed and compared with the obtained data. The present computations are performed using the Morita-Fujii formalism of OMC by extending the original formalism beyond the leading order. The participant nuclear wave functions are obtained in extended no-core single-particle model space using the spherical version of proton-neutron quasiparticle random-phase approximation (pnQRPA) with two-nucleon interactions based on the Bonn one-boson-exchange G matrix. Partial restoration of the isospin symmetry is implemented in the calculations by separately fitting the isoscalar and isovector parts of the particle-particle interaction strength of pnQRPA. Both the computed and experimental OMC strength distributions show a giant resonance at around 12 MeV. Further measurements and calculations of the OMC strength functions for double-beta-decay daughter nuclei could enable access to in-medium renormalization of the weak axial couplings and pave the way to improved accuracy of the double-beta-decay nuclear matrix elements.

Electromagnetic and axial current form factors and spectroscopy of three-flavor holographic baryons

We present an analysis of the three-flavor holographic model of QCD associated to a $D4/D8$ brane configuration, with symmetry breaking induced by a worldsheet instanton associated to a closed loop connecting $D4-D8-D6-\overline{D8}$. We calculate the electromagnetic and axial couplings of all octet and decuplet baryons, as well as several negative parity excitations, with and without symmetry breaking effects, and demonstrate qualitative and quantitative agreement with many available experimental measurements, with marked improvement over the analogous two-flavor models.

Atomki Anomaly in Family-Dependent U(1)′ Extension of the Standard Model

In the context of a gauge invariant, non-anomalous and family-dependent (non-universal) $U(1)'$ extension of the Standard Model, wherein a new high scale mechanism generates masses and couplings for the first two fermion generations and the standard Higgs mechanism does so for the third one, we find solutions to the anomaly observed by the Atomki collaboration in the decay of excited states of Beryllium, in the form of a very light $Z'$ state, stemming from the $U(1)'$ symmetry breaking, with significant axial couplings so as to evade a variety of low scale experimental constraints.

Thermal effect on vibrational behaviors of rotating functionally graded microbeams

Thermal effect on size-dependent vibrational behavior of rotating microbeams made of functionally graded materials (FGMs) is investigated. It is assumed that the material properties of FGMs change smoothly through the thickness of the microbeam according to a power-law variation. Within the framework of Timoshenko beam theory (TBT) and Euler-Bernoulli beam theory (EBT), the governing equations and associated boundary conditions of rotating hinged-hinged, clamped-free, clamped-clamped and clamped-hinged microbeams are determined by using Hamilton's principle and modified couple stress theory. The axial nonlinear coupling deformation is taken into account to capture the centrifugal stiffening effect. An assumed-mode discretization approach is applied to solve these equations numerically. Convergence study and comparative examples are presented to verify the accuracy and reliability of the present model. A detailed numerical study is carried out to analyze the effects of dimensionless material length scale parameter, slenderness ratio, dimensionless angular velocity, temperature change and FG index on the vibrational behaviors of rotating FG microbeams. Numerical results indicate that the increasing value of temperature change leads to an increase in size dependency of rotating microbeams. The size dependency of rotating microbeams considerably differs from that of stationary microbeams. In addition, the gradient change in material properties greatly affects the size dependency of rotating FG microbeams.

Axial-field-induced chiral channels in an acoustic Weyl system

Condensed-matter and other engineered systems, such as cold atoms, photonic, or phononic metamaterials, have proven to be versatile platforms for the observation of low-energy counterparts of elementary particles from relativistic field theories. These include the celebrated Majorana modes, as well as Dirac and Weyl fermions. An intriguing feature of the Weyl equation is the chiral symmetry, where the two chiral sectors have an independent gauge freedom. While this freedom leads to a quantum anomaly, there is no corresponding axial background field coupling differently to opposite chiralities in quantum electrodynamics. Here, we provide the experimental characterization of the effect of such an axial field in an acoustic metamaterial. We implement the axial field through an inhomogeneous potential and observe the induced chiral Landau levels. From the metamaterials perspective these chiral channels open the possibility for the observation of non-local Weyl orbits and might enable unidirectional bulk transport in a time-reversal invariant system.

Tool flank wear monitoring using torsional–axial vibrations in drilling

In this paper, monitoring of amplitude variation in the torsional–axial frequency is proposed for evaluating drill flank wear. Vibration signals were captured from the experiments resulting to the drilling process and investigation was focused on the role of torsional–axial coupling on instability predictions arising as a result of drill flank wear in the frequency spectrum. The first and second modes of torsional axial coupling frequencies were found through use of finite element analysis (FEA) and verified using experimental modal analysis (EMA) by the resonance frequency test. The proposed strategy uses dominant peaks of torsional–axial first mode (Tp1) and second mode (Tp2) frequency. The ratio of torsional–axial amplitudes (TP1/TP2) was considered for the monitoring and the evaluation of drill wear and also to nullify process parameter variation. Drill frequencies verified through experimental study showed their capability of predicting drill flank wear. The validation showed the proposed methodology having 80% accuracy and its ability for effective use for monitoring tool wear.

Anomaly-free dark matter with harmless direct detection constraints

Dark matter (DM) interacting with the SM fields via a Z′-boson (‘Z′-portal’) remains one of the most attractive WIMP scenarios, both from the theoretical and the phenomenological points of view. In order to avoid the strong constraints from direct detection and dilepton production, it is highly convenient that the Z′ has axial coupling to DM and leptophobic couplings to the SM particles, respectively. The latter implies that the associated U(1) coincides with baryon number in the SM sector. In this paper we completely classify the possible anomaly-free leptophobic Z′ with minimal dark sector, including the cases where the coupling to DM is axial. The resulting scenario is very predictive and perfectly viable from the present constraints from DM detection, EW observables and LHC data (di-lepton, di-jet and mono-jet production). We analyze all these constraints, obtaining the allowed areas in the parameter space, which generically prefer {m}_{Z^{prime }} ≲ 500 GeV, apart from resonant regions. The best chances to test these viable areas come from future LHC measurements.

The Expansion in Hadron Effective Field Theory**Supported by the National Natural Science Foundation of China under Grant No. 11305137

We study the Nc scalings of pion-nucleon and nucleon-nucleon scatterings in hadron effective field theory. By assuming Wittenʼs counting rules are applied to matrix elements or scattering amplitudes, which use the relativistic normalization for the nucleons, we find that the nucleon axial coupling is of order , and a consistent large Nc counting can be established for the pion-nucleon and nucleon-nucleon scatterings. We also justify the nonperturbative treatment of the low energy nucleon-nucleon interaction with the large Nc analysis and find that the deuteron binding energy is of order .

Neutron dark matter decays and correlation coefficients of neutron β−-decays

As we have pointed out in (arXiv:1806.10107 [hep-ph]), the existence of neutron dark matter decay modes n→χ+anything, where χ is a dark matter fermion, for the solution of the neutron lifetime problem changes priorities and demands to describe the neutron lifetime τn=888.0(2.0)s, measured in beam experiments and defined by the decay modes n→p+anything, in the Standard Model (SM). The latter requires the axial coupling constant λ to be equal to λ=−1.2690 (arXiv:1806.10107 [hep-ph]). Since such an axial coupling constant is excluded by experimental data reported by the PERKEO II and UCNA Collaborations, the neutron lifetime τn=888.0(2.0)s can be explained only by virtue of interactions beyond the SM, namely, by the Fierz interference term of order b∼−10−2 dependent on scalar and tensor coupling constants. We give a complete analysis of all correlation coefficients of the neutron β−-decays with polarized neutron, taking into account the contributions of scalar and tensor interactions beyond the SM with the Fierz interference term b∼−10−2. We show that the obtained results agree well with contemporary experimental data that does not prevent the neutron with the rate of the decay modes n→p+anything, measured in beam experiments, to have dark matter decay modes n→χ+anything.

Numerical Investigations of an Axial Exhaust Diffuser Coupling the Last Stage of a Generic Gas Turbine

It is well known that the last stage of a turbine and the subsequent diffuser should be viewed at and designed as a coupled system rather than as single standalone components. The turbine outlet flow imposes the inlet conditions to the diffuser, whereas the recovered dynamic pressure in the diffuser directly controls the turbine back pressure. With changing operating point, the turbine outflow can vary significantly. This results consequently in large variations of the diffuser performance. A major role in the coupled system of turbine and diffuser can be attributed to the tip leakage flow. While it is desirable to minimize the tip leakage with regard to the turbine, a higher leakage mass flow can often be beneficial for the diffuser performance. As there is currently a trend toward aggressive and hence shorter diffusers which are particularly prone to separation, the question arises where the optimum for this tradeoff problem lies. To investigate the performance in the coupled turbine/diffuser system, a generic last stage with shrouded rotor and axial exhaust diffuser has been designed. The components are representative for heavy duty stationary gas turbine applications. Results are presented for three different operating points representing part-load (PL), design-load (DL), and over-load (OL) condition. Three different seal gap widths are taken into account to control the leakage flow. The results indicate that an operating point-dependent optimum gap width can be found for the coupled system efficiency, whereas the maximum turbine performance is always achieved with a minimum gap width.

Nonquenching of gA in nuclei, Landau-Migdal fixed-point theory, and emergence of scale symmetry in dense baryonic matter

How the axial coupling constant $g_A$ in nuclear Gamow-Teller transitions described in shell model gets "quenched" to a universal constant close to 1 can be explained by nuclear correlations in Fermi-liquid fixed point theory using a scale-symmetric chiral Lagrangian supplemented with hidden local symmetric vector mesons. Contrary to what one might naively suspect -- and has been discussed in some circles, there is no fundamental quenching at nuclear matter density due to QCD condensates. When the density of many-body systems treated with the same Lagrangian increases beyond the density $n=n_{1/2}\gsim 2n_0$ (where $n_0$ is the normal nuclear matter density) at which skyrmions representing baryons fractionize to half-skyrmions, with the $\rho$ meson driven toward the vector manifestation fixed point and a scalar meson $\sigma$ driven to the dilaton-limit fixed point with the nucleons parity-doubled, the dense matter supports the "pseudo-conformal" sound velocity for $n\gsim n_{1/2}$ while the trace of the energy momentum tensor remains non-vanishing. A plausible interpretation is that this signals the emergence of scale symmetry not explicitly present or hidden in QCD in the vacuum. The fundamental constant $g_A$, unaffected by QCD condensates for $n< n_{1/2}$, does go to 1 as the dilaton-limit fixed point is approached before arriving at chiral restoration, but it is not directly related to the "quenched $g_A$" in nuclei which can be explained as a Fermi-liquid fixed point quantity. The mechanism that produces a precocious pseudo-conformal sound velocity is expected to impact on the tidal deformability $\Lambda$ in gravity waves from coalescing neutron stars.

Nonminimally coupled pseudoscalar inflaton

We consider a scenario in which the inflaton $\ensuremath{\phi}$ is a pseudoscalar field nonminimally coupled to gravity through a term of the form $\mathcal{X}R{\ensuremath{\phi}}^{2}$. The pseudoscalar is also coupled to a $U(1)$ gauge field (or an ensemble of $\mathcal{N}$ gauge fields) through an axial coupling of the form $\ensuremath{\phi}F\stackrel{\texttildelow{}}{F}$. After [M. M. Anber and L. Sorbo, Phys. Rev. D 81, 043534 (2010)], it is well known that this axial coupling leads to a production of gauge particles which acts as a friction term in the dynamics of the inflaton, producing a slow-roll regime even in presence of a steep potential. A remarkable result in this scenario is that the spectrum of the chiral gravitational waves sourced by the scalar-gauge field interplay can be enhanced due to the nonminimal coupling with gravity, leading to measurable signatures, while maintaining agreement with current observational constraints on ${n}_{s}$ and $r$. The inclusion of nonminimal coupling could be helpful to alleviate tensions with non-Gaussianity bounds in models including axial couplings.

Quark spins and anomalous Ward identity

We calculate the intrinsic quark spin contribution to the total proton spin using overlap valence quarks on three ensembles of $2+1$-flavor RBC/UKQCD domain-wall configurations with different lattice spacings. The lowest pion mass of the ensembles is around 171 MeV which is close to the physical point. With overlap fermions and topological charge derived from the overlap operator, we verify the anomalous Ward identity between nucleon states with momentum transfer. Both the connected and disconnected insertions of the axial-vector current are calculated. For the disconnected-insertion part, the cluster-decomposition error reduction (CDER) technique is utilized for the lattice with the largest volume and the error can be reduced by $10\%\sim40\%$. Nonperturbative renormalization is carried out and the final results are all reported in the $\overline{{\rm MS}}$ scheme at 2 GeV. We determine the total quark spin contribution to the nucleon spin to be $\Delta\Sigma=0.401(25)(37)$, which is consistent with the recent global fitting result of experimental data. The isovector axial coupling we obtain in this study is $g_A^3=1.256(16)(30)$, which agrees well with the experimental value of 1.2723(23).

Magnetogenesis by non-minimal coupling to gravity in the Starobinsky inflationary model

The R2 term in the Starobinsky inflationary model can be regarded as a leading quantum correction to the gravitational effective action. We assume that parity-preserving and parity-violating (axial) non-minimal couplings between curvature and electromagnetic field are also present in the effective action. In the Einstein frame, they turn into non-trivial couplings of the scalaron and curvature to the electromagnetic field. We make an assessment of inflationary magnetogenesis in this model. In the case of parity-preserving couplings, amplification of magnetic field is negligibly small. In the case of axial couplings, magnetogenesis is hampered by strong back-reaction on the inflationary process, resulting in possible amplification of magnetic field at most by the factor 105 relative to its vacuum fluctuations.

Magnetically Axial-coupled Detachable Propeller-based Portable Electromagnetic Energy-harvesting Device Using Air and Water Streams

Energy harvesting has become a highly important technology due to the development of portable electronic devices. In this study, we developed a rotary-type portable electromagnetic energy-harvesting device for charging portable electronic devices from wind and water stream. The advantage of the developed device is that it does not use a mechanical shaft because it uses the magnetic axial coupling (magnetic force) between the turbine and the device. In other words, the turbine can be easily replaced depending on the energy source. Furthermore, the device can produce the electrical power of mW class at a low rotating speed. The device consists of four inducing magnets, 16 pick-up coils, and a coupling magnet for combination between the device and the turbine. The device generated 35.15 V<SUB>rms</SUB> at 300 rpm (5 Hz), and the maximum conversion efficiency reached up to 13.52 % at 240 rpm. We are aiming for energy conversion at a low rotational speed under 400 rpm and the device achieved mW class conversion: 360 rpm produced approximately 14 mW. To verify the proposed methods, we conduced various experimental analyses.

Tests of the standard model in neutron β decay with a polarized neutron and electron and an unpolarized proton

We analyse the electron--energy and angular distribution of the neutron beta decay with polarized neutron and electron and unpolarized proton, calculated in Phys. Rev. C 95, 055502 (2017) within the Standard Model (SM), by taking into account the contributions of interactions beyond the SM. After the absorption of vector and axial vector contributions by the axial coupling constant and Cabibbo-Kobayashi-Maskawa (CKM) matrix element (Bhattacharya et al., Phys. Rev. D 85, 054512 (2012) and so on) these are the contributions of scalar and tensor interactions only. The neutron lifetime, correlation coefficients and their averaged values, and asymmetries of the neutron beta decay with polarized neutron and electron are adapted to the analysis of experimental data on searches of contributions of interactions beyond the SM. Using the obtained results we propose some estimates of the values of the scalar and tensor coupling constants of interactions beyond the SM. We use the estimate of the Fierz interference term "b_F = - 0.0028 +/- 0.0026" by Hardy and Towner (Phys. Rev. C 91, 025501 (2015)), the neutron lifetime "tau_n = 880.2(1.0)s"(Particle Data Group, Chin. Phys. C 40, 100001 (2016)) and the experimental data "N_{\exp} = 0.067 +/- 0.011_{\rm stat.} +/- 0.004_{\rm syst.}" for the averaged value of the correlation coefficient of the neutron-electron spin-spin correlations, measured by Kozela et al. (Phys. Ref. C 85, 045501 (2012)). The contributions of G-odd correlations are calculated and found at the level of 10^{-5} in agreement with the results obtained by Gardner and Plaster (Phys. Rev. C 87, 065504 (2013)).