Pseudoscalar Interaction Research Articles

The decays of bar{B}^0, bar{B}^0_s and B^- into eta _c plus a scalar or vector meson

We investigate the decays of bar{B}^0_s, bar{B}^0 and B^- into eta _c plus a scalar or vector meson in a theoretical framework by taking into account the dominant process for the weak decay of bar{B} meson into eta _c and a qbar{q} pair. After hadronization of this qbar{q} component into pairs of pseudoscalar mesons we obtain certain weights for the pseudoscalar meson-pseudoscalar meson components. In addition, the bar{B}^0 and bar{B}^0_s decays into eta _c and rho ^0, K^* are evaluated and compared to the eta _c and phi production. The calculation is based on the postulation that the scalar mesons f_0(500), f_0(980) and a_0(980) are dynamically generated states from the pseudoscalar meson-pseudoscalar meson interactions in S-wave. Up to a global normalization factor, the pi pi , K bar{K} and pi eta invariant mass distributions for the decays of bar{B}^0_s rightarrow eta _c pi ^+ pi ^-, bar{B}^0_s rightarrow eta _c K^+ K^-, bar{B}^0 rightarrow eta _c pi ^+ pi ^-, bar{B}^0 rightarrow eta _c K^+ K^-, bar{B}^0 rightarrow eta _c pi ^0 eta , B^- rightarrow eta _c K^0 K^- and B^- rightarrow eta _c pi ^- eta are predicted. Comparison is made with the limited experimental information available and other theoretical calcualtions. Further comparison of these results with coming LHCb measurements will be very valuable to make progress in our understanding of the nature of the low lying scalar mesons, f_0(500), f_0(980) and a_0(980).

Loop effects in direct detection

We consider loop level contributions to dark matter— nucleon scattering in cases where the spin independent scattering cross section is absent or suppressed at tree level. In the case of a pseudoscalar interaction, for which the tree level cross section is both spin-dependent and suppressed by 4 powers of the exchanged momentum, loop diagrams give rise to a non-zero spin independent cross section. We show that if the pseudoscalar interaction is formulated using a gauge invariant framework, loop effects generate an effective χ̄χ h vertex and result in a scattering cross section that is within reach of current or forthcoming experiments. We also consider the case of inelastic dark matter, for which the dominant interaction terms have an off diagonal χ1−χ2 structure. In this case, the tree-level direct detection cross section is negligible when the inelastic χ1 N → χ2 N process is kinematically suppressed. However, loop diagrams generate a diagonal χ1−χ1 interaction and hence permit measurable, spin independent, χ1 N → χ1 N elastic scattering. As such, we are able to probe parameter space that was previously considered inaccessible to direct detection.

Central-edge asymmetry as a probe of Higgs-top coupling in [formula omitted] production at the LHC

The Higgs-top coupling plays a central role in the hierarchy problem and the vacuum stability of the Standard Model (SM). We propose a central-edge asymmetry (ACE) to probe the CP violating Higgs-top coupling in dileptonic channel of tt¯h(→bb¯) production at the LHC. We demonstrate that the CP-violating Higgs-top coupling can affect the central-edge asymmetry through distorting Δyℓ+ℓ− distribution because of the contribution of new top charge asymmetric term. Since Δyℓ+ℓ− distribution is frame-independent and has a good discrimination even in boosted regime, we use the jet substructure technique to enhance the observability of the dileptonic channel of tt¯h production. We find that (1) the significance of dileptonic channel of tt¯h production can reach 5σ for CP phase ξ=0,π/4,π/2 when the luminosity L=795,993,1276fb−1 at 14 TeV LHC. (2) the central-edge asymmetry ACE show a good discrimination power of CP phase of tt¯h interaction, which are −40.26%, −26.60%, −9.47% for ξ=0, π/4, π/2 respectively and are hardly affected by the event selections. Besides, by performing the binned-χ2 analysis of Δyℓ+ℓ− distribution, we find that the scalar and pseudo-scalar interactions can be distinguished at 95% C.L. level at 14 TeV HL-LHC.

Search for scalar dark matter via pseudoscalar portal interactions in light of the Galactic Center gamma-ray excess

In light of the observed Galactic center gamma-ray excess, we investigate a simplified model, for which the scalar dark matter interacts with quarks through a pseudoscalar mediator. The viable regions of the parameter space, that can also account for the relic density and evade the current searches, are identified, if the low-velocity dark matter annihilates through an $s$-channel off-shell mediator mostly into $\bar{b} b$, and/or annihilates directly into two ${\it hidden}$ on-shell mediators, which subsequently decay into the quark pairs. These two kinds of annihilations are $s$ wave. The projected monojet limit set by the high luminosity LHC sensitivity could constrain the favored parameter space, where the mediator's mass is larger than the dark matter mass by a factor of 2. We show that the projected sensitivity of 15-year Fermi-LAT observations of dwarf spheroidal galaxies can provide a stringent constraint on the most parameter space allowed in this model. If the on-shell mediator channel contributes to the dark matter annihilation cross sections over 50$\%$, this model with a lighter mediator can be probed in the projected PICO-500L experiment.

The Λ(1405) state in a chiral unitary approach with off-shell corrections to dimensional regularized loop functions

The Bethe-Salpeter equation is solved in the framework of the unitary coupled-channel approximation by using the pseudoscalar meson-baryon octet interaction. The loop function of the intermediate meson and baryon is deduced in a dimensional regularization scheme, where the relativistic kinetic effect and off-shell corrections are taken into account. Based on the experimental data at the K−p threshold, the subtraction constants in the loop function are determined. The squared amplitude is suppressed strongly and only one Λ(1405) state is generated dynamically in the strangeness S=−1 and isospin I=0 sector.

Electron–nucleus scalar–pseudoscalar interaction in PbF: Z-vector study in the relativistic coupled-cluster framework

ABSTRACTThe scalar–pseudoscalar interaction constant of PbF in its ground state electronic configuration is calculated using the Z-vector method in the relativistic coupled-cluster framework. The precise calculated value is very important to set upper bound limit on -odd scalar–pseudoscalar interaction constant, ks, from the experimentally observed -odd frequency shift. Further, the ratio of the effective electric field to the scalar–pseudoscalar interaction constant is also calculated which is required to get an independent upper bound limit of electric dipole moment of electron, de, and ks and how these (de and ks) are interrelated is also presented here.

Effect of CP violation in the singlet-doublet dark matter model

We revisit the singlet-doublet dark matter model with a special emphasis on the effect of CP violation on the dark matter phenomenology. The CP violation in the dark sector induces a pseudoscalar interaction of a fermionic dark matter candidate with the SM Higgs boson. The pseudoscalar interaction helps the dark matter candidate evade the strong constraints from the dark matter direct detection experiments. We show that the model can explain the measured value of the dark matter density even if dark matter direct detection experiments do not observe any signal. We also show that the electron electric dipole moment is an important complement to the direct detection for testing this model. Its value is smaller than the current upper bound but within the reach of future experiments.

Dark matter interpretation of the Fermi -LAT observation toward the Galactic Center

The center of the Milky Way is predicted to be the brightest region of gamma-rays generated by self-annihilating dark matter particles. Excess emission about the Galactic center above predictions made for standard astrophysical processes has been observed in gamma-ray data collected by the Fermi Large Area Telescope. It is well described by the square of an NFW dark matter density distribution. Although other interpretations for the excess are plausible, the possibility that it arises from annihilating dark matter is valid. In this paper, we characterize the excess emission as annihilating dark matter in the framework of an effective field theory. We consider the possibility that the annihilation process is mediated by either pseudo-scalar or vector interactions and constrain the coupling strength of these interactions by fitting to the Fermi Large Area Telescope data for energies 1-100 GeV in the 15 x 15 degree region about the Galactic center using self-consistently derived interstellar emission models and point source lists for the region. The excess persists and its spectral characteristics favor a dark matter particle with a mass in the range approximately from 50 to 190 (10 to 90) GeV and annihilation cross section approximately from 1E-26 to 4E-25 (6E-27 to 2E-25) cm^3/s for pseudo-scalar (vector) interactions. We map these intervals into the corresponding WIMP-neutron scattering cross sections and find that the allowed range lies well below current and projected direct detection constraints for pseudo-scalar interactions, but are typically ruled out for vector interactions.

Constraints on scalar-pseudoscalar and tensorial nonstandard interactions and tensorial unparticle couplings from neutrino-electron scattering

Neutrino-electron scattering is a purely leptonic fundamental interaction and therefore provides an important channel to test the Standard Model, especially at the low energy-momentum transfer regime. We derived constraints on neutrino nonstardard interaction couplings depending on model-independent approaches which are described by a four-Fermi pointlike interaction and unparticle physics model with tensorial components. Data on $\bar{\nu}_{e}-e$ and $\nu_{e}-e$ scattering from the TEXONO and LSND experiments, respectively, are used. The upper limits and the allowed regions of scalar, pseudoscalar, and tensorial nonstandard interaction couplings of neutrinos are derived at 90\% confidence level in both one-parameter and two-parameter analysis. New upper limits for tensorial unparticle physics coupling constants and mass parameters are also placed.

Combined analysis of effective Higgs portal dark matter models

We combine and extend the analyses of effective scalar, vector, Majorana and Dirac fermion Higgs portal models of dark matter (DM), in which DM couples to the Standard Model (SM) Higgs boson via an operator of the form $\mathcal{O}_{\textrm{DM}}\, H^\dagger H$. For the fermion models, we take an admixture of scalar $\overline{\psi} \psi$ and pseudoscalar $\overline{\psi} i\gamma_5 \psi$ interaction terms. For each model, we apply constraints on the parameter space based on the Planck measured DM relic density and the LHC limits on the Higgs invisible branching ratio. For the first time, we perform a consistent study of the indirect detection prospects for these models based on the WMAP7/Planck observations of the cosmic microwave background, a combined analysis of 15 dwarf spheroidal galaxies by Fermi-LAT and the upcoming Cherenkov Telescope Array (CTA). We also perform a correct treatment of the momentum-dependent direct search cross section that arises from the pseudoscalar interaction term in the fermionic DM theories. We find, in line with previous studies, that current and future direct search experiments such as LUX and XENON1T can exclude much of the parameter space, and we demonstrate that a joint observation in both indirect and direct searches is possible for high mass weakly interacting massive particles. In the case of a pure pseudoscalar interaction of a fermionic DM candidate, future gamma-ray searches are the only class of experiment capable of probing the high mass range of the theory.

Effective Mass and Pseudoscalar Interaction in the Dirac Equation with Woods–Saxon Potential

We consider the one-dimensional Dirac equation with the Woods–Saxon potential in the Framework of position dependent mass and pseudoscalar interaction. By imposing appropriate constraints on the mass function and the pseudoscalar term new exact solvable models are obtained. A detailed study of the scattering and bound-states problems for these models is presented. Meanwhile, we work out the exact expressions for the transmission and reflection probabilities of scattered states and obtain the exact equation for the energy eigenvalues associated to bound states. In particular, transmission resonance at zero-momentum is observed for supercritical states.

Looking through the pseudoscalar portal into dark matter: Novel mono-Higgs and mono-Zsignatures at the LHC

Mono-$X$ signatures are a powerful collider probe of the nature of dark matter. We show that mono-Higgs and mono-$Z$ may be key signatures of pseudo-scalar portal interactions between dark matter and the SM. We demonstrate this using a simple renormalizable version of the portal, with a Two-Higgs-Doublet-Model as electroweak symmetry breaking sector. Mono-$Z$ and mono-Higgs signatures in this scenario are of resonant type, which constitutes a novel type of dark matter signature at LHC.

Sterile neutrinos with pseudoscalar self-interactions and cosmology

Sterile neutrinos in the electronvolt mass range are hinted at by a number of terrestrial neutrino experiments. However, such neutrinos are highly incompatible with data from the Cosmic Microwave Background and large scale structure. This paper discusses how charging sterile neutrinos under a new pseudoscalar interaction can reconcile eV sterile neutrinos with terrestrial neutrino data. We show that this model can reconcile eV sterile neutrinos in cosmology, providing a fit to all available data which is way better than the standard $\Lambda$CDM model with one additional fully thermalized sterile neutrino. In particular it also prefers a value of the Hubble parameter much closer to the locally measured value.

Self-interacting dark matter and cosmology of a light scalar mediator

We consider a fermionic dark matter candidate interacting via a scalar mediator coupled with the Standard Model through a Higgs portal. We consider a general setting including both scalar and pseudoscalar interactions between the scalar and fermion, and illustrate the relevant features for dark matter abundance, direct search limits and collider constraints. The case where dark matter has a self-interaction strength $⟨{\ensuremath{\sigma}}_{V}⟩/{m}_{\ensuremath{\psi}}\ensuremath{\sim}0.1--1\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{g}$ is strongly constrained, in particular by the big bang nucleosynthesis. We show that these constraints can be alleviated by introducing a new light sterile neutrino $N$. The allowed region for the extended model consists of two triangles as a function of the mass ${m}_{N}$ and a sufficiently small sterile-active neutrino mixing angle $\mathrm{sin}\ensuremath{\theta}l0.007$: first $10(\mathrm{sin}\ensuremath{\theta}{)}^{\ensuremath{-}2/5}\text{ }\text{ }\mathrm{MeV}\ensuremath{\lesssim}{m}_{N}\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{GeV}$ and second $15(\mathrm{sin}\ensuremath{\theta}{)}^{\ensuremath{-}2/5}\text{ }\text{ }\mathrm{keV}\ensuremath{\lesssim}{m}_{N}\ensuremath{\lesssim}1\text{ }\text{ }\mathrm{MeV}$.

Hypermagnetic gyrotropy, inflation, and the baryon asymmetry of the Universe

We investigate the production of the hypermagnetic gyrotropy when the electric and magnetic gauge couplings evolve at different rates, as it happens in the the relativistic theory of the Van der Waals forces. If a pseudo-scalar interaction breaks the duality symmetry of the corresponding equations, the gyrotropic configurations of the hypermagnetic fields can be amplified from the vacuum during an inflationary stage of expansion. After charting the parameter space of the model in terms of the rates of evolution of the magnetic and electric gauge couplings, we identify the regions where the gyrotropy is sufficiently intense to seed the baryon asymmetry of the Universe at the electroweak epoch while the backreaction constraints, the strong coupling bounds and the other astrophysical limits are concurrently satisfied.

Entanglement of Dirac bi-spinor states driven by Poincaré classes of [formula omitted] coupling potentials

A generalized description of entanglement and quantum correlation properties constraining internal degrees of freedom of Dirac(-like) structures driven by arbitrary Poincaré classes of external field potentials is proposed. The role of (pseudo)scalar, (pseudo)vector and tensor interactions in producing/destroying intrinsic quantum correlations for SU(2)⊗SU(2) bi-spinor structures is discussed in terms of generic coupling constants. By using a suitable ansatz to obtain the Dirac Hamiltonian eigenspinor structure of time-independent solutions of the associated Liouville equation, the quantum entanglement, via concurrence, and quantum correlations, via geometric discord, are computed for several combinations of well-defined Poincaré classes of Dirac potentials. Besides its inherent formal structure, our results set up a framework which can be enlarged as to include localization effects and to map quantum correlation effects into Dirac-like systems which describe low-energy excitations of graphene and trapped ions.

Constraining Dark Matter Interactions with Pseudoscalar and Scalar Mediators Using Collider Searches for Multijets plus Missing Transverse Energy.

The monojet search, looking for events involving missing transverse energy (E_{T}) plus one or two jets, is the most prominent collider dark matter search. We show that multijet searches, which look for E_{T} plus two or more jets, are significantly more sensitive than the monojet search for pseudoscalar- and scalar-mediated interactions. We demonstrate this in the context of a simplified model with a pseudoscalar interaction that explains the excess in GeV energy gamma rays observed by the Fermi Large Area Telescope. We show that multijet searches already constrain a pseudoscalar interpretation of the excess in much of the parameter space where the mass of the mediator M_{A} is more than twice the dark matter mass m_{DM}. With the forthcoming run of the Large Hadron Collider at higher energies, the remaining regions of the parameter space where M_{A}>2m_{DM} will be fully explored. Furthermore, we highlight the importance of complementing the monojet final state with multijet final states to maximize the sensitivity of the search for the production of dark matter at colliders.

Constraints on secret neutrino interactions after Planck

Neutrino interactions beyond the standard model of particle physics may affect the cosmological evolution and can be constrained through observations. We consider the possibility that neutrinos possess secret scalar or pseudoscalar interactions mediated by the Nambu-Goldstone boson of a still unknown spontaneously broken global U(1) symmetry, as in, e.g., Majoron models. In such scenarios, neutrinos still decouple at T≃ 1 MeV, but become tightly coupled again (``recouple'') at later stages of the cosmological evolution. We use available observations of the cosmic microwave background (CMB) anisotropies, including Planck 2013 and the joint BICEP2/Planck 2015 data, to derive constraints on the quantity γνν4, parameterizing the neutrino collision rate due to scalar or pseudoscalar interactions. We consider both a minimal extension of the standard ΛCDM model, and more complicated scenarios with extra relativistic degrees of freedom or non-vanishing tensor amplitude. For a wide range of dataset and model combinations, we find a typical constraint γνν4 ≲ 0.9× 10−27 (95% C.L.), implying an upper limit on the redshift zνrec of neutrino recoupling 0≲ 850, leaving open the possibility that the latter occured well before hydrogen recombination. In the framework of Majoron models, the upper limit on γνν roughly translates on a constraint g ≲ 8.2× 10−7 on the Majoron-neutrino coupling constant g. In general, the data show a weak (∼ 1σ) but intriguing preference for non-zero values of γνν4, with best fits in the range γνν4 = (0.15–0.35)× 10−27, depending on the particular dataset. This is more evident when either high-resolution CMB observations from the ACT and SPT experiments are included, or the possibility of non-vanishing tensor modes is considered. In particular, for the minimal model ΛCDM+γνν and including the Planck 2013, ACT and SPT data, we report γνν4=(0.44+0.17−0.36)×10−27 (0300 ≲ zνrec ≲ 550) at 68% confidence level.

Hyperfine splitting in muonic hydrogen constrains new pseudoscalar interactions

We constrain the possibility of a new pseudoscalar coupling between the muon and proton using a recent measurement of the 2S hyperfine splitting in muonic hydrogen.

Study of theKN−K*Ncoupled system ins-wave

We study the strangeness $+1$ meson-baryon systems to obtain improved $KN$ and ${K}^{*}N$ amplitudes and to look for a possible resonance formation by the $KN\text{\ensuremath{-}}{K}^{*}N$ coupled interaction. We obtain amplitudes for light vector meson--baryon systems by implementing the $s$-, $t$- and $u$-channel diagrams and a contact interaction. The pseudoscalar meson-baryon interactions are obtained by relying on the Weinberg-Tomozawa theorem. The transition amplitudes between the systems consisting of pseudoscalars and vector mesons are calculated by extending the Kroll-Ruderman term for pion photoproduction by replacing the photon by a vector meson. We fix the subtraction constants required to calculate the loops by fitting our $KN$ amplitudes to the data available for the isospin 0 and 1 $s$-wave phase shifts. We provide the scattering lengths and the total cross sections for the $KN$ and ${K}^{*}N$ systems obtained in our model, which can be useful in future in-medium calculations. Our amplitudes do not correspond to the formation of a resonance in any of the isospin and spin configurations.