Neutral Pseudoscalar Research Articles

The flavor of a light charged Higgs

The ATLAS Collaboration has recently reported a search for light-charged Higgs in t → H+b decay, with {H}^{+}to coverline{b} . An excess with a local significance of approximately 3σ is found at {m}_{H^{+}} ≈ 130 GeV, with a best-fit value of BR(t → H+b) × BR( {H}^{+}to coverline{b} ) = (1.6 ± 0.6) × 10−3. We study the implications of such a hypothetical signal in multi-Higgs doublet models. We take into account constraints from searches for other charged Higgs decays and from flavor-changing neutral current processes. Two Higgs doublet models with flavor structure dictated by natural flavor conservation (NFC), minimal flavor violation (MFV), or the Froggatt-Nielsen (FN) mechanism cannot account for such excess. A three-Higgs doublet model with NFC can account for the signal. The Yukawa couplings of the neutral pseudoscalar A in the down sector, {hat{Y}}_A^D , should be larger by a factor of 4 – 6 compared to the corresponding Yukawa couplings of the Higgs h, {hat{Y}}_h^D . We further present two minimal scenarios, one in which a single Yukawa coupling in the down sector, {left({hat{Y}}_A^Dright)}_{bb} , gives the only significant contribution, and one in which two Yukawa couplings in the up sector, {left({hat{Y}}_A^Uright)}_{tt} and {left({hat{Y}}_A^Uright)}_{tc} , give the only significant contributions, and we discuss possible tests of these scenarios.

Neutral pseudoscalar and vector meson masses under strong magnetic fields in an extended NJL model: Mixing effects

Mixing effects on the mass spectrum of light neutral pseudoscalar and vector mesons in the presence of an external uniform magnetic field $\vec B$ are studied in the framework of a two-flavor NJL-like model. The model includes isoscalar and isovector couplings both in the scalar-pseudoscalar and vector sectors, and also incorporates flavor mixing through a 't Hooft-like term. Numerical results for the $B$ dependence of meson masses are compared with present lattice QCD results. In particular, it is shown that the mixing between pseudoscalar and vector meson states leads to a significant reduction of the mass of the lightest state. The role of chiral symmetry and the effect of the alignment of quark magnetic moments in the presence of the magnetic field are discussed.

Effects of quark anomalous magnetic moment on the thermodynamical properties and mesonic excitations of magnetized hot and dense matter in PNJL model

Various thermodynamic quantities and the phase diagram of strongly interacting hot and dense magnetized quark matter are obtained with the $ 2 $-flavour Nambu-Jona-Lasinio model with Polyakov loop considering finite values of the anomalous magnetic moment (AMM) of the quarks. Susceptibilities associated with constituent quark mass and traced Polyakov loop are used to evaluate chiral and deconfinement transition temperatures. It is found that, inclusion of the AMM of the quarks in presence of the background magnetic field results in a substantial decrease in the chiral as well as deconfinement transition temperatures in contrast to an enhancement in the chiral transition temperature in its absence. Using standard techniques of finite temperature field theory, the two point thermo-magnetic mesonic correlation functions in the scalar ($\sigma$) and neutral pseudoscalar ($\pi^0$) channels are evaluated to calculate the masses of $\sigma $ and $ \pi^0 $ considering the AMM of the quarks.

Magnetic catalysis effect prevents vacuum superconductivity in strong magnetic fields

By comparing the two- and three-flavor Nambu--Jona-Lasinio (NJL) models, we demonstrate that the naively expected vacuum superconductivity (VSC) in constant magnetic field ${\bf B}=B\hat z$ is disfavored due to the splitting magnetic catalysis effect (MCE) to chiral condensates with different quark flavors. Based on the simple two-flavor NJL model, we illuminate, in the lowest Landau level approximation, the similar origins of $\pi^0$ and $\bar{\rho}^+_1$ (${\rho}^+$ meson with spin $S_z=1$) mass reductions with smaller $B$ and their different features at larger $B$. With the full Landau levels, the two-flavor NJL model is found to be invalid to study the magnetic field effect to $\bar{\rho}^+_1$ meson with physical vacuum mass $775~{\rm MeV}$. Then, restricted to $\rho$ meson mass below two-quark threshold in vacuum, that is $m_\rho^v<2m_q^v$, it is found that $\pi^0$ mass decreases and then increases with $B$ slowly, and $\bar{\rho}^+_1$ mass vanishing point is delayed to larger $B$ compared to the point particle result. In the more realistic three-flavor NJL model, all the quark masses split in strong magnetic field as a combinatorial result of their different current masses and electric charges. By choosing a vacuum mass closer to the physical one, $\bar{\rho}^+_1$ meson mass is found to be consistent with the LQCD results semi-quantitatively in smaller $B$ region but increase in larger $B$ region. These features are mainly outcomes of the interplay between the $S_z-B$ coupling effect and splitting MCE to the composite $u$ and $d$ quarks, which definitely disfavors VSC when the latter dominates. Furthermore, mesonic flavor mixing is modified by $B$ among the neutral pseudoscalars: $\pi^0,\eta_0$ and $\eta_8$, which is very important to suppress the mass enhancement of the effective mass eigenstates at large $B$.

No strong CP violation up to the one-loop level in a two-Higgs-doublet model

We put forward a two-Higgs-doublet model, furnished with a mathbb {Z}_3 symmetry, wherein CP is conserved in the dimension-four terms of the Lagrangian and is softly broken in the scalar potential. The new particles of our model are one neutral scalar H, one neutral pseudoscalar A, and two charged scalars H^pm . In our model the only locus of CP violation is the CKM matrix. Strong CP violation is absent both at the tree and one-loop levels. We work out the phenomenological constraints on our model, which features flavour-changing neutral Yukawa interactions, showing that the new scalar particles may in some cases be lighter than 500 GeV.

Heavy neutral pseudoscalar decays into gauge bosons in the Littlest Higgs model

We study two-body decays of a new neutral pseudoscalar into standard model gauge bosons within the context of the Littlest Higgs model. The processes induced at the one-loop level, with , are considered. Since the branching ratios of the decays result were very suppressed, only the processes are thoroughly studied. The branching ratios for the and decays are of the order of 10−5 and 10−7, respectively, for f around 3 TeV, which represents the global symmetry breaking scale of the theory. The production cross section of the boson via gluon fusion at the LHC is estimated.

Partonic structure of neutral pseudoscalars via two photon transition form factors

The $\gamma \gamma^\ast \to \eta_{c,b}$ transition form factors are computed using a continuum approach to the two valence-body bound-state problem in relativistic quantum field theory, and thereby unified with equivalent calculations of electromagnetic pion elastic and transition form factors. The resulting $\gamma \gamma^\ast \to \eta_c$ form factor, $G_{\eta_c}(Q^2)$, is consistent with available data: significantly, at accessible momentum transfers, $Q^2 G_{\eta_c}(Q^2)$ lies well below its conformal limit. These observations confirm that the leading-twist parton distribution amplitudes (PDAs) of heavy-heavy bound-states are compressed relative to the conformal limit. A clear understanding of the distribution of valence-quarks within mesons thus emerges; a picture which connects Goldstone modes, built from the lightest-quarks in Nature, with systems containing the heaviest valence-quarks that can now be studied experimentally, and highlights basic facts about manifestations of mass within the Standard Model.

Light-by-Light Hadronic Corrections to the Muon G-2 Problem Within the Nonlocal Chiral Quark Model

Results of calculation of the light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons and the dynamical quark loop to the muon anomalous magnetic moment are discussed in the framework of the nonlocal SU(3) × SU(3) chiral quark model. The model is based on four-quark interaction of the Nambu–Jona–Lasinio type and Kobayashi–Maskawa–‘t Hooft six-quark interaction. The full kinematic dependence of vertices with off-shell mesons and photons in intermediate states in the light-by-light scattering amplitude is taken into account. All calculations are elaborated in explicitly gauge-invariant manner. These results complete calculations of all hadronic light-by-light scattering contributions to aμ in the leading order in the 1/Nc expansion. The final result does not allow the discrepancy between the experiment and the Standard Model to be explained.

The anatomy of neutral scalars with FCNCs in the flavour precision era

In many extensions of the Standard Model flavour changing neutral current processes can be mediated by tree-level heavy neutral scalars and/or pseudo-scalars H^0(A^0). This generally introduces new sources of flavour violation and CP violation as well as left-handed and right-handed scalar currents. These new physics contributions imply a pattern of deviations from SM expectations for FCNC processes that depends only on the couplings of H^0(A^0) to fermions and on their masses. In situations in which a single H^0 or A^0 dominates NP contributions stringent correlations between Delta F=2 and Delta F=1 observables exist. Anticipating the Flavour Precision Era ahead of us we illustrate this by searching for allowed oases in the landscape of a given model assuming significantly smaller uncertainties in CKM and hadronic parameters than presently available. To this end we analyze Delta F=2 observables in B^0_{s,d}-bar B^0_{s,d} and K^0-bar K^0 systems and rare B and K decays with charged leptons in the final state including both left-handed and right-handed scalar couplings of H^0 and A^0 to quarks in various combinations. We identify a number of correlations between various flavour observables that could test and distinguish these different scenarios. The prominent role of the decays B_{s,d}-> mu^+ mu^- in these studies is emphasized. Imposing the existing flavour constraints, a rich pattern of deviations from the SM expectations in rare B_{s,d} decays emerges provided M_H< 1 TeV. NP effects in rare K decays are very small. Neutral SM Higgs contributions to rare B and K decays turn out to be negligible once the constraints from Delta F=2 processes are taken into account. Finally, we point out striking differences between the correlations found here and in scenarios in which tree-level FCNC are mediated by a new neutral gauge boson Z'.

The light-by-light contribution to the muon (g-2) from lightest pseudoscalar and scalar mesons within nonlocal chiral quark model

The light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons to the anomalous magnetic moment of muon is calculated in the framework of the nonlocal SU(3)x SU(3) quark model. The model is based on chirally symmetric four-quark interaction of the Nambu-Jona-Lasinio type and Kobayashi-Maskawa-t`Hooft U_A(1) breaking six-quark interaction. Full kinematic dependence of vertices with off-shell mesons and photons in intermediate states in the light-by-light scattering amplitude is taken into account. The small positive contributions from the scalar mesons stabilize the total result with respect to change of model parameters and reduces to a_\mu^{LbL,PS+S}=(6.25\pm 0.83)x10^{-10}.

The light-by-light contribution to the [formula omitted] of muon from lightest pseudoscalar and scalar mesons within nonlocal chiral quark model.

The light-by-light contribution from the lightest neutral pseudoscalar and scalar mesons to the anomalous magnetic moment of muon is calculated in the framework nonlocal S U ( 3 ) × S U ( 3 ) quark model. The model is based on a four-quark interaction of the Nambu–Jona-Lasinio type and tʼHooft six-quark interaction. Full kinematic dependencies of vertices with off-shell mesons in the light-by-light scattering amplitude is taken into account.

Holographic striped phases

We discuss new types of instabilities of D=4 electrically charged AdS-Reissner-Nordstr\"om black branes that involve neutral pseudo-scalars. The instabilities spontaneously break translational invariance and are associated with the dual three-dimensional CFTs, at finite temperature and fixed chemical potential with respect to a global abelian symmetry, acquiring striped phases. We show that such instabilities are present for the infinite class of skew-whiffed $AdS_4\times SE_7$ solutions of D=11 supergravity, albeit at a lower temperature than the known superfluid instabilities.

Scalar and vector meson exchange inV→P0P0γdecays

The scalar contributions to the radiative decays of light vector mesons into a pair of neutral pseudoscalars, $V\ensuremath{\rightarrow}{P}^{0}{P}^{0}\ensuremath{\gamma}$, are studied within the framework of the linear sigma model. This model has the advantage of incorporating not only the scalar resonances in an explicit way but also the constraints required by chiral symmetry. The experimental data on $\ensuremath{\phi}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$, $\ensuremath{\phi}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\eta}\ensuremath{\gamma}$, $\ensuremath{\rho}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$, and $\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}{\ensuremath{\pi}}^{0}\ensuremath{\gamma}$ are satisfactorily accommodated in our framework. Theoretical predictions for $\ensuremath{\phi}\ensuremath{\rightarrow}{K}^{0}{\overline{K}}^{0}\ensuremath{\gamma}$, $\ensuremath{\rho}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\eta}\ensuremath{\gamma}$, $\ensuremath{\omega}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{0}\ensuremath{\eta}\ensuremath{\gamma}$, and the ratio $\ensuremath{\phi}\ensuremath{\rightarrow}{f}_{0}\ensuremath{\gamma}/{a}_{0}\ensuremath{\gamma}$ are also given.

Searches for neutral Higgs bosons in ${\mathrm e}^+{\mathrm e}^-$ collisions from $\sqrt{s} = 191.6$ to 201.7 GeV

Neutral Higgs bosons of the Standard Model ({\sc SM}) and the Minimal Supersymmetric Standard Model ({\sc MSSM}) were searched for in the data collected in 1999 by the DELPHI experiment at centre-of-mass energies between 191.6 and 201.7~GeV with a total integrated luminosity of 228 pb$^{-1}$. These analyses, in combination with our results at lower energies, set 95\% confidence level lower mass bounds on the Standard Model Higgs boson (107.3~GeV/$c^2$) and on the lightest neutral scalar (85.9~GeV/$c^2$) and neutral pseudoscalar (86.5~GeV/$c^2$) Higgs bosons in representative scans of the {\sc MSSM} parameter space. % excluding $\tan\beta$ in the range [0.9-1.6] An extended scan of the {\sc MSSM} parameter space was also performed to test the robustness of these limits.

Addendum: Eur. Phys. J. C 17, 187–205 (2000)

Searches for neutral Higgs bosons in the Standard Model and the MSSM have been performed using data collected by the DELPHI experiment at a centre-of-mass energy of 188.7 GeV, corresponding to an integrated luminosity of 158 pb^{-1}. These analyses are used, in combination with our results from lower energies, to set new 95% confidence level lower mass bounds on the Standard Model Higgs boson (94.6 GeV/c^2) and on the lightest neutral scalar (82.6 GeV/c^2) and neutral pseudoscalar (84.1 GeV/c^2) Higgs bosons in a representative scan of the MSSM parameters. The results are also interpreted in the framework of a general two-Higgs doublet model.

ON THE η and f1(1420) COUPLINGS TO THE NUCLEON

We consider neutral pseudoscalar, η, and axial vector, f1(1420), mesons in the OZI-rule-respecting flavor basis, [Formula: see text], and suggest a scenario for their coupling to the nucleon. Within this framework, the nonstrange parts of the ηN and f1N couplings are modeled by means of triangular a0πN, and KK*(Λ/Σ) vertices, while the strange ones partly proceed via Goldberger–Treiman relations, which have been concluded solely on the grounds of current universality. The suggested model explains the observed suppression of the ηN coupling with respect to the constituent quark model expectations, and predicts the coupling of f1with the nucleon.

Searches for neutral Higgs bosons in ${\mathrm e}^+{\mathrm e}^-$ collisions around $\sqrt{s}$ = 189 GeV

Searches for neutral Higgs bosons in the Standard Model and the MSSM have been performed using data collected by the DELPHI experiment at a centre-of-mass energy of 188.7 GeV, corresponding to an integrated luminosity of 158 pb^{-1}. These analyses are used, in combination with our results from lower energies, to set new 95% confidence level lower mass bounds on the Standard Model Higgs boson (94.6 GeV/c^2) and on the lightest neutral scalar (82.6 GeV/c^2) and neutral pseudoscalar (84.1 GeV/c^2) Higgs bosons in a representative scan of the MSSM parameters. The results are also interpreted in the framework of a general two-Higgs doublet model.

Scalars from Top-Condensation Models at Hadron Colliders

We study the production and decay of neutral scalars and pseudo-scalars at hadron colliders, in theories where the top-quark mass is the result of a $t\bar t$ condensate. We show that the dominant decay channel for masses below the $t\bar t$ threshold is the flavor changing mode $tc$. This is a consequence of the non-universal nature of the underlying interactions in all top-condensation models and provides a model-independent signature of these scenarios. We show that an upgraded Tevatron is sensitive to a sizeable region of the interesting parameter space and that the LHC will highly constrain these models through this flavor violating channel.

Revisit of Glueball and Neutral Pseudoscalar Meson Admixture

Revisit of Glueball and Neutral Pseudoscalar Meson Admixture

Classical hadrodynamics: A new approach to ultrarelativistic heavy-ion collisions

We discuss a new approach to ultrarelativistic heavy-ion collisions based on classical hadrodynamics for extended nucleons, corresponding to nucleons of finite size interacting with massive meson fields. This new theory provides a natural covariant microscopic approach that includes automatically spacetime nonlocality and retardation, nonequilibrium phenomena, interactions among all nucleons and particle production. In the current version of our theory, we consider N extended unexcited nucleons interacting with massive neutral scalar (σ) and neutral vector (ω) meson fields. The resulting classical relativistic many-body equations of motion are solved numerically without further approximation for soft nucleon-nucleon collisions at p lab = 14.6, 30, 60, 100 and 200 GeV/ c to yield the transverse momentum imparted to the nucleons. For the future development of the theory, the isovector pseudoscalar ( π +, π −, π 0), isovector scalar ( δ +, δ −, δ 0), isovector vector ( ϱ +, ϱ −, ϱ 0) and neutral pseudoscalar (η) meson fields that are known to be important from nucleon-nucleon scattering experiments should be incorporated. In addition, the effects of quantum uncertainty on the equations of motion should be included by use of techniques analogous to those used by Moniz and Sharp for nonrelativistic quantum electrodynamics.