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Masayasu Harada

Publications and source records attributed to Masayasu Harada.

At least 91 records · Page 5Linked to original sources
arXiv2013

Chiral partner structure of heavy baryons from the bound state approach with hidden local symmetry

The chiral partner structure of heavy baryons is studied using the bound state approach by binding the heavy-light mesons to nucleon as soliton in an effective Lagrangian for the pseudoscalar and vector mesons based on the hidden local symmetry. In the heavy-light meson sector, we regard the $H$-doublet and $G$-doublet as chiral partners and couple them to light meson with minimal derivative. We find that the chiral partner of $Λ_c(1/2^+,2286)$ is the $Λ_c(1/2^-,3/2^-)$ heavy quark doublet with the mass of about 3.1\,GeV but not ($Λ_c(1/2^-,2595)$, $Λ_c(3/2^-,2625)$) which might be interpreted as an orbital excitation of the $Λ_c(1/2^+,2286)$. The same model is applied to the bottom sector, and the chiral partner of $Λ_b(1/2^+,5625)$ is shown to have the mass of about 6.5\,GeV. The chiral partner structures for the isospin vector heavy baryons are also discussed. For the pentaquark states, we find that the masses of the pentaquark state made of ground state heavy-light meson and its chiral partner are similar, and both of them are below the $Dp$ threshold, which therefore cannot be ruled out by the present data.

hep-ph↗
arXiv2013

Skyrmions with vector mesons in the hidden local symmetry approach

The roles of light $ρ$ and $ω$ vector mesons in the Skyrmion are investigated in a chiral Lagrangian derived from the hidden local symmetry (HLS) up to $O(p^4)$ including the homogeneous Wess-Zumino (hWZ) terms. We write a general "master formula" that allows us to determine the parameters of the HLS Lagrangian from a class of holographic QCD models valid at large $N_c$ and $λ$ ('t Hooft constant) limit by integrating out the infinite towers of vector and axial-vector mesons other than the lowest $ρ$ and $ω$ mesons. Within this approach we find that the physical properties of the Skyrmion as the solitonic description of baryons are \textit{independent} of the HLS parameter $a$. Therefore the only parameters of the model are the pion decay constant and the vector meson mass. Once determined in the meson sector, we have a totally parameter-free theory that allows us to study unequivocally the role of light vector mesons in the Skyrmion structure. We find, as suggested by Sutcliffe, that inclusion of the $ρ$ meson reduces the soliton mass, which makes the Skyrmion come closer to the Bogomol'nyi-Prasad-Sommerfield (BPS) soliton, but the role of the $ω$ meson is found to increase the soliton mass. In a stark contrast, the $Δ$-$N$ mass difference, which is determined by the moment of inertia in adiabatic collective quantization of the Skyrmion, is increased by the $ρ$ vector meson, while it is reduced by the inclusion of the $ω$ meson. All these observations show the importance of the $ω$ meson in the properties of the nucleon and nuclear matter in the Skyrme model.

hep-ph↗
arXiv2012

Hidden Local Symmetry and Infinite Tower of Vector Mesons for Baryons

In an effort to access dense baryonic matter relevant for compact stars in a unified framework that handles both single baryon and multibaryon systems on the same footing, we first address a holographic dual action for a single baryon focusing on the role of the infinite tower of vector mesons deconstructed from five dimensions. To leading order in 't Hooft coupling $λ=N_c g_{\rm YM}^2$, one has the Bogomol'nyi-Prasad-Sommerfield (BPS) Skyrmion that results when the warping of the bulk background and the Chern-Simons term in the Sakai-Sugimoto D4/D8-${\bar{\rm D8}}$ model are ignored. The infinite tower was found by Sutcliffe to induce flow to a conformal theory, i.e., the BPS. We compare this structure to that of the SS model consisting of a 5D Yang-Mills action in warped space and the Chern-Simons term in which higher vector mesons are integrated out while preserving hidden local symmetry and valid to $O(λ^0)$ and $O(p^4)$ in the chiral counting. We point out the surprisingly important role of the $ω$ meson that figures in the Chern-Simons term that encodes chiral anomaly in the baryon structure and that may be closely tied to short-range repulsion in nuclear interactions.

hep-ph↗
arXiv2012

Holographic Mean-Field Theory for Baryon Many-Body Systems

We propose a mean-field approach to analyze many-body systems of fermions in the gauge/gravity duality. We introduce a non-vanishing classical fermionic field in the gravity dual, which we call the holographic mean field for fermions. The holographic mean field takes account of the many-body dynamics of the fermions in the bulk. The regularity condition of the holographic mean field fixes the relationship between the chemical potential and the density unambiguously. Our approach provides a new framework of gauge/gravity duality for finite-density systems of baryons in the confinement phase.

hep-th↗
arXiv2012

Effect of sigma meson on the $D_1(2430) \to Dππ$ decay

We study the effect of sigma meson on the $D_1(2430) \to Dππ$ decay by constructing an effective Lagrangian preserving the chiral symmetry and the heavy quark symmetry. The sigma meson is included through a linear sigma model, in which both the $q\bar{q}$ and $qq\bar{q}\bar{q}$ states are incorporated respecting their different $U(1)_{A}$ transformation properties. We first fit the sigma meson mass and $σ$-$π$-$π$ coupling constant to the I=0, $S$-wave $π$-$π$ scattering data. Then, we show how the differential decay width $dΓ(D_1 \to D(ππ)_{I = 0, L =0})/d m_{ππ}$ depends on the quark structure of the sigma meson. We find that our study, combing with the future data, can give a clue to understand the sigma meson structure.

hep-ph↗
arXiv2011

Anomalous $ω$-$Z$-$γ$ Vertex from Hidden Local Symmetry

We formulate the general form of omega-Z-gamma vertex in the framework based on the hidden local symmetry (HLS), which arises from the gauge invariant terms for intrinsic parity-odd (IP-odd) part of the effective action. Those terms are given as the homogeneous part of the general solution (having free parameters) to the Wess-Zumino (WZ) anomaly equation and hence are not determined by the anomaly, in sharp contrast to the Harvey-Hill-Hill (HHH) action where the relevant vertex is claimed to be uniquely determined by the anomaly. We show that, even in the framework that HHH was based on, the omega-Z-gamma vertex is actually not determined by the anomaly but by the homogeneous (anomaly-free) part of the general solution to the WZ anomaly equation having free parameters in the same way as in the HLS formulation: The HHH action is just a particular choice of the free parameters in the general solution. We further show that the omega-Z-gamma vertex related to the neutrino (nu) - nucleon (N) scattering cross section sigma(nu N -> nu N (N')gamma) is determined not by the anomaly but by the anomaly-free part of the general solution having free parameters. Nevertheless we find that the cross section sigma(nu N -> nu N(N')gamma) is related through the Ward-Takahashi identity to Gamma(omega -> pi^0 gamma) which has the same parameter-dependence as that of sigma(nu N -> nu N(N')gamma) and hence the ratio sigma(nu N -> nu N(N')gamma)/Gamma(omega -> pi^0 gamma) is fixed independently of these free parameters. Other set of the free parameters of the general solution can be fixed to make the best fit of the omega -> pi^0 l^+ l^- process, which substantially differs from the HHH action. This gives a prediction of the cross section sigma(nu N -> nu N (N')gamma^*(l^+ l^-)) to be tested at nu-N collision experiments in the future.

hep-ph↗
arXiv2011

Integrating Holographic Vector Dominance to Hidden Local Symmetry for the Nucleon Form Factor

We derive a two-parameter formula for the electromagnetic form factors of the nucleon described as an instanton by "integrating out" all KK modes other than the lowest mesons from the infinite-tower of vector mesons in holographic QCD while preserving hidden local symmetry for the resultant vector fields. With only two parameters, the proton Sachs form factors can be fit surprisingly well to the available experimental data for momentum transfers $Q^2\lsim 0.5$ GeV$^2$ with $χ^2$/dof $\lsim 2$. We interpret this agreement as indicating the importance of an infinite tower in the soliton structure of the nucleon. The prediction of the Sakai-Sugimoto holographic dual model is checked against the fit values to assess its accuracy in describing the proton structure. We find that the structure of the "core" of roughly 1/3 in the proton size indicated in experiments and commonly associated with an intrinsic quark-gluon structure in QCD is "hidden" in the infinite tower in the holographic model.

hep-ph↗
arXiv2010

Properties of X(3872) as a hadronic molecule with a negative parity

We discuss the possible interpretation of X(3872) as a $DD^{\ast}$ hadronic molecule with $J^{PC} = 2^{-+}$. Using the phenomenological Lagrangian approach, we studied its radiative and strong decay properties. We find that our model with about 97.6% isospin zero component explains the existing data nicely. We predict the partial widths of the radiative and strong decays of X(3872) and show that the measurement of the ratio $\mathcal{B}(X(3872) \to χ_{c0}π^0)/\mathcal{B}(X(3872) \to χ_{c1}π^0)$ may signal the nature of X(3872).

hep-ph↗
arXiv2010

Strong and radiative decays of X(3872) as a hadronic molecule with a negative parity

Properties of X(3872) are studied by regarding it as a $DD^{\ast}$ hadronic molecule with $J^{PC} = 2^{-+}$ in the phenomenological Lagrangian approach. We find that our model with about 97.6% isospin zero component explains the existing data nicely, for example, the ratio $\mathcal{B}(X(3872) \to J/ψπ^+π^-π^0)/\mathcal{B}(X(3872) \to J/ψπ^+π^-)$. We predict the partial widths of the radiative decays of $X(3872) \to γJ/ψ$, $γψ(2S) $ and the strong decays of $X(3872) \to J/ψπ^+ π^-$, $J/ψπ^+π^-π^0$ as well as $X(3872) \to χ_{cJ}π^0$. Our analysis shows that the measurement of the ratio $\mathcal{B}(X(3872) \to χ_{c0}π^0)/\mathcal{B}(X(3872) \to χ_{c1}π^0)$ may signal the nature of X(3872).

hep-ph↗
arXiv2010

Holographic Vector Dominance for the Nucleon

We derive a two-parameter formula for the electromagnetic form factors of the nucleon described as an instanton by "integrating out" all KK modes other than the lowest mesons from the infinite-tower of vector mesons in holographic QCD while preserving hidden local symmetry for the resultant vector fields. With only two parameters, the proton Sachs form factors can be fit surprisingly well to the available experimental data for momentum transfers $Q^2\lsim 0.5$ GeV$^2$ with $χ^2$/dof $\lsim 2$, indicating the importance of an infinite tower in the soliton structure of the nucleon. The prediction of the Sakai-Sugimoto holographic dual model is checked against the fit values that we interpret as representing Nature. The nature of the "core" in the nucleon structure is reassessed in light of the results obtained with the infinite-tower structure.

hep-ph↗
arXiv2010

Holographic QCD Integrated back to Hidden Local Symmetry

We develop a previously proposed gauge-invariant method to integrate out infinite tower of Kaluza-Klein (KK) modes of vector and axialvector mesons in a class of models of holographic QCD (HQCD). The HQCD is reduced by our method to the chiral perturbation theory with the hidden local symmetry (HLS) having only the lowest KK mode identified as the HLS gauge boson. We take the Sakai-Sugimoto model as a concrete HQCD, and completely determine the ${\cal O} (p^4)$ terms as well as the ${\cal O}(p^2)$ terms from the DBI part and the anomaly-related (intrinsic parity odd) gauge-invariant terms from the CS part. Effects of higher KK modes are fully included in these terms. To demonstrate power of our method, we compute momentum-dependences of several form factors such as the pion electromagnetic form factors, the $π^0$-$γ$ and $ω$-$π^0$ transition form factors compared with experiment, which was not achieved before due to complication to handle infinite sums. We also study other anomaly-related quantities like $γ^*$-$π^0$-$π^+$-$π^-$ and $ω$-$π^0$-$π^+$-$π^-$ vertex functions.

hep-ph↗
arXiv2010

Effect of vector--axial-vector mixing to dilepton spectrum

In this write-up we summarize main results of our recent analyses on the mixing between transverse rho and a1 mesons in hot and/or dense matter. We show that the axial-vector meson contributes significantly to the vector spectral function in hot matter through the mixing. In dense baryonic matter, we include a mixing through a set of omega rho a1 -type interactions. We show that a clear enhancement of the vector spectral function appears below \sqrt{s}=m_ρfor small three-momenta of the rho meson, and thus the vector spectrum exhibits broadening.

hep-ph↗
arXiv2010

Masses of vector bosons in two-color dense QCD based on the hidden local symmetry

We construct a low energy effective Lagrangian for the two-color QCD including the "vector" bosons (mesons with J^P=1^- and diquark baryons with J^P=1^+) in addition to the pseudo Nambu-Goldstone bosons with a degenerate mass M_π(mesons with J^P=0^- and baryons with J^P=0^+) based on the chiral symmetry breaking pattern of SU(2N_f) \to Sp(2N_f) in the framework of the hidden local symmetry. We investigate the dependence of the "vector" boson masses on the baryon number density μ_B. We show that the μ_B-dependence signals the phase transition of U(1)_B breaking. We find that it gives information about mixing among "vector" bosons: e.g. the mass difference between ρand ωmesons is proportional to the mixing strength between the diquark baryon with J^P=1^+ and the anti-baryon. We discuss the comparison with lattice data for two-color QCD at finite density.

hep-ph↗
arXiv2009

Disappearance of quasi-fermions in the strongly coupled plasma from the Schwinger-Dyson equation with in-medium gauge boson propagator

We non-perturbatively study the fermion spectrum in the chiral symmetric phase focusing on the effects of in-medium corrections for gauge boson. The fermion spectrum is derived by solving the Schwinger-Dyson equation (SDE) with ladder approximation on the real time axis. It is shown that the peak of the fermion spectral function is broadened by in-medium effects for gauge boson compared with the peak obtained with the tree gauge boson propagator. The peak becomes much broader as the value of the gauge coupling increases. This broadening is caused by multiple scatterings of fermions and gauge bosons included through the non-perturbative resummation done by the SDE. In particular, the Landau damping of gauge boson propagator plays an important role in the broadening. Our results show no clear peak in the strong coupling region, implying the disappearance of quasi-fermions in the strongly coupled plasma. This indicates that quasi-particle picture may be no longer valid in the strongly coupled QGP.

hep-ph↗
arXiv2009

A novel spectral broadening from vector--axial-vector mixing in dense matter

The presence of baryonic matter leads to the mixing between transverse $ρ$ and $a_1$ mesons through a set of $ωρa_1$-type interactions, which results in the modification to the dispersion relation. We show that a clear enhancement of the vector spectral function appears below $\sqrt{s}=m_ρ$ for small three-momenta of the $ρ$ meson, and thus the vector spectrum exhibits broadening. We also discuss its relevance to dilepton measurements.

hep-ph↗
arXiv2009

Hidden Local Field Theory and Dileptons in Relativistic Heavy Ion Collisions

The notion of "hadronic freedom" is introduced based on the vector manifestation of hidden local symmetry and is used to suggest that the dileptons measured in relativistic heavy-ion collisions do not provide {\em direct} information on the spontaneous breaking of chiral symmetry and hence on the mechanism for mass generation of light-quark hadrons. We give arguments how the dileptons emitted from those vector mesons whose masses are shifted à la Brown-Rho (BR) scaling by the vacuum change in temperature -- as in heavy-ion collisions -- and/or density -- as in cold compressed matter -- could be strongly suppressed in the hadronic free region between the chiral restoration point and the "flash point" at which the vector mesons recover $\gsim 90%$ of their free-space on-shell masses and the full strong coupling strength. It may seem ironical that the very mechanism i.e., the vector manifestation in hidden local symmetry, that is to make the mass drop and modify the spectral function is in turn responsible for the dilepton suppression. A possible falsification of this drastic prediction will be indicated. We also briefly discuss the potential role played by the holographic dimension intrinsic in gravity-gauge duality that provides a unified field theory description of hadrons -- both mesons and baryons -- under extreme conditions. Baryons arise as coherent states of pions and vector mesons of holographic QCD which define the ground state or the "vacuum" on which mesonic excitations could undergo BR scaling.

hep-ph↗
arXiv2008

Quasifermion spectrum at finite temperature from coupled Schwinger-Dyson equations for a fermion-boson system

We nonperturbatively investigate a fermion spectrum at finite temperature in a chiral invariant linear sigma model. Coupled Schwinger-Dyson equations for fermion and boson are developed in the real time formalism and solved numerically. From the coupling of a massless fermion with a massive boson, the fermion spectrum shows a three-peak structure at some temperatures even for the strong coupling region. This means that the three-peak structure which was originally found in the one-loop calculation is stable against higher order corrections even in the strong coupling region.

hep-ph↗