arXiv subjects

A. Hosaka

Publications and source records attributed to A. Hosaka.

At least 37 records · Page 2Linked to original sources

arXiv2016

Thermal properties and evolution of the $U_A(1)$ factor for 2+1 flavors

Thermal evolution of the axial anomaly is investigated in the system of the linear sigma model for $2+1$ flavors. We explore the functional form of the effective potential and the coefficient of the `t Hooft determinant term. It is found that the latter develops a non-trivial structure as a function of the chiral condensate and grows everywhere with respect to the temperature. This shows that mesonic fluctuations strengthen the axial anomaly at finite temperature and it does not get vanished at the critical point. The phenomenon has been found to have significance in the thermal properties of the mesonic spectra, especially concerning the $η-η'$ system.

hep-ph↗

arXiv2015

Strategies for an accurate determination of the X(3872) energy from QCD lattice simulations

We develop a method to determine accurately the binding energy of the X(3872) from lattice data for the DD* interaction. We show that, because of the small difference between the neutral and charged components of the X(3872), it is necessary to distinguish them in the energy levels of the lattice spectrum if one wishes to have a precise determination of the the binding energy of the X(3872). The analysis of the data requires the use of coupled channels. Depending on the number of levels available and the size of the box we determine the precision needed in the lattice energies to finally obtain a desired accuracy in the binding energy.

hep-ph↗

arXiv2014

Heavy quark symmetry in multi-hadron systems

We discuss the properties of hadronic systems containing one heavy quark in the heavy quark limit. The heavy quark symmetry guarantees the mass degeneracy of the states with total spin and parity $(j-1/2)^{P}$ and $(j+1/2)^{P}$ with $j \geq 1/2$, because the heavy-quark spin is decoupled from the total spin $j$ of the light components called brown muck. We apply this idea to heavy multi-hadron systems, and formulate the general framework to analyze their properties. We demonstrate explicitly the spin degeneracy and the decomposition of the wave functions in exotic heavy hadron systems generated by the one boson exchange potential. The masses of the brown muck can be extracted from theoretical and experimental hadron spectra, leading to the color non-singlet spectroscopy.

hep-ph↗

arXiv2014

Decays of double charmed meson molecules

The interaction between pseudoscalar and/or vector mesons can be studied using hidden gauge Lagrangians. In this framework, the interaction between charmed mesons has been studied. Furthermore, doubly charmed states are also predicted. These new states are near the $D^*D^*$ and $D^*D^*_s$ thresholds, and have spin-parity $J^P=1^+$. We evaluate the decay widths of these states, named as $R_{cc}(3970)$ and $S_{cc}(4100)$ (with strangeness), and obtain $44$ MeV for the non-strangeness, and $24$ MeV for the doubly charm-strange state. Essentially, the decay modes are $DD_{(s)}π$ and $DD_{(s)}γ$, being the $Dπ$ and $Dγ$ emitted by one of the $D^*$ meson which forms the molecule.

hep-ph↗

arXiv2013

Role of vector and pseudoscalar mesons in understanding $1/2^-$ $N^*$ and $Δ$ resonances

A study of nonstrange meson-baryon systems has been made with the idea of understanding the properties of the low-lying $1/2^-$ $N^*$ and $Δ$ resonances. The coupled channels are built by considering the pseudoscalar and vector mesons together with the octet baryons. The formalism is based on obtaining the interactions from the lowest order chiral Lagrangian when dealing with pseudoscalar mesons and relying on the hidden local symmetry in case of the vector mesons. The transition between the two systems is obtained by replacing the photon by a vector meson in the Kroll-Ruderman theorem for the photoproduction of pseudoscalar mesons. The subtraction constants, required to calculate the loop-function in the scattering equations, are constrained by fitting the available experimental data on some of the reactions with pseudoscalar meson-baryon final states. As a consequence, we find resonances which can be related to $N^*(1535)$, $N^*(1650)$ (with a double pole structure), $N^*(1895)$ and $Δ(1620)$. We conclude that these resonances can be, at least partly, interpreted as dynamically generated resonances and that the vector mesons play an important role in determining the dynamical origin of the low-lying $N^*$ and $Δ$ states.

nucl-th↗

arXiv2013

Interpreting the peak structures around 1800 MeV in the BES data on $J/Ψ\to ϕπ^+ π^-$, $J/Ψ\to γωϕ$

In this talk we present an interpretation for the experimental data available on two different processes, namely, $J/Ψ\to ϕπ^+ π^-$, $J/Ψ\to γωϕ$, which seem to indicate existence of two new resonances with the same quantum numbers ($J^{πc}=0^{++}, I = 0$) and very similar mass (~1800 MeV) but with very different decay properties. However, our studies show that the peak structure found in the $ωϕ$ invariant mass, in $J/Ψ\to γωϕ$, is a manifestation of the well known $f_0(1710)$ while the cross section enhancement found in $J/Ψ\to ϕπ^+ π^-$ is indeed a new $f_0$ resonance with mass near 1800 MeV. We present an explanation for the different decay properties of these two scalar resonances.

hep-ph↗

arXiv2013

Decays of doubly charmed meson molecules

Several observed states close to the $D\bar{D}^*$ and $D^*_{(s)}\bar{D}^*_{(s)}$ thresholds, as the X(3872) and some XYZ particles can be described in terms of a two-meson molecule. Furthermore, doubly charmed states are also predicted. These new states are near the $D^*D^*$ and $D^*D^*_s$ thresholds, % Therefore, if the previous XYZ are molecules, then, there should be doubly charmed mesons with $J^P=1^+$ around the $D^*D^*$ threshold. %For this reason, it is important to evaluate observables related to them. Because of the spin$=1$, they do not decay into $DD$. In this article we compute decays to $DD^*$ and radiative decays of doubly charmed meson molecules into $DD_{(s)}γ$. and have spin-parity $J^P=1^+$. Their natural decay modes are $D_{(s)}D^*$, $DD_{(s)}π$ and $DD_{(s)}γ$ and $D^*D_{(s)}γ$. We evaluate the widths of these states, named here as $R_{cc}(3970)$ and $S_{cc}(4100)$, and obtain 44 MeV for the non-strangeness, and 24 MeV for the doubly charm-strange state. Essentially, the decay modes are $DD_{(s)}π$ and $DD_{(s)}γ$, being the $Dπ$ and $Dγ$ emitted by one of the $D^*$ meson which forms the molecule.

hep-ph↗

arXiv2013

Strategies for an accurate determination of the X(3872) energy from QCD lattice simulations

We develop a method to determine accurately the binding energy of the X(3872) from lattice data for the $D \bar D^*$ interaction. We show that, because of the small difference between the neutral and charged components of the X(3872), it is necessary to differentiate them in the energy levels of the lattice spectrum if one wishes to have a precise determination of the the binding energy of the X(3872). The analysis of the data requires the use of coupled channels. Depending on the number of levels available and the size of the box we determine the precision needed in the lattice energies to finally obtain a desired accuracy in the binding energy.

hep-lat↗

arXiv2013

$N^*$'s and $Δ$'s generated in vector, pseudoscalar meson-baryon systems

We have recently studied coupled channel interactions of vector and pseudoscalar mesons with octet baryons having total strangeness null and spin-parity $1/2^-$. We, thus, considered $πN$, $ηN$, $K Λ$, $K Σ$, $ρN$, $ωN$, $ϕN$, $K^* Λ$, and $K^*Σ$ with total isospin 1/2 and 3/2. The interactions between pseudoscalar mesons and baryons are obtained by using the Weinberg-Tomozawa theorem. For the case of vector mesons, we calculate $s$-, $t$-, $u$-exchange diagrams and a contact term. The subtraction constants, required to calculate the loop-function in the scattering equations, are constrained by fitting the available experimental data on some of the reactions with pseudoscalar meson-baryon final states. We end up finding resonances which can be related to $N^*(1535)$, $N^*(1650)$ (with a double pole structure), $N^*(1895)$ and $Δ(1620)$. We conclude that these resonances can be, at least partly, interpreted as dynamically generated resonances and that the vector mesons play an important role in determining the dynamical origin of the low-lying $N^*$ and $Δ$ states.

nucl-th↗

arXiv2013

Spin degeneracy in multi-hadron systems with a heavy quark

We study multi-hadron systems with a single heavy quark (charm or bottom) in the limit of heavy quark mass. The spin degeneracy of the states with quantum numbers $(j+1/2)^{P}$ and $(j-1/2)^{P}$ for $j \neq 0$, known in a normal hadron, can be generalized to multi-hadron systems. The spin degeneracy is the universal phenomena for any multi-hadron systems with a single heavy quark, irrespective of their internal structures, including compact multi-quarks, hadronic molecules and exotic nuclei. We demonstrate the spin degeneracy in the hadronic systems formed by a heavy hadron effective theory; $P^{(\ast)}N$ states with a $P^{(\ast)}=\bar{D}^{(\ast)}$, $B^{(\ast)}$ meson and a nucleon $N$, and a $P^{(\ast)}$ meson in nuclear matter.

hep-ph↗

arXiv2013

Breit-Wheeler process in very short electromagnetic pulses

The generalized Breit-Wheeler process, i.e. the emission of $e^+e^-$ pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field, is analyzed. We show that the production probability is determined by the interplay of two dynamical effects. The first one is related to the shape and duration of the pulse and the second one is the non-linear dynamics of the interaction of $e^\pm$ with the strong electromagnetic field. The first effect manifests itself most clearly in the weak-field regime, where the small field intensity is compensated by the rapid variation of the electromagnetic field in a limited space-time region, which intensifies the few-photon events and can enhance the production probability by orders of magnitude compared to an infinitely long pulse. Therefore, short pulses may be considered as a powerful amplifier. The non-linear dynamics in the multi-photon Breit-Wheeler regime plays a decisive role at large field intensities, where effects of the pulse shape and duration are less important. In the transition regime, both effects must be taken into account simultaneously. We provide suitable expressions for the $e^+e^-$ production probability for kinematic regions which can be used in transport codes.

hep-ph↗

arXiv2012

Exotic mesons with hidden charm and bottom near thresholds

We study heavy hadron spectroscopy near heavy meson thresholds. We employ heavy pseudoscalar meson P and heavy vector meson P* as effective degrees of freedom and consider meson exchange potentials between them. All possible composite states which can be constructed from the P and P* mesons are studied up to the total angular momentum J <= 2. We consider, as exotic states, isosinglet states with exotic J^{PC} quantum numbers and isotriplet states. We solve numerically the Schrödinger equation with channel-couplings for each state. We found B(*)barB(*) molecule states for I^G(J^{PC}) = 1^+(1^{+-}) correspond to the masses of twin resonances Zb(10610) and Zb(10650). We predict several possible B(*)barB(*) bound and/or resonant states in other channels. On the other hand, there are no B(*)barB(*) bound and/or resonant states whose quantum numbers are exotic.

hep-ph↗

arXiv2012

Enhanced subthreshold electron-positron production in short laser pulses

The emission of electron-positron pairs off a probe photon propagating through a polarized short-pulsed electromagnetic (e.g.\ laser) wave field is analyzed. A significant increase of the total cross section of pair production in the subthreshold region is found for decreasing laser pulse duration even in case of moderate laser pulse intensities.

hep-ph↗

arXiv2012

Negative parity $Λ$ and $Σ$ resonances coupled to pseudoscalar and vector mesons

An exploration of the dynamically generated $Λ$ and $Σ$ resonances has been made in the vector meson-baryon (VB) systems coupled to pseudoscalar meson-baryon (PB) channels. The VB interactions are obtained from the Lagrangians written within the hidden local symmetry which, in addition to Yukawa-type vector-baryon-baryon (VBB) vertices, naturally gives rise to a contact interaction. Using the VBB vertices, we calculate the $t$-, $s$- and $u$-channel diagrams considering the octet baryon exchange in the latter two cases. For the PB channels we rely on the the Weingberg-Tomozawa interactions and calculate the PB $\leftrightarrow$ VB transition amplitudes extending the Kroll-Ruderman theorem by replacing the photon by the vector mesons. In addition to the low-lying $Λ(1405)$, $Λ(1670)$ found in previous works, we find resonances which coincide well with: $Λ(2000)$, $Σ(1750) S_{11}$, $Σ(1940) D_{13}$, $Σ(2000) S_{11}$ and predict three $Λ^*$'s with $J^π= 3/2^-$ and masses: $1754 - i2$ MeV, $1862 - i33$ MeV, $2139 - i14$ MeV together with a broad $1/2^-$ $Σ^*$ with mass $\sim$ 1430 MeV. We find that most of these next-to-low-lying states couple weakly with the pseudoscalar mesons, which implies that it is important to study the reactions with VB final states in order to obtain a reliable information on the properties of such resonances.

nucl-th↗

arXiv2012

Vector- and Pseudoscalar-baryon coupled channel systems

In this manuscript, I will report the details of our recent work on the vector meson-baryon (VB) interaction, which we studied with the motivation of finding dynamical generation of resonances in the corresponding systems. We started our study by building a formalism based on the hidden local symmetry and calculating the leading order contributions to the scattering equations by summing the diagrams with: (a) a vector meson exchange in the t-channel (b) an octet baryon exchange in the s-, u-channels and (c) a contact interaction arising from the part of the vector meson-baryon Lagrangian which is related to the anomalous magnetic moment of the baryons. We find the contribution from all these sources, except the s-channel, to be important. The amplitudes obtained by solving the coupled channel Bethe-Salpeter equations for the systems with total strangeness zero, show generation of one isospin 3/2, spin 1/2 resonance and three isospin 1/2 resonances: two with spin 3/2 and one with spin 1/2. We identify these resonances with $Δ$ (1900) $S_{31}$, $N^*$(2080) $D_{13}$, $N^*$(1700) $D_{13}$, and $N^*$(2090) $S_{11}$, respectively. We have further extended our study by including pseudoscalar meson-baryon (PB) as the coupled channels of VB systems. For this, we obtain the PB $\rightarrow$ VB amplitudes by using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the low-lying resonances like $Λ$(1405) and $Λ$(1670), which can have important implications on certain reactions producing them. In addition to this, we find that the effect of coupling the higher mass states to the lighter channels is not restricted to increasing the width of those states, it can be far more strong.

nucl-th↗

arXiv2011

Coupling vector and pseudoscalar mesons to study baryon resonances

A study of meson-baryon systems with total strangeness -1 is made within a framework based on the chiral and hidden local symmetries. These systems consist of octet baryons, pseudoscalar and vector mesons. The pseudoscalar meson-baryon (PB) dynamics has been earlier found determinant for the existence of some strangeness -1 resonances, for example, $Λ(1405)$, $Λ(1670)$, etc. The motivation of the present work is to study the effect of coupling the closed vector meson-baryon (VB) channels to these resonances. To do this, we obtain the $PB \rightarrow PB$ and $VB \rightarrow VB$ amplitudes from the t-channel diagrams and the $PB \leftrightarrow VB$ amplitudes are calculated using the Kroll-Ruddermann term where, considering the vector meson dominance phenomena, the photon is replaced by a vector meson. The calculations done within this formalism reveal a very strong coupling of the VB channels to the $Λ(1405)$ and $Λ(1670)$. In the isospin 1 case, we find an evidence for a double pole structure of the $Σ(1480)$ which, like the isospin 0 resonances, is also found to couple strongly to the VB channels. The strong coupling of these low-lying resonances to the VB channels can have important implications on certain reactions producing them.

nucl-th↗

arXiv2011

Theoretical support for the $π(1300)$ and the recently claimed $f_0(1790)$ as molecular resonances

A study of three-pseudoscalar $πK \bar{K}$ and $ππη$ coupled system is made by solving the Faddeev equations within an approach based on unitary chiral dynamics. A resonance with total isospin one and spin-parity $J^π= 0^-$ is found with mass $\sim$ 1400 MeV when the $K \bar{K}$ system gets reorganized as the $f_0(980)$. This resonance is identified with the $π(1300)$ listed by the Particle Data Group. Further, the two-body amplitude which describes the interaction between a $π$ and the $f_0(980)$ is extracted from the study of the $πK\bar K$ and $ππη$ system and is then employed to study the $f_0(980)ππ$ system. As a result, a scalar resonance is found near 1790 MeV which drives the two $ f_0 (980)π$ systems to resonate as the $π(1300)$ while the invariant mass of the two pions falls in the mass region of the scalar $σ(600)$. These findings support the existence of a new $f_0$ resonance near 1790 MeV, as found by the BES and Crystal Barrel collaborations. Our results show that this $f_0(1790)$ is definitely distinct to $f_0(1710)$, the latter of which seems to possess a glueball structure dominantly.

nucl-th↗

arXiv2011

Composite and elementary natures of a1(1260) meson

We develop a practical method to analyze the mixing structure of hadrons consisting of two components of quark-composite and hadronic composite. As an example we investigate the properties of the axial vector meson a1(1260) and discuss its mixing properties quantitatively. We also make reference to the large Nc procedure and its limitation for the classification of such a mixed state.

hep-ph↗