Pion electromagnetic form factor at finite temperature

Abstract

Temperature effects on the electromagnetic couplings of pions in hot hadronic matter are studied with an effective chiral Lagrangian. We show that the Ward-Takahashi identity is satisfied at non-zero temperature in the soft pion limit. The in-medium electromagnetic form factor of the pion is obtained in the time-like region and shown to be reduced in magnitude, especially near the vector-meson resonance region. Finally, we discuss the consequences of this medium effect on dilepton production from hot hadronic matter.

Thermal dilepton production from droppingρbased on the vector manifestation

“…7 (a) g ρ (s), m ρ and Γ ρ in the form factor include only the hadronic temperature corrections and g γππ andḡ ρππ have no temperature dependence. There is no remarkable shift of the ρ meson mass but the width becomes broader with increasing temperature, which is consistent with the previous study [40]. In Fig.…”

Duality and chiral restoration from low-mass dileptons at the CERN-SpS

“…Nevertheless, the low-energy mixing theorem (5) is satisfied through temperature corrections of the VDM coupling constant, g ργ (T ) [12]. The application to calculating the in-medium pion electromagnetic form factor within a low-temperature pion-loop expansion shows a strong reduction and broadening of the ρ resonance structure (with practically no mass shift), leaving a rather small enhancement in the corresponding dilepton rates towards the two-pion threshold [13]. A third avenue of finite temperature calculations proceeds with effective meson Lagrangians [14][15][16][17][18][19][20] where the emphasis is on incorporating all phenomenologically important scattering processes which also go beyond SU(2) chiral symmetry.…”

Low-mass dileptons at the CERN-SpS: evidence for chiral restoration?

“…Several theoretical approaches have been pursued to study medium effects in dilepton production rates from hot/dense matter, e.g., the 'dropping rho mass' scenario (within a mean-field type treatment) [3][4][5], the chiral reduction formalism (based on chiral Ward identities in connection with low-density expansions) [6], chiral Lagrangian frameworks [7] or many-body-type calculations of in-medium vector-meson spectral functions [8][9][10][11]. As a further complication, the quantitative impact of inmedium effects on the final spectra depends on another important ingredient, namely the modeling of the spacetime evolution of the global heavy-ion collision dynamics.…”