Estimate of a universal critical-amplitude ratio from itsɛexpansion up toɛ2

The exponent $\alpha$ of the specific heat $C$ vanishes at some value $n_0$ of the number $n$ of components of the order parameter. $n_0$ is estimated (1.942±0.026) from the available long series at $d=3\mathrm{}$ in powers of the ${\Phi }^4$ coupling. Knowing that the ratio $\frac{A^{+}}{A^{-}}=1\mathrm{}$ ($A^{\pm }$ are the critical amplitudes of $C$ above and below $T_c$) for $n=n_0$, the estimate at $d=3\mathrm{}$ of this ratio for $n=2\mathrm{}$ obtained from $\varepsilon$ expansion up to ${\varepsilon }^2$ is improved. The cases $n=1\mathrm{} \mathrm{and} 3$ are also considered.