Approximate Analytic Spectra of Reionized CMB Anisotropies and
  Polarization generated by Relic Gravitational Waves
  We present an approximate, analytical calculation of the reionized spectra
$C_l^{XX}$ of cosmic microwave background radiation (CMB) anisotropies and
polarizations generated by relic gravitational waves (RGWs). Three simple
models of reionization are explored, whose visibility functions are fitted by
gaussian type of functions as approximations. We have derived the analytical
polarization $\beta_l$ and temperature anisotropies $\alpha_l$, both consisting
of two terms proportional to RGWs at the decoupling and at the reionization as
well. The explicit dependence of $\beta_l$ and $\alpha_l$ upon the reionization
time $\eta_r$, the duration $\Delta\eta_r$, and the optical depth $\kappa_r$
are demonstrated. Moreover, $\beta_l$ and $\alpha_l$ contain $\kappa_r$ in
different coefficients, and the polarization spectra $C_l^{EE}$ are $C_l^{BB}$
are more sensitive probes of reionization than $C_l^{TT}$. These results
facilitate examination of the reionization effects, in particular, the
degeneracies of $\kappa_r$ with the normalization amplitude and with the
initial spectral index of RGWs. It is also found that reionization also causes
a $\kappa_r$-dependent shift $\Delta l\sim 20$ of the zero multipole $l_0$ of
$C_l^{TE}$, an effect that should be included in order to detect the traces of
RGWs. Compared with numerical results, the analytical $C_l^{XX}$ as
approximation have the limitation. For the primary peaks in the range $l\simeq
(30, 600)$, the error is $\le 3%$ in three models. In the range $l < 20$ for
the reionization bumps, the error is $\le 15%$ for $C_l^{EE}$ and $C_l^{BB}$ in
the two extended reionization models, and $C_l^{TT}$ and $C_l^{TE}$ have much
larger departures for $l<10$. The bumps in the sudden reionization model are
too low.
