Tsallis holographic inflation in $f(R,T)$ gravity: CMB constraints, reheating, and swampland implications
Understanding how early-universe inflation may emerge from generalized holographic energy densities within modified gravity motivates the present analysis. We develop a self-consistent inflationary scenario in which the Tsallis holographic dark energy (THDE) density effectively acts as the inflaton potential in $f(R,T)$ gravity. Using the Granda-Oliveros infrared cutoff, we derive the corresponding slow-roll relations and identify a broad region of the parameter space $(\alpha,\beta,\delta,\lambda)$ that remains consistent with ACT DR6 (P-ACT-LB) constraints. By exploiting the dependence of the THDE density on the Hubble rate, we reconstruct the inflaton potential $V(\phi)$ and show that both the field excursion $\Delta\phi$ and the normalized potential gradient $|V'|/(V M_{p})$ are predominantly controlled by the matter-geometry coupling $\lambda$. We demonstrate that $\lambda \gtrsim \mathcal{O}(10^{2})$ suppresses the field excursion below the Planck scale and ensures $|V'|/(V M_{p}) \ge 1$, thereby satisfying both the distance conjecture and the refined de Sitter swampland bound. We also analyze the reheating stage. In addition to the primordial nucleosynthesis requirement $T_{\rm BBN} \approx 4~\mathrm{MeV}$, which sets a lower limit on the reheating temperature, the observational bound $\Delta N_{\rm eff} \le 0.17$ imposes an additional constraint from primordial gravitational waves (PGWs). During stiff reheating phases with $\omega_{\rm re} > 1/3$, the high-frequency PGW spectrum is significantly enhanced, producing a distinct signature that may fall within the sensitivity of upcoming detectors. Overall, this work provides an observationally consistent realization of holographic inflation in $f(R,T)$ gravity, jointly constrained by CMB data, swampland criteria, reheating physics, and PGW limits.