Symmetry-protected α-attractor hybrid inflation in supergravity and constraints from ACT DR6 and DESI DR2

We present a symmetry-protected supergravity effective realization of hybrid α -attractor inflation with a sequestered Stückelberg uplift. The model contains four chiral multiplets, an inflaton modulus T , a stabilizer field S , and a pair of oppositely charged waterfall multiplets ( Ψ , ̅ ̅ ̅ ̅ ̅ ̅ Ψ ) , together with a hidden Stückelberg U (1) D sector that generates an approximately constant positive contribution to the scalar potential. Along the real inflationary trajectory, the F-term potential realizes the E-model plateau 𝑈 ⁡ ( 𝜙 ) = 𝑉 0 ⁢ ( 1 − 𝑒 − √ 2 / ( 3 ⁢ 𝛼 ) 𝜙 ) 2 , while the sequestered uplift shifts the total energy density without directly modifying the tree-level inflaton slope. We derive the background evolution, the analytic N – ϕ relation, the waterfall stability condition, and the leading predictions for the scalar spectral index and tensor-to-scalar ratio. The model retains the characteristic red-tilted α -attractor behavior, with 𝑛 𝑠 ≃ 1 − 2 / 𝑁 * and tensor amplitudes controlled primarily by the curvature parameter α , while the uplift and the hybrid end point generate only subleading corrections at fixed N * . We also discuss the assumptions required for an effectively single-field trajectory, including the treatment of the light angular component of T , and examine the sensitivity of the sequestered uplift to Planck-suppressed cross-couplings. The resulting construction provides a controlled supergravity embedding of hybrid α -attractor inflation compatible with current CMB constraints, including Planck, ACT DR6, and DESI DR2, while remaining testable by future B -mode searches such as LiteBIRD and CMB-S4.