Double pole structures of X₁(2900) as the P-wave D̄^*K^* resonances

We reveal the double pole structures of the manifestly exotic tetraquark state X₁(2900) in the scenario of P-wave D̄^*K^* dimeson resonance. We find that the observed enhancement signal associated with X₁(2900) in B⁺ → D⁺D⁻K⁺ by LHCb contains two P-wave poles denoted as Tcs1-(2900) and T^cs1-(2900), respectively. After considering the channel couplings among the D̄K, D̄^*K, D̄K^* and D̄^*K^* and the width of the K^* meson, the masses and widths of the S-wave pole Tcs0+(2900) and two P-wave poles Tcs1-(2900) and T^cs1-(2900) coincide with those of the X₀(2900) and X₁(2900) remarkably, which provides strong support for identifying X₀(2900) and X₁(2900) as D̄(*)K(*) dimeson states. Furthermore, we extensively calculate all S-wave and P-wave D̄(*)K(*) systems up to $J=3$ and predict four new isoscalar charmed-strange dimeson-type tetraquark states: an S-wave state Tcs1+(2900) with quantum number JP=1⁺, three P-wave states Tcs1-(2760) with JP=1⁻, Tcs0-(2760) with JP=0⁻ and Tcs2-(2900) with JP=2⁻. These near-threshold poles can be searched for at LHCb, Belle II and BESIII.