Khandro K. Chokyi, Surajit Chattopadhyay
Abstract We examine non-singular bounce cosmology within the framework of a phantom scalar field coupled to the Gauss–Bonnet term in both non-viscous and bulk-viscous cases. Using the scale factor ansatz $$\alpha (t)=\left( \frac{\alpha }{\eta }+t^2\right) ^{\frac{1}{2 \eta }}$$ α ( t ) = α η + t 2 1 2 η , we reconstruct the scalar field potential V ( t ), and observe a smooth potential well centered at the bounce point. The resulting energy density, pressure, and equation-of-state parameter show NEC violation necessary for successful bounce, while viscosity controls post-bounce dynamics with a positive and smooth squared speed of sound. In contrast, for the non-viscous model, sharp divergences occur just at the bounce and continues to be negative in the expanding phase, which in turn emphasises the stabilising role of dissipative effects. The energy condition analysis indicates a temporary NEC and SEC violation in the viscous scenario, whereas its persistent violation within the non-viscous model suggests a continuous accelerated expansion. Observational viability is found through Bayesian MCMC fitting in regards to the Pantheon+ supernova data, with best-fit parameters providing a reduced chi-squared of $$\chi _{red}^2 =0.995$$ χ red 2 = 0.995 while the inflation observables derived from the reconstructed potential place our model predictions inside $$68\%$$ 68 % CL Planck 2018 confidence contours. Our findings suggest that bounce cosmologies could offer a physically reasonable and observationally acceptable alternative or pre-inflationary scenario, while highlighting the role that viscosity could play for a stable and smooth cosmological evolution.