We investigate the prospect of constraining scalar field dark energy models using HI 21-cm intensity mapping surveys. We consider a wide class of coupled scalar field dark energy models whose predictions about the background cosmological evolution are different from the ΛCDM predictions by a few percent. We find that these models can be statistically distinguished from ΛCDM through their imprint on the 21-cm angular power spectrum. At the fiducial z = 1.5, corresponding to a radio interferometric observation of the post-reionization HI 21 cm observation at frequency 568MHz, these models can infact be distinguished from the ΛCDM model at SNR > 3σ level using a 10,000 hr radio observation distributed over 40 pointings of a SKA1-mid like radio-telescope. We also show that tracker models are more likely to be ruled out in comparison with ΛCDM than the thawer models. Future radio observations can be instrumental in obtaining tighter constraints on the parameter space of dark energy models and supplement the bounds obtained from background studies.

In standard cosmologies, dark energy interacts only gravitationally with dark matter. An extension to this picture is interacting quintessence (IQ) model where scalar field coupled directly to cold dark matter. The percentage deviation is studied in IQ model wrt ΛCDM for varied values of interacting parameter W. We investigated the effect of interaction on matter , kaiser and galaxy power spectrums. Deviation in power spectrum increases with interaction on both large and small scales. On small scale, variation is comparatively smaller than on large scale. On large scale ,it is due to dark energy perturbation while it is background evolution that causes a difference on small scale. These variations decreases with increase in redshift. Herein thawing class of model with linear potential is studied. I. INTRODUCTIONThe late time acceleration in the standard Einstein gravity is propelled by a mysterious energy component which consist of a huge negative pressure that expands the Universe. This is called dark energy [1][2][3][4]. Keeping in mind the standard cosmological model, the DE undertake the simplest form of cosmological constant Λ, which has absolutely no spatial fluctuations but a negative pressure and constant energy density which covers the entire expansion history of the Universe.That leads to ΛCDM model. Cosmic Microwave Background (CMB) [5] , Supernova Type-Ia (SnIa) (SnIa) [6], Baryon Acoustic oscillation (BAO) measurement in galaxy surveys [7] : can be demonstrated via ΛCDM model . However, it gets into serious conceptual problems like " fine tuning problem " [8] and "coincidence problem" [9,14]. Recent observational results also indicate inconsistency with ΛCDM model [10][11][12][13].In order to solve these problems, a number of scalar field models including quintessence [15][16][17][18][19][20][21][22][23][24][25][26][27], phantom field [28-32], rolling tachyon [33-36] and others have been proposed. Another way to look at this problem is through interaction between dark energy and other matter species in the * Electronic address: azamhussain@ctp-jamia.res.in