Resonating delay equation

We propose here a delay differential equation that exhibits a new type of resonating oscillatory dynamics. The oscillatory transient dynamics appear and disappear as the delay is increased between zero to asymptotically large delay. The optimal height of the power spectrum of the dynamical trajectory is observed with the suitably tuned delay. This resonant behavior contrasts itself against the general behaviors where an increase of delay parameter leads to the persistence of oscillations or more complex dynamics.

Hilltop Inflation and Generation of Helical Magnetic Field

Primordial magnetic field generated in the inflationary era can act as a viable source for the present day intergalactic magnetic field of sufficient strength. We present a fundamental origin for such a primordial generation of the magnetic field, namely through anomaly cancellation of U(1) gauge field in quantum electrodynamics in the context of hilltop inflation. We have analysed at length the power spectrum of the magnetic field, thus generated, which turns out to be helical in nature. We have also found that magnetic power spectrum has significant scale-dependence giving rise to a non-trivial magnetic spectral index, a key feature of this model. Interestingly, there exists a large parameter space, where magnetic field of significant strength can be produced.

Large power spectrum and primordial black holes in the effective theory of inflation

We study the generation of a large power spectrum, necessary for primordial black hole formation, within the effective theory of single-field inflation. The mechanisms we consider include a transition into a ghost-inflation-like phase and scenarios where an exponentially growing mode is temporarily turned on. In the cases we discuss, the enhancement in the power spectrum results from either a swift change in some effective coupling or a modification of the dispersion relation for the perturbations, while the background evolution remains unchanged and approximately de Sitter throughout inflation. The robustness of the results is guaranteed thanks to a weakly broken galileon symmetry, which protects the effective couplings against large quantum corrections. We discuss how the enhancement of the power spectrum is related to the energy scale of the operators with weakly broken galileon invariance, and study the limits imposed by strong coupling and the validity of the perturbative expansion.

Constraining beyond ΛCDM models with 21cm intensity mapping forecasted observations combined with latest CMB data

We explore constraints on dark energy and modified gravity with forecasted 21cm intensity mapping measurements using the Effective Field Theory approach. We construct a realistic mock data set forecasting a low redshift 21cm signal power spectrum P 21(z,k) measurement from the MeerKAT radio-telescope. We compute constraints on cosmological and model parameters through Monte-Carlo Markov-Chain techniques, testing both the constraining power of P 21(k) alone and its effect when combined with the latest Planck 2018 CMB data. We complement our analysis by testing the effects of tomography from an ideal mock data set of observations in multiple redshift bins. We conduct our analysis numerically with the codes EFTCAMB/EFTCosmoMC, which we extend by implementing a likelihood module fully integrated with the original codes. We find that adding P 21(k) to CMB data provides significantly tighter constraints on Ωc h 2 and H 0, with a reduction of the error with respect to Planck results at the level of more than 60%. For the parameters describing beyond ΛCDM theories, we observe a reduction in the error with respect to the Planck constraints at the level of ≲ 10%. The improvement increases up to ∼ 35% when we constrain the parameters using ideal, tomographic mock observations. We conclude that the power spectrum of the 21cm signal is sensitive to variations of the parameters describing the examined beyond ΛCDM models and, thus, P 21(k) observations could help to constrain dark energy. The constraining power on such theories is improved significantly by tomography.

Potential reconstruction from general power spectrum in single-field inflation

We suggest a new method to reconstruct, within canonical single-field inflation, the inflaton potential directly from the primordial power spectrum which may deviate significantly from near scale-invariance. Our approach relies on a more generalized slow-roll approximation than the standard one, and can probe the properties of the inflaton potential reliably. We give a few examples for reconstructing potential and discuss the validity of our method.