Browsing by Author "Hazra, Dhiraj Kumar"

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    Cosmological parameter estimation with free-form primordial power spectrum
    (IUCAA, 2015-02) Hazra, Dhiraj Kumar; Shafieloo, Arman; Tarun, Sauradeep
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    Oscillation in the inflaton potential: Exact numerical analysis and comparison with the recent and forthcoming CMB datasets
    (2011-06-15) Aich, Moumita; Hazra, Dhiraj Kumar; Sriramkumar, L.; et al.
    Amongst the multitude of inflationary models currently available, models that lead to features in the primordial scalar spectrum are drawing increasing attention, since certain features have been found to provide a better fit to the CMB data than the conventional, nearly scale invariant, primordial spectrum. In this work, we carry out an exact numerical analysis of two models that lead to oscillations over all scales in the scalar power spectrum. We consider the model described by a quadratic potential which is superposed by a sinusoidal modulation and the recently popular axion monodromy model. Since the oscillations continue even onto smaller scales, in addition to the WMAP data, we also compare the models with the small scale data from ACT. Though, both the models, broadly, result in oscillations in the spectrum, interestingly, we find that, while the monodromy model leads to a considerably better fit to the data in comparison to the standard power law spectrum, the quadratic potential superposed with a sinusoidal modulation does not improve the fit to a similar extent. We also carry out forecasting of the parameters using simulated Planck data for both the models. We show that the Planck mock data performs better in constraining the model parameters as compared to the presently available CMB datasets.
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    Oscillations in the inflaton potential
    (2011-08-11) Hazra, Dhiraj Kumar
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    Primordial features due to a step in the inflaton potential
    (2010-05-12) Hazra, Dhiraj Kumar; et al.; Aich, Moumita; Jain, Rajeev Kumar
    Certain oscillatory features in the primordial scalar power spectrum are known to provide a better fit to the outliers in the cosmic microwave background data near the multipole moments of ℓ = 22 and 40. These features are usually generated by introducing a step in the popular, quadratic potential describing the canonical scalar field. Such a model will be ruled out, if the tensors remain undetected at a level corresponding to a tensor-to-scalar ratio of, say, r ≃ 0.1. In this work, in addition to the popular quadratic potential, we investigate the effects of the step in a small field model and a tachyon model. With possible applications to future datasets (such as PLANCK) in mind, we evaluate the tensor power spectrum exactly, and include its contribution in our analysis. We compare the models with the WMAP (five as well as seven-year), the QUaD and the ACBAR data. As expected, a step at a particular location and of a suitable magnitude and width is found to improve the fit to the outliers (near ℓ = 22 and 40) in all these cases. We point out that, if the tensors prove to be small (say, r . 0.01), the quadratic potential and the tachyon model will cease to be viable, and more attention will need to be paid to examples such as the small field models.
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    Primordial power spectrum from Planck
    (IUCAA, 2015-02) Hazra, Dhiraj Kumar; Shafieloo, Arman; Tarun, Sauradeep
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    Primordial power spectrum: a complete analysis with the WMAP nine-year data
    (IUCAA, 2015-02) Hazra, Dhiraj Kumar; Shafieloo, Arman; Tarun, Sauradeep