Ph.D. Projects:

Phase transitions during inflation and hemispherical asymmetry.

Sub-Planckian inflation models with large tensor-to-scalar ratio.

The dark matter-baryon asymmetry connection.

My research area is the intersection of particle physics and cosmology, known as particle cosmology or astro-particle physics.

My past and present research interests include:

Dark matter models (thermal relic MSSM neutralino and non-thermal gravitino dark matter, Higgs portal gauge singlet scalar dark matter, RH sneutrino condensate dark matter, alternative thermal production ("freeze-in") mechanisms for MeV and keV dark matter), the cosmology of the minimal supersymmetric standard model (MSSM) and its extensions (flat directions, Affleck-Dine baryogenesis and leptogenesis, Q-ball formation and decay, curvatons and right-handed sneutrinos), inflation models (non-minimally coupled scalar inflation ("Higgs Inflation"), sub-Planckian axion inflation, supersymmetric hybrid inflation models, oscillon formation and reheating) and baryogenesis (Affleck-Dine, electroweak, baryon-to-dark matter ratio ("Baryomorphosis")).

My most recent research focuses on the following themes:

(i) Hemispherical asymmetry of the CMB temperature fluctuations

The cosmic microwave background radiation (CMB) is the remnant radiation from the Big Bang. It has a mean temperature T = 2.725 K, on top of which there are temperature fluctuations of magnitude about 1/10000 of the mean temperature. Analysis of the temperature fluctuations observed by NASA's Wilkinson Microwave Anisotropy Probe (WMAP) and ESA's Planck satellite have found that there is an asymmetry in the magnitude of the temperature fluctuations observed on one side of the sky compared to the opposite side, with a 12-14% difference. This is known as the Hemispherical Power Asymmetry. It is not expected to exist in conventional cosmology models, which predict a difference of no more than 6%. I am presently studying unconventional models based on cosmological phase transitions which occur during inflation, which are able to generate an asymmetric scalar field on the scale of the observed Universe. The hope is that this field may be able modulate the CMB temperature fluctuations across the sky, without introducing unwanted features such as a change in the statistics of the microwave fluctuations or a change in the mean CMB temperature.

[Publications: "Isocurvature and Curvaton Perturbations with Red Power Spectrum and Large Hemispherical Asymmetry", arXiv:1305.0525 [astro-ph.CO], JCAP 1307 (2013) 043; "Hemispherical Power Asymmetry from Scale-Dependent Modulated Reheating", arXiv:1309.1122 [astro- ph.CO], JCAP 1311 (2013) 041; "Hemispherical Power Asymmetry from a Space-Dependent Component of the Adiabatic Power Spectrum", arXiv:1403.2076 [astro-ph.CO], Phys.Rev. D89 (2014) 127303; "Negative Running of the Spectral Index, Hemispherical Asymmetry and the Consistency of Planck with Large r", arXiv:1403.6650 [astro-ph.CO], JCAP 1411 (2014) 012.]

(ii) Sub-Planckian inflation models with a large gravitational wave signature

Inflation might be able to generate primordial gravitational waves, whose detection would serve as a 'smoking gun' for inflation as the explanation of the observed structure of the Universe. However, in order to generate a large gravitational wave signal, the simplest inflation models require scalar fields which are larger than the Planck scale, the scale at which quantum gravity effects become large and the new physics associated with the unification of gravity and other particles and forces is expected to become important. Therefore conventional inflation theories which can generate a large gravitational wave signal are expected to break down. This raises the question of whether it is possible to construct inflation models which can generate a large gravitation wave signal but which do not require scalar field values larger than the Planck scale. I am studying field theory inflation models based on simple axion models which achieve this and which make clear predictions for both the magnitude of the gravitational wave signal ("tensor-to-scalar ratio") and the slope of CMB fluctuation spectrum ("scalar spectral index").

[Publications: "Sub-Planckian Two-Field Inflation Consistent with the Lyth Bound", arXiv:1404.4620 [hep-ph], JCAP 1409 (2014) 09, 027; "A Minimal Sub-Planckian Axion Inflation Model with Large Tensor-to-Scalar Ratio", arXiv:1407.7471 [hep-ph], JCAP 1501 (2015) 018; "Signatures of Planck Corrections in a Spiralling Axion Inflation Model", arXiv:1412.6943 [hep-ph].]