Publications

Here is a full list of my publications. You can also find my publications either here on arXiv or here on ADS. Below is a summary of different research projects that I have worked on.


Projects in Cosmology

Sparse decomposition of galaxies

Modeling galaxy shapes is important for various tasks. Simple light profiles such as Sersic profiles are helpful to capture the broad features of the galaxies and reduce them to a handful of numbers. More complex models include decomposition of galaxy images onto a basis set such as shapelets, which involve strictly an infinite number of coefficients. Along with Dr. Aswin Sankaranarayanan in the Department of Electrical and Computer Engineering, we adopt a novel technique to represent the galaxies. Using overcomplete Dictionaries instead of (in)complete basis sets, we attempt to find sparse representations for galaxies. The dictionaries that will be learned from a training set of images will provide a signal model which can then be used to separate the intrinsic galaxy image from the noise (denoising). By learning the joint distribution of coefficients given a dictionary, we can equip ourselves with a generative model for the galaxies.

This is still a work in progress.

Impact of Interpixel Capacitance on shear calibration bias

Interpixel Capacitance (IPC) refers to the cross-talk between pixels in hybrid-CMOS detectors such as those that will be used in WFIRST mission. IPC being a linear effect, affects both the PSFs and the galaxy images. While measuring the intrinsic galaxy shapes, the effect of PSF is corrected for, which should also correct for most of the effects due to IPC. However, because of the way we define shapes, the cancellation is not exact and some residual effect of IPC remains. In this study, we seek to find if it contributes significantly to the bias in the lensing shear measurements.

This is still a work in progress.

Impact of Interpixel Capacitance in WFIRST detectors on its PSFs

Accounting the effects of the point spread function (PSF) of a telescope is one of the most challenging tasks for weak gravitational lensing. Accurate knowledge of the PSF is thus an essential for surveys that attempt to obtain scientific conclusions from weak lensing. Future surveys such as WFIRST have strict PSF requirements in order to achieve their promise. Detector non-idealities downgrade the PSFs from being diffraction limited and introduce some variation in the PSFs. We studied one such detector non-ideality called the Interpixel Capacitance (IPC) in detail. IPC is a form of cross-talk between pixels. The effect of IPC is to broaden the PSF decreasing the effective resolution of the telescope and correlates the noise.

Using the WFIRST module in GalSim, we simulated realistic WFIRST PSFs in the bands that we care for weak lensing. Using our results on these simulated PSFs,we translated the PSF requirements into IPC requirements. Our work forms an important guideline in specifying the detector requirements. This work was done in collaboration with teams at the Jet Propulsion Laboratory, Pasadena and at the Goddard Space Flight Center, Maryland.

You can find our paper on this study here.

Impact of cosmic variance in weak lensing image simulations

In this work, we highlight the shortcomings of using a deep narrow sample as a training sample to obtain redshift-dependent shear calibration biases for large surveys. Using COSMOS catalog, which is the largest contiguous survey from the Hubble Space Telescope, we showed that individual redshift bins were dominated by a single (or few) overdensities and voids. Thus, they cannot be used to obtain the redshift-dependent calibration for shear estimates since the sample is dominanted by local environment and is not a representative sample of the Universe. We tried a few possible techniques to mitigate this effect, but nonetheless, the environment effects were too strong to obtain a useful training sample from COSMOS.

You can find our paper on this study here.


Project(s) in Quantum Information

Persistent Entanglement in Quantum Heisenberg spin-glass

A collection of spins or qubits will have a definite z-component of the total angular momentum. This conserved angular momentum component is also referred to as a particle-number. Definite-particle states are quantum states of the entire system with a definite particle-number. Earlier works have showed that that in the case of random one-particle states, the average entanglement between any two qubits decreases with the number of spins and that in the case of random two-particle states, the average entanglement between any two qubits decreases with the square of the number of spins. While this is true when averaged over all two-particle states, we find a special class of two-particle states, which can be obtained fron one-particle states, for which the average entanglement still scales inversely to the first power of the number of qubits. We also show that such states occur very naturally in systems such as the Heisenberg spin-glass. We provide both analytical and results from numerical simulations and distinguish these states from typical two-particle states.

You can find our paper on this study here.