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Dhiraj Kumar Hazra
Physics faculty at the Institute of Mathematical Sciences (IMSc), Chennai, India

What is your name, affiliation, academic position, and job title?
Dhiraj Kumar Hazra, Physics faculty at the Institute of Mathematical Sciences (IMSc), Chennai, India.

What is your journey? (Where did you live, learn and work?)
I grew up in Asansol, West Bengal, India. I studied Bachelor of Science Physics at Jadavpur University. After that I moved to Harish Chandra Research Institute, Allahabad, India for an integrated Masters and PhD program. Before joining IMSc, I worked as a postdoctoral researcher at the Asia Pacific Centre for Theoretical Physics, Pohang, Korea, Laboratoire APC – PCCP, Université Paris Diderot, Paris, France, Istituto Nazionale Di Fisica Nucleare, Bologna, Italy and INAF – Osservatorio di astrofisica e scienza dello spazio di Bologna, Italy.

What is your field of research and/or what project are you involved in?
I work in the field of cosmology, where I explore the models and data related to early Universe and structure formation.
A significant part of my research till now has been dominated by inflationary cosmology where I build models and compare them with the data to address potential anomalies. At the same time, I also reconstruct the signature of new physics directly from the data in model independent ways. For the last few months, I have been exploring whether these anomalies and tensions are correlated in order to find a common solution from primordial physics.
Ionization of neutral hydrogen by high energetic sources, or reionization is another area of my interest. Here I mainly take a model independent approach to combine cosmic microwave background and the low redshift data. For the next few years, I will be closely following the consistency between James Webb Space Telescope results and existing results from the Cosmic Microwave Background (CMB) and neutral hydrogen observations.
During the last 3 years, I have been releasing the codes that are essential in studying cosmology (at master’s and PhD level). I plan to make the website –, a hub of codes in cosmology. While these codes do not represent my ongoing research, I treat this project as part of open-source movement.

How does CosmoVerse fit within those plans?
CosmoVerse creates a platform where cosmological tensions and the roles of systematics and new physics are discussed regularly. I think my present research and CosmoVerse objectives have a good overlap.

Which of your skills are you most proud of, or find most useful?
Model building and reconstruction. In an extended project, model independent reconstruction presents the possible hints of new physics in the data; and model building provides a theoretical/phenomenological source for the new physics. ‘One Spectrum’ as a solution to cosmological anomalies and tensions is an appropriate example of such reconstruction motivated model building.

What new skills would you like to learn in the next year?
I plan to explore the convolutional neural network and a few other aspects of deep learning that can be applied to the reconstruction of properties of the Universe.

What are the most exciting open questions in your research area?
The energy scale of inflation. We have already constrained the amplitude and tilt of the primordial spectrum. We also have detected B-mode spectrum from non-primordial sources. Given the upcoming space based and ground based surveys, I think we are very close to detecting primordial gravitational waves that can lead us directly to the inflation model.
Of course, it will be fascinating if we can solve a few other puzzles like dark energy, dark matter, cosmological constant problem, etc.

What advances or new results are you excited about or looking forward to?
As a theoretical physicist, I get excited about anomalies and tensions within and between datasets, simply because they provide the opportunity to hunt for new physics. In this regard, discrepancy between the Cosmic Microwave Background measurements and local measurements of H0 is interesting.

What is your view on cosmic tensions? How does your work connect with this open question in the community?
Actually, I am yet to pick a side in this debate. The views are divided into 2 major categories, new physics vs. systematics. Several works warn us regarding the systematics in the local Hubble measurements. Having said that, I will be happy if new physics emerges from these tensions.
Usually, modification of gravity and changes in dark energy equation of state are the most explored avenues in the search of new physics. I tried to take a different route. With my collaborators, I investigated whether a modification of the primordial spectrum can help reducing the tensions. Initial few efforts were not very successful. However, in a recent work with my collaborators, I addressed the question – ‘can CMB anomalies and the cosmological tensions be threaded together?’. We found that the anomalies and tensions are correlated and certain primordial spectrum – ‘One Spectrum’ can be a common solution to them. We find that ‘One Spectrum’ solves CMB lensing anomaly in a flat Universe and also increases H0 and reduces S8, which, in turn, makes the low redshift measurements more compatible to CMB.

In your career so far, at what point were you the most excited, and what were you excited about?
BICEP-2 results. For the first few months I really believed that BICEP had observed primordial B-modes. While that was bringing in tension with Planck temperature measurements, we proposed a model ‘Whipped Inflation’ that was very successful to solve the tension. So, I thought – that’s it, we did it. However, dust had other plans.

What is the biggest obstacle that is slowing down your research field right now?
Funding. There is not much funding available for cosmological surveys. In the last 10 years many brilliant mission proposals were turned down owing to the lack of funding.

What role do you think a community network like CosmoVerse can play in developing theoretical astroparticle physics and cosmology?
This is an interesting question. With the growth of this network, I think CosmoVerse members can put together a proposal for cosmological missions dedicated to resolve or to better understand the tensions. The network joins the expertise of theoretical physicists to experimentalists across different continents. Since scientists from various nationalities represent the network, a joint effort for missions with different space agencies involved will not be a difficult leap.

What’s your favourite food? Why?
Biriyani. Not sure why. I just love it. When I am in Italy, Tagliatelle Al Ragù is something I cannot miss.

Your favourite scientist and/or science fiction film?
Back to the future

How do you relax after a hard day of work?
Playing with my daughter; watching movies with my wife; cooking.

What non-physics interests do you have and want to share?
Computational biology. During the early months of COVID-19 pandemic, I extensively worked on models and data analysis of the reported data. This experience was enough to get me hooked into many other interesting problems in biology.
I like to play chess. My rating fluctuates between 1100-1250. Unfortunately, I am not able to go beyond this level. I have been told that I need to learn more theory of chess to proceed further. Maybe in the next decade…
Skywatching. I own a Dobsonian 6-inch telescope.
Photography. Here are some of my captures: I also take decent portrait photos (certified by my wife).
I used to paint at some point of time.

What do you hope to see accomplished scientifically in the next 50 years?
Observation of primordial B-mode.
Detection of dark matter.