Research


The Observable Universe: probes of different epochs in its history.

What do I do?

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Opening Up New Windows to Study the Universe

The Standard Model of Cosmology aims to explains the cosmic evolution from a fraction of a second after the Big-Bang singularity to the current period of accelerated expansion with only a handful of parameters. Over the past decade, it has withstood a wide series of observational tests. Yet several gaping holes remain in the theory:
- How did inflation begin and come to an end?
- What makes up the dark matter in the Universe?
- What is the nature of dark energy?
- How did galaxies and clusters of galaxies form and evolve to make up the large scale structure we observe today?
Going forward, we must develop new ways to probe these fundamental questions by accessing the full volume of the observable Universe. This is the focus of my research.


For more details about my research, including links to relevant talks and publications, click on the topics below:

The Cosmic Microwave Background: Exploring the Early Universe

Why am I interested?

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The Cosmic Microwave Background

My interest in the CMB has been focused on cosmological Inflation, our best theoretical framework to explain why the Universe is flat, homogenous and isotropic, and most importantly how tiny quantum fluctuations are imprinted onto cosmic scales to provide primordial seeds for structure formation. The anisotropies in the CMB temperature can be used to test inflationary scenarios in various ways. Above all, the curl component (or B-mode) of the CMB polarization, a unique imprint of inflationary tensor fluctuations (or primordial gravitational waves), is a key prediction of many models of Inflation and is widely considered the holy grail of cosmology, as I reviewed in Kamionkowski and Kovetz (ARAA, 2016).

My focus of late has been on forecasting the ability of upcoming CMB experiments to probe a variety of features related to Inflation and Dark Matter.
With J. Munoz and colleagues, we laid out a novel second-order estimator of compensated isocurvature perturbations (Munoz et al. 2016) and investigated how well the running of the spectral index can be constrained (Munoz, Kovetz et al. 2017). Recently, with colleagues at JHU, IAS and Tel-Aviv, We performed an improved CMB analysis to search for dark matter–baryon scattering with a Rutherford cross section (a velocity dependence of v^-4) corresponding to a Coulomb-type interaction. In particular, we developed a new and robust prescription for incorporating the relative bulk velocity between the dark matter and baryon fluids into the standard linear Boltzmann calculation. Using an iterative procedure, we self-consistently include the effects of the bulk velocities in a cosmology in which dark matter interacts with baryons. Furthermore, we investigated how these constraints change when only a subcomponent of dark matter is interacting, with important implications for the dark-matter explanation of the recent anomalous 21cm absorption profile detected by the EDGES experiment at z~17.


Left: The 95% C.L. excluded region for the coefficient of the DM–proton momentum-transfer cross section as a function of DM mass, obtained by analyzing Planck 2015 data, when the interacting fraction fχ of the total DM energy density is fixed to (from the lightest to the darkest pink): 1, 0.1, and 0.01. From Boddy, Gluscevic, Poulin, Kovetz, Kamionkowski and Barkana (PRD, 2018).
Right: 68% confidence ellipses in the αs − βs plane for the S4 CMB experiment (purple), S4+DESI (yellow), and S4+SKA (blue). We show the current Planck constraint in green. In gray we plot the range predicted by slow-roll single-field inflation. The region above the dash-dotted black line could produce PBHs with masses Mpbh > 1e15 gr, if extrapolated to the smallest scales. From Munoz, Kovetz, Raccanelli, Kamionkowski and Silk (JCAP, 2017).

Related publications:
  • Munoz, Grin, Dai, Kamionkowski and Kovetz, PRD (2016): "Search for Compensated Isocurvature Perturbations with Planck Power Spectra"
  • Munoz, Kovetz, Raccanelli, Kamionkowski and Silk, JCAP (2017): "Towards a measurement of the spectral runnings"
  • Boddy, Gluscevic, Poulin, Kovetz, Kamionkowski and Barkana, PRD (2018): "A Critical Assessment of CMB Limits on Dark Matter–Baryon Scattering: New Treatment of the Relative Bulk Velocity"
  • Abadi and Kovetz, PRD (2021): "Can Conformally Coupled Modified Gravity Solve The Hubble Tension?"

    • Observation

    The quest to detect B-mode polarization is daunting, largely due to contamination from Galactic foregrounds. To confront this issue, I set out to construct adaptive survey strategies to efficiently balance the exploration vs. exploitation tradeoff, which shows up in surveys with partial sky coverage. As the measurement sensitivity depends on a multitude of factors, including instrumental noise, diffuse foregrounds, point sources and sample variance, I showed that it may be greatly improved by adaptively converging onto "cleaner" regions of sky for longer integration. I then proposed to dedicate a low-cost experiment to identifying such patches, so that they can be concentrated on in prolonged observations by more sensitive telescopes.
    An alternative approach to locating low-contamination sky patches beforehand is to develop means to identify the presence of Galactic dust contamination in CMB maps after they are generated. I introduced a unique such tool which uses tailored estimators to detect statistical anisotropy of the polarization orientation due to the large-scale coherence of the Galactic magnetic field.
    Top: A B-mode polarization map, exhibiting the characteristic swirling pattern (with opposite orientation around hot/cold spots). Bottom: A simulated B-mode map with constant polarization orientation, exhibiting a local hexadecapolar anisotropy, i.e. dominated by Fourier modes oriented at 45 degrees w.r.t. the polarization orientation. The departure from statistical isotropy due to a slowly-varying orientation angle can be captured with appropriate statistical estimators and used to identify dust foreground contamination. From Kamionkowski and Kovetz (ARAA, 2016).
    Related talks:

    Collaborations

    I have taken part and continue to be involved in the preparation of experimental proposals for future CMB missions to tackle the detection of B-modes, such as the CMB-S4 collaboration and ESA's CORE Satellite mission.
    Related collaboration papers:

    Line-Intensity Mapping: Astrophysics and Cosmology at High Redshifts

    Gravitational waves from Mergers of Compact Objects: a Powerful New Probe

    Odds and Ends