CV and full scientific publication list (pdf).

Most of my scientific papers are available on ArXiv and/or ADS.

## Research activity

I am a theoretical astrophysicist and my research is mostly focused on comparing models and simulations with astronomical data, in order to advance our knowledge of the workings of the universe.

Currently, my main research interest is in astrobiology, the interdisciplinary study of the origin, evolution, distribution and future of life in the universe. I am working on models of planetary and galactic habitability, and on the search for biosignatures and technosignatures.

In the past I have done work in many areas of physical cosmology, including the analysis of the cosmic microwave background anisotropy, the large-scale structure of the universe, inflation, dark matter and dark energy.

Below is an annotated list (in rough inverse chronological order) of some of my past and present research projects.

- Supermassive black holes and planetary habitability
- Modeling the spatiotemporal distribution of observers in the universe
- Real-time cosmology
- Violations of isotropy
- Gravitational lensing of the cosmic microwave background
- Non-gaussianity of primordial perturbations
- Dark energy and integrated Sachs-Wolfe effect
- Unified models of dark matter and dark energy
- Dark energy and quintessence
- Planck (a cosmic microwave background satellite experiment)
- BOOMERANG (a cosmic microwave background ballon experiment)
- MAXIMA (a cosmic microwave background balloon experiment)
- Cosmic microwave background data analysis
- Thermal history of the universe

## Research projects

### Supermassive black holes and planetary habitability

There is a huge black hole at the center of the Milky Way, and at the beginning of its history it went through an active phase, which released large amounts of ionizing radiation in space. This might have had large-scale consequences on the habitability of planets in the galaxy, affecting their atmospheres and possibly their surface biosphere. This is one of the first studies on the subject, which I will explore further in ongoing work. (For press coverage of this study, see here, here, here and here)

- The habitability of the Milky Way during the active phase of its central supermassive black hole – Balbi, A., Tombesi, F.,
*NatSR*, 7, 16626 (2017)

### Modeling the spatiotemporal distribution of observers in the universe

The discovery of thousands of exoplanets has given new impulse to the search of technological species in the universe, whose presence we might infer through remote astronomical observations. With this goal in mind, it is crucial to produce realistic predictions of the number and distribution of such species, both in space and time. I started by producing a two-parameter temporal model that expands and complement the standard approach based on the Drake equation. More to come.

- The Impact of the Temporal Distribution of Communicating Civilizations on their Detectability – Balbi, A.,
*AsBio*, 18, 54 (2018)

### Real time cosmology

The idea, originally proposed by Allan Sandage in the 1960s, is that one can observe the evolution of cosmological redshift in time, by means of ultra-high precision spectroscopy. This can give interesting information on cosmological models as well as on the dynamics of bound objects. I explored the implications of the idea in a number of papers and summarized them in a review.

- Real-time cosmology – Quercellini, C., Amendola, L., Balbi, A., Cabella, P., Quartin, M.
*Physics Reports*, Volume 521, Issue 3, p. 95-134 (2012) - The time evolution of cosmological redshift as a test of dark energy – Balbi, A. and Quercellini, C.
*MNRAS*382, 1623 (2007) - Mapping the galactic gravitational potential with peculiar acceleration – Quercellini, C., Amendola, L., and Balbi, A.
*MNRAS*391, 1308 (2008) - Peculiar acceleration – Amendola, L., Balbi, A., and Quercellini, C.
*PhLB*660, 81 (2008) - Cosmic parallax as a probe of late time anisotropic expansion – Quercellini, C., Cabella, P., Amendola, L., Quartin, M., and Balbi, A.
*PhRvD*80, 063527 (2009)

### Gravitational lensing of the cosmic microwave background

Observing the effect of gravitational lensing of the cosmic microwave background produced by matter distribution in the universe can give important cosmological information. I explored this issue in the following papers.

- Neutrinos and dark energy constraints from future galaxy surveys and CMB lensing information – Santos, L., Cabella, P., Balbi, A., Vittorio, N.,
*PhRvD*, 88, 043505 (2013) - Forecasting isocurvature models with CMB lensing information: Axion and curvaton scenarios – Santos, L., Cabella, P., Balbi, A., Vittorio, N.,
*PhRvD*, 86, 023002 (2012)

### Violations of isotropy

CMB data from the WMAP satellite showed hints of possibile anomalies in the statistical isotropy of temperature fluctuations, one of the tenets of standard cosmology. This can be due to instrumental effects or to physical mechanisms. I investigated the issue in a number of papers.

- Quadrant asymmetry in the angular distribution of cosmic microwave background in the Planck satellite data – Santos, L., Cabella, P., Villela,

T., Balbi, A., Vittorio, N., Wuensche, C. A.,*A&A*, 569, A75 (2014) - Searching for a dipole modulation in the large-scale structure of the Universe – Fernández-Cobos, R., Vielva, P., Pietrobon, D., Balbi, A.,

Martínez-González, E., Barreiro, R. B.,*MNRAS*, 441, 2392 (2014) - Needlet bispectrum asymmetries in the WMAP 5-year data – Pietrobon, D., Cabella, P., Balbi, A., Crittenden, R., de Gasperis, G., and Vittorio, N.
*MNRAS*402, L34 (2010) - Needlet detection of features in the WMAP CMB sky and the impact on anisotropies and hemispherical asymmetries – Pietrobon, D., Amblard, A., Balbi, A., Cabella, P., Cooray, A., and Marinucci, D.
*PhRvD*78, 103504 (2008) - Cosmological parameters and the WMAP data revisited – Hansen, F. K., Balbi, A., Banday, A. J., and Górski, K. M.
*MNRAS*354, 905 (2004)

### Non-gaussianity of primordial perturbations

Inflationary models predict that density perturbations in the early universe have a non-gaussian statistics. Measuring the amount of non-gaussianity can constrain theoretical models. I investigated the issue through the analysis of CMB data.

- Foreground influence on primordial non-Gaussianity estimates: needlet analysis of WMAP 5-year data – Cabella, P., Pietrobon, D., Veneziani, M., Balbi, A., Crittenden, R., de Gasperis, G., Quercellini, C., and Vittorio, N.
*MNRAS*405, 961 (2010) - Constraints on primordial non-Gaussianity from a needlet analysis of the WMAP-5 data – Pietrobon, D., Cabella, P., Balbi, A., de Gasperis, G., and Vittorio, N.
*MNRAS*396, 1682 (2009) - Tests for Gaussianity of the MAXIMA-1 Cosmic Microwave Background Map – Wu, J. H. P., and 11 colleagues
*PhRvL*87, 251303 (2001)

### Dark energy and integrated Sachs-Wolfe effect

One of the ways of studing dark energy is through the imprint that the onset of the accelerating phase of the universe leaves on the CMB. This is called integrated Sachs-Wolfe effect, and can be observed by cross-correlating the CMB with large-scale structure data. I authored (with my then student Davide Pietrobon) one of the first studies finding evidences of this signal in the data, using a new statistical technique (courtesy of Domenico Marinucci).

- Integrated Sachs-Wolfe effect from the cross correlation of WMAP 3year and the NRAO VLA sky survey data: New results and constraints on dark energy – Pietrobon, D., Balbi, A., and Marinucci, D.
*PhRvD*74, 043524 (2006)

### Unified models of dark matter and dark energy

According to some theoretical models, dark matter and dark energy may be the same thing under different form. Our analyses showed that this might be the case, but observations available at the time could not tell the difference from alternative explanations.

- Affine parametrization of the dark sector: Constraints from WMAP5 and SDSS – Pietrobon, D., Balbi, A., Bruni, M., and Quercellini, C.
*PhRvD*78, 083510 (2008) - Late universe dynamics with scale-independent linear couplings in the dark sector – Quercellini, C., Bruni, M., Balbi, A., and Pietrobon, D.
*PhRvD*78, 063527 (2008) - ΛαDM: Observational constraints on unified dark matter with constant speed of sound – Balbi, A., Bruni, M., and Quercellini, C.
*PhRvD*76, 103519 (2007) - Affine equation of state from quintessence and k-essence fields – Quercellini, C., Bruni, M., and Balbi, A.
*CQGra*24, 5413 (2007)

### Dark energy and quintessence

One of the possible explanations of dark energy is that it is caused by the presence of a fundamental field called “quintessence”. The advantage of these models is that they may alleviate the so-called “coincidence problem”, that is the weird fact that the vacuum energy density have begun to dominate with respect to the density of matter roughly at present time.

- Scalar field dark energy and cosmic microwave background– Baccigalupi, C., Balbi, A., Matarrese, S., Perrotta, F., and Vittorio, N.
*NuPhS*124, 68 (2003) - Probing Dark Energy with the Cosmic Microwave Background: Projected Constraints from the Wilkinson Microwave Anisotropy Probe and Planck – Balbi, A., Baccigalupi, C., Perrotta, F., Matarrese, S., and Vittorio, N.
*ApJ*588, L5 (2003) - Constraints on flat cosmologies with tracking quintessence from cosmic microwave background observations – Baccigalupi, C., Balbi, A., Matarrese, S., Perrotta, F., and Vittorio, N.
*PhRvD*65, 063520 (2002) - Implications for Quintessence Models from MAXIMA-1 and BOOMERANG-98 – Balbi, A., Baccigalupi, C., Matarrese, S., Perrotta, F., and Vittorio, N.
*ApJ*547, L89 (2001)

### Planck

Planck was an ESA space mission designed to observe the CMB to unprecedented details. I started collaborating to Planck in 1996 (when it was still in the study phase) and continued until 2012, with the intermediate data release, contributing to many of the procedures that were used to analyze its data, and to extract its scientific consequences.

- Planck early results. I. The Planck mission – Planck Collaboration, and 274

colleagues, A&A, 536, A1 (2011) - Optimising Boltzmann codes for the PLANCK era – Hamann, J., Balbi, A., Lesgourgues, J., and Quercellini, C.
*JCAP*4, 11 (2009) - Making maps from Planck LFI 30 GHz data – Ashdown, M. A. J., and 18 colleagues
*A&A*471, 361 (2007) - Making sky maps from Planck data – Ashdown, M. A. J., and 18 colleagues
*A&A*467, 761 (2007) - Cosmology from Planck – Balbi, A.
*NewAR*51, 281 (2007) - CMB power spectrum estimation for the Planck Surveyor – Balbi, A., de Gasperis, G., Natoli, P., and Vittorio, N.
*A&A*395, 417 (2002)

### BOOMERANG

I briefly collaborated to the second phase of the BOOMERANG balloon experiment, that studied the polarized component of the cosmic microwave background.

- BOOMERanG results – Polenta, G., and 41 colleagues
*AdSpR*36, 1064 (2005) - Measuring CMB polarization with Boomerang – Montroy, T., and 40 colleagues
*NewAR*47, 1057 (2003) - BOOMERANG returns – Mauskopf, P. D., and 40 colleagues
*NewAR*47, 733 (2003)

### MAXIMA

MAXIMA was a balloon-borne experiment that produced, in 2000, one of the first high-resolution images of the cosmic microwave background temperature fluctuations. MAXIMA results put precise constraints on cosmological models, showing that we live in a universe with flat geometry. I gave a relevant contribution to all of MAXIMA scientific results and data analysis, and I was the first author of the cosmological parameter paper. Here is MAXIMA official press release with a summary of results. Other non-technical information can be found here and here and in articles that appeared on Physics Today and Scientific American. MAXIMA results also got strong coverage in the press, with articles on The San Francisco Chronicle, The Economist, The New York Times, The Washington Post and again The New York Times. The PBS show NOVA discussed MAXIMA in one of its episodes.

- Constraints on Cosmological Parameters from MAXIMA-1 – Balbi, A., and 18 colleagues
*ApJ*545, L1 (2000) - MAXIMA-1: A Measurement of the Cosmic Microwave Background Anisotropy on Angular Scales of 10′-5° – Hanany, S., and 21 colleagues
*ApJ*545, L5 (2000) - Cosmology from MAXIMA-1, BOOMERANG, and COBE DMR Cosmic Microwave Background Observations – Jaffe, A. H., and 41 colleagues
*PhRvL*86, 3475 (2001) - Cosmological Implications of the MAXIMA-1 High-Resolution Cosmic Microwave Background Anisotropy Measurement – Stompor, R., and 19 colleagues
*ApJ*561, L7 (2001) - A High Spatial Resolution Analysis of the MAXIMA-1 Cosmic Microwave Background Anisotropy Data – Lee, A. T., and 19 colleagues
*ApJ*561, L1 (2001) - MAXIMA: A balloon-borne cosmic microwave background anisotropy experiment – Rabii, B., and 22 colleagues
*RScI*77, 071101 (2006) - Determining Foreground Contamination in Cosmic Microwave Background Observations: Diffuse Galactic Emission in the MAXIMA-I Field – Jaffe, A. H., and 13 colleagues
*ApJ*615, 55 (2004) - Multiple methods for estimating the bispectrum of the cosmic microwave background with application to the MAXIMA data – Santos, M. G., and 13 colleagues
*MNRAS*341, 623 (2003) - Frequentist estimation of cosmological parameters from the MAXIMA-1 cosmic microwave background anisotropy data – Abroe, M. E., and 14 colleagues
*MNRAS*334, 11 (2002) - Estimate of the Cosmological Bispectrum from the MAXIMA-1 Cosmic Microwave Background Map – Santos, M. G., and 13 colleagues
*PhRvL*88, 241302 (2002)

### Cosmic microwave background data analysis

Extracting cosmological information from CMB data is challenging and computing-intensive. Some of my research activity was devoted to finding new algorithms, statistical techniques and tools to maximize the scientific output of observations.

- NeedATool: A Needlet Analysis Tool for Cosmological Data Processing – Pietrobon, D., Balbi, A., Cabella, P., & Gorski, K. M.,
*ApJ*, 723, 1 (2010) - Spherical needlets for cosmic microwave background data analysis – Marinucci, D., and 8 colleagues
*MNRAS*383, 539 (2008) - Comparison of map-making algorithms for CMB experiments – Poutanen, T., and 14 colleagues
*A&A*449, 1311 (2006) - Unbiased estimation of an angular power spectrum – Polenta, G., Marinucci, D., Balbi, A., de Bernardis, P., Hivon, E., Masi, S., Natoli, P., and Vittorio, N.
*JCAP*11, 1 (2005) - ROMA: A map-making algorithm for polarised CMB data sets – de Gasperis, G., Balbi, A., Cabella, P., Natoli, P., and Vittorio, N.
*A&A*436, 1159 (2005) - Making maps of the cosmic microwave background: The MAXIMA example – Stompor, R., and 12 colleagues
*PhRvD*65, 022003 (2002) - Asymmetric Beams in Cosmic Microwave Background Anisotropy Experiments – Wu, J. H. P., and 12 colleagues
*ApJS*132, 1 (2001)

### Thermal history of the universe

The universe went through different physical phases, as its temperature changed from the big bang to the present epoch due to the expansion of space. Some of the pivotal moments in the history of the cosmos (such as the synthesis of light nuclei, or the formation of neutral hydrogen atoms, or of the ignition of the first stars) can be explored through cosmological observations. I addressed the study of the thermal history of the universe in some of my earliest scientific papers.

- On the Primordial Helium Content: Cosmic Microwave Background and Stellar Constraints – Bono, G., Balbi, A., Cassisi, S., Vittorio, N., and Buonanno, R.
*ApJ*568, 463 (2002) - Secondary CMB anisotropies from the kinetic SZ effect – Valageas, P., Balbi, A., and Silk, J.
*A&A*367, 1 (2001) - Cosmic Microwave Background Anisotropy at Degree Angular Scales and the Thermal History of the Universe – de Bernardis, P., Balbi, A., de Gasperis, G., Melchiorri, A., and Vittorio, N.
*ApJ*480, 1 (1997)