# Past events

RECENT ACTIVITIES

*Wednesday, May 17th, 2017 - Department of Physics, University of Milan - 3:30pm*

**Post-Born effects and all-sky mock catalogs for CMB-lensing** by Matteo Calabrese

I will present a complete study of the gravitational lensing effect beyond-the-Born-approximation on the Cosmic Microwave Background (CMB) anisotropies. The study exploits ray-tracing techniques to follow the photons’ path from the last scattering surface, as they travel throughout an all-sky lightcone built by compressing the matter distribution of N-Body numerical simulations into a set of lensing shells. The impact of second-order effects accounts for the non-linear evolution of large-scale structures, and it is evaluated by propagating the full CMB lensing Jacobian together with the light rays trajectory. I will show the robustness of the approach against several numerical effects both in the ray-tracing procedure and in the N-body simulation, finding no evidence of large contaminations of the signal. I will show the impact of post-Born CMB observables, comparing the results with recent analytical corrections on lensed predictions, and discussing the detection prospect of post-Born effects in future CMB experiments. Finally, I will apply the simulation pipeline to model the cross-correlation between CMB lensing and large scale structure tracers, by means of all-sky, galaxy mock catalogues. The simulated signal can enable a thorough investigation of structure formation over cosmic time, thus mimicking possible measurements from the forthcoming ESA-mission Euclid.

*Wednesday, April 5th, 2017 - Aula Caldirola, Department of Physics - 3:30pm*

** A microscopic theory for cosmic structure formation **by** **Matthias Bartelmann (Heidelberg University)

*Thursday, April 6th, 2017 - Aula Caldirola, Department of Physics - 4pm*

**Lessons from gravitatinal lensing **by** **Matthias Bartelmann (Heidelberg University)

Even though we do not know what the dark matter is composed of, we have a clear idea of how much there is, and where, in the Universe. Much of this knowledge is derived from gravitational light deflection, or gravitational lensing, which does not need any symmetry or equilibrium assumptions to reveal the matter distribution in cosmic structures and its evolution throughout cosmic history. In this talk, I shall briefly review the foundations of gravitational lensing and then discuss several examples of its application from the smallest to the largest scales in the hierarchy of cosmic objects.

*Friday, March 17th, 2017 - Aula Caldirola, Department of Physics - 11:30am*

**Testing gravity with small scale redshift space galaxy clustering **by Jianhua He (Durham University)

Understanding the nature of gravity is one of the most important motivations of future large galaxy surveys such as Euclid and DESI. Although the accuracy of the measurements of galaxy clustering has been improved dramatically during the past decade, approaching percent level, there are still some challenges to make a final conclusion of theory of gravity and tell the fate of the Universe. This is largely due to the potential systematics in observations and uncertainties in theories.

In this talk, I will talk about major challenges and systematics in testing gravity on cosmological scales and also discuss possible ways to get around them. My talk has three parts. In the first part, I will talk about the challenges on the theory side. In the second part, I will talk about systematics in real data and how to mitigate them. In the last part, I will compare theory with data and show that predictions in LCDM match data very well. Therefore, the possibilities of modified theories of gravity are diminished.

**Tuesday 8 November 2016, Department of Physics, Milan, Via Celoria 16, 2:30pm**

**Critical Tests of Theory of the Early Universe using the CMB** by Eiichiro Komatsu

The Cosmic Microwave Background (CMB), the fossil light of the Big Bang, is the oldest light that one can ever hope to observe in our Universe. The CMB provides us with a direct image of the Universe when it was still an “infant” - 380,000 years old - and has enabled us to obtain a wealth of cosmological information, such as the composition, age, geometry, and history of the Universe. Yet, can we go further and learn about the primordial universe, when it was much younger than 380,000 years old, perhaps as young as a tiny fraction of a second? If so, this gives us a hope to test cosmic inflation, the leading paradigm on the origin of our Universe at ultra high energies. In my talk I will review the physics of temperature and polarization anisotropies of the CMB and the key results from the recent experiments, and discuss future prospects on our quest to probe the physical conditions of the very early Universe.

**Monday 19 and Wednesday 21 September 2016, Library, Merate, 2pm-5pm**

**CosmoMC course** by Jason Dossett

With the wealth of available cosmological observables, we have entered into an era of precision cosmology. By combining multiple cosmological probes we are able to place tight constraints on our cosmological parameters. In order to fit theory to observation and constrain our cosmological parameters quickly we take advantage of modern computing and write programs to do this. One of the state of the art programs to do this is CosmoMC (Cosmological Monte Carlo). This program consists of two parts CAMB (Code for Anisotropies in the Microwave Background), which calculates the CMB anisotropies, the matter power spectrum, as well as the expansion history for a given set of cosmological parameters; and CosmoMC itself which is a sampling program that uses an MCMC sampling algorithm to explore the cosmological parameter space and computes the likelihoods for various cosmological observables.

*Wednesday, 2o July 2016 - Merate (Library) - 11am*

**The Warm Dark Matter Power Spectrum** by Dida Markovič

Warm Dark Matter (WDM) is a generalisation of the standard Cold Dark Matter model in the sense that it does not assume dark matter particles to be absolutely cold. In the simplest models all dark matter is made of the same particles, which started out in thermal equilibrium and cooled to effectively become cold today. If such particles have masses of the order of a keV or less, they leave an observable imprint on the dark matter density field. At late times, the perturbations in the matter density field become non-linear. This means that they cannot be described perturbatively any longer. For this reason, N-body simulations are a good way to understand the formation of non-linear structure. Simulating WDM can be a challenge, because unlike CDM, it’s relatively large thermal velocities can introduce unwanted Poisson noise on small scales. With better computing resources nowadays it has become possible to examine WDM cosmologies with simulations. This talk will summarise some of the results of such simulations. It will outline some of the methods developed for calculating non-linear corrections to the matter power spectrum, which describes the matter density field today.

**Wednesday, 8 June 2016 - Merate, POE - 11am**

Optimal measurements of the power-spectrum of the Universe by Lado Samushia

The power spectrum of galaxies provides invaluable information about dark energy, gravity and initial conditions of the Universe. It is therefore extremely important that we measure it in the most optimal way possible, especially given that the total cosmological volume available to galaxy surveys is limited. My talk will be based on a recent work by my group that looks into the ways of measuring the power-spectrum when multiple galaxy types are present in the overlapping volume. We developed a weighting scheme that can reduce the variance of key measured cosmological parameters, such as e.g. the growth rate, by up to 40 per cent.

**Tuesday, 10 May 2016 - Merate, POE - 2pm**

Cosmology with a massive multi-tracer survey of large-scale structure by Luis Raul Abramo

The J-PAS survey will map the 3D structure of the cosmic web to unprecedented depth, completeness and redshift accuracy. It will determine, over 1/5 of the observable sky, the positions of hundreds of millions of galaxies up to z=1.2, and of millions of quasars up to at least z=4. Besides the greatly improved constraints on the nature of dark energy (with a Figure of Merit in the hundreds), J-PAS will study the large-scale structures in the regime of very high-completeness, when dark matter halos are traced by large numbers of galaxies of different types. J-PAS will be the first survey to take full advantage of the different clustering strengths associated with different tracers of large-scale structure, enhancing our understanding of the halo occupation distribution of galaxies, their bias, as well as redshift-space distortions and primordial non-Gaussianities. In order to take advantage of this new feature of forthcoming surveys, we have developed the generalization of the Feldman-Kaiser-Peacock weighting scheme, obtaining the optimal estimators that should be used in the Fourier analysis of the next generation of galaxy surveys. Finally, I will illustrate how multi-tracer surveys can impose vastly improved constraints on parameters such as $f_{NL}$, as well as on modified gravity theories.

*Tuesday, 15 March 2016 - Merate, POE - 11am*

Slices and Folds in the Cosmos by Mark Neyrinck

In the current cosmological paradigm, an initially flat three-dimensional manifold that pervades space (the 'dark-matter sheet') folds up to build concentrations of mass (galaxies), and a cosmic web between them. Galaxies are nodes, connected by a network of filaments and walls. The folding is in six-dimensional (3D position, plus 3D velocity) phase space. The positions of creases, or caustics, mark the edges of structures.

**Tuesday, 1 March 2016 - Brera (Cupola Fiore) - 2pm**

**Spectroscopic Studies of Galaxies in the Heart of the Reionization Era** by Richard Ellis

Deep exposures with the Hubble Space Telescope (HST) have provided the primary evidence that star-forming galaxies were present in the first billion years of cosmic history. Sometime during this early period the intergalactic medium transitioned from a neutral gas to one that is fully ionized. How did this `cosmic reionization' occur and were star-forming galaxies responsible? Imaging of deep fields with HST's Wide Field Camera 3 in conjunction with Spitzer photometry and Keck spectroscopy has provided important new insight into understanding when reionization occurred and the role of early galaxies in the process. Recent Planck results on the optical depth of electron scattering to CMB photons provide complementary information. I will review this rapid progress in our understanding of the last missing piece in our overall picture of cosmic history and discuss the remaining challenges ahead of future facilities such as JWST and E-ELT.

**Tuesday, 16 February 2016 - Merate, POE - 11am**

**Constraining gravity theories on cosmological scales** by Valentina Salvatelli

Understanding how gravity works on scales larger than the Solar system is one of the biggest challenges of modern cosmology. Some interesting results have been found in recent experiments, like PLANCK, and more precise tests will be enabled by ongoing and future large-scale surveys. In this context the search for efficient ways to test systematically a broad class of gravity theories is crucial to succeed in probing gravity with cosmological data. In this talk I will summarize the state-of-the-art of the cosmological gravity constraints, I will present the Effective Field Theory of Dark Energy (EFT) as promising framework to explore gravity theories and I will show some of the results we can obtain by applying this formalism.

***

**OLDER ACTIVITIES**

*Wednesday, 9 December 2015 - ***Multi-Wavelenght Synergies To Test the Fundaments of Cosmology** by Stefano Camera

*Wednesday, 23 September 2015 -* **1-day workshop: Science with LSS and CMB cross-correlations**

XC-Day_Program / XC-Day Presentations

*Wednesday, 24 June 2015 - ***On-the-fly Cosmology in the European-Extremely Large Telescope Era** by Marco Landoni

*Thursday, 18 June 2015 - ***Planck 2015: Implications for Cosmology** by Michele Liguori

*Wednesday, 15 April 2015 - ***Studying the Universe from Deep Underground **by Davide Trezzi

*Thursday, 26 March 2015 -* **Cosmological tests of gravity: A parameterized approach** by Jason Dossett

*Thursday, 26 February 2015 -* **On initial conditions for cosmological N-body simulations and gauge issues on large scales** by Wessel Valkenburg

*Wednesday, 11 February 2015 - ***21cm cosmology: modeling the neutral hydrogen distribution in the post-reionization era **by Francisco Villaescusa-Navarro

*Thursday, 29 January 2015 -* **From data to theory at the cosmic dawn **by Paul Sutter

*Friday, 28 November 2014 -* **Astronomy in the era of the LSST: understanding our universe a bit at a time** by Andy Connolly

*Monday, 24 November 2014 - ***Running many many cosmological simulations** by Jun Koda

*Wednesday, 19 November 2014 - ***Much Ado About Nothing: a Void Review** by Rien van de Weijgaert

*Wednesday, 12 November 2014** - ***Recent Progress in Large-Scale Structure** by Roman Scoccimarro

*Thursday, 16 October 2014 -** ***The Morphology of Large-Scale Structure using Minkowski Functionals** by Carlo Schimd

*Wednesday, 1st October 2014 - ***Clustering with angular cross-correlations: Combining Spectroscopic and Photometric Galaxy Surveys** by Enrique Gaztanaga

*21/25 July 2014 - Sexten Center for Astrophysics - *

**Measuring and Modelling Redshift-Space Distortions in Galaxy Surveys**- Darklight Workshop

*Wednesday, 2 July 2014 -** ***Star formation in dark matter halos** by Aurélie Penin

*Wednesday, 18 June 2014 -** ***An accurate tool for the fast generation of dark matter halo catalogues** by Pierluigi Monaco

*Tuesday, 27 May 2014 - *

**Novel Clustering Measures in Redshift Surveys**by Ravi Sheth

*Tuesday, 13 May 2014 - *

**, by Luigi Guzzo**

**DARKLIGHT***Thursday, 20 March 2014 – *

**Latest Baryon Acoustic Oscillation Measurements from BOSS**, by Will Percival

*Sunday, 16 March 2014 - *

**L’espansione dell’universo e l’enigma dell’energia oscura**, by Luigi Guzzo

*Thursday, 13 March 2014 - ***Infrared Galaxies in the AKARI eye**, by Kasia Malek

*Wednesday, 05 March 2014 - ***Growth Index of Cosmological Perturbations and the Effective Field Theory**, by Heinrich Steigerwald

*Wednesday, 26 February 2014 - ***Gravitational Lensing from Microlensing to Cosmic Shear**, by Ben Metcalf

*Wednesday, 12 February 2014 - *

**Analytical Approximations in the Era of Precision Cosmology**, by Aseem Paranjape

*Wednesday, 08 January 2014 - ***Halo Bias for Precision Cosmology**, by Vincent Desjacques

*Friday, 18 October 2013 - ***Physics: The Mystery of Dark Energy**, by Luigi Guzzo

*Wednesday, 17 April 2013 - ***Cosmological implications of the clustering of galaxies in BOSS** by Ariel Sánchez

*Thursday, 10 Aprile 2013 *-

**Nascita ed Evoluzione dell'Universo**by Luigi Guzzo

*Wednesday, 02 April 2013 - *

**AGN/Galaxy co-evolution: using observations to constrain our theoretical perspective**by Fabio Fontanot

*Wednesday, 20 March 2013* - **Non-Gaussianity of the Large-Scale Structure **by Emiliano Sefusatti* *

*Thrusday, 28 February 2013* - **15 Billion Years of History of the Universe: from the Big Bang to our Times **by Luigi Guzzo

*Wednesday, 13 February 2013* - **Testing the laws of gravity with cosmic shear and redshift space distortions**** **by Fergus Simpson

*Tuesday, 11 December 2012* - **"Probing the Mystery of Cosmic Acceleration with Galaxy Surveys" **by Luigi Guzzo

*Tuesday, 27 November 2012* - **Non-Gaussianity in Photometric Redshift Surveys **by Adam Hawken

*Monday, 26 November 2012* - **The mysteries of cosmic expansion** by Luigi Guzzo

*Tuesday, 20 November 2012* - **From alpha, delta to omega: measuring cosmology from a galaxy survey **by Benjamin Granett

*Tuesday, 19 June 2012* - **Measuring and Explaining Dark Energy** by John Peacock

*Tuesday, 12 June 2012* - **The Backreaction Conjecture to Explain Dark Energy** by Thomas Buchert