We searched for scintillation caused by molecular gas within visible dark nebulae as well as by hypothetical halo clumpuscules of cool molecular hydrogen (H2-He) with the ESO-NTT telescope. Within a few thousands of densely sampled light-curves, we found one candidate that shows variabilities compatible with a strong scintillation effect through a turbulent structure of the B68 nebula. Furthermore, since no candidate has been found toward the SMC, we were also able to establish upper limits on the contribution of gas clumpuscules to the Galactic halo mass.
I will discuss the perspectives of synchronized observations with two large distant telescopes, to observe the time decorrelation between the light curves, an undisputable signature of the scintillation process. I will then show that a few nights of observation using the so-called « movie-mode » of LSST should allow one to significantly constrain the last unknown baryonic contribution to the Galactic mass.
]]>I will discuss theoretical issues involved in finding an optimal framework to
study deviations from General Relativity on cosmological scales, giving an
overview of recent progress, with a focus on model-independent, parametrized
approaches. I will summarize where we stand and what are the next steps
we should take.
After giving an overview of the theoretical motivations, I will discuss how to search for these signatures in the CMB. Fast oscillations are difficult to search for with traditional estimation techniques, and I will demonstrate how targeted expansions, that exploit the symmetry properties of the shapes, allow to circumvent these difficulties. As a member of the Planck collaboration, I will discuss the Planck results that have been obtained using these methods in the bispectrum, as well as related results in the power spectrum. Due to their low overlap with other non-gaussian shapes, oscillating bispectrum shapes are not exhaustively constrained and a potential discovery in the CMB is therefore not yet ruled out.
]]>The greatest uncertainty in whether this technique will be successful is the unknown nature of FRB sources. A new observation tells us more about the environment of a source than ever before through the polarization and scattering properties of a burst. More observations of this type, along with observations that identify host galaxies, will soon tell whether FRBs will provide a new probe of structure.
]]>2. Keir Rogers, "Spin-SILC: CMB polarisation component separation for next-generation experiments",
Abstract:
B-mode polarisation is a powerful cosmological observable which in principle allows the detection of a stochastic background of gravitational waves predicted by inflation, and gives strong constraints on the neutrino sector using the weak gravitational lensing of the cosmic microwave background (CMB). Astrophysical foregrounds present a formidable obstacle in extracting these signatures of new physics from CMB polarisation data. Indeed, recent forecasts for post-2020 CMB experiments predict one sigma constraints on, for example, the tensor-to-scalar ratio of about 10^-4 and the sum of neutrino masses of about 30 meV. However, these constraints are predicated on highly-accurate foreground and noise removal. I will present the first component separation method specifically developed for this task and tested on the latest-release Planck data. The method, Spin-SILC, is an internal linear combination algorithm that uses spin wavelets to fully analyse the spin polarisation signal P = Q + iU, where Q and U are the measured Stokes parameters. This allows all the information in the measured signal to be used in extracting the cosmological background. Furthermore, Spin-SILC is the first method to simultaneously and efficiently perform component separation and the E-B decomposition necessary for cosmological analyses thanks to the construction of the spin wavelets we use. Spin-SILC also uses the morphological information of the foregrounds and CMB to better localise the cleaning algorithm. This is because the wavelets we use are additionally directional, and, when convolved with signals on the sphere, can separate the filamentary structures which are characteristic of both the CMB and foregrounds. I will present the results of applying these novelties to Planck data and discuss further how Spin-SILC can also mitigate the E-B leakage problem of future CMB experiments.
]]>First, I will briefly review the status of one of the most promising ideas, massive gravity: cosmological solutions, some formal aspects and recent developments. Then, I will present recent work aimed at constraining such models with LSS probes.
]]>Through the kSZ effect, the baryon momentum field is imprinted on the CMB. I will report significant evidence for the kSZ effect from ACTPol and peculiar velocities reconstructed from BOSS. I will present the prospects for constraining cluster gas profiles and energetics from the kSZ effect with SPT-3G, AdvACT and CMB S4. This will provide constraints for galaxy formation and feedback models.
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]]>black hole can transfer rotational energy to a force-free plasma, offering a possible mechanism for energy and jet emissions from quasars and other astrophysical sources. This Blandford-Znajek (BZ) mechanism is a Penrose process, which exploits the presence of an ergosphere supporting negative energy states, and it involves currents of electrical charge sourcing the toroidal magnetic field component of the emitted Poynting flux.
In this talk, I will discuss a version of the BZ process requiring only vacuum electromagnetic fields outside the black hole. The setting is somewhat artificial, since it assumes the black hole is cylindrical rather than spheroidal, or that the black hole lives in 2 spatial dimensions, but it is nevertheless of theoretical interest. The radiation power and horizon regularity relations are identical to those of the BZ mechanism with plasma, and the solution can be given in simple, closed form for a wide class of metrics, so it helps to illuminate the nature of the original mechanism. For asymptotically Anti-de Sitter black holes it presumably has an interesting dual CFT description, but we haven't quite yet figured out what that is.
]]>which could potentially leave signatures of the dark matter particle nature in the properties of galaxies. In this talk, I will describe a framework we have proposed that generalizes the theory of structure formation (in both the linear and non-linear regimes) to include new dark matter physics in order to explore galaxy formation and evolution in the broadest sense.
]]>For an axion coupled to U(1) gauge fields preheating is efficient for a wide range of parameters. In certain cases the inflaton is seen to transfer all its energy to the gauge fields within a few oscillations. Identifying the gauge field as the hypercharge sector of the Standard Model can lead to the generation of cosmologically relevant magnetic fields.
Coupling the inflaton-axion to Majorana fermions leads to the biased production of fermion helicity-states which can have interesting phenomenological implications for leptogenesis.
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]]>The MESS is the natural quantity to parametrize in a model independent way the effects produced on curvature perturbations by multi-fields systems, particle production and modified gravity theories and could be conveniently used in the analysis of LSS observations, such as the ones from the upcoming EUCLID mission or CMB radiation measurements. It can be also useful to study in a model independent way the production of primordial black holes.
Beside the degeneracy due to different theoretical scenarios producing the same MESS, we show that in absence of entropy or effective anisotropic stress there is an additional degeneracy related to the freedom in the choice of the initial energy scale of inflation, or to the sign of the Hubble parameter. This implies the existence of an infinite family of dual slow-roll parameters histories which can produce the same spectrum of comoving curvature perturbations, implying that in general there is no one-to-one correspondence between the spectrum and higher order correlation functions. Bounce models are examples of the members of this infinite class of dual models.
The combined analysis of data from future CMB and gravitational wave experiments could allow to distinguish between dual models because the primordial tensor perturbations spectra of dual models are in general different.
]]>In galaxy clustering example, I will use the observations of galaxy surveys to reconstruct the initial Lagrangian field. Here, we develop a novel framework with neural networks to forward model halo masses and positions and demonstrate that our method outperforms standard reconstruction in both real and redshift space. This reconstructed initial field has enhanced signal for baryon acoustic oscillations and can enhance science returns for surveys like DESI.
For neutral hydrogen surveys, we lose over 50% of the modes at high redshifts due to foregrounds and it severely hampers their feasibility for cosmological analysis. With a novel bias framework for the forward model, I will show that we are able to reconstruct over 90% of these modes and this recovers cross-correlations with photo-z surveys like LSST and tracers like CMB lensing.
Lastly, I will briefly touch upon assumptions made in this reconstruction framework regarding noise models and likelihood. I will discuss preliminary ways to improve upon them using deep learning.
]]>Have we counted all significant contributions to the entropy inventory? There is one number which we have not considered: the number of degrees of freedom in our vibrant, complex biosphere. What is the entropy of life? Is it sizeable enough to need to be accounted for at the Big Bang, or negligible compared to vacuum entropy?
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]]>In this talk we review what is currently known, what is still a mystery and highlight some of our recent work on the role of climate, blood type and vaccinations on the transmission of the disease and on the extent of "dark infections", the asymptomatic and untested proportion of infections. We end with a list of open research questions that may be amenable to techniques from physics and data science.
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In this talk, I will present a pedagogical introduction to the EFTofLSS, discussing its motivation and basic formalism, as well as a few of its theoretical challenges. To demonstrate the utility of the theory beyond the blackboard, I will discuss the analysis of galaxy power spectra. Using this model, competitive constraints can be placed on cosmology utilizing all the large-scale spatial information, not just the position of the Baryon Acoustic Oscillations. In particular, this yields the strongest CMB-independent measurement of H0.
In answering the second question, I will introduce two less conventional applications of the EFTofLSS. Firstly, the marked density field. This is simply the matter field weighted by its local overdensity, and recent works have shown its power spectrum to be capable of placing strong constraints on the neutrino mass. I will discussing its perturbative modeling, highlighting its unusual features, and how the model allows us to shed light on the surprising constraining of the statistic. An additional statistic of interest is weak lensing. Creating an analytic model for this has its own complications, since it is sensitive to a large range of scales, requiring extensions to the usual EFTofLSS modeling. Crucial to this effort is the development of a matter power spectrum model which is accurate on all scales; I will present the results of recent modeling efforts within the ‘Effective Halo Model’, and discuss future applications to integrated statistics such as weak lensing.
Zoom Link: https://pitp.zoom.us/j/91697113596?pwd=OTh3ZjZ5SHd5Q09sTFdReUMyb0hpUT09
]]>Based on recent work arXiv:1902.08207 and arXiv:1911.02018 with E. Verlinde.
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