List of PhD offers of laboratory.
The predictivity of the Standard Model (SM) of particle physics remains unchallenged by experimental results. After the tantalizing discovery of the Higgs boson at LHC, the measurements of properties such as its mass, spin, parity and its couplings with other SM particles have confirmed its SM-like nature. This goes hand in hand with the absence of direct signs of TeV physics beyond the SM from current direct searches.
The excellent performance of the LHC in terms of delivered luminosity allowed the ATLAS and CMS experiments to set stringent limits on new particle masses well beyond the EW scale, thus worsening the naturalness problem. If the new physics scale lies well above the present experimentally probed energies, one would be left with the only experimental perspective of searching for deviations within the LHC precision measurements, and with no solid theoretical explanation of why the new physics should be so unnaturally heavy. There is, however, another logical possibility: new physics may be hidden at lower energies although weakly coupled to the SM known particles, so that its signals could be swamped in the SM background.
The possibility of recording low energy signatures rely on the capacity of processing the enormous amount of data provided by the LHC. For this ATLAS uses an advanced two-level trigger, the first level implemented in custom hardware, and High Level Trigger that relies on selections made by algorithms implemented in software. Moreover, a series of detector upgrades have been realized to face the challenges posed by the current Run 3 LHC high luminosity data taking. This allows the implementation of efficient algorithms to trigger low energy thresholds at much harsher LHC collision conditions.
In light of the above-mentioned theoretical scenarios, only little can be predicted in a model-independent way about the couplings of new light resonances to the SM. Therefore, we envisage considering specific models, focusing on particular final states. An example of this low mass resonance is an axion-like particle (ALP), which further acts as a mediator to Dark Matter. We will determine the region of parameter space where all existing collider, astrophysical, cosmology constraints are respected, and the relic density is obtained. We will then study the prospects of producing such an ALP which subsequently decays to b-anti-b pairs at the LHC. This will allow us to pinpoint novel signatures, providing a complementary handle on the models in question, signatures that will be then looked for by the candidate, analyzing ATLAS data recorded during Run 3.
The Aix-Marseille University and the ATLAS CPPM group in Marseille have an opening for a PhD (already funded) in the domain of IC design and characterization of depleted CMOS sensors and hybrid pixel electronics for future applications at particle colliders.
The Centre de Physique des Particules de Marseille (CPPM) is a joint research unit of the Centre National de la Recherche Scientifique (CNRS) and the Aix-Marseille University. The CPPM is a leading player in research in Particle Physics, Astroparticle Physics and Observational Cosmology. It is present in the largest physics experiments currently underway or being developed throughout the world.
The CPPM ATLAS group has a long-standing experience on hybrid pixel technologies. It is currently involved in the ATLAS Inner Tracker (ITk) upgrade project, targeting the High Luminosity phase of the Large Hadron Collider (HL-LHC project), and also in developments of technologies for future applications at collider experiments.
We are seeking candidates to join the group and develop CMOS sensors and hybrid pixel electronics in small feature size for particle physics pixel detectors at high intensity and high radiation dose, in the context of several international collaborations and projects.
We are seeking motived candidates that should have skills or strong will to acquire experience in:
- Microelectronics and circuit design.
- Silicon semiconductor process technologies.
- Deep submicron CMOS technologies.
- Design tools, simulation, design and verification.
- Experimental verification, designing test systems, acquisition software.
- Testing complex devices, data processing and data analysis.
Further inquiries can be addressed to: barbero@cppm.in2p3.fr
Application should be made under:
https://emploi.cnrs.fr/Offres/Doctorant/UMR7346-ANNPOR-077/Default.aspx
The data acquisition and trigger electronics of the ATLAS liquid argon calorimeter will be fully replaced as part of the second phase of upgrade of the ATLAS detector. The new backend electronics will be based on high-end FPGAs that will compute on-the-fly the energy deposited in the calorimeter before sending it to the trigger and data acquisition systems. New state-of-the-art algorithms, based on neural networks, are being developed to compute the energy and improve its resolution in the harsh conditions of the HL-LHC.
The candidate is expected to take a role in the development of data processing algorithms allowing to efficiently compute the energies deposited in the LAr calorimeters in the high pileup conditions expected at the HL-LHC. These algorithms will be based on AI techniques such as recurrent neural networks will be adapted to fit on hardware processing units based on high-end FPGAs. The successful candidate will be responsible of designing the AI algorithms, using python and keras, and assessing their performance. The candidate will also assess the effect of employing such algorithms for electromagnetic object reconstruction (especially at trigger level). She/he will work closely with the engineers designing the electronic cards at CPPM in order to adapt the AI algorithm to the specifics of FPGAs. Candidates with a strong interest for hardware will be encouraged to take part in the design of the firmware to program the FPGAs.
Prior knowledge of keras, python and C++ is desirable but not mandatory.
Physics at the Large Hadron Collider (LHC) at CERN (European Organization for Nuclear Research) is the high priority research field of the Particle Physics community worldwide. ATLAS is one of the two general purpose experiments installed at the LHC that discovered a Higgs boson in July 2012, key piece for the understanding of the fundamental interactions and the origin of elementary particle mass. Its physics program extends beyond Higgs property measurements to the search for signs of physics beyond the Standard Model of particle physics.
The ATLAS group of the Centre de Physique des Particules de Marseille (CPPM) is deeply involved in this scientific program, in particular linked to its expertise of the electromagnetic calorimeter. The latter is a key component for the identification and energy measurement of electrons and photons, which were at the core of the Higgs boson discovery. The group is also at the forefront of the study of this boson and the search for supersymmetry in the 2015-2018 data taking campaign known as Run 2 and the ongoing one known as Run 3, with major implications in several analyses with electromagnetic particles in the final state. Moreover, for the upgrade of the accelerator performances, high luminosity phase of the LHC (HL-LHC), this calorimeter has a major ongoing development program to dramatically upgrade its trigger and readout to which the CPPM group is actively involved. The LHC Run 3 started in 2022, and is expected to continue until 2025. The data from proton-proton collisions collected during this period by the ATLAS experiment will allow the large particle physics research programme to continue, improving the measurements of the Standard Model (SM) parameters and the limits on new physics phenomena, before the high-luminosity phase of the LHC (HL-LHC) from 2029.
Among the studied processes, the search for pp->HH Higgs boson pair production appears to be a new frontier, as its observation would allow a direct measurement of the self-coupling of this long-predicted scalar particle, discovered in 2012 only. This process predicted by the SM is particularly rare, and analysis of the HL-LHC data should be necessary to observe it. However, beyond-the-SM theories predict the existence of new scalar (S) particles, which could be produced in proton-proton collisions in association with a Higgs boson: pp->SH. The CPPM ATLAS team is involved in the search for the pp->HH process, in particular in the channel with a bottom quark-antiquark pair and two photons in the final state.
The proposed thesis topic aims to search for pp->SH processes with the Run 3 data, in the same decay channel. The student will participate to this analysis, to the necessary detector performance studies related to the team areas of expertise, in particular on aspects related to photon reconstruction and identification, and to the liquid argon calorimeter operation. In this framework, the student will have to do frequent stays at CERN and the research work will combine physics analysis on real and simulated data as well as studies and operation of experimental systems.
The study of the Higgs boson pair production is generating a growing interest in the particle physics community, in particular in view of the High-Luminosity phase of LHC. In addition to the Higgs self-coupling, the VVHH coupling is also an important parameter to improve our understanding of the electroweak symmetry breaking, which can be probed through the search for di-Higgs events in the VBF production mode.
The ATLAS detector is ideally suited for such studies, with its design optimised to reconstruct and identify most of the decay products of the Standard Model particles produced in rare physics processes involving Higgs bosons, such as the di-Higgs production modes. This thesis will include some work on the optimisation of the algorithms used to identify jets produced in the hadronization of b-quarks for the upgrade of the ATLAS detector planned for the High-Luminosity phase of the LHC. Those algorithms play a major role in all the final states involving b-quarks, produced in the decay of the top quark and of the Higgs boson for instance.
Very strong constrains on the VVHH coupling can already be achieved with the LHC Run 3 dataset, in particular combining the low and high m(HH) regions. The corresponding analyses are the focus of a collaborative research effort involving several French laboratories members of the ATLAS Collaboration at CERN. The PhD position would complement this research effort, with a particular focus on the analysis of the bbtautau resolved final state, benefitting from the strong expertise of the ATLAS group at CPPM in b-tagging and di-Higgs studies [1-2].
Applications should include a CV, a letter of motivation, academic records from bachelor to master and contacts of two reference persons willing to provide reference letters.
[1] ATLAS flavour-tagging algorithms for the LHC Run 2 pp collision dataset https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/FTAG-2019-07/
[2] Search for Higgs boson pair production in the final state with two bottom quarks and two photons in pp collisions at ?s = 13 TeV with the ATLAS detector https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HDBS-2018-34/
Dark matter is today one of the main puzzles in fundamental physics. Indeed, its contribution to the total mass of the Universe is 85%, but it cannot be explained in the framework of the Standard Model (SM) of particle physics. Several candidates exist in theories beyond the SM, and the WIMP (Weakly Interacting Massive Particle) is one of the best motivated of these candidates, as it allows to also solve the SM hierarchy problem, directly linked to the stability of the Higgs boson mass.
Experiments searching directly for dark matter thus use our galaxy halo as a potential source of WIMPs. Since 2010, the most sensitive technology is based on the measurement of the scintillation light from the scattering of a WIMP on a liquid noble atom argon or xenon. In this framework, the DarkSide-20k (DS-20k) experiment, which will be installed 1.4 km underground in the Gran Sasso laboratory in Italy, is the third generation of liquid argon detectors. It will use a time projection chamber of 3.5 m diameter and 3.5 m high filled with 50 tons of purified argon and read out by 200,000 silicon photomultipliers. This will allow to have the world leading discovery potential for WIMPs after few years of data taking. The actual work is dedicated to the construction of the detector. Data taking should start in 2027. The increase of the liquid argon volume, compared to the first and second generation, will allow DS-20k to have the best sensitivity of all the liquid argon detectors after only one month of data.
The goal of this thesis, already financed by the Agence Nationale de la Recherche between October 2024 and September 2027, is to prepare and to participate to the analysis of the first data, for which the CPPM computed the sensitivity to WIMPs of low (<10 GeV) and high mass (>100 GeV). First, the student will participate to the simulation and the installation of the calibration system, designed and validated at CPPM. In parallel, the student will improve data reconstruction algorithms by using artificial intelligence techniques (e.g. neural networks), to optimize the separation between signal and backgrounds. Finally, he (she) will participate to the analysis of calibration data taken by DS-20k, and to the first physics analyses. These activities bring a complete education in particle physics, including instrumental aspects, software and data analysis.
In this framework, the student will have to do stays at Gran Sasso, especially to install the calibration system.
More details about the CPPM Dark Matter team: https://www.cppm.in2p3.fr/web/en/research/particle_physics/#Dark%20Matter
The CTA (Cherenkov Telescope Array) is a worldwide project to construct the next generation ground based very high energy gamma ray instrument [1]-[2]. CTA will use tens of Imaging Air Cherenkov Telescopes (IACT) of three different sizes (mirror diameter of 4 m, 12 m and 23 m) deployed on two sites, one on each hemisphere (La Palma on the Canary Islands and Paranal in Chile). The observatory will detect gamma-rays with energy ranging from 20 GeV up to 300 TeV by imaging the Cherenkov light emitted from the charged particle shower produced by the interaction of the primary gamma ray in the upper atmosphere.
The unconventional capabilities of CTA will address, among others, the intriguing question of the origin of the very high energy galactic cosmic rays by the search for galactic sources capable of accelerating cosmic rays up to the PeV energies, called PeVatrons. Recently, the Supernova Remnant (SNR) G106.3-2.7 has been indicated as a highly promising PeVatron candidate [4]. In fact, G106.3-2.7 emits gamma-rays up to 500 TeV from an extended region (~0.2o) well separated from the SNR pulsar (J2229+6114) and in spatial correlation with a local molecular cloud.
The CTA observatory completion is foreseen in 2025 but the first Large-Sized Telescope (LST1) is already installed and taking data in La Palma. LST1 is placed very close to the two MAGIC telescopes [3], which are one of the presently active IACT experiments. This configuration permits to perform joint observations of the same source with the three telescopes LST1+MAGIC increasing the effective detection area and improving the energy and angular resolution, thanks to the enhanced quality reconstruction of stereoscopic data. While the LST1+MAGIC telescopes cannot reach enough sensitivity to access energies above 100 TeV, they can provide exclusive and unprecedented data for establishing the spectral morphology of this exciting PeVatron candidate in the 100 GeV-100 TeV energy region. A campaign of joint observations of G106.3-2.7 will start in 2022 and will continue in the following years.
The PhD project will be on the analysis of the data of the coming campaign, its ambitious target will be to contribute in disclosing the hadronic or leptonic nature of this promising PeVatron. In order to maximize the effective area at very high energy, G106.3-2.7 will be observed at large zenith angle (LZA), 62o-70o, which represents a challenging detection condition. The project will start with the development and verification of the joint LST1+MAGIC stereo reconstruction chain [5] at LZA, using Monte Carlo (MC) data. This MC study will aim to optimize the data reconstruction and selection in order to reach a high quality Instrument Response Function and sensitivity for this specific source. Real data will be then reconstructed so as to achieve both a morphological and a spectral reconstruction of the source in the 100 GeV-100 TeV energy range. Finally, the high-quality LST1-MAGIC data will be used for a multiwavelength analysis that will compare different emission models and try to disentangle the nature of the source.
The project will include the participation to the LST1+MAGIC observation campaign with stays of four weeks in the Roque de los Muchachos Observatory in La Palma.
The CPPM CTA group works since several years in the building and commissioning of the LST1 telescope and on the preparatory studies for the research of galactic PeVatrons with CTA [6][7].
Candidates should send their CV and motivation letter as well as grades (Licence, M1, M2) to cassol@cppm.in2p3.fr and costant@cppm.in2p3.fr before 10/4/2022. Applications will be selected on the base of qualifications and an oral interview.
References:
[1] Science with the Cherenkov Telescope Array: https://arxiv.org/abs/1709.07997
[2] https://www.cta-observatory.org/
[3] MAGIC Collaboration, Aleksi?, J. et al. Astropart. Phys. 72 (2016) 7694.
[4] Z. Cao et al. Nature, 594, 3336 (2021); M. Amenomori et al. Nature Astronomy, 5, 460464 (2021)
[5] https://github.com/cta-observatory/magic-cta-pipe
[6] O. Angüner et al. Cherenkov Telescope Array potential in the search for Galactic PeVatrons, ICRC 2019
[7] G. Verna et al. HAWC J2227+610: a potential PeVatron candidate for the CTA in the northern hemisphere, ICRC 2021
The Centre de Physique des Particules de Marseille (CPPM) in collaboration with the University of Toulon is opening a doctoral position (3 years), funded by the Aix Marseille University (AMU). The successful candidate will integrate CPPM to carry out research on neutrino oscillations with the ORCA detector and its possible upgrades.~
ORCA is a megaton scale natural water Cerenkov neutrino detector being constructed by the KM3NeT collaboration on the sea bed at 40 km offshore Toulon and at a depth of 2400 m. The primary purpose of the detector is to study neutrino oscillations using atmospheric neutrinos. While the detector construction should be over by 2027, the first detection units deployed since 2018 are fully operational, and the data collected have already allowed to observe the neutrino oscillations phenomena. The detector is now reaching a size that allows to probe unexplored physics territories. The Ph.D. student will participate in these data analyses, in particular, to the study of the appearance of tauic neutrinos in the atmospheric neutrino flux.
In addition to the atmospheric neutrinos studies, the Ph.D. student will also participate in a team work to develop of a novel technique for accelerator-based experiments called neutrino tagging. The very large size of the natural water Cerenkov detectors such as ORCA (few megatons) allows to perform experiments with neutrino beams of modest intensity for which the beam line can be instrumented. These instruments allow to get first-hand information (energy, direction, flavour, chirality) on each of the produced neutrinos. Ongoing studies indicate that such experiments would offer an unprecedented precision on the leptonic CP violating phase. The Ph.D. will take part to this pioneering design phase of a tagged neutrino experiment (e.g. sensitivity estimate, tracker R\\&D etc...).
The research activities will be conducted in tight collaboration with the Signal and Tracking group at University of Toulon, but also with the CERN Physics Beyond Colliders (PBC) study group (for the tagging part).
We are seeking for a highly motivated person who would ideally have:
The student interested in applying for the internship must provide:
This information should be sent to -tln.fr?subject=">-tln.fr?subject=[PhD-2326-KM-04]>mathieu.perrin-terrin@cern.ch and antoine.roueff@univ-tln.fr by July 31st.
Neutrinos are unique messengers to study the high-energy Universe as they are neutral and stable, interact weakly and therefore travel directly from their point of creation to the Earth without absorption and path deviation. Nowadays, the sources of very high-energy cosmic rays are still unknown. Doing neutrino astronomy is a long quest for neutrino telescopes. Several observational hints have been detected by ANTARES and IceCube (active galaxy nuclei, tidal disruption events).
KM3NeT is the second-generation neutrino detector in the Mediterranean Sea. It will be distributed in two sites: a low energy site ORCA in France (1 GeV-10 TeV) and a high energy site ARCA in Italy (1 TeV-10 PeV). Its main goals are to study of neutrino oscillations, with as flagship measurement the determination of the neutrino mass ordering and to perform neutrino astronomy. Both detectors are already collecting data with the first detection units and will soon reach significantly better sensitivities for the detection of cosmic neutrinos surpassing by far the ANTARES one. Thanks to the unprecedented angular resolution, the extended energy range and the full sky coverage, KM3NeT will play an important role in the rapidly evolving multi-messenger field. A good sensitivity over such a large energy coverage can only be obtained by combining the data of the two detectors. KM3NeT will achieve a precision of <0.1 degrees for the muon neutrino tracks at very high energies, and <1.5º for the cascade events (electron, tau charge current + all flavor neutrino neutral current interactions). With KM3NeT, we will be able to perform a very efficient all-flavour neutrino astronomy.
The main goal of the thesis is to develop multi-messenger analyses in the two KM3NeT detectors. With the early data, we have performed a lot of studies to understand the behaviour of the detectors by setting the calibration procedures and by implementing very detailed Monte Carlo simulations that reproduce quite well the data taking. It has also permitted to start the development of the online analysis framework. Most of the elements are in operation (online reconstruction, neutrino classifier, reception of external transient triggers, alert sending). At the beginning of the PhD, the student will have to develop and implement efficient all-flavour neutrino selection over the atmospheric backgrounds. These selections will be performed using advanced analysis methods such as machine learning algorithms, that will be used to classify the nature of all the KM3NeT events between neutrino tracks (charged current muon neutrinos), neutrino cascades (all others neutrino flavours) and background events (atmospheric muons and neutrinos). The second step of the PhD will be to use these neutrino streams to look for time and space correlation with external triggers from electromagnetic transients, gravitational waves and high-energy neutrinos. This correlation analysis will be developed in two steps, starting with the implementation of a simple counting analysis that looks for a signal excess in a pre-optimized region of interest and in a given time window. For the most interesting neutrinos, the PhD student will also participate to the development of the alert sending system and the multi-wavelength follow-ups (radio, visible, X-ray and VHE). The student will have to develop the neutrino filters based on the false alarm rates of those alerts, their energies and angular resolutions Real-time multi-messenger campaigns are crucial in unveiling the sources of the most energetic particles and the acceleration mechanisms at work. The student will also participate to set the multi-wavelength follow-up of the KM3NeT alerts.
The candidate should have a good background in astroparticle physics and astrophysics. The interest in the data analysis is expected together with knowledge of statistics. The analyses will be performed using C++, Python and Root on Linux platforms.
KM3NeT: http://www.km3net.org
KM3NeT/ORCA (Oscillation Research with Cosmics in the Abyss) is a deep sea neutrino telescope currently under construction at a depth of 2500m in the Mediterranean Sea off the coast of Toulon. KM3NeT/ORCA is optimised for the detection of low energy (3-100 GeV) atmospheric neutrinos and will allow precision studies of neutrino properties. Currently the detector takes data with 15 detection strings which instrument a volume of about 1Mton - much larger than underground detectors with a similar science program. Several years of data are available, waiting to be analysed.
The task of the student is to participate in data taking, construction and calibration of the KM3NeT/ORCA detector and to analyse several Mton-years of neutrino data. This will allow for a cutting edge measurement of the atmospheric neutrino oscillation parameters and a first estimation of the neutrino mass ordering.
Links:
https://arxiv.org/abs/1601.07459
https://arxiv.org/abs/2103.09885
The Standard Cosmological Model has passed many precise observational tests in both the early and late-time universe. Nonetheless, the Cosmological Model still suffers from some important observational and theoretical difficulties. On the observational side, there are discrepancies between different independent measurements of the expansion rate of the Universe, the Hubble constant (H0).
Gravitational waves (GWs) open a new opportunity to shed light on the H0-tension. Differently from SNIa, GWs sources are unique tracers of the luminosity distance and can therefore be used to measure the expansion history of the Universe through the distance-redshift relation (Schutz, Nature 1986). These GW detections used as standard sirens provide independent measurements of H0. However, one of the key ingredients is precisely to obtain an independent measurement of the redshift of the galaxy that hosted the merger. In case the GW event is detected together with its electromagnetic (EM) counterpart (bright standard sirens), the redshift information is inferred from the unique identified host galaxy. In the absence of EM counterpart, which concerns the ~100 GW observations without an identified host galaxy, GW events are called dark standard sirens. Dark sirens require knowledge of the position and redshift of the ensemble of potential host galaxies within a volume of confidence. Among the different ways to extract the redshift information from GW sources, a promising method is to use galaxy surveys.
The proposed PhD project aims to establish that the new generation of galaxy surveys, such as the Dark Energy Spectroscopic Instrument (DESI) and the Euclid mission, used in the context of gravitational waves can provide competitive constraints on the measurement of the Hubble constant H0, and can overcome the inconsistency between historical measurements from the CMB and from supernovae. To this end, several objectives have been identified: a) to build novel techniques for GW cosmology, by developing new statistical approaches applied to galaxy samples; b) to infer cosmological constraints using current data, with the goal to bring competitive constraints on the Hubble constant H0 compared to other methods; and c) to prepare tomorrow's analyses with the arrival of the next generation observatories.
The Centre de Physique des Particules de Marseille (CPPM) team in Marseille, France, invites applications for a 3-year PhD fellowship in the area of Gravitational Wave (GWs) Cosmology. The PhD programme will be jointly tutored by the Aix-Marseille Université (IPhU [Institute for the Physics of the Universe] / CPPM [Centre de Physique des Particules de Marseille]) and Sapienza University of Rome, in the framework of the CIVIS European University Alliance.
The successful candidate will spend the first half of the PhD programme at the University of Rome Sapienza, working in collaboration with Dr. S. Mastrogiovanni and other scientists of the Virgo group, and will be joining the Virgo collaboration.
(S)he will spend the second half of the PhD programme at CPPM in Marseille working in collaboration with Dr. S Escoffier, Dr. E. Kajfasz and other experts in large galaxy surveys, and will be joining the Euclid consortium.
(S)he will also have the opportunity to travel for collaboration with other French Virgo groups such as the L2IT group in Toulouse led by Dr. N. Tamanini. At the end of the successful PhD programme, a diploma will be released by both Aix-Marseille Université and Sapienza University of Rome.
Application is now open until June 19th, 2023. Interviews will be scheduled during the first 10 days of July. The expected thesis starting date is November 1st, 2023. The PhD funding is acquired.
Applicants must hold a Master of science or equivalent in fundamental physics or astrophysics (or related subjects) by the end of October 2023. A good level of English is necessary. Programming skills (python, C++), strong motivation and interest in cosmology as well as the ability to work in large international collaborations will be valuable assets.
Please send your application to Dr. E. Kajfasz (eric.kajfasz@univ-amu.fr), including:
? A motivation letter (maximum two pages).
? A curriculum vitae
? A brief description of research interest and past achievements
? Two reference letters (Head of the Master's program, supervisor of the Master internship) to be sent directly to eric.kajfasz@univ-amu.fr
? A transcript of all university records (Bachelor and Master)
? A copy of the master's diploma
The context: More than twenty years after the discovery of the accelerated nature of the Universe's expansion, there is still no definitive explanation for its physical origin. Several types of dark energy or even alternatives/extensions to general relativity have been proposed in the literature attempting to explain the acceleration of the expansion. By accurately measuring of both the expansion rate of the Universe as well as the growth rate of structures as a function of cosmic time, we can learn more about this cosmological mystery. Particularly at low redshift when the expansion is accelerated and dark energy dominates the expansion, we are interested in obtaining the best constraints on the growth rate of structures. These measurements can be achieved by combining galaxy positions and their velocities. The statistical properties of the density and velocity field are tightly connected to the underlying cosmological model.
Experiments: Measurements of the expansion and growth rates of the Universe are the main scientific goal of current and future experiments such as the Dark Energy Spectroscopic Instrument (DESI), the Zwicky Transient Facility (ZTF), Euclid and the Vera Rubin Observatory Legacy Survey of Space and Time (Rubin-LSST).
DESI is currently measuring the 40 million galaxy positions (with their redshift) and their lower redshift sample will be the most complete to date.
The ZTF survey will discover more than 6000 type-Ia supernovae, from which we can derive galaxy velocities. Rubin-LSST will increase this number to the hundreds of thousands.
Goal of thesis: The selected candidate will work towards the joint analysis of DESI and ZTF datasets, which contain millions of galaxies and thousands of type-Ia supernovae. The candidate will get familiarised with the physics and the statistics of galaxy clustering, will code their own analysis pipeline, test it on state-of-the-art simulations, and hopefully apply it on real data.
Profile required: The candidate has to have large interest by cosmology, statistics, data analysis and programming (we use mostly python). English proficiency and team work skills are also required.
Twenty years after the discovery of the accelerating expansion of the universe through supernova measurements, the supernova probe remains one of the most accurate means of measuring the cosmological parameters of this recent period in the history of our universe, dominated by the so-called dark energy.
The Rubin Observatory with the Large Survey of Space and Time (Rubin/LSST) will be commissioned in 2024 and will be fully operational by mid-2025. It is an 8.4-m telescope equipped with a 3.2-billion-pixel camera, the most powerful ever built.
This telescope will take a picture of half the sky every three nights for ten years. This survey will make it possible to measure billions of galaxies with great precision, and to track the variation over time of all transient objects. Together with many other astrophysical studies, it will be a very powerful machine for determining cosmological parameters using many different probes and, in particular, will impose strong constraints on the nature of dark energy. The LSST project aims to discover up to half a million supernovae. This improvement of two to three statistical orders of magnitude over the current data set will enable precise testing of the parameters of dark energy, test general relativity and also impose new constraints on the isotropy of the universe.
During the thesis, we propose to prepare and then participate in the analysis of the first LSST supernova data. The preparation will be done using existing HSC/Subsaru data.
The student will participate in the commissioning of Rubin/LSST. He/she will be in charge of pursuing developments in deep learning methods for supernova identification, and applying them to the first observations.
He/she will then take part in the first analyses using the supernovae he/she has helped to identify.
The LSST group at CPPM is already involved in precision photometry for LSST, with direct involvement in the validation of algorithms within DESC/LSST [1][2][3], and has proposed a new deep learning method to improve photometric identification of supernovae [4] and photometric redshifts [5].
[1] https://www.lsst.org/content/lsst-science-drivers-reference-design-and-anticipated-data-products
[2] https://arxiv.org/abs/1211.0310
[3] https://www.lsst.org/about/dm
[4] https://arxiv.org/abs/1901.01298
[5] https://arxiv.org/abs/1806.06607
[6] https://arxiv.org/abs/1401.4064
Although the universe is well described by the concordance model ?CDM, the nature of its components, dark matter and dark energy, remains a major puzzle of modern cosmology. While historically most attention has been paid to the overdense regions, the underdense regions account for about 80 per cent of the total volume of the observable Universe and strongly influence the growth of large-scale structure. As voids are nearly devoid of matter, they have proved to be very promising objects for exploring the imprint of possible modifications of General Relativity (GR) such as f(R) gravity or extended gravity theories.
The RENOIR cosmology team at CPPM focuses on the understanding of the history and composition of our Universe, particularly on its dark components. The team is particularly involved in large spectroscopic surveys Dark Energy Spectroscopic Instrument at Mayall, US and the European space mission Euclid, that will provide the observation of 40 million of galaxies, the largest 3D map of the Universe ever made.
A promising way to probe modified gravity models is to constrain the growth of structure of the Universe using information from Redshift Space Distortions around cosmic voids. The aim of the PhD thesis is on the extraction of cosmological constraints using Alcock-Paczynski deformation information and RSD information around voids, with DESI data which started its observations in June 2021 for 5 years, and the Euclid mission that will be launched in July 2023.
In the late 90s, measurements of the distance of Supernovae and the redshift of their host galaxies revealed that the expansion of the Universe was accelerating. More than 20 years after this discovery, the nature of the dark energy at the origin of this phenomenon remains unknown.
The CDM concordance model describes a homogeneous, isotropic Universe on large scales, subject to the laws of general relativity (GR). In this model, most of the Universe's energy content comes from cold dark matter and dark energy, introduced as a cosmological constant. The latter behaves like a perfect fluid with negative pressure p, equation of state p = - rho, where rho is the energy density.
Some alternative models (see [1] for a review) introduce scalar fields (quintessence) whose evolution is responsible for the accelerated expansion. These scalar fields can vary in time and space. They can therefore have a time-dependent equation of state and generate anisotropic expansion.
Other models propose to modify the law of gravitation on large scales, mimicking the role of dark energy.
Supernovae remain one of the most accurate probes of the Universe's expansion and homogeneity. In addition, part of the redshift of galaxies is due to a Doppler effect caused by their particular velocities. We can then use supernovae to reconstruct the velocity field on large scales, and measure the growth rate of cosmic structures. This will enable us to test the law of gravitation.
An anisotropy of expansion on large scales, a modification of GR, or an evolution of the equation of state for Dark Energy, would all be revolutionary observations that would challenge our current model.
Until now, supernova surveys have gathered data from multiple telescopes, complicating their statistical analysis. Surveys by the Zwicky Tansient Facility (ZTF: https://www.ztf.caltech.edu/) and the Vera Rubin/LSST Observatory (https://www.lsst.org/) will change all that. They cover the entire sky and accurately measure the distance to tens (hundreds) of thousands of nearby (distant) supernovae.
The CPPM has been working on ZTF data since 2021 and has been involved in the construction and implementation of LSST for years, preparing for the arrival of data in 2025.
Within the group, we are working on the photometric calibration of the ZTF survey, essential for the measurement precision we need (see ubercalibration [2,3]). A recent PhD student has developed a pipeline to simulate ZTF and measure the growth rate of structures ([4]), and a current PhD student is adapting this exercise to LSST. In addition, a post-doc has just joined the group to work on ZTF, and a Chair of Excellence (DARKUNI, see Julian Bautista's internship/thesis) is extending this work by combining these data with spectroscopic data from DESI.
The aim of the thesis is to develop and perfect this analysis pipeline for measuring the growth rate of structures with real ZTF data, and to prepare the analysis of LSST data.
Other aspects may be added to the thesis, such as the study of the homogeneity of the expansion, the photometric calibration of the data, and so on.
This is an observational cosmology thesis, for a candidate interested in cosmology and data analysis.
[1] https://arxiv.org/abs/1601.06133
[2] https://arxiv.org/abs/astro-ph/0703454v2
[3] https://arxiv.org/abs/1201.2208v2
[4] https://arxiv.org/abs/2303.01198 https://snsim.readthedocs.io/
The various observations of the Universe have been indicating for twenty years now that the expansion of the Universe is accelerating. The standard model of cosmology, known as the LCDM model, describes the Universe as composed of 27% dark matter and 68% dark energy. Understanding the nature of these two energy components remains one of the greatest challenges in contemporary physics. Next-generation galaxy surveys, such as Euclid or DESI, will make it possible to measure several tens of millions of galaxy spectra in the coming decade and tighten constraints on the cosmological model, or probe its alternatives like modified gravity models.
The most promising tools to constrain dark energy and gravity properties are based on the observation of large structures in the Universe. The structure of the Universe also reveals the presence of large under-dense regions, enclosed by filaments of matter. These cosmic voids, which occupy nearly 80% of the volume of the Universe, contain very few matter, and are therefore an ideal laboratory for testing dark energy scenarios.
The subject of the thesis is to extract the integrated Sachs-Wolfe (ISW) signal by cross-correlating cosmic voids with Cosmic Microwave Background (CMB). Indeed the time evolution of gravitational potentials imprints secondary anisotropies in the CMB, in addition to the primordial CMB anisotropies generated near the last scattering surface. These additional anisotropies are caused by gravitational interactions of CMB photons with the growing cosmic large-scale structure. The ISW signal is challenging to measure since it is very weak compared to primordial CMB photons. However the signature of the ISW
effect can be observed as a non-zero signal in the cross-correlation between the distribution of foreground tracers of dark matter (such as galaxies) and the temperature of CMB, providing a direct probe of the late-time expansion of the Universe. Recent work (Kovacs 2021) has shown that the ISW signal amplitude exhibits an excess over the expectations of the standard LCDM model, at the 3 sigma level, especially when the study is applied to superstructures such as supervoids.
The thesis project focuses on the ISW effect and the cross-correlation between the CMB and cosmic voids. The work of the student will consist in building the void catalogs from galaxy catalogs, developing estimators and likelihoods associated with the ISW effect and quantifying how the ISW effect impacts onto dark energy and modified gravity parameters.
The CPPM is involved in the two projects DESI and Euclid, both dedicated to the measurement of cosmological parameters to constrain dark energy and test modified gravity models.
DESI is a galaxy survey that started in 2021 for 6 years and will observe nearly 40 million spectra of galaxies up to a redshift of 3.5. Euclid was selected by the European Space Agency (ESA) in 2011 and will be launched in 2023 to probe the Universe over a 6 year-period. These data will revolutionize our ability to map the Universe and better understand the nature of dark energy or put Einstein's General Relativity (GR) in default.
Application should be done via the CNES website:
A CNES/CNRS funding can be obtained for this thesis.