Appel à candidatures 2014

traduction en français à venir

The ILP invites applications for the third class of Lagrange thesis fellowships. These fellowships will include a net stipend of approximately EUR 1,400/month (approx. $1,900/month)* for three years and generous travel and research funds. The new Lagrange thesis fellows are expected to start in the Fall semester of 2014.

Successful candidates will have demonstrated academic excellence, outstanding potential for creative research, and leadership qualities.

Lagrange thesis fellows will be immersed in an internationally visible, world-class research environment in terms of intellectual, and computational resources, an extensive visitors' program, and significant involvement in the world's leading astronomical and (astro-)particle physics projects, such as Planck, Herschel, Euclid, CFHTLS, TeraPix, BOSS, SDSS III, VIPER, Square Kilometer Array, LHC, HESS, Auger, etc.

The Lagrange thesis fellows will be enrolled in a doctoral school of the Université Pierre et Marie Curie, part of Sorbonne Universités, with access to intensive short courses in cutting edge areas of the field, such as dark matter and dark energy research, theoretical and experimental (astro-)particle physics, recent advances in quantum field theory and string theory. Special short courses will be offered in emerging research methods such as astrostatistics, discovery in petascale data sets, etc. The Lagrange Institute will support yearly summer or winter schools where thesis fellows can meet their future colleagues. All courses will be offered in English and taught by the leading experts in each field - either members of ILP or guest professors, including the Lagrange award holders.

The list of thesis project proposals written by members of the Institute is now online! Candidates are invited to contact their potential advisors directly before submitting their application.

Candidates should submit their application to references-phd[at]ilp.upmc.fr and arrange for 3 letters of reference to be sent to the same address before the deadline of January 15, 2014.

*with a salary supplement of approximately EUR270/month in case of teaching activities.

Project proposals 2014

- Phenomenology of extensions of the Standard Model
- Precision measurements of neutrino oscillation parameters
- Searching for cosmogenic photons
- Ultra high energy cosmic rays and origin of the “ankle”: What do large scale anisotropies tell us?
- Numerical and theoretical studies of particle acceleration in relativistic astrophysical outflows
- Are constants of Physics constant?
- Improving the Planck cosmological results with component separation
- Primordial galaxy formation with radiative hydrodynamics simulations
- Particle Physics at LHC - Thesis opportunity in the ATLAS group of Paris
- Flux vacua in heterotic and type II strings: properties and applications

Phenomenology of extensions of the Standard Model

Laboratory: LPTHE
Contact persons:
Karim Benakli /// kbenakli[at]lpthe[dot]jussieu[dot]fr
Mark Goodsell /// goodsell[at]lpthe[dot]jussieu[dot]fr
Pietro Slavich /// slavich[at]lpthe[dot]jussieu[dot]fr
Website: www.lpthe.jussieu.fr

The Beyond the Standard Model research team - consisting of Karim Benakli, Mark Goodsell and Pietro Slavich - will have a PhD position starting in Autumn 2014.

The Standard Model provides neither a Dark Matter candidate nor a mechanism to generate matter-anti-matter asymmetry, while extensions of it are constrained by data from experiments at the LHC, dark matter searches, astrophysical and cosmological observations. In particular, when confronted with the experimental measurements, a precise theoretical computation of the Higgs boson mass and of the branching ratios of its decays restricts the parameter space of the Minimal Supersymmetric Standard Model, and motivates new approaches which have recently been receiving a growing interest.

The subject of this thesis is the investigation of various aspects of these extensions of the Standard Model. Depending also on the preferences of the candidate, the focus of the thesis may vary from model-building aspects to precision computations and analysis of expected collider signatures.

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Precision measurements of neutrino oscillation parameters

Laboratory: LPNHE (Paris) /// Group: T2K
Contact person: Boris Popov /// popov[at]lpnhe[dot]in2p3[dot]fr
Website: lpnhe.in2p3.fr

The group T2K is currently involved in two on-going experiments: a world-leading long baseline neutrino oscillation experiment (T2K in Japan) and an auxiliary hadron production experiment (NA61/SHINE at CERN). The group has already made crucial contributions to both experiments and continues the data analysis with a clear goal of reaching the most precise determination of the neutrino oscillation parameters.

The group has developed a generic tool - based on ROOT Virtual Monte Carlo (VMC) - for precise prediction of neutrino fluxes in the on-going and future long-baseline neutrino experiments. The validation of this tool is performed in the framework of the NA61/SHINE and T2K experiments.

We are also involved in common efforts of combining together the results from different neutrino experiments in order to extract the neutrino oscillation parameters with the best possible precision (PMNSFitter: Neutrino Oscillations Global Fitting Group).

Finally the group is also planning to take an active part in the next-generation LAGUNA-LBNO neutrino project to determine the neutrino mass hierarchy and to study the CP-violation in the lepton sector which is extremely important to understand the matter-antimatter asymmetry in the Universe. A prototype of large-volume LAr TPC will be constructed and tested at CERN in the coming years.

The PhD candidate should discuss with the group to define the thesis subject along these lines of research.

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Searching for cosmogenic photons

Laboratory: LPNHE (Paris) // Group: Auger
Contact person: Antoine Letessier-Selvon /// antoine[dot]letessier-selvon[at]lpnhe[dot]in2p3[dot]fr
Website: lpnhe.in2p3.fr

The cosmic ray spectrum at ultra high energies (above 10¹⁸ eV or 0.1 J) was measured by the Pierre Auger Observatory with remarkable precision. Two spectral features are clearly identified from these measurements. The first one, called the “ankle” corresponds to a flattening of the spectrum with a change of the spectral index from -3.23 to -2.67 at a cosmic ray energy just below 1 J. The second feature is the flux exponential extinction that starts at energies above 8 J.

The origins of those spectral characteristics are not yet identified with certainty. They could arise either from the cosmic ray source properties and distribution or from interactions during their journey to Earth of the cosmic rays with the photons of the cosmic microwave background.

In the case of protons, at energy above 8 J these interactions produces charges and neutral pions which subsequently decay producing photons and neutrinos around 1 J. If proton dominates at the highest energy this mechanism would be responsible for the spectral exponential cut-oft (this is know as the Greisen-Zatsepin-Kuzmin or GZK cutoff). The neutrinos and photons from the pion decays are called cosmogenic because they are produced in the cosmos along the protons trajectories.

A recent upgrade, designed in our laboratory, of the detectors of the Auger Observatory allows us to very significantly improve our sensitivity to those photons. This upgrade makes their detection very likely in the hypothesis where protons dominates the comic ray spectrum at ultra high energies. If proton do not dominate, stringent limits will be put their flux fraction at the highest energies.

These major results will give indications on the nature of exponential cut off observed in the spectrum and on the possibility to construct observatories based on protonic astronomy.

During its three PhD years the applicant will participate into data taking, he/she will design selection criteria to extract photon candidates, he/she will model detection efficiencies, calculate fluxes and upper limits, and he/she will confront his/her results to existing, and self-developped, predictions.

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Ultra high energy cosmic rays and origin of the “ankle”: What do large scale anisotropies tell us?

Laboratory: LPNHE (Paris) /// Group: Auger
Contact person: Antoine Letessier-Selvon /// antoine[dot]letessier-selvon[at]lpnhe[dot]in2p3[dot]fr
Website: lpnhe.in2p3.fr

The cosmic ray spectrum at ultra high energies (above 10¹⁸ eV or 0.1 J) was measured by the Pierre Auger Observatory with remarkable precision. Two spectral features are clearly identified from these measurements. The first one, called the “ankle” corresponds to a flattening of the spectrum with a change of the spectral index from -3.23 to -2.67 at a cosmic ray energy just below 1 J. The second feature is the flux exponential extinction that starts at energies above 8 J.

The origins of those spectral characteristics are not yet identified with certainty. They could arise either from the cosmic ray source properties and distribution or from interactions during their journey to Earth of the cosmic rays with the photons of the cosmic microwave background. The Ankle can for exemple either be explained by the production of e+/e- pair by protons originating from distant extra-galactic sources or by a change of cosmic ray sources (two different types in the Galaxy or a transition from Galactic to extra-galactic sources).

In the case of a transition from Galactic to extragalactic sources, a trace of this transition should be left in the distribution of arrival directions of cosmic rays on the sky. Current data from the Pierre Auger Observatory led us to believe that such a discovery is at hand.

A recent upgrade, designed in our laboratory, of the detectors of the Auger Observatory augmented the sensitivity to cosmic rays of 0.1 to 0.5 J by a factor of at least 5. This will allow us to multiply by three the available statistics in less than 2 years leading to dipole detection sensitivity of a fraction of a percent.

These major results will give direct indications on the nature of the Ankle and on the origin of ultra high energy cosmic rays, a question left open for more than 100 years.

During its three PhD years the applicant will participate into data taking, using the tools developed by the Auger collaboration he/she will correct the data from spurious local effects, he/she will calculate the first moment of the spherical harmonic developments (up to the quadrupole), he/she will compare the results to personal or existing models, combining hypothesis on the source distributions, their chemical composition and the influence of the Galactic magnetic field.

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Numerical and theoretical studies of particle acceleration in relativistic astrophysical outflows

Laboratories: Institut d'Astrophysique de Paris /// CEA, DAM, DIF
Contact persons:
Martin Lemoine /// lemoine[at]iap[dot]fr
Laurent Gremillet /// laurent[dot]gremillet[at]cea[dot]fr
Website: www.iap.fr

Mechanisms of particle acceleration in powerful astrophysical sources represent one of the cornerstones of modern astroparticle physics. Acceleration physics indeed plays a key role in the interpretation of observational data of non-thermal sources such as pulsar winds, active galactic nuclei, gamma-ray bursts, just as it plays a key role in understanding the origin of very high energy cosmic rays. Important progress has been achieved in this field in recent years, notably through massive particle-in-cell (PIC) simulations, which allow a direct ab initio simulation of the dynamics of collisionless plasmas.

This PhD thesis proposes to study the mechanisms of particle acceleration in relativistic outflows, through the conjunction of PIC simulations and analytical studies. This PhD will be co- supervised by Laurent Gremillet (Direction des Applications Militaires du CEA, Bruyères le Chatel), who is specialized in laser-plasma interactions and PIC simulations, and Martin Lemoine (Institut d'Astrophysique de Paris, Paris), astrophysicist. The PhD will thus follow a double sided approach with, on the one hand, the development and the conduction of PIC simulations of astrophysical sources and, on the other hand, the analytical study of acceleration physics and its astrophysical consequences. The PIC code is already available, but it has been developped for use in laser-plasma interaction studies, hence it needs to be optimized for its application to astrophysical topics.

An in-depth simulation of a relativistic and magnetized collisionless shock wave, as found in gamma-ray bursts outflows or in active galactic nuclei, represents a major objective Γ= (1-β²)^-1/2, and as a function of the degree of magnetization of the ambient plasma. Simulations for a moderate Γ~2^-10 are particularly interesting because such shocks correspond to internal shocks in a relativistic outflow, and because their physics remain at present largely unexplored. In particular, one does not know whether acceleration takes place, and if yes, up to which energy. Analytical studies will complement the PIC simulations, by defining the most pertinent simulations, and by extracting astrophysical consequences both in terms of radiative signatures and high energy particle production.

Numerous other applications of such simulations can be envisaged in the course of this PhD, since PIC codes have just made their way into the community of high energy astrophysics and astroparticles.

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Are constants of Physics constant?

Laboratory: Institut d'Astrophysique de Paris
Contact person: Patrick Petitjean /// petitjean[at]iap[dot]fr
Website: www.iap.fr

The light emitted by high redshift quasars travels during billions of years through the universe before being recorded by big telescopes on Earth. During this travel, the light goes across numerous gaseous objects that are located by chance along the line of sight to the quasar (intergalactic clouds, disk and haloes of galaxies). These objects absorb selectively the light in transitions which, when observed and measured, can yield information about the chemical composition and physical state of the gas, its kinematics and space distribution. Absorption line systems observed in the spectra of high redshift quasars are a unique tool to observe and study the intergalactic medium and the interstellar medium of high redshift galaxies. Following the evolution over cosmic time (at different redshifts) brings clue information on how galaxies form.

Since we can observe the young universe as it was, we can test whether physics was at that time the same as it is on Earth now. We can in particular test whether fundamental constants of physics have varied over cosmic time. This represents a fundamental test of our standard model and more generally of General Relativity. For this, we can measure very accurately the positions of absorption transitions to derive the variations with time of the fine structure constant or of the proton-to-electron mass ratio. To date, although some claims have been published, no confirmed relative variation has been seen at any redshift down to about 10^-5.

This field of research has driven the construction of a highly stable spectrograph (ESPRESSO) to be installed on VLT next year and is one of the main drivers of the project for a high-resolution spectrograph to be installed on the European extremely large telescope (ELT).

A European team has gathered forces to convince ESO to allocate a large amount of UVES-VLT observing time to this issue through an ESO Large Program. Exquisite high resolution and high SNR spectroscopic data have been obtained over more than 30 nights. Most of these data are reduced and ready for analysis. The most important goal of the PhD is to gain one order of magnitude on the limits achieved; this will be possible by chasing systematics. One source of uncertainty in this measurement however is the isotopic composition of the measured species (carbon, oxygen, iron or magnesium) because it can lead also to wavelength shifts. This composition depends strongly on the star formation history of the gas which is probed by the quasar line of sight.

The PhD will be dedicated to lift the degeneracy between the effect of isotopic abundances and that of the variation of the fine structure constant using data from the Large Program. The ultimate goal would be to open a brand new field of research which consists in measuring the isotopic composition of different species and, by combining all physical information (metallicities, physical state of the gas...) to constrain the star formation history of the associated galaxies. Although the subject is mostly observational, interaction with theorists working in this field in IAP will be encouraged.

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Improving the Planck cosmological results with component separation

Laboratory: Institut d'Astrophysique de Paris
Contact persons: Jean-François Cardoso /// cardoso[at]iap[dot]fr
Karim Benabed /// benabed[at]iap[dot]fr
Website: www.iap.fr

Even though Planck is mapping the full microwave sky, only a fraction (about half) of the celestial sphere surface is actually used to measure the cosmological model. Indeed, the astrophysical foregrounds are obfuscating the microwave background emission and the cosmological analysis can only be performed with sufficient accuracy where the foreground contamination is low enough.

Being able to either remove or more finely model the foregrounds in the rest of the sky would greatly increase the value of the Planck data. Yet, the Planck team was also able to build an almost full sky clean CMB map. However, the statistical description of this cleaned map and its foreground residual content are not sufficiently well understood yet. This prevents for now, the use of this map for solid cosmological inference. Polarised data, with different contamination and different geometrical properties complicates even more the picture.

The PhD student will work with Jean-Francois Cardoso (who built Planck CMB cleaned map), and Karim Benabed (who worked on the Planck likelihood). His goal will be to build a better understanding of the statistical content of the cleaned cmb map and use that knowledge to improve the cosmological value of the Planck data. This will be done by re-thinking the component separation algorithm in view of the cosmological parameter measurement. In doing so, he will also evaluate the opportunity of revising the current way of handling polarized data in those component separation method, in order to minimize leakage due to the mask between the different polarization modes. Finally, he will assess how much those methods can be used to extract improved information on some faint, small scale foregrounds and in particular on SZ and CIB.

The student will also have the opportunity to interact with the other Planck scientists at ILP, such as François Bouchet (Planck scientific coordinator), Eric Hivon (beam and likelihood) and Benjamin Wandelt (NG and likelihood).

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Primordial galaxy formation with radiative hydrodynamics simulations

Laboratory: LERMA,Observatoire de Paris, UPMC
Contact person: Benoit Semelin /// benoit[dot]semelin[at]obspm[dot]fr
Website: lerma.obspm.fr

The Epoch of Reionization (EoR) is finally coming under the scrutiny of our latest instruments. The Epoch of Reionization is a period corresponding to the first billion years in the history of the universe (from z=20-30 down to z=6). It begins when the light emitted by the first stars born from the gravitational collapse of primordial density fluctuations, start to ionize the surrounding intergalactic medium. The resulting ionized regions grow until they overlap, finally confining neutral hydrogen into small dense clumps embedded in vast diffuse regions of ionized gas by z~6. During this process the large scale properties of the universe are strongly coupled to the small-scale physics of galaxy formation.

Modeling the EoR in its full complexity is becoming vital as observations are becoming available and will improve drastically in terms of quality and quantity in the next few years. To mention but two; observations with the WFC3 on Hubble have made it possible to build luminosity functions at z~8 of the sources of reionization (be to much improved with JWST) and 21cm observations of the neutral intergalactic medium are just around the corner, with LOFAR starting its survey in 2013 and the SKA being build for 2020.

One of the main and least understood processes setting the pace of reionization is the escape of ionizing photons from primordial galaxies. Indeed a large but uncertain fraction of the emitted photons is absorbed in the dense, fast-recombining intragalactic medium before it ever reaches the intergalactic medium. All modeling of the EoR depends on this process. Characterizing it is the subject of this thesis, as observations are scarce and the few existing simulations do not reach a consensus.

To tackle this issue we can use large numerical cosmological simulations including both dynamics and radiative transfer. Running very high resolution simulations of primordial galaxies with a radiative hydrodynamics code LICORICE, will make it possible to get robust estimations of the so-called escape fraction at z>6, depending on the mass of the galaxy and other environmental parameters. To reach this goal it will be necessary to implement new physics in the code such as formation of H_2, dust, or the action of radiation pressure: the quantitative impact of those on global reionization is still either a matter of debate or completely unknown.

A possible development will be to use those predictions of the escape fraction and implement them in the much larger scale simulations needed to predict the 21cm signal that will be observed by the SKA. They will go in as sub-grid recipes as such large scale simulations cannot resolve the intragalactic medium. Robust prediction for the 21 cm signal should result, ready for comparison with the observations of LOFAR and SKA.

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Particle Physics at LHC - Thesis opportunity in the ATLAS group of Paris

Laboratory: LPNHE (Paris) /// Group: ATLAS
Contact persons:
G. Calderini /// giovanni[dot]calderini[at]lpnhe[dot]in2p3[dot]fr
S. De Cecco /// sandro[dot]dececco[at]lpnhe[dot]in2p3[dot]fr
B. Laforge /// betrand[dot]laforge[at]lpnhe[dot]in2p3[dot]fr
G. Marchiori /// giovanni[dot]marchiori[at]lpnhe[dot]in2p3[dot]fr
J. Ocariz /// jose[dot]ocariz[at]lpnhe[dot]in2p3[dot]fr
M. Ridel /// melissa[dot]ridel[at]lpnhe[dot]in2p3[dot]fr

Website: http://lpnhe.in2p3.fr/spip.php?rubrique5

The ATLAS group at LPNHE is composed of about 30 physicists and engineers, heavily contributing to physics analysis and with strong experience in detector design, construction and commissioning. Our physics interests include: the study of the Higgs boson properties in the decay modes to two photons, to Z-photon and to pairs of b quarks. In the first case, the group has traditionally played a leading role in this analysis in the ATLAS Collaboration and this is going to continue, in particular with the refinement of the Higgs spin analysis, the study of its natural width and CP properties and the addition of new event topologies. In the case of the Higgs decay to pairs of b quarks, this analysis is performed in special topologies as the associated production with a Z or W boson or in tt-Higgs events and is becoming strategic with the new luminosity that will be delivered by the LHC in the next few years. In the Higgs sector new analyses are also being started in the LPNHE group in conjunction with the search for New Physics beyond the Standard Model and Dark Matter. The group is also involved in jet reconstruction and energy calibration and in the measurements of top quark mass and production rate. We are very active in the Insertable B-Layer (IBL) construction and commissioning and R&D studies for the track-trigger upgrade (FastTrack) and the Phase-II upgrade of the ATLAS tracking system. Our laboratory takes part in the Tier-2 GRIF in Paris area.

The successful candidate is expected to contribute to the group activities and commitments in ATLAS. He/She will be based in Paris with frequent travels to CERN.

The candidates are encouraged to contact the potential PhD supervisors to discuss the fine details of the possible thesis work.

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Flux vacua in heterotic and type II strings: properties and applications

Laboratory: LPTHE (Paris)
Contact persons:
Dan Israël /// israel[at]lpthe[dot]jussieu[dot]fr
Michela Petrini /// petrini[at]lpthe[dot]jussieu[dot]fr

Website: www.lpthe.jussieu.fr

With the successful ongoing experiments at the LHC and the results from the PLANCK CMB probe, our knowledge of the structure of matter and of the history of the Universe is dramatically improving. A theoretical understanding of these results, requires a knowledge of the law of physics at very high energy scales. String theories can provide conceptual and technical tools for addressing these issues. An important challenge is to interpolate with known particle physics at lower energies. To this extent it is important to reach a better control of string compactifications, finding suitable compactification models, understanding the structure of the effective theories and the geometry of the internal manifolds. In the last few years, new tools and ideas have tremendously improved the potential of both type II and heterotic compactifications for phenomenology. Several possible topics covered by this thesis are given below, using the two complementary approaches of supergravity and of two-dimensional world-sheet theories.

Heterotic string theory have many appealing features to provide extensions of the Standard Model. At the same time it allows for a worldsheet description using standard two-dimensional field theory methods. On general grounds, supersymmetric compactifications correspond to torsional manifolds endowed with exotic gauge bundles. Gauged linear sigma-models with (0,2) supersymmetry have been developed in the last few years as a powerful tool that allows to explore such compactifications. The applicant is expected to develop various aspects of these models, such as dualities, one-loop corrections for compactifications with torsion and the identification of IR fixed points.

At the level of supergravity theory, the applicant is expected to further explore compactifications with fluxes both in heterotic and in type II, and to understand the non-perturbative duality relations between them. In this perspective, new classes of torsional solutions will be studied using the powerful methods of G-structures and of Generalised Geometry. In type II supergravities, black holes and domain wall solutions correspond often to backgrounds of backreacted D-branes that are phenomenologically interesting and are also relevant for gauge/gravity duality; in both cases it crucial to understand the geometry of such backgrounds. Gauged supergravities, that arise as consistent truncations of the ten-dimensional theories, provide a very useful and complementary approach to this problem, as well as to understand the role of dualities.

Most of the progress so far in flux compactifications relies on supersymmetry. However, the observed world is not supersymmetric, and one key question is to understand the mechanisms of supersymmetry breaking and generation of a positive and very small cosmological constant.

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