Thesis
Last call opened (already closed):
74 thesis registered
Thesis by domain: (some thesis are registered in 2 domains)
Astroparticle Physics | 16 | Astrophysics | 27 |
Cosmology | 8 | Experimental Particle Physics | 34 |
General Relativity | 7 | Theoretical Particle Physics | 15 |
Call: PhD Programme 2017
Title: Big data, Machine Learning and object classification in high energy hadronic collisions |
The extremely large amounts of data generated by particle colliders make the use of ML both a necessity and a potentially very fruitful path to follow. ML techniques are used extensively in many areas of high energy particle physics with application ranging from low level tasks, such as identification of physical objects in collider data (top quarks, W and Z bosons, tau, ...) to high-level physics analyses discriminating between specific and rare signals and known backgrounds. More recently, ML has proved to be a powerful physics discovery tool allowing to identify important properties of physical objects (e.g. QCD jets) from 'detector-level' information that had escaped the imagination of theorists.
This thesis will have a dual focus: (i) the application of ML to the efficient identification of physical objects in proton-proton, proton-nucleus and nucleus-nucleus collisions at LHC and future collider energies; (ii) development of systematic methods to learn Physics from the ML, that is to identify what is learnt by the machine and match to either existing analytical calculations or carry on those calculations. All work will be carried out using both Monte-Carlo generated samples and Open (publicly available) LHC data. The selected candidate will develop both strong and highly transferable computational skills and solid competence in Quantum Chromodynamics.
The thesis will be co-supervised by an experimentalist (Nuno Castro) and a phenomenologist/theorist (Guilherme Milhano) and the selected candidate will divide her/his time between Braga and Lisbon.
Title: Bootstraping CFTs |
The aim of this project will be to search for new CFTs, carving the space of possible CFTs in several dimensions. This project will be conducted in close collaboration with the team of the “Simons collaboration on the Non-perturbative Bootstrap”.
Title: Effect of strong magnetic fields on transport coefficients |
There have been several works on electron conduction along quantizing magnetic fields in neutron star envelopes and outer crusts [Potekhin99]. Recently, these works were generalised to warm matter with 10^9
We will consider the case of strongly degenerate particles and we will assume quantizing magnetic fields. The collision term, which we will treat in the relaxation time approximation, will be added to the Vlasov equation, in order to calculate the transport properties ([Laundau81], [Heiselberg93]). A variational formulation of transport theory is needed to treat the electromagnetic interaction due to ist singularity [Heiselberg93]. A small temperature or charge chemical potential variation will give rise to a perturbation of the distribution function. The moment relaxation time will be determined, followed by the calculation of the transverse and longitudinal electric and thermal conductivities as well as the viscosity. We will provide accurate fits of the calculated transport coefficients.
Chamel08 - Nicolas Chamel and Pawel Haensel, Living Rev. Relativ. 11, 10 (2008).
Harutyunyan16 - Arus Harutyunyan and Armen Sedrakian, Phys. Rev. C 94, 025805 (2016).
Potekhin99 - A. Y. Potekhin, Astron. and Astrophys. 351, 787 (1999).
Ziman60 - J. M. Ziman, Electrons and phonons, Oxford University Press
Landau81 - L.P. Pitaevskii; E.M. Lifshitz (1981). Physical Kinetics. Vol. 10 (1st ed.). Pergamon Press.
Heiselberg93 - H. Heiselberg and C J Pethick, Phys. Rev. D 48, 2916 (1993)
Title: Hunting for new Physics in the LHC run 2 era |
The present proposal aims at investigating possible evidences of new physics in the framework of theoretical scenarios with extended scalar and/or lepton sectors, in the light of experimental information obtained by experiments operating at the energy and intensity frontiers, like the LHC (or future colliders) and flavour physics facilities. Besides acquiring a strong background in theoretical particle physics and a capability of designing new observables and developing new methods, the student will master several simulation and data analysis techniques. The research programme will be carried out under the supervision of F.R. Joaquim from IST and J. A. Aguilar-Saavedra from the University of Granada. Although the host institution will be IST, the candidate will spend periods of time at the University of Granada during the course of the PhD programme. The results obtained from the candidate’s research will be published in high-impact peer-review journals and presented in international scientific events.
Title: Investigating the propagation of quarks in a hot medium |
The calculation of the fundamental Green’s functions using the lattice formulation of QCD such as the propagators enables a first principles determination of the propagators and, therefore, allows to study the generation of mass scales, i.e. chiral symmetry breaking, and access some of the properties linked to the confinement and deconfinment mechanisms. The knowledge of the mass functions are crucial to the understanding of modern heavy ion experimental programs and for the history of the Universe.
In this project we aim to compute, on the lattice, the quark propagator at finite temperature. This will allow to have a clear picture of chiral symmetry breaking and confinement patterns as a function of the temperature. The simulations will be performed using the supercomputer facilities at the University of Coimbra. The candidate will join a team with a large experience in lattice QCD simulations.
Title: Jet sub-structure as a probing tool of the Quark Gluon Plasma |
The experimental and theoretical heavy-ion research programme has evolved from its initial QGP-discovery phase (CERN-SPS and BNL-RHIC) to a full-fledged QCD-probing effort at the LHC. Extraction of QGP properties from data requires the availability of adequate probes — that are both under excellent theoretical control and that are generated within the QGP as its very short lifetime (10^-23 seconds) precludes any external probing approach.
At the LHC at CERN, Lead nuclei are collided at the highest ever centre-of-mass energy (~5 TeV per nucleon pair, a factor 25 increase from RHIC). The large collision energy leads to the abundant production of QCD jets that have proved to have a huge potential as detailed probes of the QGP. In particular the sub-structure properties of jets offer unique opportunities to fully characterize the QGP.
The aim of this thesis is to develop the theory of jet sub-structure for jets that are created within and travel through the QGP, to simultaneously carry out event-generator based phenomenological studies aimed at establishing the sensitivity of specific sub-structure observables to specific QGP properties. Our group is at the forefront of efforts in this domain. The selected candidate will develop both strong and highly transferable computational skills and solid competence in Quantum Chromodynamics.
The thesis work, co-supervised by Guilherme Milhano and Liliana Apolinário, will take place within the Heavy Ion Phenomenology group at LIP-Lisbon (HIP@LIP) in close collaboration with colleagues at CERN, Santiago de Compostela, and MIT.
Title: Magnetized neutron stars |
A fully general relativistic approach will be employed in which we will focus on the global structure properties of uniformly rotating and magnetized NS relevant for astrophysical applications such as mass, polar and equatorial radii, angular velocity, moment of inertia, quadrupole moment and gravitational wave (GW) amplitude. This will be done for a selected sample of EoS with different symmetry energy slopes and a unified inner-crus EoS. Star properties such as the mass and radius will be determined from the integration of the coupled Einstein-Maxwell equations by means of a pseudo-spectral method, taking into consideration the anisotropy of the energy-momentum tensor due to the B-field and also the effects of the centrifugal force induced by rotation in order to obtain both rotating and magnetized stellar models [Bonazzola93,Bocquet95,Franzon15,Franzon16a]. For that purpose, we are going to use the Lorene C++ library for numerical relativity [Lorene]. The already existing codes for a poloidal magnetic field will be generalized to a toroidal magnetic field. Recent calculations indicate that the crust-core transition density could be larger for magnetized stars with B-fields stronger than $10\times 10^{15}$ G in the crust [Fang16]. The effect of the strong B-fields and rotation on the crust thickness of the stars and onset density of the direct Urca will be studied
The influence of an unified EoS in GW radiation emitted by fast rotating and magnetized neutron stars will be investigated, and self-consistently relativistic solutions for NS with poloidal and toroidal B-fields will be computed by solving the Einstein-Maxwell field equations. The B-field supplies an anisotropic pressure, leading to the breaking of the spherical symmetry of the star. The quadrupole moment of the mass distribution will be calculated and an estimation of the GW of such objects will be performed in the same spirit as in Refs. [Franzon16,Bonazzola96]. The the GW amplitude of our stellar models will be compared with the sensitivity curves of current ground-based GW interferometers. In particular, the effect of an unified crust-core EoS on gravitational wave radiation emitted by isolated and binary neutron star systems will be investigated.Such a calculation and the models presented in this work will serve in the future as the initial data conditions for simulations of realistic EoS hydrodynamical mergers.
Bonazzola93- S. Bonazzola, E. Gourgoulhon, M. Salgado, and J. Marck, Astron. and Astrophys. 278, 421 (1993).
Bocquet95- M. Bocquet, S. Bonazzola, E. Gourgoulhon, and J. Novak, Astron. and Astrophys. 301, 757 (1995).
Fortin16 - M. Fortin, C. Providencia, A. R. Raduta, F. Gulminelli, J. L. Zdunik, P. Haensel, and M. Bejger, Phys. Rev. C 94, 035804 (2016).
lorene- www.lorene.obspm.fr.
Fang16 - J. Fang, H. Pais, S. Avancini, and C. Provid\^encia, Phys. Rev. C 94, 062801(R) (2016).
Franzon16 - B. Franzon and S. Schramm, Mon. Not. Roy. Astron. Soc. 467, 4484 (2017)
Bonazzola96 - S. Bonazzola and E. Gourgoulhon, Astron. Astrophys. 312, 675 (1996).
Title: Neutrinos at the Energy, Intensity and Cosmic Frontiers |
The present PhD research proposal aims at contributing to the theoretical understanding of several fundamental phenomena by combining analytical and numerical methods adopted in particle physics and cosmology. This strategy will be developed in the light of present and upcoming results from several sources, namely the LHC, neutrino experiments and cosmological observations.
Title: New Physics from Multi-Higgs Models |
Title: Perturbative evaluation of Electroweak Precision Observables in the Standard Model and Beyond |
Some issues are still open problems in the literature:
1- a gauge-invariant prescription for the $\gamma_5$ algebra. In particular, the author of [1,2] presents the so called Rightmost Ordering in which all $\gamma_5$ should be moved to the rightmost position of the amplitude before its dimensionality is altered. Another proposal focuses on an integral representation for the trace involving gamma matrices [3]. Nevertheless, in both cases the authors intend to obtain a prescription which allows dimensional regularization to be applied to dimension specific objects as the $\gamma_5$ matrix. Another proposal, in the case of four-dimensional regularization, was envisaged by the authors of [4].
2- In the particular instance of supersymmetry breaking, it is neither straightforward nor conclusive that supersymmetry is a symmetry of the full quantum theory in any particular case. However, as discussed in [5], there have been claims about a supersymmetry anomaly which turned out erroneous because of the difficulty to distinguish between a genuine and a spurious anomaly. The latter is an apparent violation of a supersymmetric Ward identity due to use of a regularization method that violates supersymmetry.
3- Electroweak precision observables are extremely well measured data which serve to test Physics beyond the standard model. Examples are the W boson mass, the effective leptonic weak mixing angle, the anomalous magnetic moment of the muon and the mass of the lightest Higgs boson (CP-even) in the Minimal supersymmetric standard model. For instance the muon anomalous magnetic moment a_\mu{exp} measured in the experiment E821 in Brookhaven [6] and theoretical calculations a_mu^{SM} involving the standard Model [7], yield a discrepancy [8]
\Delta a_\mu^{today} = a_\mu^{exp} - a_\mu^{SM} = (287 (+\-) 80) 10^{-11}.
Such difference can prove supersymmetric models compatible or not with phenomenology. If discarded, extensions in the Higgs sector appear as new possible venues.
We intend to apply Implicit Regularization (IR), see e.g. [9-19], to theoretical calculations which need an invariant regularization, particularly to evaluate electroweak precision observables.
The basic idea of IR is based on the observation that ultra-violet (UV) singularities are independent of the kinematics. This is used to isolate the UV singular part of loop integrals. In IR, the UV singular part is expressed in terms of implicit integrals and boundary terms (that have to be set to zero to respect gauge invariance). The resulting UV finite integrals are evaluated in strictly four dimensions.
Bibliography:
[1] E. C. Tsai, Phys. Rev. D83 (2011) 025020.
[2] E. C. Tsai, Phys. Rev. D83 (2011) 065011.
[3] R. Ferrari, Int. J. Theor. Phys. 56 (2017) 691.
[4] G. Cynolter and E. Lendvai, Mod. Phys. Lett. A 26 (2011) 1537.
[5] I. Jack, D. R. T. Jones, Perspectives on Supersymmetry (G. L. Kane, ed), hep-ph/97077278.
[6] G. Bennett, et al., (Muon $g-2$ collaboration), Phys. Rev. D73 (2006) 072003.
[7] The Physics case for the New Muon $g-2$ Experiment, D. W. Hertzog, James P. Miller, Eduardo de Rafael, B. L. Roberts, D. Stockinger, arXiv:0705.4617.
[8] Michel Davier et al., Eur.Phys.J. C71 (2011) 1515; Erratum-ibid. C72 (2012) 1874.
[9] A.P.B. Scarpelli, M. Sampaio and M.C. Nemes, Phys. Rev. D 63 (2001) 046004.
[10] A.L. Cherchiglia, M. Sampaio and M.C. Nemes, Int. J. Mod. Phys. A 26 (2011) 2591.
[11] L.C. Ferreira, A.L. Cherchiglia, Brigitte Hiller, Marcos Sampaio and M.C. Nemes, Phys. Rev. D 86 (2012) 025016.
[12] A.L. Cherchiglia, L.A. Cabral, M.C. Nemes and M. Sampaio, Phys. Rev. D 87 (2013) no.6, 065011.
[13] J.C.C. Felipe, A. R. Vieira, A.L. Cherchiglia, A.P.B. Scarpelli and M. Sampaio, Phys. Rev. D 89 (2014) no.10, 105034.
[14] A. R. Vieira, A. L. Cherchiglia and M. Sampaio, Phys. Rev. D 93 (2016) no.2, 025029.
[15] A.L. Cherchiglia, A.R. Vieira, B. Hiller, A.P.B. Scarpelli, M. Sampaio, Annals Phys. 351 (2014) 751.
[16] O. A. Battistel and G. Dallabona, Eur. Phys. J. C 45 (2006) 721.
[17] D.E. Carneiro, A.P.B. Scarpelli, M. Sampaio and M.C. Nemes, JHEP 0312 (2003) 044
[18] H.G. Fargnoli, B. Hiller, A.P.B. Scarpelli, M. Sampaio and M.C. Nemes, Eur. Phys. J. C 71 (2011) 1633.
[19] A.L. Cherchiglia, M. Sampaio, B. Hiller and A.P.B. Scarpelli, Eur. Phys. J. C 76 (2016) no.2, 47
Title: Phenomenology of Beyond the Standard Model (BSM) models at the Large Hadron Collider |
This work is about examining how the possible extensions of the scalar sector of the SM, that could solve those discrepancies, can be tested at the LHC and future colliders through the Higgs sector. The work will be performed in close collaboration with ATLAS experimentalists to devise the best strategies to adopt in order to acquire sensitivity to all such models.?
Title: Quantum gravity and the bootstrap |
The aim of this project is to study the relation between the physics of quantum gravity in AdS and CFTs. This project will be conducted in close collaboration with the team of the “Simons collaboration on the Non-perturbative Bootstrap”.
Title: Searches for resonances in models of composite dark matter |
The goal of this proposal is two folded. Firstly, identify, from the theoretical point of view, the possible properties of these particles (masses, quantum numbers, etc.) depending of the amount of dark matter that they account for. And secondly, study their signals at the ATLAS experiment using Monte Carlo simulations as well as real data. These two goals will allow the student to become an expert on the particle physics both from an experimental and a theoretical point of view.
Title: Study of high energy hadronic cascade through muons |
The first interactions occur at centre of mass energies up to 400 TeV, more than one order of magnitude above the most energetic man made accelerator. This means that UHECRs are a unique opportunity to study particle physics above the LHC energy scale.
However, although the EAS encodes the information about the nature of the primary (which is expected to be of hadronic nature – proton to iron) and about the characteristics of the hadronic interaction (which shapes the development of the EAS), this information is degenerated.
A promising tool to break this degeneracy is the study of muons. Muons come from the decays of charged mesons, which are a direct by-product of hadronic interactions. Moreover, muons can travel many kilometers from the hadronic shower almost unaffected, carrying valuable information. The understanding of the muons distributions is an essential key to break the degeneracy between the uncertainties on the extrapolation of the hadronic interaction models to the highest energies and the composition of the UHECR beam.
The study of the air shower can be done by means of the cascade equations, assuming some simplifications, or by means of full Monte Carlo simulations that include many important details difficult to account for otherwise. On the other hand, Heitler models offer a simplified version of the main multiplicative process of a cascade and serves to qualitatively understand the most important features, giving approximated values for relevant variables of the cascade. Although Monte Carlo simulations offer the most complete description of the shower, this is done at the cost of losing understanding to the main underlying physics.
Hence, in this thesis we propose to investigate the muon distributions of the EAS using analytical models. This is a complex physics problem that requires a combined effort from different points of view: mathematical, statistical and analytical.
This would allow not only to identify the main shower properties that drive the muon distributions main characteristics, but also would give a profound knowledge over its connection to the hadronic shower.
The results from this work would naturally be used to extract information about the high-energy hadronic interaction from the experimental measurements on the muon distributions, in particular those conducted at the Pierre Auger Observatory.
Title: Study of top quark and Higgs bosons properties at the LHC |
This research project will be supported jointly by the University of Minho and Institute de Recherche sur les Lois Fundamentales de l'Univers (IRFU) Saclay/Paris, member of the Paris-Saclay University, in great proximity with the theoretical group at the Borough of Manhattan Community College (BMCC) in New York with the goal of providing a general understanding of the current research in the field and of stimulating enthusiasm for scientific research. In this proposal, specific topics of the physics program of the LHC will be addressed from both the phenomenological and theoretical points of view, centered in two main tasks:
1. The objective of the first task is to study the main top quark decay to a W boson and a bottom quark. New analysis strategies and new observables (including angular distributions and asymmetries) will be proposed and studied in detail in order to probe new anomalous physics contributions to the Wtb vertex Lorentz structure. Strong collaboration between experimentalists and theorists is expected for this task, once the use and development of global fitters applied to top quark physics, like TopFit, are of utmost importance. The students supervision will be performed within a group with a long tradition of publishing in this area of scientific research. António Onofre was a former convener of the Top Quark Properties sub-group of the ATLAS experiment. During the execution of the work plan, foreseen stays, at IRFU,Paris-Saclay University, are expected to happen under the supervision of Frederic Deliot,who is currently the Top Quark group convener of the ATLAS experiment. Miguel Fiolhais is also expected to help on the students supervision, once he did his PhD in precise this type of measurements and can, at the same time, ensure an optimal bridge with the theoretical group at BMCC, New York. As was acknowledge recently by the team, combining all available experimental information concerning top quark physics and including more observables like new asymmetries (proposed in the literature but not measured yet by the experiments), is fundamental to achieve the best precision on the evaluation of the Wtb vertex structure, better then waiting by the end of all Runs at the LHC with only the few observables measured already.
2. The second task of this project is dedicated to the study of the associated production of the Higgs boson with a top quark pair in proton-proton collisions at a center-of-mass energy of 13 TeV at the LHC. New angular distributions of the decay products, as well as angular asymmetries, will be explored in order to probe the CP nature of the Higgs coupling to top quarks, and reduce the contribution from the dominant irreducible background contributions. For this task, it is of utmost importance the bridge with the BMCC theoretical group, under a close supervision of Miguel Fiolhais once this gives the chance of understanding the production mechanism of ttH events at the LHC to NLO in fixed order perturbation theory with resummation of soft emission radiation to NLL accuracy.
Although the applications for this specific call are for fellowships in the country (Portugal) IRFU and BMCC are currently considering covering the expenses for stays at those cites, during the execution of the current work plan, taking maximum profit from supervision expertise in all sites. The PhD degree expected at the end of the work plan, is to be attributed by the institutions involved, for which all necessary steps are under way.
Contact point - LIPAv. Elias Garcia, nº14 - 1 1000-149 Lisboa - Portugalwww.lip.pt :: idpasc.portugal@lip.pt |