Master thesis proposals: Particles and Gravitation


For further information on possible Master Thesis projects and advisors in this speciality, please contact Tomeu Fiol at


Title: Buiding the first quantum processor in Barcelona.

Advisor: Pol Forn Díaz (BSC)

Abstract: We are approaching the age of quantum computers [1]. Throughout the world, many initiatives, both public and private, aspire to construct the first generation of quantum processors able to surpass the computational power of the most powerful classical computers [2]. Among all the candidate systems on which to build such a device, superconducting quantum circuits [3] are among the most promising. These circuits behave as artifically engineered atomic systems in the microwave frequency domain, allowing their quantum state to be efficiently initialized, controlled, and read out [4].

In a collaboration between the University of Barcelona (UB) and the Barcelona Supercomputing Center (BSC), we are starting a project to aim at building the first quantum processor in Barcelona using the technology of superconducting circuits. The construction of such system requires a multi-disciplinary effort of physics, electronics, material science and computer science.

We propose to construct a class of circuits to perform quantum annealing [5], which is one of the possible ways to perform quantum computation in a quantum processor. The first circuits will need to be designed using advanced software tools and tested in an actual experimental setting. 


[1] Quantum Computation and Quantum Information, Nielsen and Chuang, Cambridge University Press (2000).


[3] Superconducting Circuits for Quantum information: an outlook. M. H. Devoret, R. J. Schoelkopf, Science 339, 1169 (2013). 

[4] Superconducting quantum circuits at the surface code threshold for fault tolerance, R. Barends et al., Nature 508, 500 (2014).

[5] Evidence for quantum annealing with more than one hundred qubits, S. Boixo et al., Nature Physics 10, 218 (2014).

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Title: Quantum computation by quantum annealing.

Advisor: José Ignacio Latorre (UB) 

Abstract: We will investigate new algorithms to be run a quantum annealing devices. This thesis is associated with the Barcelona Supercomputing Center.

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Title: Non-relativistic gravities.

Advisor: Joaquim Gomis (UB) and Carles Batlle (UPC)

Abstract: We will study non-relativistic holography using non-relativistic gravity.


R. Andringa, E. Bergshoeff, S. Panda, M. de Roo, "Newtonian Gravity and the Bargmann Algebra", Class.Quant.Grav. 28 (2011), arXiv:1011.1145 [hep-th]

R. Andringa, E. Bergshoeff, J. Gomis, M. de Roo, 'Stringy' Newton-Cartan Gravity", Class.Quant.Grav. 29 (2012) 235020, arXiv:1206.5176 [hep-th]

E. Bergshoeff, J. Gomis, B. Rollier, J. Rosseel, T. ter Veldhuis, "Carroll versus Galilei Gravity", JHEP 1703 (2017) 165, arXiv:1701.06156 [hep-th]

E. Bergshoeff, J. Rosseel, "Three-Dimensional Extended Bargmann Supergravity", Phys.Rev.Lett. 116 (2016) no.25, 251601, arXiv:1604.08042 [hep-th] 

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Title: Particles in electromagnetic fields as free Lie algebras.

Advisor: Joaquim Gomis (UB) and Carles Batlle (UPC)

Abstract: We will study the symmetries of moving particles in an electromagnetic background.


S. Bonanos, J. Gomis, "Infinite Sequence of Poincare Group Extensions: Structure and Dynamics", J.Phys. A43 (2010) 015201, arXiv:0812.4140 [hep-th]

J. Gomis, A. Kleinschmidt, "On free Lie algebras and particles in electro-magnetic fields", JHEP 1707 (2017) 085, arXiv:1705.05854 [hep-th] 

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Title: `Cracks' in the current Cosmological Paradigm: possible signs of dynamical dark energy in the Universe

Advisor: Joan Solà Peracaula

Abstract:: Dark energy (DE)  is believed to be the physical cause that produces the measured accelerated expansion of the universe. Within the standard model of cosmology (i.e. the current paradigm)  the DE is identified with a strict cosmological constant. However, the plain simplicity of this idea lies at the root of its unconvincing theoretical status.  In addition, phenomenologically, the standard model is also disputable at present.  Tensions of various sorts and of different degrees are known to be present among existing datasets within  such framework. For example, the recently measured local value of the Hubble parameter, H0, is significantly higher than the one inferred from the measurements of the anisotropies in the cosmic microwave background (CMB) by the Planck satellite. Also, the current paradigm predicts exceeding structure formation power as compared to the  observations etc.  The possibility that these facts are actually pointing to serious  `cracks'  in the current cosmological paradigm is slowly but strongly setting in. 

In this work, the student will have the opportunity to explore the nature of these cosmological problems as well as some theoretical models of  dynamical DE capable to alleviate them. Among these models, the dynamical vacuum models are well-motivated from the theoretical point of view (e.g. within quantum field theory in curved spacetime). Interestingly, they also predict a possible time variation of the fundamental "constants" of Nature, including the masses and couplings  of the elementary particles, what could act as an additional signature of physics beyond the standard models both of particle physics and cosmology.


[1] P.J. Peebles, B. Ratra, "The Cosmological constant and dark energy", Rev. Mod. Phys. 75 (2003) 559, e-Print: astro-ph/0207347

[2] J. Solà, "Cosmological constant and vacuum energy: old and new ideas", J.Phys.Conf.Ser. 453 (2013) 012015,  arXiv:1306.1527.

[3] H. Fritzsch, J. Solà, "Matter Non-conservation in the Universe and Dynamical Dark Energy", Class.Quant.Grav. 29 (2012) 215002, arXiv:1202.5097

[4] J. Solà, A. Gómez-Valent, and J. de Cruz Pérez,  "First evidence of running Cosmic Vacuum: challenging the Concordance Model", Astrophys. J.  836 (2017)  43 , arXiv:1602.02103

[5] Gong-Bo Zhao et al., "Dynamical Dark Energy in light of the latest observations'',  Nature Astronomy  1  (2017)  627,  arXiv:1701.08165

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TitleThe hyperfine splitting in heavy quarkonium hybrids

Advisor: Joan Soto

Abstract Heavy quarkonium hybrids are charmonium or bottomonium mesons with a non-trivial gluon content. Some of these hybrid mesons are candidates for the so called XYZ states [1]. It turns out that the spin dependent interactions leading to the hyperfine splitting are enhanced by a power of the heavy quark mass with respect to the ones in standard quarkonium. However, the potential controlling these interactions is not known at the moment. We propose to estimate it from Non-Relativistic QCD [2] by calculating its short distance behavior in perturbative QCD, and its long distance behavior in the QCD effective string theory [3]. Once an estimate of the potential is obtained, the hyperfine splittings can be calculated, either in quantum mechanical perturbation theory using known wave functions or by numerically solving the Schrödinger equation including this potential. 

[1] R.   Oncala   and   J.   Soto,   Phys.   Rev.   D 96 (2017), 014004 doi:10.1103/PhysRevD.96.014004 [arXiv:1702.03900 [hep-ph]].

[2]  N.   Brambilla,   A.   Pineda,   J.   Soto   and A.  Vairo,  Rev.  Mod.  Phys. 77,  1423  (2005) [arXiv:hep-ph/0410047].

[3] M.    Luscher    and    P.    Weisz, JHEP 0407 (2004)    014 doi:10.1088/1126-6708/2004/07/014 [hep-th/0406205].

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Title: Rescattering in the On-shell Effective Theory

Abstract: The so called final state interacions or rescattering effects give rise to large uncertainties in the cross sections of hadronic collisions. They are due to the fact that the hadrons produced in a collision may suffer non-negligible interactions between themselves before reaching the detector. A recently proposed effective theory [1] may be instrumental to systematically address this problem. We propose to initially explore this issue in the scattering of scalar particles, and eventually in the relevant case of the Chiral Lagrangian [2].


[1] On-shell effective field theory: A systematic tool to compute power corrections to the hard thermal loops. C. Manuel, J. Soto and S. Stetina, Phys. Rev. D94, n. 2 025017 (2016).

[2] Chiral perturbation theory, G. Ecker. Prog. Part. Nucl. Phys. 35 (1995) 1-80,

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Title: Bjorken-like model for non-central relativistic heavy ion collisions

Advisor: Volodymir Magas

Abstract: One of the simplest, but rather non-trivial, model simulating relativistic heavy ion collisions is the famous Bjorken model. Analyzing recent experimental data from RHIC@BNL and LHC@CERN one can conclude that the Bjorken model is too much idealized and is not supported by the experiment. On the other hand, in order to describe only the very initial stages of the reaction, the Bjorken ideas still can be used. In particular, aiming to simulate the early stages of the non-central ultra relativistic heavy ion collision one needs to generalize the Bjorken model for asymmetric reactions. This project is in progress now. The basic aspects of the relativistic heavy ion collision physics, including the classical Bjorken model, can be found in [1].


[1] L.P. Csernai, "Introduction to Relativistic Heavy Ion Collisions", (2008),

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Title: Quantum stability of dark energy models

Advisor: Cristiano Germani

Abstract: The Universe is accelerated by an unknown energy density. One possible source for this acceleration is in form of a very slowly evolving scalar field (Dark Energy). In this case, quantum corrections to the DE evolution might become important during the radiation era, as discussed in [1]. The aim of this thesis is to calculate the logarithmic corrections to the one-loop effective action of Galilean DE, by the use of the results obtained in [2].


[1] C. Germani, "Initial conditions for the Galileon dark energy", arXiv: 1609.06598 [astro-ph.CO].

[2] A. O. Barvinsky, Y. V. Gusev, V. V. Zhytnikov and G. A. Vilkovisky, "Covariant perturbation theory. 4. Third order in the curvature", arXiv: 0911.1168 [hep-th].

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Title: The heavy quarkonium spectrum above the open flavor threshold

Advisor: Joan Soto

Abstract: The plethora of charmonium (and some bottomonium) resonances discovered during the last decade, the so called XYZ states [1], challenge our current understanding of QCD.    An important ingredient to describe those states is the interaction of heavy quarkonia with heavy-light meson pairs. We propose to include a realistic estimate of this interaction in the calculation of the heavy quarkonium spectrum. The estimate should be first obtained by fitting lattice QCD data on the string breaking phenomena of refs. [2,3], and extrapolating them to realistic values of the light quark masses [4]. The outcome should be then incorporated in a coupled-channel Schrödinger equation and the spectrum calculated numerically. 

[1] S.L. Olsen, T. Skwarnicki and D. Zieminska, arXiv:1708.04012 [hep-ph]

[2] G. S. Bali et al. [SESAM Collaboration], Phys. Rev. D 71, 114513 (2005) doi:10.1103/PhysRevD.71.114513 [hep-lat/0505012].

[3] V. Koch, J. Bulava, B. Horz, F. Knechtli, G. Moir, C. Morningstar and M. Peardon, PoS LATTICE 2015, 100 (2016) [arXiv:1511.04029 [heplat]].

[4] F. Redondo Fontrodona, "The light quark mass dependence of the QCD string breaking parameters", Master Thesis, Universitat de Barcelona, September 2017.

contact e-mail:

Title: Primordial Inflation, gauge fields and gravitational waves.

Advisor: A. Notari.

Abstract:  Primordial Inflation is a very early stage of expansion of the Universe at very high energy, which is thought to explain many observed properties of our Universe. We aim to study the connection with Particle Physics of such models, in particular the presence of photons and other gauge fields during inflation, in order to compute observable consequences of this possible connection. We also look for models which can produce detectable gravitational wave signals.

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Title: Cosmology of the QCD Axion, as a dark matter candidate and a hot relic. 

Advisors: A. Notari.

Abstract: The QCD Axion is one of the best motivated extra particles, beyond the  the Standard Model of Particle Physics, which may also explain the dark matter problem. We propose to study its production in the Early Universe in several different scenarios and forecast its detectability in the near future.

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Title: Optimisation study of the LHCb experiment trigger lines based on neutral objects.

Advisors: L. Garrido, R. Graciani, E. Graugés.

Abstract:The radiative topological lines are designed to efficiently trigger on any B decay with at least 2 tracks and one high-pT neutral object. This is achieved by using an inclusive strategy very similar to that used by the cut-based topological trigger. With this idea, cuts on variables such as the B candidate mass, the pointing angle or the impact parameter of such candidate cannot be used.

Title: Study of the measurement of the photon polarisation in b --> s gamma decay processes at LHCb

Advisors: L. Garrido, R. Graciani, E. Graugés.

Abstract: Rare b—> s gamma flavour changing neutral current processes are can be very sensitive to new physics (NP) effects. These transitions are allowed only at loop level and NP may arise from the exchange of new heavy fermions in the electroweak penguin loop, distorting the SM picture of this decays modifying amplitudes, phases and the Lorentz structure. While measurements of the inclusive rate and CP violation asymmetries agree with SM calculations, no evidence exist for the polarisation of photons in this type of decays. The SM model predicts that the photon emitted in b—> s gamma decays is predominantly left handed, since the recoil s quark that couples to the W boson is left-handed. That implies a maximal parity violation up to small corrections of the order m_s / m_b. Two different LHCb experiment data analysis of B meson radiative decays are sensitive to the photon polarisation: The
first (still in process within LHCb) is based on the experimental study of the time dependent decay rate of the B_s—> Phi gamma process.
The second (already published) is based on the angular study of the B —> Kππ gamma decays.

Title: LHCb experiment CALO operation, maintenance and upgrade.

Advisors: L. Garrido, R. Graciani, E. Graugés.

Abstract: The LHCb experiment is due to be upgraded in 2018. The full detector will be able to take data from LHC collisions at 40MHz rate taking full advantage of the collider bunch crossing rate. The calorimeter electronics must be fully re-designed for the upgrade. One of the key ingredients of the new calorimeter upgrade is the ICECAL chip from the Barcelona group. The ASIC passed the Electronics Design Review in April 2015 The last version should be the final one before proceeding to the Production Readiness Review. It must be verified in, realistic conditions that the performances of the ASIC Response. For instance, the ASIC response depends on the pulse shape and therefore some test beam is to be used and the corresponding data analized to validate the final design to be produced for the Upgraded detector.

Title: Finding resonances in extended electroweak symmetry breaking sectors

Advisor: Domènec Espriu

Abstract: After the experimental discovery of a particle with the Higgs quantum numbers two years ago, one of the most urgent questions is whether this particle is the Higgs particle of the minimal Standard model or, on the contrary, is a composite state, the lightest resonance in a strongly interacting extended electroweak symmetry breaking sector. In this case, other resonances with various quantum numbers must exist and indeed they are predicted when unitarization is demanded on this extended sector. In this work we propose to do a phenomenological study of these resonances in order to facilitate their possible experimental detection in the new LHC run starting in spring 2015.


Unitarity and causality constraints in composite Higgs models. D. Espriu and  F. Mescia. Phys.Rev. D90 (2014) 015035 . e-Print: arXiv:1403.7386.

Radiative corrections to WL WL scattering in composite Higgs models. D. Espriu, F. Mescia and B. Yencho . Phys.Rev. D88 (2013) 055002. e-Print: arXiv:1307.2400 

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Title: Gravitational waves in de Sitter space time

Advisor: Domènec Espriu

Abstract: Pulsar Tinming Arrays are one of the most promising candidates for a first direct detection of certain types of gravitational waves. The propagation of gravitational waves in de Sitter space time, with a cosmological constant, is usually treated by simply introducing the cosmological red-shift. We have proven that there are other effects that need to be included, in particular a careful treatment of the difference in the reference frames where the waves are produced and detected. This analysis potentially leads to a way of measuring the cosmological constant. In this work we propose to study this in detail, including the effects of the matter density.


Local measurement of \Lambda using pulsar timing arrays. D. Espriu and D. Puigdomenech. Astrophys.J. 764 (2013) 163. e-Print: arXiv:1209.3724

Gravitational waves in the presence of a cosmological constant. J Bernabeu, D Espriu and D Puigdomenech. Phys.Rev. D84 (2011) 063523, Erratum-ibid. D86 (2012) 069904. e-Print: 1106.4511

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Title: Black holes in the limit of very many dimensions

Advisor: Roberto Emparan

Abstract: General Relativity encompasses a huge variety of physical phenomena, from the collision of astrophysical black holes, to the dynamics (via holography) of strongly-coupled plasmas and the spontaneous symmetry-breaking in superconductors. Black holes play a central role in all this. However, their equations are exceedingly hard to solve. The apparent lack of a generic tunable parameter that allows to solve the theory perturbatively (like the electric coupling constant in electrodynamics, or the rank of the gauge group in large-NYang-Mills theory) is arguably the single most important obstacle for generic efficient approaches to the physics of strong gravity and black holes. In General Relativity, one natural parameter suggests itself: the number of dimensions D. Recently we have demonstrated that the limit of large is optimally tailored for the investigation of black holes, classical and potentially also quantum. A simple picture emerges in which, among other things, the shape of the black hole is determined by the same equations that describe soap bubbles.


The large D limit of General Relativity" JHEP 1306 (2013) 009 (e-Print: arXiv:1302.6382)

"Effective theory of Black Holes in the 1/D expansion", JHEP 1506 (2015) 159 (e-Print: arXiv:1504.06489)

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Title: Dynamical vacuum energy in the expanding Universe

Advisor: Joan Solà

Abstract: The study of the dark energy is a central subject in cosmology and fundamental physics. Despite the many efforts, our theoretical understanding of the ultimate nature of the dark energy component of the universe still lags well behind the astounding experimental evidence achieved from the increasingly sophisticated observational tools at our disposal. While the canonical possibility is a strict cosmological constant, the exceeding simplicity of this possibility lies also at the root of its unconvincing theoretical status. In this work the student will have the opportunity to explore the cosmological implications of the dynamical models of the vacuum energy. Some of these models are actually well-motivated from the theoretical point of view (e.g. within quantum field theory in curved spacetime) and may provide a rich phenomenology that could be explored in future observations. In particular, the dynamics of vacuum can affect the Hubble expansion and the details of structure formation, as collected e.g. from the data on type Ia supernovae, the Cosmic Microwave Background and the Baryonic Acoustic Oscillations. In this study the cosmology of some these models will be solved and confronted with the data. At the same time the relation of these vacuum models on possible evidence of dynamical dark energy recently pointed out in the literature will also be addressed.


T. Padmanabhan, "Cosmological constant: The Weight of the vacuum", Phys. Rept. 380 (2003) 235, e-Print: hep-th/0212290.

P.J. Peebles, B. Ratra, "The Cosmological constant and dark energy", Rev. Mod. Phys. 75 (2003) 559, e-Print: astro-ph/0207347.

V. Sahni, A. Shafieloo, A. A. Starobinsky, "Model independent evidence for dark energy evolution from Baryon Acoustic Oscillations", Astrophys. J. 793 (2014)    L40, e-Print: arXiv:1406.2209.

J. Solà, "Cosmological constant and vacuum energy: old and new ideas", J.Phys.Conf.Ser. 453 (2013) 012015, e-Print: arXiv:1306.1527.

H. Fritzsch, J. Solà, "Matter Non-conservation in the Universe and Dynamical Dark Energy", Class.Quant.Grav. 29 (2012) 215002, e-Print: arXiv:1202.5097.

J. Solà, "Dark matter, dark energy and the time evolution of masses in the Universe", Int.J.Mod.Phys. A29 (2014) 1444016, e-Print: arXiv:1408.4427

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    Title: The on-shell effective field theory and the chiral anomaly

    Advisor: Cristina Manuel (IEEC)

    Tutor: Joan Soto

    Abstract: A new effective field theory has been proposed which describes physical phenomena dominated by on-shell degrees of freedom. It has been recently  applied to study the high temperature limit of the photon polarisation tensor of QED for soft external momenta, as it is known that it is dominated by the contribution of the on-shell fermions and antifermions of the plasma. It is possible to generalise the on-shell effective field theory for a non-vanishing value of a chemical potential and chiral chemical potential, and check that also these techniques allow one to study a set of variety of phenomena in these cases. In particular, we will concentrate in the study of chiral anomalous effects at finite density. The student is supposed to learn the basics of the real time formalism of thermal field theory, which generalises QFT from the vacuum to a thermal state, and be able to carry out one-loop calculations with it.


    [1]  C. Manuel, J.Soto and S. Stetina,   ``On-shell effective field theory: A systematic tool to compute power corrections to the hard thermal loops,''   Phys. Rev. D94, no. 2,  25017 (2016)   [arXiv:1603.05514 [hep-ph]].

    [2] C. Manuel and J. M. Torres-Rincon,   ``Chiral transport equation from the quantum Dirac Hamiltonian and the on-shell effective field theory,'' Phys. Rev. D90, no. 7,  76007 (2014)     [arXiv:1404.6409 [hep-ph]].

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    Title: BMS symmetries. Supertranslations and superrotations.

    Advisor: Joaquim Gomis (UB) and Carles Batlle (UPC)

    Abstract: We will study BMS symmetries as canonical symmetries of quantum field theories, and the relation with other realizations.


    G. Longhi, M. Materassi,  "A Canonical realization of the BMS algebra", J.Math.Phys. 40 (1999) 480-500, hep-th/9803128

    A. Strominger, "Lectures on the Infrared Structure of Gravity and Gauge Theory", arXiv:1703.05448 [hep-th] (2017) 

    C. Batlle, D. Delmastro, J. Gomis, Non-Relativistic BMS algebra, Class. Quantum Grav. 34 (2017) 184002.  arXiv:1705.03739 [hep-th]

    C. Batlle, V. Campello, J. Gomis, Canonical realization of (2+1)-dimensional  Bondi-Metzner-Sachs symmetry,    Phys. Rev. D 96, 025004 (2017). doi: 10.1103/PhysRevD.96.025004.   arXiv:1703.01833 [hep-th]. 

    Contact e-mail:,

    Title: Effective Lagrangians for Higgs Physics

    Advisor: Concha Gonzalez Garcia

    Abstract: Presently LHC has observed a state which is compatible with the Standard Model Higgs Scalar responsible for electroweak symmetry breaking (EWSM) . On the other hand no direct signature of new physics staes has been observed.

    This allows to parametrize the possible effects of NP in the electroweak symmetry breaking sector in terms of an effective lagrangian containing higher dimension operators. Recently we have performed an analysis of the existing data in order to constraint the coefficients of these operators. The proyect will review this subject and will evaluate the maximum allowed deviations from the SM predictions in the Higgs related signatures at the future high precision runs of the LHC.


    T.~Corbett, O.~J.~P.~Eboli, J.~Gonzalez-Fraile and M.~C.~Gonzalez-Garcia, ''Robust Determination of the Higgs Couplings: Power to the Data'', Phys.\ Rev.\ D {\bf 87}, 015022 (2013). [arXiv:1211.4580 [hep-ph]].

    W.~Buchmuller and D.~Wyler, ''Effective Lagrangian Analysis of New Interactions and Flavor Conservation'', Nucl.\ Phys.\ B {\bf 268}, 621 (1986)

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    Title: Neutrino Oscillations from Analysis of Daya-Bay Spectrum

    Advisor: Concha Gonzalez Garcia

    Abstract: During the last 15 years neutrino oscillation experiments have produced results which show that neutrinos are massive and oscillate in flavour. One of the most recent results come from the Daya-Bay experiment which measures the disappearance of reactor antineutrinos at distances of the order of km. This experiment was the first one to provide with statistical significance a measurement of the last mixing angle of the leptonic mixing matrix, theta_13 based on the observation of a deficit in the observed over expected number of events. This summer Daya-Bay has released their data on the energy spectrum of their events which can provide additional information. The project proposes to review the formalism of neutrino oscillations and to proceed wiht the relevant computations to make an statistical analysis of the observed energy spectrum.


    M.~C.~Gonzalez-Garcia, M.~Maltoni, J.~Salvado and T.~Schwetz, ''Global fit to three neutrino mixing: critical look at present precision'', JHEP {\bf 1212}, 123 (2012). [arXiv:1209.3023 [hep-ph]].

    The Daya Bay experiment webpage

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    Title: Applications of the AdS/CFT duality

    Advisor: David Mateos

    Abstract: We will use the equivalence between strongly coupled gauge theories and gravity in Anti de Sitter space to study various aspects of gauge theories.


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    Title: Gamma gamma to pi+ pi-

    Advisor: P. Talavera

    Tutor: J. Soto

    Abstract: The aim is to consider a well understood cross-section to set constraints on an hypothetical light scalar particle. This will be done by fitting the theoretical expectations with the existing experimental data.

    J.Soto, P.Talavera and J.Tarrus, "Chiral Effective Theory with A Light Scalar and Lattice QCD,'' Nucl. Phys.B 866 (2013) 270

    J.Bijnens and F.Cornet, "Two Pion Production in Photon-Photon Collisions,'' Nucl. Phys. B 296 (1988) 557.

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