For further information on possible Master Thesis projects and advisors in this speciality, please contact Josep Maria Solanes at jm.solanes@ub.edu.
Title: Quantum properties of dark matter.
Advisor: Sofyan Iblisdir
Abstract: Dark matter is a mysterious constituent of the universe, 5 times more abundant than ordinary (or visible) matter. The characterisation of its properties remains one of the most pressing problems of particle physics. In particular, dark matter could be in a degenerate quantum state in some galaxies, with novel phenomenological consequences. The proposed work would consist in studying a toy model of fermions with attractive long range interaction to mimic the peculiar properties of these galaxies, which can be done using state-of-the-art tensor network techniques. The student is expected to investigate the ground state (and thermal) properties of this quantum model, and understand which new properties may appear in the final virialized states ('halos') from quantum degeneracy pressure as compared to their classical counterpart. Because of its interdisciplinary nature, this work would be done in co-supervision with Prof. Diego Blas from Universitat Autònoma de Barcelona, and Prof. Mari Carmen Bañuls from Max Planck Institute for Quantum Optics (Garching, Germany). The student would moreover have the opportunity to visit the MPQ to work closely with Prof. Bañuls for a period of one to a few weeks (all expenses covered).
Contact email: iblisdir@fqa.ub.edu
Title: Entanglement entropy in quantum simulators
Advisor: Bruno Julia Diaz
Abstract: We will study the entanglement entropy of a well-known class of quantum simulators: multicomponent Bose-Hubbard models. In particular, we will concentrate on two component systems which can be mapped into spin models which a notably intricate structure, e.g. hosting critical phases. We may explore the case analogous to the recently discovered droplet phase due to quantum fluctuations [1]. On the way, we will use DMRG and tensor networks tools to unveil the quantum correlations in the system, as in [2].
References:
Contact email: bruno@fqa.ub.edu
Title: Exact results in non-abelian gauge theories from supersymmetric localization
Advisor: Jorge Russo
Abstract: Localization is a technique to compute functional integrals exactly. The location technique applied to the calculation of exact physical observables is one of the most spectacular recent results in non-abelian gauge theories.
This led to the calculation of the exact partition function, Wilson loop operators in supersymmetric theories, including all perturbative and non-perturbative contributions, with an exact account on all instanton effects. This master thesis will investigate several open problems in relation to four-dimensional non-abelian gauge theories by means of supersymmetric localization of path integrals.
References:
Introduction to localization in quantum field theory
V. Pestun and M. Zabzine,
https://arxiv.org/pdf/1608.02953.pdf
Localization at Large N
J. Russo and K. Zarembo, arXiv:1312.1214 [hep-th].
Contact email: jrusso@ub.edu
Title: Conformal boundary anomalies and holography on Anti de Sitter space and spheres.
Advisor: Jorge Russo
Abstract: Superstring theory in anti de Sitter space is dual to superconformal field theories, that is, to field theories invariant under scale symmetries and supersymmetries. In the last 20 years, this AdS/CFT duality has led to multiple applications, including classical and quantum gravitational physics, condensed matter, integrability and several aspects of superstring theory, representing the main trending topic in theoretical physics. This master thesis will study conformal field theories in spaces which are direct product of anti de sitter spaces and spheres, with the aim of understanding boundary anomalies and their AdS/CFT counterpart.
References:
Free energy and boundary anomalies on S^a x H^b spaces
D.Rodriguez-Gomez and J.G. Russo,
JHEP 1710 (2017) 084 [arXiv:1708.00305 [hep-th]].
Boundary Conformal Anomalies on Hyperbolic Spaces and Euclidean Balls
D.Rodriguez-Gomez and J.G. Russo,
JHEP 1712 (2017) 066
[arXiv:1710.09327 [hep-th]].
Contact email: jrusso@ub.edu
Title: Black hole fusion in the extreme-mass-ratio limit
Advisor: Roberto Emparan
Abstract: The fusion of two black holes — a signature phenomenon of General Relativity — is usually regarded as a process so complex that nothing short of a supercomputer simulation can accurately capture it. But no -- not always. In this work the student will see how the event horizon of the merger can be found in a simple way in the limit where one of the black holes is much smaller than the other, which is a situation that does occur in nature. Remarkably, the ideas and techniques involved are elementary: the equivalence principle, null geodesics in the Schwarzschild or Kerr solutions, and the notion of event horizon itself. The student will get a deeper appreciation of these notions, as well as develop some skills with Mathematica in the numerical solution of (simple) differential equations and in the graphic presentation of a realistic phenomenon that is happening right now in our Universe.
References:
Exact Event Horizon of a Black Hole Merger
R. Emparan, M. Martinez
Class.Quant.Grav. 33 (2016) no.15, 155003
e-Print: arXiv:1603.00712
Black hole fusion made easy
R. Emparan, M. Martínez
Int.J.Mod.Phys. D25 (2016) no.12, 1644015
Black hole fusion in the extreme mass ratio limit
R. Emparan, M. Martinez, M. Zilhao
Phys.Rev. D97 (2018) no.4, 044004
e-Print: arXiv:1708.08868
contact e-mail: emparan@ub.edu
Title: Towards the solution of the flavour problem at LHC and DarK Matter
Advisor: Federico Mescia
Abstract:
Based on quark and lepton masses, as well as on the CKM mixing pattern, the couplings of Higgs with fermions ( seem to be highly hierarchic. That hierarchy is expected to be due to the severe breaking of an underlying flavour symmetry group.
New improved results on the size of the flavour changing neutral processes collected at LHC are helpful in building New Physics models which encompass the observed since of CP violation and of the hierarchy among various species of quarks and leptons. Most significantly recent LHCb results on b -> s mu mu suggest some tensions with respect to the Standard Model (SM).
Moreover, models which explain these tensions can be handle Dark matter candidates.
References
Loop effects of new scalars and fermions in b->s mumu,
Pere Arnan, Federico Mescia et al. JHEP 02 (2019) 109, 1901.06315 [hep-ph].
contact e-mail: mescia@ub.edu
Title: Dark Matter and XENON Experiment
Advisor: Federico Mescia
Abstract:
The XENON1T collaboration has recently reported an intriguing excess in the direct detection of Dark Matter. The axion hypothesis explains the data well but it is in contradiction with astrophysical data. Alternative solutions are still possible and under investigation.
References
Solar axions cannot explain the XENON1T excess,
Federico Mescia et al. 2006.12487 [hep-ph].
Exploring New Physics with O(keV) Electron Recoils in Direct Detection Experiments
Itay M. Bloch et al. 2006.14521 [hep-ph]
contact e-mail: mescia@ub.edu
Title: Effective Actions, Phase Transitions and Holography
Advisor: Jorge Casalderrey Solana
Abstract: The gauge/gravity duality, or holography, is a versatile tool to study the strongly coupled dynamics of gauge theory matter. One of areas were the holographic principle shows its strengths is in the computation of the phase diagram of quantum field theories with known gravity duals. For certain realisations of the duality, the field theory enjoys non-trivial phase diagrams, including phase transitions of different degrees. The goal of this project is to determine the effective action of a particular class of models and to relate this effective action to their known phase structure.
References:
1) Effective actions and bubble nucleation from holography
Fëanor Reuben Ares, Oscar Henriksson, Mark Hindmarsh, Carlos Hoyos, Niko Jokela, 2109.13784 [hep-th]
2) Phase Transitions, Inhomogeneous Horizons and Second-Order Hydrodynamics, Attems et al, JHEP 06 (2017) 129 • e-Print: 1703.02948 [hep-th]
3) Thermodynamics, transport and relaxation in non-conformal theories, Attems et al, JHEP 10 (2016) 155 • e-Print: 1603.01254 [hep-th]
Contact e-mail: jorge.casalderrey@ub.edu
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.
References:
[1] Quantum Computation and Quantum Information, Nielsen and Chuang, Cambridge University Press (2000).
[2] https://www.sciencenews.org/article/quantum-computers-are-about-get-real
[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).
Contact e-mail: pol.forndiaz@bsc.es
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.
Contact e-mail: j.i.latorre@gmail.com
Title: Non-relativistic gravities and supergravities.
Advisor: Joaquim Gomis (UB) and Carles Batlle (UPC)
Abstract: We will study non-relativistic holography using non-relativistic strings and non-relativistic gravities.
References:
J. Gomis and H. Ooguri, "Nonrelativistic closed string theory", J. Math. Phys. 42(2001) 3127, hep-th/0009181
L.Aviles, E. Frodden, J.Gomis, D. Hidalgo, J. Zanelli, "JHEP 1805 (2018) 047, arXiv: 1802.8453
E. Bergshoeff, J. Gomis, Z. Yan, Nonrelativistic string theory and T-Duality, arXiv:1806.06071
Contact e-mail: joaquim.gomis@ub.edu, carles.batlle@upc.edu
Title: Symmetries of M Theory and free Lie superalgebras.
Advisor: Joaquim Gomis (UB) and Carles Batlle (UPC)
Abstract: We will study the symmetries of M theory and the connection free Lie superalgebras.
References:
J. Gomis, A. Kleinschmidt, " On free Lie algebras and particles in electromagnetic fields",
JHEP 1707 (2017) 0b5, arXiv:1705.05854
J. Gomis, A. Kleinschmidt, J. Palmkvist, "Symmetries of M theory and free Lie superalgebras"
arXiv:1809.09171
Contact e-mail: joaquim.gomis@ub.edu, carles.batlle@upc.edu
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.
References:
[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
Contact e-mail: sola@fqa.ub.edu
Title: Renormalization of the energy-momentum tensor of a non-minimally coupled scalar field in an FLRW background, including both QFT and string-theory effects.
Advisor: Joan Solà Peracaula
Abstract: Despite the vacuum energy and in general the dark energy (DE) is postulated as being the physical cause that produces the measured accelerated expansion of the universe, the usual prediction in quantum field theory (QFT) is much too large as compared to the critical density of the Universe. The mismatch is ultimately responsible for the "Cosmological Constant Problem", which is the biggest conundrum of fundamental physics ever. The main problem stems from the usually proposed renormalization procedures of the energy-momentum tensor in QFT, which lead to contributions proportional to the quartic powers of the mass of the quantum fields (i.e. proportional to $m^4$). However, if one considers an appropriate variant of the adiabatic regularization and renormalization of quantum fields in a FLRW background it is possible to provide a well defined result which can elude the $m^4$ terms and ultimately provides a dynamical vacuum energy density $\rho_{vac}(H)$ evolving as powers of the Hubble rate, H, and its derivatives, therefore sufficiently small.
In this work, the student will have the opportunity to perform such a QFT calculation in an appropriate context, in which matter is represented by a scalar field non-minimally coupled to curvature. He/she will verify that $\rho_{vac}(H)$ evolves as a constant term (representing the cosmological constant part of the final result) plus some dynamical components of order $H^2$ and $H^4$. The higher powers are relevant for the early universe only, where they can trigger fast inflation through effective string-theory effects generating those terms. These are induced by the presence of anomalous Chern-Simon couplings involving the Kalb-Ramond field of the gravitational multiplet. At present, $\rho_{vac}(H)$ is dominated by the additive constant term accompanied by a tiny dynamical component of order $H^2$. This result tells us that the vacuum energy density is not just constant but evolves with time. Its current variation is small enough, but still potentially measurable. At the phenomenological level, it looks as a kind of effective quintessence behavior. In point of fact, however, there is not a real quintessence field but an underlying QFT vacuum changing (`running') very mildly with the cosmic expansion.
Some references:
P.J. Peebles, B. Ratra, "The Cosmological constant and dark energy", Rev. Mod. Phys. 75 (2003) 559 [e-Print: astro-ph/0207347].
J. Solà, "Cosmological constant and vacuum energy: old and new ideas", J.Phys.Conf.Ser. 453 (2013) 012015 [e-Print: arXiv:1306.1527].
C. Moreno-Pulido and J. Solà, "Running vacuum in quantum field theory in curved spacetime..." , Eur. Phys. J. C 80 (2020) 692 [e-Print: arXiv:2005.03164]
S. Basilakos, N. E. Mavromatos and J. Solà, "Gravitational and Chiral Anomalies in the Running Vacuum Universe and Matter-Antimatter Asymmetry", Phys.Rev. D101 (2020) 045001 [e-Print: arXiv:1907.04890]
Contact e-mail: sola@fqa.ub.edu
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].
References:
[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). http://arxiv.org/abs/arXiv:1611.02939
[2] Chiral perturbation theory, G. Ecker. Prog. Part. Nucl. Phys. 35 (1995) 1-80, http://arxiv.org/pdf/hep-ph/9501357.pdf
contact e-mail: soto@fqa.ub.edu
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].
References:
[1] L.P. Csernai, "Introduction to Relativistic Heavy Ion Collisions", (2008), http://www.csernai.no/Csernai-textbook.pdf
contact e-mail: vladimir@fqa.ub.edu
Title: Dynamically generated S=-1 resonances due to S-, P- and D-wave meson baryon interaction in chiral unitary model
Advisor: Volodymir Magas
Abstract: We study baryon resonances in the strangeness S=−1 sector that are generated dynamically within a unitary meson-baryon coupled-channel model. We consider the meson-baryon interaction in S, P and D waves, employing a chiral SU(3) Lagrangian up to next-to-leading order (NLO) and implementing unitarization in coupled channels. The parameters of this Lagrangian have been fitted to a large set of experimental data in different two-body channels, paying special attention to the Kbar N→KΞ reaction, which is particularly sensitive to the NLO terms.
References:
[1] Phys.Rev. C99 (2019) no.3, 035211 (only S-wave interaction)
contact e-mail: vladimir@fqa.ub.edu
Title: Primordial Black Holes production in a matter dominated era
Advisor: Cristiano Germani
Abstract: In this thesis we will calculate the amount of black holes formed during an hypothetical early time matter epoch of our Universe. Those black holes, if copious enough, might be the missing dark matter.
References: for a very general introduction to the topic see https://arxiv.org/pdf/2006.02838.pdf
contact e-mail: germani@icc.ub.edu
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: soto@fqa.ub.edu
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.
Contact e-mail: nalessio@icc.ub.edu
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.
Contact e-mail: nalessio@icc.ub.edu
Title: Preparation of LHCb early measurements with first Run 3 data for the validation of electron reconstruction
Supervisor: Carla Marín
Abstract: The upgraded LHCb detector will start to take data during 2022 at an increased instantaneous luminosity, after a major upgrade of the subdetectors and exploiting a new unique fully software-based trigger and a real-time reconstruction. Validating the reconstruction and understanding its performance with the first data are critical for a successful physics programme. In particular, electron reconstruction is a key ingredient to perform Lepton Universality tests with an unprecedented accuracy, which will enable us to confirm or deny the hints for new physics currently seen in these observables. The abundant decay B -> Jpsi K, with Jpsi -> e+e-, will be used for this purpose.
References: http://arxiv.org/abs/2103.11769, http://arxiv.org/abs/1903.01360, http://arxiv.org/abs/1909.02957
Contact email: cmarin@fqa.ub.edu
Title: Integration and Commissioning of the LHCb CALO Upgrade readout electronics for the LHC Run3 data taking period.
Advisors: L. Garrido, E. Graugés, D. Gascón.
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 has been 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 Reviewof the LHCb collaboration and Production . Now the full electronics, where the ASIC is integrated into the PCB boards, connected to the remaining elements of the new LHCB CALO must be tested and comissioned, before it will start operation in early 2021. Together with the group of the LAL-Orsay, a mini-DAQ has to be tested and debugged to make sure the final installation will be capable to readout the CALO data at a 40 MHz rate
Title: Development of Ultrafast photo-sensor instrumentation for the LHCb experiment Upgrade II for the HL-LHC regime.
Advisors: L. Garrido, E. Graugés, D. Gascón.
Abstract: After 2025 the LHC collider will enter the High Luminosity regime (HL-LHC), where the instantaneous luminosity will be enhanced an order of magnitud with respect to present 4 x 10^33 /cm^2 /s . The Upgraded (2021) LHCb detector will have to run after 2025 with the LHC beam slightly defocused (using again the lumi leverage method to get a constant lumi in LHCb) so that its detectors and DAQ system can cope with the a inelastic interaction rate per bunch crossing rate similar to that before the HL-LHC. An R&D program within the experimental heavy flavour community has started to make possible with a second LHCb Upgrade to take advantage of the full potential of the HL-LHC also in LHCb. The scheduled calendar aims to installing some prove-of-concept sub-detectors in 2025 at LHCb, in those areas that will be most affected the ageing of the current detectors. With that experience, a major refurbishing of the LHCb detector, aka LHCb Upgrade II, is foreseen in 2030 to be able to take as much data as available from the LHC and collected a total of 300/fb of pp-collision data by the end of the operation of the LHC (circa 2036). The ICCUB has started an R&D program to build a new CALO for LHCb with increased granularity (to cope with the increased multiplicity of the HL-LHC regime), increased radiation hardness and an ultrafast RO electronics capable to provide a time stamp of the data collected with a resolution below 100ps to provide time separation between the different inelastic proton-proton collisions that will take place in each LHC bunch crossing (aprox. 40). The TFM proposed will address the test of different combination of sensors (scintillating crystals), photo-sensor (SiPM, PMTs, SPADS, etc..), readout electronics (FastIC, MusIC, etc...) to consider a possible solution for an upgraded LHCb CALO for the HL-LHC..
Title: Test of Lepton Universality with b-baryon decays at LHCb
Advisor: Carla Marin
Abstract: The LHCb detector at the LHC has observed a number of small deviations with respect to the Standard Model predictions in b -> sll transitions, most notably in tests of Lepton Universality comparing the couplings to muons and electrons. While a pattern is emerging, it is of uttermost importance to confirm if these deviations are present in the whole family of b -> sll decays. A first measurement of Lepton Universality with Lambda_b decays was performed by LHCb with a fraction of the collected data, with results consistent with the deviations observed in the meson sector but also with the SM predictions. It is thus critical to update this measurement with the full dataset. In particular, optimisation of the event selection and a study of the pK spectrum will enable improvements beyond the pure statistical gain from the size of the analysed data sample.
References: http://arxiv.org/abs/1912.08139, http://arxiv.org/abs/2103.11769, https://arxiv.org/abs/1605.07633
Contact email: cmarin@fqa.ub.edu
Title: Gravitational waves in an expanding universe
Advisor: Domènec Espriu
Abstract: The propagation of gravitational waves (GW) in an expanding universe, whose composition is dominated by dark energy and dark matter, is usually treated by simply introducing the cosmological red-shift in the frequency. While this is enough for many applications, 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 and other cosmological parameters. In this work we propose to study this in detail. Detection of GW in Pulsar Timing Arrays (PTA) is a possibility and the influence of these effects on the current bounds on the graviton mass is another venue of investigation.
References:
Effect of the cosmological parameters on gravitational waves: general analysis, Domènec Espriu and Marc Rodoreda, e-Print: 2108.09567 [gr-qc]
Measuring H_0 with pulsar timing arrays, Domènec Espriu, Luciano Gabbanelli and Marc Rodoreda, Class.Quant.Grav. 37 (2020) 8, 085013, e-Print: 1908.08472 [gr-qc]
On the propagation of gravitational waves in a \LambdaΛCDM universe, Jorge Alfaro, Domènec Espriu and Luciano Gabbanelli, Class.Quant.Grav. 36 (2019) 2, 025006, e-Print: 1711.08315 [hep-th]
Local measurement of \Lambda using pulsar timing arrays, D. Espriu and D. Puigdomenech. Astrophys.J. 764 (2013) 163. e-Print:1209.3724
Contact e-mail: espriu@icc.ub.edu
Title: Probing the nature of the Higgs particle
Advisor: Domènec Espriu
Abstract: The Higgs particle is one of the cornerstones of the Standard Model of particle physics. Yet, we are not sure whether this particle is truly elementary or, on the contrary, is a composite state, the lightest resonance in a strongly interacting extended electroweak symmetry breaking sector perhaps. In this case, other resonances with various quantum numbers must exist and indeed they are predicted when requirements of unitarization and causality are demanded on this extended sector. In this work we propose to consider various possible alternatives for the Higgs and investigate proposal to experimentally reveal whether these alternatives may be the one chosen by Nature.
References:
Introducing tools to test Higgs interactions via WW scattering I: one-loop calculations and renormalization in the HEFT, Domènec Espriu, Federico Mescia and Iñigo Asiáin, e-Print:2109.02673 [hep-ph]
Strongly coupled theories beyond the Standard Model, Antonio Dobado and Domènec Espriu, Prog.Part.Nucl.Phys. 115 (2020) 103813, e-Print: 1911.06844 [hep-ph]
Production of vector resonances at the LHC via WZ-scattering: a unitarized EChL analysis, R.L. Delgado, A. Dobado, D. Espriu, C. Garcia-Garcia, M.J. Herrero, X. Marcano and .J. Sanz-Cillero, JHEP 11 (2017) 098, e-Print: 1707.04580 [hep-ph]
Contact e-mail: espriu@ecm.ub.edu
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 D is optimally tailored for the investigation of black holes, classical and potentially also quantum. We have derived a simple set of nonlinear equations that describe the dynamical evolution of black holes, strings and branes that efficiently capture a surprisingly large amount of black hole physics.
References:
R. Emparan, R. Suzuki, K. Tanabe "Effective theory of Black Holes in the 1/D expansion", JHEP 1506 (2015) 159 (e-Print: arXiv:1504.06489)
R. Emparan, C. P. Herzog “The Large D Limit of Einstein's Equations” e-Print: 2003.11394 [hep-th]
Contact e-mail: emparan@ub.edu
Title: Einstein’s equations from thermodynamics and entanglement
Advisor: Roberto Emparan
Abstract: It is well known that using Einstein’s equations one can prove a set of laws of “black hole thermodynamics” where the horizon area plays the role of entropy. In 1995 Jacobson showed that it is possible to reverse this logic and derive the Einstein equations by assuming that dynamical spacetime satisfies a first law of thermodynamics. More recently, in a related but different set up, the Einstein equations have been derived from a hypothesis about vacuum entanglement.
References:
T. Jacobson, “Thermodynamics of space-time: The Einstein equation of state”, Phys.Rev.Lett. 75 (1995) 1260-1263, e-Print: gr-qc/9504004 [gr-qc]
T. Jacobson, “Entanglement Equilibrium and the Einstein Equation”, Phys.Rev.Lett. 116 (2016) 20, 201101, e-Print: 1505.04753 [gr-qc]
Contact e-mail: emparan@ub.edu
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.
References:
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
Contact e-mail: sola@fqa.ub.edu
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.
References:
[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]].
Contact e-mail: cmanuel@ieec.uab.es
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.
References:
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. https://doi.org/10.1088/1361-6382/aa8388. 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: joaquim.gomis@ub.edu, carles.batlle@upc.edu
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.
References:
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)
Contact e-mail: concha@ecm.ub.edu
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.
References:
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 http://dayabay.ihep.ac.cn/twiki/bin/view/Public/
Contact e-mail: concha@ecm.ub.edu
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.
References:
http://arxiv.org/abs/arXiv:0709.1523
http://arxiv.org/abs/arXiv:1101.0618
http://arxiv.org/abs/hep-th/9905111
Contact e-mail: dmateos@icrea.cat
Title: Dark Matter Bound States
Advisor: Joan Soto
Abstract: If dark matter particles are very heavy, they may form bound states mediated by the interaction with Standard Model particles. Direct detection experiments may be sensitive to break-up events. We propose to build an effective field theory in which dark matter particles are non-relativistic, and explore the possible existence of bound states, both in the case that the SU_L(2) x U_Y(1) symmetry is linearly realized and in the case that it is non-linearly realized (composite Higgs).
References:
Contact e-mail: soto@fqa.ub.edu
Title: Generalized Geometry as a language for Physics
Advisor: Roberto Rubio
Abstract: Generalized geometry is a new framework for geometric structures, which, in particular, regards complex and symplectic structures as two particular cases of the same structure: a generalized complex structure. This, and other features (like the appearance of B-fields as generalized diffeomorphisms), made generalized geometry become a very suitable language for some aspects of string theory, like mirror symmetry and M-theory.
This main goal of this project is acquiring a basic but strong conceptual understanding of generalized geometry, which would allow the student to deal with mathematical and physical literature in the future as well as making independent use of the main concepts involved in generalized geometry.
The student is expected to review the basics of the theory from the viewpoint of her/his interests with the close supervision of the tutor. Moreover, and in a more independent way, the student should approach and discuss some uses of generalized geometry in Theoretical Physics from a mathematical point of view.
This project requires a good mathematical background.
References:
- Marco Gualtieri. Generalized complex geometry. Ann. of Math. (2), 174(1):75–123, 2011.
- Marco Gualtieri. Generalized Kähler geometry. Comm. Math. Phys., 331(1):297 331, 2014.
- Nigel Hitchin. Generalized Calabi-Yau manifolds. Q. J. Math., 54(3):281 -308, 2003.
- Nigel Hitchin. Generalized geometry - an introduction. In Handbook of pseudo-Riemannian geometry and supersymmetry, pages 185 -208. Eur. Math. Soc., Zürich, 2010.
Contact email: roberto.rubio@ub.edu
Title: Photoproduction of baryon resonances
Advisors: Vincent Mathieu, Volodymyr Magas
Abstract: The primary goal of the GlueX and CLAS12 experiments, which are performed at Jefferson Laboratory in Virginia, USA, is to search for and study exotic mesons such as hybrid meson (q qbar pair with an extra gluon), tetraquark state (qq qbar qbar) or two meson molecules. These experiments are searching for these exotic particles in photon scattering on a hydrogen target; and in order to find the signals of new mesons they need to control very well the background, coming from the final state interactions between the produced particle. This project concentrates on two-meson photoproduction on a
hydrogen target, in particular on the gamma + p --> p + K+ + K- reaction, and consists in including baryon resonances into (anti)kaon-baryon final state interactions.
References:
- GlueX and V. Mathieu, https://arxiv.org/pdf/2107.12314.pdf
- V. Mathieu et al, Phys. Rev. D 100 (2019) 054017
- https://inspirehep.net/files/f024c81468fb78f2d352bf56efcf2d80
Contact email: vmathieu@ub.edu
Title: Photoproduction of exotic meson resonances
Advisors: Vincent Mathieu
Abstract: The Jefferson Laboratory in Virginia hosts two experiments (GlueX and CLAS12) dedicated to the study of meson interaction. These experiments are searching for exotic mesons produced by photons on a hydrogen target. The most promising signal of an exotic meson, in this case a state composed of a q qbar together with an extra gluon, has been observed in the P-wave of the eta+pi0 final state. However the confirmation of this discovery requires a comparison between theoretical predictions and experimental observables.
The project consists in studying the reaction gamma + p --> eta + pi0 + p at high energies and developing a model for the production of exotic meson in this reaction (to be compared with GlueX preliminary data)
References:
- http://www.gluex.org/
- C.A. Meyer, E.S. Swanson, https://arxiv.org/pdf/1502.07276.pdf
- V. Gribov, Camb.Monogr.Part.Phys.Nucl.Phys.Cosmol. 27 (2012)
- V. Mathieu et al, Phys. Rev. D 100 (2019) 054017
- https://inspirehep.net/files/f024c81468fb78f2d352bf56efcf2d80
Contact email: vmathieu@ub.edu
Title: Looking for unknown gravitational wave sources
Supervisor: Ruxandra Bondarescu
Abstract: Gravitational waves are constantly passing us. However, even the strongest waves that come from merging black holes have a tiny effect on the arms of the gravitational wave detectors on Earth. They stretch and squeeze them by a thousand of the width of a proton.
You will search for gravitational waves in LIGO-Virgo data to find short unknown signals. You will demonstrate the potential of the maximum entropy method to determine the properties of exotic, unknown signals. This technique recovers coherent signals from a network of gravitational wave detectors. It assumes that signal behaves differently from noise, i.e., that the signal is correlated at different detectors in the network, while the noise is uncorrelated. You will learn numerical methods, noise modelling, some of the mathematics behind the data analysis, and practice on real detector data. You will start by reconstructing very short events of possible exotic origin like GW190521.
Requirements: linear algebra, python, complex analysis
References:
T.Z. Summerscales et al., 2008 ApJ 678, 1142, arXiv:0704.2157
https://iopscience.iop.org/article/10.1086/528362/meta
Abbott et al., PRL 125 (10), 101102, arXiv: 2009.01190
Contact email: ruxandra@icc.ub.edu
Title: Mapping the gravitational wave sky with Stokes parameters
Abstract: Just like light waves, gravitational waves are most generally characterized by their propagation direction and time-dependent waveform in each of two independent polarization states. These properties of incident gravitational plane waves can be inferred from observations made in a properly oriented network of detectors. You will learn to characterize the wave polarization via its (frequency dependent) Stokes parameters to infer important, general properties of the wave's source: e.g., point sources of circularly polarized radiation must be non-axisymmetric and radiating angular momentum, while point sources of linearly polarized waves must be either axisymmetric or oriented so that the direction of angular momentum loss is orthogonal to the observer line-of-sight. This is particularly interesting for more exotic sources, e.g., black hole binaries with high spin or high eccentricity. You will find the regions of the gravitational wave sky where the LIGO-Virgo network is sensitive to both gravitational wave polarizations, and estimate the number of sources.
The first event where both polarizations were detected is GW170814. You will start by computing the Stokes parameters for this event.
References: Abott et al. 119 (14): 141101. arXiv:1709.09660
Requirements: tensor theory, linear algebra, python, complex analysis
Contact email: ruxandra@icc.ub.edu
Title: Properties of eccentric binary black hole mergers from globular clusters
Advisor: Mark Gieles, Tomas Andrade and Ruxandra Bondarescu
Abstract: After the discovery of gravitational waves (GWs, Abbott et al. 2017), the LIGO-Virgo gravitational wave (GW) interferometers have detected dozens of binary black hole (BBH) mergers. Various models exist to successfully explain the merger rate and evolution and properties of black hole binaries: they may originate from massive star binaries, or from dynamical interactions in dense stellar environments, such as globular clusters (GCs). Although model predictions differ, the data does not yet allow us to discriminate between formation channels. There is so far no clear dominant formation channel. The relative contribution of each of these channels could be anywhere between 20-90%.
A unique prediction of the dynamical channel is the existence of BBH with measurable eccentricity (i.e., at the LIGO-Virgo frequencies). In this project you will make predictions for the properties of eccentric mergers that occur in GCs as the result of GW capture. You will use the model predictions for the evolution of GCs and their BHs (Antonini & Gieles 2020a,b), and combine these with recipes for mergers following GW capture in single-single and single-binary encounters (Samsing et al. 2020). The goal of this project is to quantify where these eccentric BBH mergers lie in the mass-eccentric diagram.
References:
- Abbott et al. 2016, PhRvL, 116, 061102 https://ui.adsabs.harvard.edu/abs/2016PhRvL.116f1102A/abstract
- Antonini & Gieles 2020a, PhRevD, 102, 123016 https://ui.adsabs.harvard.edu/abs/2020PhRvD.102l3016A/abstract
- Antonini & Gieles 2020b, MNRAS, 492, 2936 https://ui.adsabs.harvard.edu/abs/2020MNRAS.492.2936A/abstractm
- Samsing et al. 2020, PhRevD, 101, 123010 https://ui.adsabs.harvard.edu/abs/2020PhRvD.101l3010S/abstract
Contact e-mail: mgieles@icc.ub.edu, tandrade@icc.ub.edu, ruxandra@icc.ub.edu