Dipòsit Digital de la Universitat de Barcelona

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El Dipòsit Digital de la Universitat de Barcelona és el repositori institucional que conté en format digital els materials derivats de l'activitat docent, investigadora i institucional de la comunitat universitària.

Enviaments recents

Satellite-observed sea surface salinity: real trends or instrumental drifts?
(2026-06) Plana Casadellà, Paula; Tutor xxx
Monitoring global water cycle intensification through satellite sea surface salinity (SSS) requires distinguishing genuine geophysical trends from instrumental artifacts. This work analyses eight years (2011–2018) of uncorrected SMOS observations to address this problem without relying on external reference datasets. By fitting independent linear regressions for each combination of geographic and antenna-frame coordinates, antenna-frame consistency (trend invariance across the instrument’s field of view) is used as the primary diagnostic for signal separation. Trend significance is assessed via a Student’s T test at the 95% confidence level. An exploratory classification of ocean cells within ±60◦ latitude identifies 52.7% as geophysical trends and 23.5% as instrumental artifacts, with the remainder being inconclusive or statistically non-significant. These results demonstrate that antenna-frame analysis recovers genuine geophysical variability that can be dismissed as noise or removed by standard bias correction and filtering procedures
Tensor operator contribution to magnetic-dipole nuclear moments
(2026-06) Perpinyà Alòs, Ricard; Menéndez Sánchez, Javier
Excited states in atomic nuclei decay into lower-energy nuclear states through γ emission. These decays provide key information about nuclear structure and dynamics. This work studies magnetic dipole (M1) observables in medium-mass nuclei within the nuclear shell model. Since shell-model calculations are performed in a truncated valence space, the standard free-nucleon M1 operator requires effective corrections, and we include a tensor term to account for these effects. We derive analytically the one-body matrix elements of this operator and implement them in a state-of-the-art nuclear shell-model code. We focus on the calculation of magnetic moments for ground and excited states of several nuclei. We find that the tensor contribution is generally small (below 15%), but is enhanced when the magnetic moment of a state is close to zero. The relative weight of proton and neutron contributions to the tensor term is quite sensitive to the nuclear state
Cosmology with gravitational-wave dark sirens: Estimating H0 with EM-informed redshift priors from biased dark matter distributions
(2026-06) Pérez Álvarez, Paula; Nanadoumgar-Lacroze, Dounia; Bulashenko, Oleg
Dark-siren gravitational-wave cosmology infers the Hubble constant by statistically associating events with the large-scale structure that hosts them, connecting H0 to the clustering and bias of the chosen tracer. This thesis presents an end-to-end forward-modelling framework, where synthetic compact-binary catalogues are generated from non-linear matter overdensities on a past lightcone, projected onto a terrestrial detector network with realistic selection thresholds, and analysed with a hierarchical Bayesian framework. We recover the injected cosmology without bias, with H0 constrained to a ∼6% statistical precision. Linearly biased tracers differ only in how strongly they cluster relative to the underlying matter: galaxies, GW hosts, and Hi each rescale the amplitude of the host field, but all preserve the spatial pattern carrying the cosmological information. The dominant systematic is instead the angular resolution of the host map, while extreme cluster bias breaks the linear model itself.
Collective Light-Matter Interactions and Superradiance: A Tensor-Network Approach
(2026-06) Patón Vázquez, Ían; Juliá-Díaz, Bruno; Moreno Cardoner, Maria
In this thesis, we investigate the driven-dissipative dynamics of an array of atoms addressed by an external field using Matrix Product Density Operators. Using the Time-Dependent Variational Principle, we overcome the exponential scaling of the Lindblad master equation. We validate the method against the exact Dicke limit, capturing the cooperative superradiant cascade, and demonstrate that spatial separation between emitters rapidly suppresses this collective emission. Under continuous laser driving, we characterize the competition between coherent pumping and superradiant dissipation, showing that global detuning acts as an energy penalty that restricts population transfer and lowers the steady-state excitation fraction. This establishes a robust computational approach for studying complex light-matter interactions in extended many-body arrays
High dimensional quantum teleportation
(2026-06) París Ferrer, Unai; Taron i Roca, Josep
This work extends the conceptual framework of quantum teleportation beyond spin-1/2 systems or two-dimensional Hilbert spaces. We derive quantum state teleportation in threedimensional Hilbert spaces and then generalize the phenomenon to continuous variables. For the latter, an idealized process is first presented to establish the conceptual foundations, followed by an experimentally feasible modification which has been implemented in real experiments