Category: Doktorsvörn

Midway evaluation, Daniel Amankwah

Sigurður Örn Stefánsson, nóvember 30, 2020

Room: Via Zoom. Link to be sent.
Time: Friday, December 11, at 10:00.

Doctoral student: Daniel Amankwah

Project title: Scaling limits of random, face-weighted, tree like planar maps.

Project description: The doctoral project lies in the scope of random planar maps. We investigate scaling limits of various classes of discrete planar maps which are by construction “tree-like”. These include Halin maps, outerplanar maps, series-parallel maps and more. The Brownian Continuum Random tree (CRT), introduced by David Aldous has been known to be the limit of various different discrete models of planar maps uniformly sampled. We focus on the case when each face in the maps is assigned a heavy tailed weight so that a typical face is in the domain of attraction of a stable law. It is known that for several such models for treelike graphs the scaling limits are the so-called stable looptrees. We aim to understand how generically this happens. For this reason we will consider classes of maps which have not been studied in this scope in the literature. Examples include Halin maps, Series-Parallel maps and Maps of bounded tree-width.

Supervisor: Sigurður Örn Stefánsson

Juan Fernando Angel Ramelli

Valentina Giangreco, nóvember 4, 2020

PhD defense, Friday November 6 at 14.00, in Veröld, room 023

Entanglement in Quantum Lifshitz Theories

The defense will be streamed

Live stream:https://www.youtube.com/user/HIvarp/live

Opponents: 
Dr. Stefan Vandoren, Professor at Utrecht University, The Netherlands.
Dr. Jens Hjörleifur Bárðarson, Associate Professor at KTH Royal Institute of Technology, Sweden

Advisor: Dr. Valentina Giangreco Puletti, Professor at the Faculty of Physical Sciences, University of Iceland 

Doctoral committee: 

Dr. Lárus Thorlacius, Professor at the Faculty of Physical Sciences, University of Iceland
Dr. Þórður Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland
Dr. Erik Tonni, Associate Professor at SISSA, Italy.

Chair of Ceremony: Dr. Einar Örn Sveinbjörnsson, Professor and the Head of the Faculty of Physical Sciences, University of Iceland

Abstract:
In recent years, the study of entanglement properties of quantum field theories has led to deep insights in fields as diverse as quantum gravity and condensed matter physics. Originating as effective field theories for certain quantum dimer models, the Quantum Lifshitz Model (QLM) and its generalizations are bosonic quantum field theories with anisotropic scaling symmetry between space and time. Being closely related to conformal field theories, they provide a fruitful playground, where diverse entanglement calculations can be performed analytically.

In this thesis, we concentrate on two entanglement measures, the entanglement entropy and logarithmic negativity. Motivated to extract subleading universal behavior, we perform analytic calculations in two and higher even dimensions. In order to make the calculations tractable, we put the QLM on compact manifolds, such as spheres and tori, where the spectrum of a certain operator appearing in the ground state of the theory is explicitly known. Mostly by means of the replica method, we then find analytic expressions for the finite subleading terms of the entanglement entropy and logarithmic negativity of the ground state, as well as the entanglement entropy of the excited states of the QLM. In the case of the ground state entanglement entropy, we provide analytic expressions for the sub-leading terms as functions of the dimension and the dynamical critical exponent. For the excited states we provide analytic formulae of the sub-leading coefficients as functions of the excitation numbers.

Lukas Schneiderbauer

Valentina Giangreco, september 24, 2020

PhD defense, Friday September 25 at 14.00, in Veröld, room 023

Semi-Classical Black Hole Holography 

The defense will be streamed: https://www.youtube.com/user/HIvarp/live

Dissertation title: Semi-Classical Black Hole Holography 

Opponents: Dr. Veronika Hubeny, Professor of Physics at UC Davis,USA
Dr. Mukund Rangamany, Professor of Physics at UC Davis, USA

Advisor: Dr. Lárus Thorlacius, Professor at the Faculty of Physical Sciences, University of Iceland

Doctoral committee: Dr. Bo Sundborg, Professor at the Department of Physics at Stockholm University, Sweden
Dr. Valentina Giangreco M. Puletti, Professor at the Faculty of Physical Sciences, University of Iceland
Dr. Þórður Jónsson, Professor at the Faculty of Physical Sciences, University of Iceland

Chair of Ceremony: Dr. Einar Örn Sveinbjörnsson, Professor and the Head of the Faculty of Physical Sciences, University of Iceland

Abstract:
This thesis discusses two aspects of semi-classical black holes.
First, a recently improved semi-classical formula for the entanglement entropy of
black hole radiation is examined. This entropy is an indicator of information loss and determines whether black hole evaporation is an information preserving process or destroys quantum information. Assuming information conservation, Page expressed the entanglement entropy as a function of time, which is referred to as the “Page curve.” Using the improved formula for evaporating black hole solutions of a gravitational model introduced by Callan, Giddings, Harvey and Strominger (CGHS) and modified by Russo, Susskind and Thorlacius (RST), we find that the entanglement entropy follows the Page curve and thus is consistent with unitary evolution.
Second, the notion of quantum complexity is explored in the context of black holes. The quantum complexity of a quantum state measures how many “simple operations” are needed to create that state. Susskind conjectured that the quantum complexity of a black hole state corresponds to a certain volume inside the black hole. A modified conjecture equates the quantum complexity with the gravitational action evaluated for a certain region of spacetime which intersects the black hole interior. We test the complexity conjectures for semi-classical black hole solutions in the CGHS/RST model and find that both conjectures yield the expected behavior.

Doktorsvörn – Warsha Singh

Benedikt Magnússon, júní 12, 2015
Hvenær hefst þessi viðburður: 12. júní 2015 – 10:00
Staðsetning viðburðar: Aðalbygging
Nánari staðsetning: Hátíðarsalur

Háskóli ÍslandsFöstudaginn 12. júní ver Warsha Singh doktorsritgerð sína í vistfræðilíkönum við Raunvísindadeild Háskóla Íslands. Ritgerðin ber heitið: Bættar aðferðir við stofnmat sjávarbotndýra með notkun djúpfars (Towards efficient benthic survey design with the use of autonomous underwater vehicles).

Andmælendur eru dr. Michael Fogarty, forstöðumaður Ecosystem management program við Northeast Fisheries Science Center, Bandaríkjunum, og dr. Arthur Trembanis, dósent í haffræði og jarðvísindum við University of Delaware, Bandaríkjunum.

Leiðbeinandi var dr. Gunnar Stefánsson, prófessor við Raunvísindadeild Háskóla Íslands. Auk hans sátu í doktorsnefnd dr. Erla Björk Örnólfsdóttir, rektor Háskólans á Hólum, Jörundur Svavarsson, prófessor við Líf- og umhverfisvísindadeild Háskóla Íslands, og dr. Tómas Philip Rúnarsson, prófessor við Iðnaðarverkfræði-, vélaverkfræði- og tölvunarfræðideild Háskóla Íslands.

Dr. Hafliði Pétur Gíslason, prófessor og deildarforseti Raunvísindadeildar, stjórnar athöfninni.

 

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Doktorsvörn í tölfræði – Anna Helga Jónsdóttir

Benedikt Magnússon, apríl 16, 2015
Hvenær hefst þessi viðburður: anna_helga17. apríl 2015 – 14:00
Staðsetning viðburðar: Hátíðarsalur, Aðalbygging
Föstudaginn 17. apríl ver Anna Helga Jónsdóttir doktorsritgerð sína í tölfræði við Raunvísindadeild Háskóla Íslands. Ritgerðin ber heitið Þróun og prófun á opnu vefkennslukerfi í stærðfræði og tölfræði (Development and testing of an open learning environment to enhance statistics and mathematics education).

Andmælendur eru dr. Per B. Brockhoff, prófessor við Danmarks Tekniske Universitet, og dr. Robert C. delMas, dósent við University of Minnesota.

Leiðbeinandi var dr. Gunnar Stefánsson, prófessor við Raunvísindadeild Háskóla Íslands.
Auk hans sátu í doktorsnefnd dr. Freyja Hreinsdóttir, dósent við Menntavísindasvið Háskóla Íslands og dr. Auðbjörg Björnsdóttir,  forstöðumaður Kennslumiðstöðvar Háskólans á Akureyri.

Dr. Oddur Ingólfsson, prófessor og varadeildarforseti Raunvísindadeildar stjórnar athöfninni.

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