Holographic thermal entropy and modular conjugation from geodesic bit threads
2025-09-09 11:30 - 13:30 (Europe/Madrid)
Speaker: Francesco Gentile

Institution: SISSA

Location&Place: Grey Room 2

Abstract:

In this talk, I will discuss some new interesting properties of geodesic bit threads in static backgrounds.
Bit threads are an insightful tool for investigating holographic entanglement entropy, providing a reformulation of the Ryu-Takayanagi formula in terms of the maximal flux of a bounded and divergenceless vector field.
An explicit realization of bit threads is given by geodesic bit threads.
I will first argue that, for a spherical region on AdS boundary and for an interval on the BTZ boundary, geodesic bit threads display a surprising connection with modular conjugation in CFT.
Then, I will show that for an interval on the BTZ boundary and for a spherical region on the boundary of Schwarzschild AdS, the flux of geodesic bit threads hitting the event horizon provides the holographic thermal entropy, i.e. the product of a thermal entropy density with the volume of the spherical region.

Entangle This VI: 100 years of quantum
2025-09-15 09:00 - 2025-09-19 20:00 | Parque del Retiro, Plaza Murillo, 2,, Madrid, 28014,, Spain
As part of the International Year of Quantum Science and Technology, the workshop Entangle This VI will bring together experts at the forefront of quantum theory and experiment. It is organized by the Quantum groups at IFT and IFF.
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Exploring infinite distance limits of type II Calabi–Yau compactifications
2025-09-15 10:00 - 11:30 | Blue Room, Instituto de Física Teórica (IFT) - C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Luca Melotti

Institution: IFT UAM/CSIC

Location&Place: Blue Room

Abstract:

This thesis explores infinite distance limits in the vector multiplet moduli space of type II string theory on Calabi–Yau threefolds. First we classify such limits, identify the towers of light states, and test the Emergence Proposal, which links IR kinetic terms to loop corrections from such states. We then study the scalar curvature of the moduli space along infinite distance trajectories, focusing on cases where it diverges positively. We argue that such divergences signal decoupled field theory sectors and propose this as the only mechanism for curvature divergences in quantum gravity. Extending the analysis, we relate these limits to higher-dimensional rigid theories (5d/6d SCFTs and Little String Theories), interpreting divergences as a parametric separation between the strength of gravitational and gauge interactions. Finally, we connect curvature divergences with rigid limits and the existence of BPS states with divergent charge-to-mass ratios.

Supervisor: Fernando Marchesano

On the Asymptotic Global Structure of Duality Frames in Quantum Gravity
2025-09-15 12:00 - 13:30 | Blue Room, Instituto de Física Teórica (IFT) - C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Ignacio Ruiz García

Institution: IFT UAM/CSIC

Location&Place: Blue Room

Abstract:

This thesis studies the global asymptotic structure of moduli spaces in effective field theories compatible with Quantum Gravity, focusing on the Swampland Distance Conjecture. We develop taxonomy rules that determine the arrangement of towers of light states and duality frames at infinite distance, showing a finite set of possible global structures. These towers, interpreted as emergent degrees of freedom, are linked to the lowering of the EFT cut-off scale, leading to a universal relation between the leading tower and the cut-off depending only on spacetime dimension. We test these patterns in string and M-theory compactifications, recovering known constructions and suggesting new landscape corners or Swampland constraints. Finally, we explore generalizations in lower-supersymmetry settings, including non-Lorentzian decompactifications, changing fibration structures, and additional asymptotic scales, to better understand the consistency rules for EFTs admitting UV completion to Quantum Gravity.

Supervisor: Irene Valenzuela Agüí

Will we know the Neutrino Mass Ordering by the end of 2026?
2025-09-15 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
The JUNO reactor neutrino experiment has recently begun collecting data, marking the start of a new precision era in neutrino research. With its unparalleled precision, JUNO is poised to refine our understanding of most neutrino oscillation parameters. Its cornerstone measurement – the determination of the neutrino mass ordering — holds the promise of a breakthrough. In this talk we will explore the physics behind the two distinct ways JUNO data can be used to probe the mass ordering, one of which could lead to the resolution of this fundamental question in the near future. Additionally, we will examine the conditions necessary for such a discovery and address potential
theoretical caveats that could influence the interpretation of the outcome.

Light Dark World 2025
2025-09-16 09:00 - 2025-09-19 17:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Light Dark World 2025 (LDW’25) is the tenth meeting of the annual Light Dark World International Forum, which will take place between September 16 and September 19, 2025, at the Instituto de Física Teórica (IFT) in Madrid (Spain). The workshop will gather international specialists from both experimental and theoretical backgrounds in order to examine recent progress and create new avenues for investigating the existence of light particles beyond the Standard Model, including light gauge bosons, scalars, dark matter, axions, sterile neutrinos, and dark energy fields.
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Aspects of symmetries throughout the String Theory Moduli Space
2025-09-16 10:00 - 11:30 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Roberta Angius

Institution: IFT UAM/CSIC

Location&Place: Red Room

Abstract:

This thesis aims to explore various corners of the string theory moduli spaces using symmetries as a guiding principle to uncover properties of the corresponding theories and their implications for spacetime dynamics.

Within the Swampland Program, the absence of global symmetries in consistent quantum gravity theories is a key principle, reformulated in string theory as the Cobordism Conjecture: any consistent configuration must admit spacetime boundaries, often realized by stringy defects that trivialize cobordism charges. The first part of this thesis implements this idea in effective field theory throughDynamical Cobordism solutions, where codimension-1 end-of-the-world (ETW) branes appear as finite-distance singularities with scalars diverging to infinite field space. These provide a framework to probe infinite-distance limits in the moduli/field space and Swampland constraints. We construct explicit examples with one or multiple scalars, including networks of intersecting ETW branes, and apply them to study infinite-distance singularities in Calabi–Yau fourfold moduli spaces, described via asymptotic Hodgetheory.

On the other hand, we turn to a microscopic approach to string theory and investigate worldsheet generalized symmetries, defined by topological operators with possibly non-invertible fusion rules. In particular, we analyze the category of topological defects commuting with spectral flow and N=(4,4) superconformal symmetry in K3 sigma models. Bystudying their fusion with boundary states, we argue that while certain models admit infinitely many, or even continuous families of defects, at generic points in the K3 moduli space the category is actually trivial.

Supervisor: Ángel Uranga

Dynamical Cobordism in String Theory and Holography
2025-09-16 12:00 - 13:30 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Jesús Huertas Castellanos

Institution: IFT UAM/CSIC

Location&Place: Red Room

Abstract:

This thesis investigates the intricate relationship between topology, gravity, and quantum field theory within String Theory, centering on the Cobordism Conjecture, which asserts that any consistent quantum gravity theory must allow spacetime boundaries. It begins by introducing Dynamical Cobordism through models that realize end-of-the-world branes dynamically, linking them to Swampland constraints. It then explores Bubbles of Nothing as non-perturbative instabilities, classifying them and analyzing their behavior across various theories. The third section applies Dynamical Cobordism to AdS/CFT, reinterpreting known duals in type IIB string theory as boundary-terminating geometries. Finally, it examines topological couplings and anomalies in holographic setups, introducing the SymTFT framework and uncovering new anomaly inflow mechanisms and Chern-Simons structures.
Supervisor: Ángel Uranga

Aspects of inflation beyond the single-field, slow-roll regime
2025-09-17 10:00 - 11:30 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Alejandro Pérez Rodríguez

Location&Place: Red Room

Abstract:

In this thesis, we explore two departures from the single field, slow-roll paradigm of inflation. The first part is dedicated to warm inflation. We revisit the theory of linear perturbations in this framework, develop computational techniques for the calculation of the primordial power spectrum and apply them to the analysis of CMB constraints and the production of primordial black holes. The second part focuses on the primordial non-Gaussianity arising from a phase of ultra slow-roll during single field inflation. We study the scope and limitations of the classical delta N formalism as a probe of such non-Gaussianity and determine the extent of its correspondence with the stochastic delta N formalism.
Supervisor: Guillermo Ballesteros Martínez

Dualities and scale-separated AdS3 vacua
2025-09-18 12:00 - 13:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: George Tringas

Institution: Lehigh U.

Location&Place: Red Room

Abstract:

After the usual paper discussion, our guest George Tringas (Lehigh U.) will give a talk on Dualities and scale-separated AdS3 vacua

Measuring Stochastic Gravitational Wave Backgrounds with Pulsar Timing Arrays
2025-09-18 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Mauro Pieroni

Institution: IEM-CSIC

Location&Place: Red Room

Abstract:

My talk focuses on using Pulsar Timing Array (PTA) data to measure Gravitational Waves (GWs). In particular, I will focus on Stochastic GW Background (SGWB) measurements. After a general introduction to the topic, I will discuss a new (simplified) approach to constrain SGWBs with PTA data. This methodology significantly reduces the computational cost of the analysis, opening up new avenues to explore the constraining power of PTA experiments. Within this framework, I’ll revisit the constraints current and future PTA experiments can set on cosmological scenarios.

Vacuum stability for gravity compactifications
2025-09-22 15:00 - 16:15 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Alessandro Tomasiello (Milano Bicocca)

Venue&Time: 15:00 / Red Room

Abstract: Compactifying from higher dimensions typically produces many different vacuum solutions; this leads to multiple possible decay channels, mediated by the nucleation of bubbles. In string theory, the latter can be expanding D-branes. Supersymmetry provides a stabilization mechanism; I will describe how to replicate it for supersymmetry-breaking vacua, with some partial success.

PhD dissertation: Advancing Gravitational Wave Data Analysis and Exploring New Sources
2025-09-24 10:30 - 12:00 | Blue Room, Instituto de Física Teórica (IFT) - C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Gonzalo Morrás PhD dissertation.

Supervisor: Juan García-Bellido

Venue&Time: Blue Room / 10:30 AM

Abstract: Gravitational wave (GW) astronomy has opened a new window onto the Universe, allowing us to study compact objects and fundamental physics. This thesis develops new methods and models to improve the detection and interpretation of GW signals, with a focus on exotic and underexplored sources. It includes pioneering searches for close hyperbolic encounters, studies of low-mass and sub-solar-mass binaries, analyses of local cosmic effects on merger rates, and the development of advanced waveform models and data analysis algorithms. These contributions enhance our ability to uncover new astrophysical phenomena and will support future GW observations with current and next-generation detectors.

QIJC: Higher Abelian Quantum Double Models: Introduction to the Characterization and Classification of the Ground State Subspace
2025-09-24 11:30 - 12:30 | Gray Room 3, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Quantum Information Journal Club
Speaker: Javier Ignacio Lorca Espiro (Universidad de la Frontera, Chile)
Venue&Time: Grey Room 3 / 11:30 AM
Abstract: Higher dimensional abelian quantum double models have been shown to be well defined in any finite dimension and exhibit the characteristic behavior of SPT phases models. In this talk, we will introduce the problem and discuss the characterization of the topological ground state subspace and ts classification scheme. We will discuss the connection of these models with pressing problems in condensed matter physics and quantum computation.

Kaluza-Klein Amplitudes in AdS: the Virasoro-Shapiro and the Veneziano Amplitudes
2025-09-24 15:00 - 16:00
Speaker: Bo Wang from Zhejiang U. Inst. Mod. Phys.
Venue&Time: Red Room / 3:00 PM
Abstract:
I will report recent progress on AdS Virasoro-Shapiro and Veneziano amplitudes for half-BPS operators with arbitrary Kaluza-Klein modes. The key ingredient is a bootstrap built directly in the world-sheet representation, together with a novel formalism. This approach yields a structural string description of AdS amplitude and a precise correspondence with correlators in N=4 SYM: at first curvature order we obtain a unique solution. I will also discuss the applications to broader holographic models beyond AdS5*S5.

SPS JC: de Sitter and Machine Learning
2025-09-25 12:00 - 13:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
SPS Journal Club

Speaker: Bruno De Luca

Venue&Time: Red Room / 12:00

Abstract:
The problem of constructing de Sitter vacua in quantum theories of gravity is constrained by no-go theorems and made computationally challenging by the absence of supersymmetry. A popular approach to make it more tractableis to start from a supersymmetric compactification, such as on a Calabi-Yau manifold. This simplification comes at the price of greatly restricting the allowed physical sources and possible geometries.

In this introduction, I will discuss some of my works on how to break supersymmetry at the compactification scale by directly solving the equations of motion. This allows for more general internal geometries and thus more general physical configurations, including four-dimensional de Sitter vacua supported by Casimir energy on negatively-curved manifolds, and scale-separated AdS4 vacua.

However, describing the corresponding geometries in detail can sometimes require to solve Einstein-like PDEs on non-trivial manifolds. This problem is intractable even numerically, with standard methods. Luckily, Machine Learning is emerging as a method to overcome these difficulties, and we will discuss a recent proposal for using Machine Learning techniques to explicitly construct negatively-curved geometries.

Time permitting, we will also describe the other way around: how we can use insights from physics to design algorithms with broad applicability to Machine Learning and beyond, focusing on optimization and sampling algorithms obtained from energy-preserving chaotic Hamiltonians with non-standard kinetic terms.

Some references:
2501.00093
2104.13380
2212.02511
2201.11137

Stirring up the intracluster medium with substructures
2025-09-25 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Go Ogiya from Zhejiang University

Venue&Time: Red Room / 3:00 PM

Abstract:
The origin of the turbulent motion of the intracluster medium (ICM) has been a longstanding open question. Stirring by substructures (member galaxies and dark matter subhaloes) orbiting within a galaxy cluster is a possible mechanism to generate and maintain the ICM turbulence. We develop a semi-analytic model considering three processes of energy transfer from substructures to the ICM (dynamical friction, ram pressure, and sloshing), and propagation and dissipation of the deposited energy. The model reproduces the gas velocity structure derived from hydrodynamical simulations. We find that dynamical friction is responsible for explaining the strong turbulence (~ 500 km/s) in the cluster outskirts (> 1 Mpc), while sloshing explains the mild turbulence (~100 km/s) in the cluster centre. In the talk, we will also discuss implications for X-ray observations of the new generation, such as XRISM and eROSITA.

To bind or not to bind, a tale of two nucleons
2025-09-26 11:30 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: André Walker-Loud (LBNL)
Venue&Time: Red Room / 11:30 AM
Abstract: Our ability to understand the emergence of nuclear physics from the Standard Model requires an understanding two nucleon interactions from the underlying quark and gluon degrees of freedom. Due to the non-perturbative nature of QCD at low-energies, the only method to provide such predictions, with quantifiable uncertainties is lattice QCD. Yet the application of lattice QCD to the two-nucleon problem is beset by a number of significant challenges, such that it has remained uncertain whether di-nucleon systems form bound states at pion masses heavier than nature. I will present recent work exploring this question with all varieties of methods in the literature, including the HAL QCD potential method, on a single set of gauge ensembles, enabling for a direct comparison of the methods.

Delta N formalism: non-linear evolution of scalar and tensor perturbations during inflation
2025-09-26 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Danilo Artigas

Institution: Kyoto University

Location&Place: IFT Seminar Room/Red Room

Abstract:

Linear-perturbation theory has proven to be an extremely powerful tool to compare inflationary models with observational data. Recently, the newcoming high-precision observations call for predictions beyond linear perturbations. Such effects are known to be relevant for example in the production of primordial black holes or scalar-induced gravitational waves. The delta N formalism proposes to capture some of these non-linearities by describing the universe as a set of homogeneous patches evolving independently. After reviewing its formulation, I will apply it to the case of a single scalar field following a slow-roll evolution, briefly interrupted by a phase of ultra-slow roll where the potential is nearly flat. Taking care of the correlation of the patches, I will show how to obtain correlation functions of scalar perturbations. As a final note, I will briefly show how this procedure can also be applied to describe primordial gravitational waves.

LHC Working Group on Forward Physics and Diffraction
2025-09-29 09:00 - 2025-10-02 18:30 | Blue Room, Instituto de Física Teórica (IFT) - C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
The September 29-October 2 2025 four-day workshop in Madrid of the LHC Physics Centre at CERN (LPCC) Forward Physics Working Group provides a forum at CERN for experimental collaborations and theorists to meet and exchange latest results across all topics of forward physics at the LHC.
The workshop will take place at the Institute of Theoretical Physics (Campus de Cantoblanco 28049 Madrid Spain) and we will be hosted by Prof. Agustin Sabio Vera. To come to IFT, you can take Line C-4 (Colmenar Viejo or Alcobendas/San Sebastián de los Reyes), that takes you to the University (Cantoblanco-Universidad Station). You can pick it up in Atocha (main station in the Centre/South of Madrid), Nuevos Ministerios (Paseo de la Castellana) and Chamartín (main station in the North). After Chamartín, the second station is Cantoblanco-Universidad, where you should exit.
More info.

Muon g-2: nuts and bolts and lattice QCD
2025-09-29 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Andreas Kronfeld (Fermilab)
Venue&Time: Red Room / 3:00 PM
Abstract: This seminar consists of two parts. First, it is discussed how various approaches to the hadronic vacuum polarization (HVP) for the anomalous magnetic moment of the muon, g-2, are connected. Second, results for the HVP from lattice QCD are presented, focusing on the work of the Fermilab Lattice, HPQCD, and MILC collaborations.

Seminar by Roberto Vega-Morales
2025-09-29 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Roberto Vega-Morales from Granada U.

Venue&Time: Red Room / 3:00 PM

Abstract: TBA

SPS Journal Club: 'Landau-Ginzburg Models and Flux Vacua'
2025-10-02 12:00 - 13:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Muthusamy Rajaguru (IFT Madrid)

Venue&Time: Red Room / 12:00 PM

Abstract: In this talk, I will give an overview of recent progress that has been made in constructing non-geometric flux vacua. In particular, I will focus on type IIB string compactifications where the internal geometry is described by the 2^6 and 1^9 Landau-Ginzburg (LG) models. These LG models have no Kähler moduli and allow us to realize GKP-type vacua explicitly in the interior of the complex structure moduli space. I will summarize the properties of these vacua and their implications for certain Swampland conjectures.

Relevant literature – 2503.16599, 2407.16756, 2407.16758, 2406.03435, 2306.15714, 2203.15818

Fast inference for slow likelihoods with probabilistic machine-learning
2025-10-02 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Jesús Torrado from IEM-CSIC

Venue&Time: Red Room / 3:00 PM

Abstract: Inference for slow likelihoods can require weeks or months, if possible at all, with traditional Monte Carlo samplers. This would be the case, for example, when fitting expensive non-linear matter spectrum models, or when characterizing individual long-duration GW events. I will introduce a fast machine-learning Bayesian inference algorithm for general non-Gaussian posteriors with a moderate number of parameters. I will present a pedagogical discussion of some general aspects of it, such as dealing with the curse of dimensionality, characterizing a region of interest, or parallelising active learning. I will show that the total number of expensive likelihood evaluations can be reduced by at least two orders of magnitude compared to traditional Monte Carlo methods, at low overhead costs and no pre-training. I will demonstrate its performance on a couple of real cosmological and GW problems.

César Gómez (1954–2025): A rich life in theory
2025-10-03 10:00 - 17:30 | Blue Room, Instituto de Física Teórica (IFT) - C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Venue&Time: Blue Room / 10:20 – 17:30
More info: workshops.ift.uam-csic.es/CesarGathering/
César Gómez, whose profound contributions to gauge theory, string theory and quantum gravity were matched by his vision and generosity, passed away on 7 April 2025. After earning his PhD in Salamanca, he held positions at Harvard, the IAS and CERN before joining the CSIC in Madrid, where he became a founding member of the Instituto de Física Teórica, his true scientific home.
His career spanned key areas of theoretical physics: from the quantum vacuum in QCD and two-dimensional conformal field theory to holography, black holes and the quantum structure of spacetime. In recent years he embarked on bold new ideas about symmetry breaking and the quantum origin of the universe, entering one of his most creative periods when his life was cut short.
Beyond his scientific achievements, César was a gifted teacher, an inspiring presence at seminars and a remarkable conversationalist. He leaves behind not only a lasting scientific legacy, but also the memory of a colleague and friend who enriched every exchange with curiosity, insight and humanity.
The meeting will be an opportunity to celebrate Cesar’s life and career through the personal recollections of some of his friends and collaborators.
Read CERN’s obituary

Cosmology Journal Club
2025-10-07 14:00 - 15:00, 2025-10-14 14:00 - 15:00 | Discussion room 5th floor, C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, Madrid, 28049, Spain
Every Tuesday at 2:00 PM in the discussion room on the 5th floor.
Join the IFT cosmology/gravity journal club at benty-fields.com to vote for papers and volunteer to present them.

SPS Journal Club: Symmetric Moduli Spaces, the Swampland Distance Conjecture (...and the Emergent String Conjecture?)
2025-10-09 12:00 - 13:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Bernardo Fraiman (IFT)

Venue&Time: Red Room / 12:00

Abstract: For non-compact, locally symmetric moduli spaces M, the set of geodesics and the geometry of the boundary can be completely characterised using group theory. Under the assumption that M is “compactifiable” and some mild conditions on the spectrum of states, we prove the SDC for all locally symmetric spaces. We show that the states necessarily transform in some representation of the local isometry group, and that the convex hull encoding the exponential rate at which the leading tower of states becomes light coincides with the convex hull of the weights of the representation.

In this talk I will discuss briefly some aspects of the proof, the domain of applicability of our assumptions and their limitations. If time permits, I will also explain how the relation between towers and weights allows one to classify moduli spaces, particle state representations and space time dimensions compatible with the Emergent String Conjecture. Based on 2508.18401 and work in progress.

Large neutrino mass in cosmology and keV sterile neutrino dark matter from a dark sector
2025-10-09 15:00 - 16:00 | IFT Seminar Room/Red Room, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Thomas Schwetz from Karlsruhe Institute of Technology (KIT)

Venue&Time: Red Room / 3:00 PM

Abstract:
Recent results from cosmology place sever upper bounds on the sum of neutrino masses, starting to be in conflict with lower bounds from neutrino oscillations. If this neutrino tension persists, it may indicate new physics in cosmology and/or neutrino physics. After a brief review of the present state, I discuss a new physics scenario able to explain this tension. It is based on an extended seesaw model for neutrino mass, including a number of massless neutrinos acting as dark radiation, as well as a keV state as a dark matter candidate. The dark sector is brought into equilibrium with neutrinos between BBN and recombination. This scenario predicts a slight increase in the effective number of neutrino species Neff at recombination, potentially detectable byfuture CMB missions.

Holo Club: Explicit Connections Between Krylov and Nielsen Complexity
2025-10-14 11:30 - 13:00 | Gray Room 3, Instituto de Física Teórica (IFT) -C. Nicolás Cabrera, 13-15, Fuencarral-El Pardo, Madrid, 28049,, Spain
Speaker: Le-Chen Qu (IFT)

Venue&Time: Grey Room 3 / 11:30

Abstract: We establish a precise correspondence between Krylov complexity and Nielsen complexity in quantum many-body systems. By identifying the Krylov basis with the generators of elementary gates in Nielsen’s geometric framework, the Krylov complexity of precursor operators acquires a geometric interpretation as the length of straight-line paths in Nielsen geometry. This construction provides an upper bound on Nielsen complexity, which becomes exact in the small-precursor limit. Employing the SYK model as a test case, we demonstrate that the straight-line trajectory satisfies the Nielsen geodesic equation and remains both locally and globally minimizing up to a critical value of $z$, beyond which conjugate points and geodesic loops arise. Within this framework, cost functions quadratic in the Krylov index are further shown to reproduce the conjectured proportionality between the complexity growth rate and the operator size.
