Searcharxiv⌕ Search

arXiv subjects

Samuel Laliberte

Publications and source records attributed to Samuel Laliberte.

14 recordsLinked to original sources
arXiv2026

Additional constraints for the tensor bootstrap

Recently, new positivity constraints were suggested to constrain arbitrary unitary tensor integrals. In the present work, we explore two variants of these positivity constraints: one built from ``open bubbles'', which are tensor-like objects found by removing a tensor from a bubble invariant, and the second built from ``color matrices'', which are matrices found by removing a color contraction from a bubble invariant. Using these positivity constraints, we find sharp bounds on unitary tensor integrals at finite $N$, and probe deviations from Gaussian universality in this limit.

hep-th↗
arXiv2026

Finite-$N$ Bootstrap Constraints in Matrix and Tensor Models

We explore how matrix bootstrap techniques can be used to constrain matrix and tensor models at finite $N$, where $N$ is the dimension of the matrix/tensor, taking a Gaussian model with a quartic interaction as example. For matrix models, we find further evidence that bounds do not depend explicitly on $N$, but rather on properties of multi-trace expectation values. For tensor models, the structure of the Schwinger-Dyson equations allow for bounds that vary as a function of $N$, admitting a broader scan of the parameter space of the theory. In the latter case, we find novel bounds on the two-point function as a function of the quartic coupling of the theory.

hep-th↗
arXiv2025

Bootstrapping supersymmetric (matrix) quantum mechanics

We apply the quantum-mechanics bootstrap to supersymmetric quantum mechanics (SUSY QM) and to its matrix relative, the Marinari-Parisi model, which is conjectured to describe the worldvolume of unstable $D0$ branes. Using positivity of moment matrices together with Heisenberg, gauge, and (zero-temperature) thermal constraints, we obtain rigorous bounds on ground-state data. In the cases where SUSY is spontaneously broken, we find bounds that apply to the lowest-energy normalizable eigenstate. For $N = 1$ SUSY QM with a cubic superpotential, we obtain tight bounds that agree well with available approximation methods. At weak coupling they match well with the semiclassical instanton contribution to SUSY-breaking ground-state energy, while at strong coupling they exhibit the expected scaling and match well with Hamiltonian truncation. For the SUSY matrix QM, we construct a $44 \times 44$ bootstrap matrix and obtain bounds at large $N$. At strong coupling, we obtain the expected $E \sim \kappa \ g^{2/3}$ scaling of $E$ with $g$ and extract a lower bound on the coefficient $\kappa > .196$. At small coupling, the theory has a critical point $g_c$ where the two wells merge into one. We find a spurious kink at $g = \sqrt{2} g_c$. We attribute this to truncation error and solver limitations, and discuss possible improvements.

hep-th↗
arXiv2024

Effective mass and symmetry breaking in the IKKT matrix model from compactification

The IKKT model is a promising candidate for a non-perturbative description of Type IIB superstring theory. It is known from analytic approaches and numerical simulations that the IKKT matrix model with a mass term admits interesting cosmological solutions. However, this mass term is often introduced by hand, and serves as a regulator in the theory. In the present paper, we show that an effective mass matrix can arise naturally in the IKKT model by imposing a toroidal compactification where the space-time fermions acquire anti-periodic boundary conditions. When six spatial dimensions are chosen to be compact, the effective mass matrix breaks the SO(1,9) space-time symmetry of the IKKT model to SO(1,3) $\times$ SO(6). This paves the way for space-time solutions of the IKKT model where SO(1,9) symmetry is naturally broken to SO(1,3) $\times$ SO(6).

hep-th↗
arXiv2023

IKKT thermodynamics and early universe cosmology

Matrix theory is a proposed non-perturbative definition of superstring theory in which space is emergent. Recently, it was shown that space-time can emerge with a scale-invariant spectrum of cosmological perturbations which is sourced by thermal fluctuations of the BFSS model at finite temperature. Inspired by these results, we begin a study of the IKKT model at finite temperature. We find that in this model, which is closely related to the BFSS model at finite temperature, thermal fluctuations can also source a scale-invariant spectrum of scalar and tensor fluctuations.

hep-th↗
arXiv2023

TCC bounds on the static patch of de Sitter space

Recently, Pei-Ming Ho and Hikaru Kawai have argued that treating particles as wave packets can lead to a shutdown of Hawking radiation after a scrambling time in the case of Schwarzschild black holes. This shutdown arises from viewing quantum field theory near the black hole horizon as an effective field theory, and imposing an appropriate UV cutoff. We show that this effect is also present in the static patch of de Sitter space, leading to a shutdown of Gibbons-Hawking radiation at late times. Assuming this effect is due to the breakdown of effective field theory, we obtain a bound $t \lesssim H^{-1} \ln (H^{-1} M_P)$ on the time scale of validity of effective field theory in de Sitter space, which matches with the predictions of the Trans-Planckian Censorship Conjecture.

hep-th↗
arXiv2022

Spontaneous symmetry breaking in the BFSS model: Analytical results using the Gaussian expansion method

We apply the Gaussian expansion method to the BFSS matrix model in the high temperature limit. When the (Euclidean) BFSS action is expanded about a Gaussian ansatz, it is shown that the SO(9) symmetry is spontaneously broken, analogous to what happens in the IKKT model. The analysis of the free energy, using the set of gap equations which determines the width of the Gaussian terms, is sufficient to show that this symmetry breaking happens only when the fermionic terms are included and is absent in the bosonic case.

hep-th↗
arXiv2022

Emergent Metric Space-Time from Matrix Theory

The IKKT matrix model yields an emergent space-time. We further develop these ideas and give a proposal for an emergent metric. Based on previous numerical studies of this model, we provide evidence that the emergent space-time is continuous and infinite in extent, both in space and in time, and that the metric is spatially flat. The time evolution describes the transition from a string-theoretic emergent phase to a phase in which the $SO(9)$ symmetry of the model is spontaneously broken to $SO(6) \times SO(3)$, with three dimensions of space expanding, becoming classical and at later times evolving like in a radiation-dominated universe, and the remaining six dimensions of space stabilized at the string scale. We speculate on how this analysis can be extended to yield an early universe cosmology which, in addition to the above-mentioned properties, also leads to a roughly scale-invariant spectrum of cosmological fluctuations and gravitational waves.

hep-th↗
arXiv2022

Emergent Early Universe Cosmology from BFSS Matrix Theory

The BFSS matrix model is a suggested non-perturbative definition of string theory. Starting from a thermal state of this matrix model, we show how space and time can emerge dynamically. Results from the IKKT matrix model indicate that the $SO(9)$ symmetry of space is spontaneously broken to $SO(3) \times SO(6)$, with the three-dimensional subspace becoming large. Given this initial state for the universe, we show that cosmological perturbations and gravitational waves with scale-invariant spectra are generated, without the need of postulating an early phase of cosmological inflation. The Big Bang singularity is automatically resolved.

hep-th↗
arXiv2021

Emergent Cosmology from Matrix Theory

Matrix theory is a proposed non-perturbative definition of superstring theory in which space is emergent. We begin a study of cosmology in the context of matrix theory. Specifically, we show that matrix theory can lead to an emergent non-singular cosmology which, at late times, can be described by an expanding phase of Standard Big Bang cosmology. The horizon problem of Standard Big Bang cosmology is automatically solved. We show that thermal fluctuations in the emergent phase source an approximately scale-invariant spectrum of cosmological perturbations and a scale-invariant spectrum of gravitational waves. Hence, it appears that matrix theory can lead to a successful scenario for the origin of perturbations responsible for the currently observed structure in the universe while providing a consistent UV-complete description.

hep-th↗
arXiv2020

String Gases and the Swampland

In this paper, we study some aspects of moduli stabilization using string gases in the context of the Swampland. In the framework which we derive, the matter Lagrangian for string gases yields a potential for the size moduli which satisfies the de Sitter conjecture with the condition $\frac{|\nabla V|}{V} \geq \frac{1}{\sqrt{p}}\frac{1}{M_p}$, where $p$ is the number of compactified dimensions. Moreover, the moduli find themselves stabilized at the self-dual radius, and gravity naturally emerges as the weakest force.

hep-th↗
arXiv2019

Ionization from Cosmic Strings at Cosmic Dawn

Cosmic strings produce charged particles which, by emitting electromagnetic radiation, partially ionize neutral hydrogen during the dark ages. Corrections to the ionization fraction of neutral hydrogen induced by cosmic strings could lead to new observational effects and/or new constraints on the string tension around $Gμ\sim 10^{-16} - 10^{-22}$ for values of the primordial magnetic field in the range $B_0 \sim 10^{-11}-10^{-9}$ Gauss.

astro-ph.CO↗
arXiv2018

Cosmic String Wake Detection using 3D Ridgelet Transformations

Three-dimensional ridgelet statistics are used to search for the signals of cosmic string wakes in the distribution of dark matter. We compare N-body simulations of the dark matter distribution in cosmological models with and without a cosmic string wake, assuming that the dominant sources of fluctuations are those predicted in the standard $Λ$CDM model. Cosmic string wakes lead to overdense regions with planar topology, and hence three-dimensional ridgelet statistics are a promising analysis tool. The string signal is easier identifiable for larger string tensions and at higher redshift. We find that a wake produced by a string of tension $Gμ= 10^{-7}$ (a value slightly lower than the best current robust upper bound) can be detected at $6 \, σ$ confidence level at a cosmological redshift $z = 10$.

astro-ph.CO↗