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Patrick Jentsch24/09/2024, 14:30
The Vicsek simulation model of flocking together with its theoretical treatment by Toner and Tu in 1995 were two foundational cornerstones of active matter physics. However, despite the field's tremendous progress, the actual universality class (UC) governing the scaling behavior of Viscek's "flocking" phase remains elusive. Here, we use nonperturbative, functional renormalization group...
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Jonas Stoll24/09/2024, 14:30
Low-energy models are often used to study properties of strong-interaction matter, in particular at low temperatures. We investigate regularization scheme dependences of the quark-meson model in the mean-field and local potential approximation. To this end, we work out a meaningful comparison procedure for calculations with different regularization schemes using renormalization-group...
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Marc Schiffer24/09/2024, 14:30
Asymptotically safe quantum gravity might cure the Landau pole of the Abelian hypercharge-sector of the Standard Model by adding a screening contribution to its scale-dependence, ultimately rendering it asymptotically free. On the other hand, gravitational fluctuations also induce higher order gauge-field operators, which cannot be set to zero consistently at high energies. These can lead to...
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Louis Heitz24/09/2024, 14:30
Since two decades, Ab Initio methods in nuclear physics have have undergone considerable development. These methods have two pillars : on one hand interactions between nucleons are derived order by order from chiral EFT ; on the other hand many-body techniques are applied to solve the Schrödinger equation. Such methods have provd successful and reliable in describing the properties of nuclei...
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Patrick Niekamp24/09/2024, 14:30
Euclidean approaches such as the functional renormalization group (FRG) have been abundantly and successfully used to study the universal static critical behavior of various physical systems near continuous phase transitions. For the study of critical dynamics, on the other hand, one usually relies on real-time methods. Our research aims to connect and relate the two approaches by comparing...
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Marcel Gievers24/09/2024, 14:30
The study of the Fermi-edge singularity in x-ray absorption spectra of metals is a paradigmatic fermionic model, which exhibits logarithmic divergences in perturbation theory. Thus, it offers a playground for different diagrammatic approximations. It has been shown that a summation of parquet diagrams and, even more restricted, a 1-loop fRG approach are sufficient to include all...
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Athanasios Kogios24/09/2024, 14:30
In this talk, I will present the Dilaton Quantum Gravity in the context of the Asymptotic Safety Scenario. We consider a scalar field non-minimally coupled to gravity a la Brans-Dicke and after deriving the corresponfing flow equations for the couplings (now functions of the scalar field), we first explore the behavior of the system on its fixed point. Performing a large field expansion in...
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Charlie Cresswell-Hogg24/09/2024, 14:30
Theories of self-interacting fermions play an important role in particle and condensed matter physics, covering effective descriptions of the strong nuclear force, the critical behaviour of Dirac materials such as graphene, and more. In this talk, I discuss functional RG flows for fermionic systems in the large-N limit. Working directly in terms of fermionic field variables and using a...
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Mateusz Homenda24/09/2024, 14:30
We study the functional renormalization group flows of fermionic self energy close to quantum criticality in two dimensional systems of fermions coupled to a collective order parameter mode. Taking into account the flow of the bosonic mass we analyze how the non-Fermi liquid state is generated upon reducing the cut-off scale close to the quantum criticality. Within our framework we capture the...
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Aiman Al-Eryani24/09/2024, 14:30
Recently, due to tremendous progress in materials synthesis the family of strongly-correlated systems exhibiting superconductivity has been extended substantially, e.g., through the experimental study of magic-angle bilayer graphene and other graphene-based heterostructures, and more. Yet, the origin of the superconducting pairing mechanism(s) in these materials is far from being clear as...
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Jonas Arnold24/09/2024, 14:30
Exact functional renormalization group (FRG) flow equations for quantum systems can be derived directly within an operator formalism without using functional integrals. This simple insight opens new possibilities for applying FRG methods to models for strongly correlated electrons with projected Hilbert spaces, such as the t model, obtained from the Hubbard model at infinite on-site repulsion....
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Sankarshan SAHU24/09/2024, 14:30
The Central Limit Theorem does not hold for strongly correlated stochastic variables, as is the case for statistical systems close to criticality. Recently, the calculation of the probability distribution function (PDF) of the magnetization mode has been performed with the functional renormalization group (FRG) in the case of the three dimensional Ising model . We show how this PDF or,...
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Pavan Dharanipragada24/09/2024, 14:30
It has been conjectured that the 3d free O(N) vector model has an AdS4 dual which is Vasiliev's higher spin theory. Higher spins naturally arise in string theory, and they could soften the UV properties of quantum gravity. Since the boundary theory is a free theory, this duality is an ideal setting to understand higher spin theory through the much simpler free O(N) model. In fact, Vasiliev's...
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Tim Stötzel24/09/2024, 14:30
Hydrodynamics is an effective, long-range field theory whose properties emerge from the underlying short-range behaviour. The description of dissipative fluids needs knowledge about transport coefficients like viscosities or conductivities that govern the relaxation of a system back to its equilibrium state and depend solely on the systems microscopic properties. In this talk I will present an...
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Ryota Nasu24/09/2024, 14:30
We demonstrate that quantum error correction is realized by the renormalization group in scalar field theories. We construct q-level states by using coherent states in the IR region. By acting on them the inverse of the unitary operator U that describes the renormalization group flow of the ground state, we encode them into states in the UV region. We find that the Knill-Laflamme condition is...
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Richard Schmieden24/09/2024, 14:30
We investigate nonperturbative aspects of the interplay of chiral transitions in the standard model in the course of the renormalization flow. We focus on the chiral symmetry breaking mechanisms provided by the QCD and the electroweak sectors, the latter of which we model by a Higgs-top-bottom Yukawa theory. The interplay becomes quantitatively accessible by accounting for the...
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Edoardo D'Angelo24/09/2024, 14:30
The Renormalization Group (RG) Equation determines the flow of the effective action under changes in an artificial energy scale, which roughly corresponds to the scale of the system under consideration. I report on a rigorous construction of a non-perturbative RG flow for the effective action in Lorentzian manifolds. I give the main ideas of a proof of local existence of solutions for the RG...
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Agustín Silva24/09/2024, 14:30
Asymptotic safety is a powerful mechanism for obtaining a consistent and predictive quantum field theory beyond the realm of perturbation theory. It hinges on an interacting fixed point of the Wilsonian renormalization group flow, which controls the microscopic dynamics. Connecting the fixed point to observations requires constructing the set of effective actions compatible with this...
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Ugo Mire24/09/2024, 14:30
We study a quark-meson-diquark model with omega vector meson, including the fluctuations of the sigma and pion, in an LPA truncation. We discuss the effect of the sigma and pion fluctuations on the phase structure and the equation of state. The effects of different diquark and vector couplings are also investigated.
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Diego Buccio24/09/2024, 14:30
Running coupling were introduced in quantum filed theory in order to preserve perturbativity in scattering amplitudes, despite the appearance of large logs of external momenta. It is commonly believed that these logarithms are directly related to UV divergencies in one-loop perturbation theory, however this is not completely true in higher derivative theories, where large logs can emerge also...
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Yunxin Ye24/09/2024, 14:30
In this work, Quark-Meson model is formulated in real-time, taking into account the dynamic properties (dissipation of $\sigma$ and $\pi$) by considering the system interacting with a heat bath. The symmetry of thermal equilibrium of the real-time action combined fermionic system is studied. Real-time functional renormalization group method is employed to study the flow of the effective...
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Jonas Wessely24/09/2024, 14:30
In this talk, we report on recent results within spectral functional methods. We focus in particular on spectral Callan-Symanzik flows and the computation of spectral functions in the scaling limit of a scalar theory, the Quark-Meson model and gravity. Furthermore, discuss spectral Bethe-Salpeter equations at the example of a scalar theory and the extension of the spectral funtional framework...
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Julian Schirrmeister24/09/2024, 14:30
We study the renormalization flow of generic actions that depend on the invariants of the field strength tensor of an abelian gauge field. While the Maxwell action defines a Gaussian fixed point, we search for further non-Gaussian fixed points or rather fixed functions, i.e., globally existing Lagrangians of the invariants. For the construction of a globally existing fixed function, we pay...
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Benedikt Schneider24/09/2024, 14:30
The quantum-to-classical correspondence (QCC) in spin systems is the phenomenon that the static correlator of quantum spin models agree with their classical counterpart at a different temperature within QMC error bars in bold-line diagrammatic Monte-Carlo. The quantum fluctuations appear to only "heat up" the system. Currently, the QCC is a purely empirical observation. We show that the QCC is...
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Gabriel Assant24/09/2024, 14:30
We compute the asymptotically safe graviton propagators of the transverse-traceless and scalar mode within Lorentzian quantum gravity. To that end, we determine the interacting UV fixed point in Lorentzian signature, find connecting UV-IR trajectories, and solve the coupled system of running Kallen-Lehmann spectral representations. The resulting spectral functions are compatible with causality...
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Kevin Falls24/09/2024, 14:30
I will discuss how scaling exponents in quantum gravity can be defined for diffeomorphism invariant operators. I will the report recent progress on the computation of the exponents using the essential renormalisation group.
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97. Single-boson exchange formulation of the Schwinger-Dyson equation and its application to the fRGMiriam Patricolo24/09/2024, 14:30
We extend the recently introduced single-boson exchange (SBE) formulation to the computation of the self-energy from the Schwinger-Dyson equation. In particular, we derive its general expression both in diagrammatic and in physical channels and show that the SBE formulation of the Schwinger-Dyson equation can be naturally applied also to non-local interactions. We furthermore discuss its...
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Yuepeng Guan24/09/2024, 14:30
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Yadikaer Maitiniyazi24/09/2024, 14:30
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Santiago Cabrera Sosa24/09/2024, 14:30
It is well known that the symmetries of a theory often restrict its form, and sometimes allow to totally determine it. In particular, it has been long conjectured that the O(N) models’ critical regime is characterized by the presence of the complete conformal symmetry. Moreover, it has been proven for the specific values of N=1, 2, 3 and 4, that this is in fact the case. There exist numerous...
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Marcel Krämer24/09/2024, 14:30
The DMF2RG has been introduced to overcome the weak-coupling limitation of the fermionic functional renormalization group (fRG). This approach builds on the idea to exploit the dynamical mean-field theory (DMFT) as starting point for the fRG flow, thus capturing local nonperturbative correlations via DMFT together with perturbative nonlocal correlations generated during the flow. We show how...
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Thomas Sheerin24/09/2024, 14:30
Developing a predictive theory of non-Fermi liquids (NFLs) in two spatial dimensions remains a key challenge to modern condensed matter physics. At the level of real materials, it could provide insight into such pressing problems as high-T_c superconductivity, while in the abstract it is paradigmatic of the poorly understood scenario of 2-D criticality induced by a gapless boson interacting...
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Daniel Litim, Nahzaan Riyaz24/09/2024, 14:30
Using RG methods, I study the UV conformal window of weakly coupled gauge theories weakly with matter. Using beta functions up to four-loop in perturbation theory, I discuss results for fixed points and scaling dimensions as power series in a small Veneziano parameter. Particular emphasis is put on the mechanism resonsible for the end of the conformal window, and a competition between the loss...
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Bilal Hawashin24/09/2024, 14:30
Not all possible phase transitions occurring in nature are captured by the Landau-Ginzburg-Wilson-Fisher paradigm. An exciting class of such non-Landau transitions are deconfined quantum critical points (DQCP) which exhibit emergent fractional excitations and gauge fields at criticality. The primary example in the study of DQCPs has been a system of half-integer spins on a square lattice with...
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Alexander Jercher
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Andrey Katanin
I discuss application of local 2PI Vertex Approximation (also known as a coupled ladder approximation) to description of charge, spin instabilities in graphene nanoflakes, as well as spin instabilities in magnetic systems. In graphene nanoflakes for strong on-site repulsion the spin density wave instability is obtained, while for strong non-local interaction the charge density wave instability...
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Markus B. Fröb
We employ a recently derived diffeomorphism-covariant Lorentzian flow equation to compute RG flows of metric fluctuations in de Sitter spacetime. We work in the Einstein-Hilbert truncation, which results in a 6-parameter space, and we explore various corners of this space. Joint work with Edoardo D'Angelo and Renata Ferrero.
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