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Gero von Gersdorff

Publications and source records attributed to Gero von Gersdorff.

At least 19 recordsLinked to original sources
arXiv2026

Revisiting the Page curve and its moments. A combinatorial approach

We revisit the calculation of the von Neumann (or "entanglement") entropy of a subsystem of a pure quantum state, under the assumption that the latter is drawn at random from a uniform distribution on the full Hilbert space. We derive simple and closed expressions for all power moments, from which the moments of the entropy can be computed by simple differentiation. Our approach (different from the usual one based on random matrix theory and Laguerre polynomials) makes use of Schur-Weyl duality and the character theory of the symmetric group $S_N$ . The paper is self-contained, providing all the necessary mathematical background.

quant-ph↗
arXiv2026

Feynman integral reduction by covariant differentiation

We show how a large class of Feynman integrals can be efficiently reduced to master integrals by suitable covariant differentiation on the vector space dual to the one spanned by the master integrals. The connections needed in the covariant derivatives have to be built only once for a given topology and then apply to any configuration of internal propagator masses. We implement our algorithm in the Mathematica code Method for Reduction of Loop Integrals (MERLIN).

hep-ph↗
arXiv2025

Heat Kernel Methods for Multiloop Calculations in Curved Spacetime: Nonzero Spin

In a previous paper we have presented a general formalism for computing Feynman diagrams for scalar fields in curved spacetime at any loop order using heat kernel methods. The main technique used is the expansion of the fully off-diagonal heat kernel in Riemann normal coordinates. In this work we extend this to include fields of nonzero spin, in particular spin-$\frac{1}{2}$ fermions.

hep-th↗
arXiv2025

Inequalities for Standard Model Yukawa Couplings

We show that the Standard Model Yukawa matrices satisfy a set of simple yet nontrivial inequalities. The relations we derive are independent of the basis used to define the fermion fields, and, amongst other things, place strong constraints on the alignment of the columns of the up-type and down-type Yukawa matrices, as well as their cofactor matrices. The reason why one can obtain such strong statements can be traced back to the hierarchical nature of the fermion masses and quark mixings. The inequalities should be seen as very strong necessary conditions on the Standard Model Yukawa couplings and thus are useful for constraining flavor models.

hep-ph↗
arXiv2023

Factorization of covariant Feynman graphs for the effective action

We prove a neat factorization property of Feynman graphs in covariant perturbation theory. The contribution of the graph to the effective action is written as a product of a massless scalar momentum integral that only depends on the basic graph topology, and a background-field dependent piece that contains all the information of spin, gauge representations, masses etc. We give a closed expression for the momentum integral in terms of four graph polynomials whose properties we derive in some detail. Our results can also be useful for standard (non-covariant) perturbation theory.

hep-ph↗
arXiv2023

New Covariant Feynman Rules for Effective Field Theories

We provide a new and completely general formalism to compute the effective field theory matching contributions from integrating out massive fields in a manifestly gauge covariant way, at any desired loop order. The formalism is based on old ideas such as the background field method and the heat kernel, however we add some crucial new ingredients that greatly improve the simplicity and general applicability of the approach. We formulate our method in terms of Feynman rules, the resulting effective action is expressed in terms of local heat kernel coefficients. We also provide as supplementary material a mathematica code that facilitates the computation of these coefficients.

hep-ph↗
arXiv2022

Measurement of interaction-dressed Berry curvature and quantum metric in solids by optical absorption

The quantum geometric properties of a Bloch state in momentum space are usually described by the Berry curvature and quantum metric. In realistic gapped materials where interactions and disorder render the Bloch state not a viable starting point, we generalize these concepts by introducing dressed Berry curvature and quantum metric at finite temperature, in which the effect of many-body interactions can be included perturbatively. These quantities are extracted from the charge polarization susceptibility caused by linearly or circularly polarized electric fields, whose spectral functions can be measured from momentum-resolved exciton or infrared absorption rate. As a concrete example, we investigate Chern insulators in the presence of impurity scattering, whose results suggest that the quantum geometric properties are protected by the energy gap against many-body interactions.

cond-mat.str-el↗
arXiv2022

Searching for anomalous top quark interactions with proton tagging and timing detectors at the LHC

We study the LHC sensitivity to new broad neutral resonances produced in two-photon fusion and decaying to a top quark pair, $γγ\to t\bar{t}$. This is probed in central exclusive $t\bar{t}$ production in proton-proton collisions, $pp \to p t\bar{t} p$. We use the tagging of the intact protons by PPS (CMS) and AFP (ATLAS) and consider the semi-leptonic $t\bar t$ channel. The sensitivity is also mapped onto a set of dimension-8 $γγt\bar{t}$ operators in the large mass limit. Using the kinematical correlations between the intact protons and the reconstructed $t\bar{t}$ system, we obtain a sensitivity to the couplings of the dimension-8 operators of $1.4 \cdot 10^{-11}~\mathrm{GeV}^{-4}$ at 95% CL. The sensitivity to the anomalous couplings is significantly improved down to about $7\cdot 10^{-12}~\mathrm{GeV}^{-4}$ if the proton time-of-flight is known with a precision of 20 ps in future measurements. The 95% CL sensitivity to broad neutral resonances reaches masses of order $ 1500~\mathrm{GeV} $ when using timing information.

hep-ph↗
arXiv2022

White Paper on Forward Physics, BFKL, Saturation Physics and Diffraction

The goal of this whitepaper is to give a comprehensive overview of the rich field of forward physics. We discuss the occurrences of BFKL resummation effects in special final states, such as Mueller-Navelet jets, jet gap jets, and heavy quarkonium production. It further addresses TMD factorization at low x and the manifestation of a semi-hard saturation scale in (generalized) TMD PDFs. More theoretical aspects of low x physics, probes of the quark gluon plasma, as well as the possibility to use photon-hadron collisions at the LHC to constrain hadronic structure at low x, and the resulting complementarity between LHC and the EIC are also presented. We also briefly discuss diffraction at colliders as well as the possibility to explore further the electroweak theory in central exclusive events using the LHC as a photon-photon collider.

hep-ph↗
arXiv2021

Measurement of Topological Order based on Metric-Curvature Correspondence

A unified expression for topological invariants has been proposed recently to describe the topological order in Dirac models belonging to any dimension and symmetry class. We uncover a correspondence between the curvature function that integrates to this unified topological invariant and the quantum metric that measures the distance between properly defined many-body Bloch states in momentum space. Based on this metric-curvature correspondence, a time-resolved and angle-resolved photoemission spectroscopy experiment is proposed to measure the violation of spectral sum rule caused by a pulse electric field to detect the quantum metric, from which the topological properties of the system may be extracted.

cond-mat.mes-hall↗
arXiv2021

Unification of topological invariants in Dirac models

Topological phases of materials are characterized by topological invariants that are conventionally calculated by different means according to the dimension and symmetry class of the system. For topological materials described by Dirac models, we introduce a wrapping number as a unified approach to obtain the topological invariants in arbitrary dimensions and symmetry classes. Given a unit vector that parametrizes the momentum-dependence of the Dirac model, the wrapping number describes the degree of the map from the Brillouin zone torus to the sphere formed by the unit vector that we call Dirac sphere. This method is gauge-invariant and originates from the intrinsic features of the Dirac model, and moreover places all known topological invariants, such as Chern number, winding number, Pfaffian, etc, on equal footing.

cond-mat.mes-hall↗
arXiv2020

A Clockwork Solution to the Doublet-Triplet Splitting Problem

Maybe the biggest puzzle in grand unified theories (GUTs) is the apparent large splitting of the doublet and triplet Higgs masses. We suggest a novel mechanism to solve this puzzle, which relies on the clockwork mechanism to generate large hierarchies from order-one numbers. The tension between gauge coupling unification and proton lifetime from minimal SU(5) GUTs is also removed in this scenario, and the theory remains perturbative until the Planck scale.

hep-ph↗
arXiv2020

Realistic GUT Yukawa Couplings from a Random Clockwork Model

We present realistic models of flavor in SU(5) and SO(10) grand unified theories (GUTs). The models are renormalizable and do not require any exotic representations in order to accommodate the necessary GUT breaking effects in the Yukawa couplings. They are based on a simple clockwork Lagrangian whose structure is enforced with just two (one) vectorlike U(1) symmetries in the case of SU(5) and SO(10) respectively. The inter-generational hierarchies arise spontaneously from products of matrices with order one random entries.

hep-ph↗
arXiv2019

A Random Clockwork of Flavor

We propose a simple clockwork model of flavor which successfully generates the Standard Model flavor hierarchies from random order-one couplings. With very few parameters we achieve distributions of models in excellent agreement with observation. We explain in some detail the interpretation of our mechanism as random localization of zero modes in theory space. The scale of the vectorlike fermions is mostly constrained by lepton flavor violation with secondary constraints arising from rare meson decays.

hep-ph↗
arXiv2019

Universal Approximations for Flavor Models

We develop a systematic analytical approximation scheme for the singular value decompositions of arbitrary complex three dimensional matrices Y with non-degenerate singular values. We derive exact expressions for the errors of this approximation and show that they are bounded from above by very simple ratios of the form (yi/yj)2n where yi < yj are singular values of Y and n is the order of the approximation. The applications we have in mind are the analytical and numerical treatments of arbitrary theories of flavor. We also compute upper bounds for the errors of the Cabbibo Kobayashi Maskawa (CKM) matrix that only depend on the ratios of the masses and the physical CKM angles.

hep-ph↗
arXiv2018

Searching for axion-like particles with proton tagging at the LHC

The existence of an axion-like particle (ALP) would induce anomalous scattering of light by light. This process can be probed at the Large Hadron Collider in central exclusive production of photon pairs in proton-proton collisions by tagging the surviving protons using forward proton detectors. Using a detailed simulation, we estimate the expected bounds on the ALP--photon coupling for a wide range of masses. We show that the proposed search is competitive and complementary to other collider bounds for masses above 600 GeV, especially for resonant ALP production between 600 GeV and 2 TeV. Our results are also valid for a CP-even scalar, and the efficiency of the search is independent of the width of the ALP.

hep-ph↗
arXiv2017

Probing the anomalous $γγγZ$ coupling at the LHC with proton tagging

The sensitivities to the anomalous quartic gauge boson coupling $γγγZ$ are estimated via $γZ$ production with intact protons in the forward region at the LHC. Proton tagging proves to be a powerful tool to suppress the background, which allows consideration of the hadronic decays of the $Z$ boson in addition to the leptonic ones. We discuss the discovery potential for an integrated luminosity of $300\,\mathrm{fb}^{-1}$ and $3000\,\mathrm{fb}^{-1}$. The sensitivity we obtain at $300\,\mathrm{fb}^{-1}$ goes beyond the one expected from LHC bounds on the $Z\rightarrow γγγ$ decay by about three orders of magnitude. The $γZ$ channel provides important discriminatory information with respect to the exclusive $γγ$ channel, as many particles beyond the Standard Model (such as a radion or Kaluza Klein gravitons) predict a signal in the latter but not the former.

hep-ph↗