This project aims at predicting the energy scale of cosmological inflation and the strength of the inflationary gravitational wave signal from string theory. Observations of the cosmic microwave background (CMB) temperature fluctuations have drastically changed cosmology into quantitative science. The results provide strong evidence for two phases of accelerated expansion in our Universe. The late-time phase of acceleration, termed ’dark energy’, is consistent with an extremely small positive cosmological constant, while the evidence for a very early phase of acceleration increasingly supports cosmological inflation. Very recently, the BICEP2 experiment reported the detection of B-mode polarization in the CMB. Pending future corroboration, this may correspond to a detection of primordial gravitational waves with a fractional power of about 10% of the CMB temperature fluctuations. In the context of inflation this implies an inflationary energy scale close to the scale of Grand Unification, and a large field excursion of the inflationary scalar field. Hence, the inflationary scalar potential needs symmetries to protect it from dangerous quantum corrections. These features strongly motivate the study of high-scale inflation in string theory as a candidate theory of quantum gravity. We will determine the range of predictions for large-field high-scale inflation in string theory driven by the mechanism of axion monodromy, which was co-discovered by the PI. For this purpose, we will establish a catalog of primary sources for large field ranges from axion monodromy in combination with assistance effects from multiple axion fields. We will analyze the generic effects of the interplay between large-field models of inflation in string theory with its necessary prerequisite, moduli stabilization. Finally, we will study the distribution of inflation mechanisms among the many vacua of string theory. In combination, this gives us a first chance to make string theory testable.

In 2012, the ATLAS and CMS experiments at the Large Hadron Collider at CERN announced a ground-breaking discovery: both experiments observed a new particle. Subsequent measurements confirmed it to be a Higgs boson. In the Standard Model (SM) of particle physics, which describes the known elementary particles and their interactions, as well as in many extensions of the SM, the Higgs boson is fundamentally linked to the question of how elementary particles acquire mass. A thorough program of measurements is necessary to determine if this particle has indeed the properties of a Higgs boson as predicted by the SM or one of its extensions, and to gain a complete understanding of the mass generation for elementary particles. Studies of the Higgs sector now open a unique window to the discovery of New Physics. The aim of the presented project is to perform a detailed analysis of the Higgs differential distributions measured in Higgs decays to diphotons and to four leptons, using the data collected by the ATLAS experiment between 2015 and 2021. These distributions are sensitive to effects from New Physics and will be confronted with precise theoretical predictions. In this way, the indirect extraction of Higgs couplings and the search for effects from new heavy particles can lead to a discovery of New Physics. The detailed analysis of differential distributions goes substantially beyond the standard analyses based on measured event counts. A dedicated program is needed to achieve these goals. With an ERC Starting Grant, I will assemble a team to make decisive contributions to these challenging measurements and build a unique research program. As a former leader of the ATLAS Higgs-to-diphoton physics group and current leader of the electron and photon reconstruction group I am in an ideal position to establish a strong research team. This team will build on the important contributions to the Higgs boson discovery and property studies made by my Young Investigators Group.

Four decades after its prediction, the axion remains the most compelling solution to the strong CP problem and a well motivated dark matter candidate, inspiring several ultrasensitive experiments based on axion-photon mixing. The experimental landscape for axion searches is evolving extremely fast: consolidated detection techniques are now facing next-generation experiments with ambitious sensitivity goals, while novel and ingenious detection concepts promise to open for exploration new ranges of parameter space previously considered unreachable. AXIONRUSH deals with an ambitious program to reshape the parameter space of the QCD axion by developing new model building directions and by revisiting from an ultraviolet perspective axion couplings to photons, nucleons, electrons, including also flavour and CP violating ones. The main goal of AXIONRUSH is to bridge theoretical aspects of axion physics with experiments and to provide a global comparison of general axion models with experimental sensitivities and astrophysical bounds. The development of these new theoretical tools will enlarge the physics scopes of the axion experimental program at DESY, Hamburg, by further addressing specific research goals related to the experiments ALPS-II, IAXO, MADMAX and Belle II. A complementary objective of AXIONRUSH is to investigate scenarios where the Peccei Quinn mechanism is embedded into grand unified theories. The latter provide a predictive framework for narrowing down the axion mass range, with a potential impact on the scanning strategy of the axion dark matter experiments CASPER-Electric and ABRACADABRA. A major intention of this latter objective is the construction of a minimal, unified scenario aiming at a self-contained description of particle physics, from the electroweak scale to the Planck scale, and cosmology, from inflation until today.

Symmetries serve as our main guide in studying physical phenomena. The more symmetric a system is, the more constrained are its degrees of freedom and the better prospects we have to understand and solve it. Significant progress has been achieved in the study of theories with high amounts of symmetry in the last decades. Supersymmetry and conformal invariance are the main reasons why the beautiful idea of holography materialised into the AdS/CFT correspondence and the discovery of hidden symmetries (integrability) in gauge theories was possible. Thanks to supersymmetry, modern mathematical techniques allowed the evaluation of the otherwise unfathomable path integral and the comprehensive study of a long list of physical observables. Finally, the successful revival of the conformal Bootstrap program is based on conformal invariance. These breakthroughs are, unfortunately, applicable only to theories with unrealistic amounts of symmetry. BrokenSymmetries will break this impasse by applying the aforementioned ideas to more realistic theories, where some of the supersymmetry and/or conformal invariance are broken. The key innovation of BrokenSymmetries is to still make use of a broken symmetry. Symmetries are captured by Ward identities which we can still derive in various cases of symmetry breaking. Broken symmetries also imply powerful non-perturbative relations that observables obey. We will combine these with the developments mentioned above, producing novel exact results. Our approach will give a handle on otherwise insoluble problems. The objectives of BrokenSymmetries are to obtain exact results while breaking: 1) conformal invariance spontaneously, keeping supersymmetry intact; 2) supersymmetry explicitly, keeping conformal invariance intact; 3) both supersymmetry and conformal invariance turning on the temperature; 4) (super)symmetry generators in the context of integrability, which get upgraded to quantum groups' generators.

Without doubt, one of the most intriguing questions in modern astronomy is whether habitable planets, potentially supporting life, exist outside our solar system. In the upcoming era of large aperture astronomical telescopes and highly stable spectrometers, answering these questions is for the first time a tangible possibility. Successfully finding answers to these questions will, however, critically rely on non-incremental advances in astronomical instrumentation. The objective of the proposed research is, developing and demonstrating novel photonic-chip laser frequency combs to support the revolutionary advances in astronomical precision spectroscopy required to enable detection and characterization of habitable Earth-like planets. Habitable exo-planets can be discovered by observing minute wavelength-shifts in the optical spectra of their host stars. These wavelength-shifts are so small that exquisitely accurate and precise wavelength-calibration of astronomical spectrometers is required. It has been recognized that laser frequency combs (LFCs), broadband spectra of laser-lines with absolutely-known optical frequencies, can provide the required level of precision, provided the LFC’s lines can be resolved by the spectrometer. Generating such frequency comb spectra (“astrocombs�) with resolvable lines remains, however, exceedingly challenging. Here, we will develop and demonstrate a novel class of photonic-chip microresonator-based astrocombs that can naturally provide broadband spectra of resolvable lines, potentially from visible to mid-infrared wavelengths, thereby overcoming key challenges in astrocomb generation. In order to achieve this goal we will pursue radically different microresonator designs and new nonlinear optical regimes in order to overcome long-standing limitation in microresonator physics. The developed astrocombs will not only be pivotal to astronomy but indeed can directly and profoundly impact the way we transfer data, monitor our environm