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Position-space sampling for local multiquark operators in lattice QCD using distillation and the importance of tetraquark operators for
No full textObtaining hadronic two-point functions is a central step in spectroscopy calculations in lattice QCD. This requires solving the Dirac equation repeatedly, which is computationally demanding. The distillation method addresses this difficulty by using the lowest eigenvectors of the spatial Laplacian to construct a subspace in which the Dirac operator can be fully inverted. This approach is efficient for nonlocal operators such as meson-meson and baryon-baryon operators. However, local multiquark operators with four or more (anti)quarks are computationally expensive in this framework: the cost of contractions scales with a high power of the number of Laplacian eigenvectors. We present a position-space sampling method within distillation that reduces this cost scaling by performing the momentum projection only over sparse grids rather than the full spatial lattice. We demonstrate the efficiency of this unbiased estimator for single-meson, single-baryon and local tetraquark operators. Using Wilson-clover fermions at the -flavour-symmetric point, we apply this method to study the importance of local tetraquark operators for the finite-volume spectrum. To this end, we extend a large basis of bilocal and scattering operators by including local tetraquark operators. The inclusion of local operators leads to significant shifts in several energy levels. Finally, we show the effect of these shifts on the scattering phase shift from a single-channel -wave Lüscher analysis
Bempedoic acid directly binds and activates PPARα
No full textBempedoic acid (BA) is a recently approved drug that lowers cholesterol and hepatic lipids, yet its mechanism of action remains incompletely understood. Here, we combine transcriptomic, biochemical, and structural approaches to show that BA directly binds to and activates peroxisome proliferator-activated receptor alpha (PPARα). BA treatment robustly induced PPARα signaling and fatty acid oxidation in primary hepatocytes and mouse liver. Through X-ray crystallography, we uncovered that BA binds to the ligand-binding domain of PPARα and stabilizes its active conformation. BA activated PPARα target genes independently of very-long-chain acyl-coenzyme A (CoA) synthetase (ACSVL1), the liver-enriched enzyme that converts BA to its bempedoyl-CoA form. Notably, BA-mediated induction of fatty acid oxidation required PPARα. Together, this work reveals direct PPARα activation as a key mechanism of BA action, providing a molecular basis for its lipid-lowering effects and suggesting broader therapeutic potential beyond the liver
Differentiating Between Enantiomers with Nuclear Quadrupole Coupling Using Microwave Three-Wave Mixing
No full textWe demonstrate the application of microwave three-wave mixing to the amino alcohol valinol, which displays a hyperfine structure in the rotational spectrum due to nuclearquadrupole coupling. The hyperfine structure complicates the typical triad of rotational states, leading to overlapping microwave three-wave mixing cycles. We identified a set of cyclesaccessible within the hyperfine substructure of the rotational states |JKaKc⟩ = |101⟩, |212⟩, and |202⟩ by applying the selection rules for rotational transitions and nuclear quadrupole coupling. To address an individual cycle of hyperfine transitions or subsets of cycles simultaneously, we explored different pulse schemes exploiting single-frequency or chirped microwave pulses. Each pulse scheme generated a distinct chiral signal, which shows clear enantiomer differentiation. The experimental findings agree very well with numerical simulations using an effective model for the hyperfine interaction. This study thus extends the applicability of microwave three-wave mixing to previously unexplored molecular systems containing quadrupolar nuclei
Ultrahigh-energy Cosmic Rays from Neutrino-emitting Tidal Disruption Events
No full textWe revisit ultrahigh-energy cosmic-ray (UHECR) production in tidal disruption events (TDEs) in light of recent evidence of neutrino-TDE associations. We use an isotropically emitting source-propagation model, which has been developed to describe the neutrino production in AT2019dsg, AT2019fdr, and AT2019aalc. These TDEs have strong dust echoes in the infrared (IR) range, which are potentially linked to the neutrino production. A mechanism where neutrinos originate from cosmic-ray (CR) scattering on IR photons implies CRs in the ultrahigh-energy range, thus suggesting a natural connection with the observed UHECR. We extrapolate the three TDE associations to a population of neutrino- and UHECR-emitting TDEs, and postulate that these TDEs power the UHECRs. We then infer the source composition, population parameters, and local rates that are needed to describe UHECR data. We find that UHECR data point toward a mix of light to mid-heavy injection isotopes, which could be found, e.g., in oxygen-neon-magnesium white dwarfs, and to a contribution of at least two groups of TDEs with different characteristics, dominated by AT2019aalc-type events. The required local TDE rates of O(102)Gpc−3yr−1, however, are more indicative of the disruption of main-sequence stars. We propose an enhanced efficiency in the acceleration of heavier nuclei that could address this discrepancy. The predicted diffuse neutrino fluxes suggest a population of astrophysical neutrino sources that can be observed by future radio neutrino detection experiments. The derived source parameters are consistent with those expected from the individual neutrino observations
Structural and Functional Versatility of the Amyloidogenic Non-Amidated Variant of the Antimicrobial Peptide Citropin 1.3
No full textCitropin 1.3 is an antimicrobial peptide produced by the amphibian Litoria citropa (Southern bell frog), which self-aggregates into distinct fibrillar structures, however, the function of the fibrils remains unclear and largely unexplored. In this study, the structural and functional properties of citropin 1.3 were investigated using cryogenic electron microscopy and fluorescence microscopy in the presence of membrane and cell models, and with X-ray crystallography. Canonical amyloids, multilayered nanotubes, and a novel mixed fibril were observed. Experiments with negatively charged giant unilamellar vesicles revealed that the peptide facilitates membrane fusion while simultaneously undergoing phase separation in the presence of phospholipids. In presence of mammalian cells, citropin 1.3 permeabilizes membranes, leading to cell death, and over time, colocalizes with genetic material. Overall, this work provides new insights into the structural dynamics of the amyloidogenic antimicrobial peptide citropin 1.3 and its interactions with different systems
Meson thermalization with a hot medium in the open Schwinger model
No full textQuantum field theories treated as open quantum systems provide a crucial framework for studying realistic experimental scenarios, such as quarkonia traversing the quark-gluon plasma produced at the Large Hadron Collider. In such cases, capturing the complex thermalization process requires a detailed understanding of how particles evolve and interact with a hot medium. Considering the open lattice Schwinger model and using tensor network algorithms, we investigate the thermalization dynamics of mesonic particles in a hot medium, such as the Schwinger boson or the electric flux string. We simulate systems with up to 100 lattice sites, achieving accurate preservation of the electric field parity symmetry, demonstrating the algorithm's robustness and scalability. Our results reveal that the thermalization time increases with stronger dissipation from the environment, increasing environment temperature, higher background electric field and heavier fermion masses. Further, we study the quantum mutual information between the two halves of the flux string connecting a meson's constituent particles and analyze its relation to relevant dynamical observables
Status of two-baryon scattering in lattice QCD
No full textIn these proceedings, I will review lattice QCD calculations of baryon-baryon scattering, their methods, and their challenges. In the last few years, there has been a new generation of calculations with increased focus on controlling systematic uncertainties. Contrary to the findings of earlier exploratory calculations, it now appears probable that at heavy pion masses there is no nucleon-nucleon bound state
Spectral dynamics in broadband frequency combs with overlapping harmonics
No full textOptical frequency combs and their spectra of evenly spaced discrete laser lines are essential to modern time and frequency metrology. Recent advances in integrated photonic waveguides enable efficient nonlinear broadening of an initially narrowband frequency comb to multi-octave bandwidth. Here, we study the nonlinear dynamics in the generation of such ultra-broadband spectra where different harmonics of the comb can overlap. We show that a set of interleaved combs with different offset frequencies extending across the entire spectrum can emerge, which transform into a single evenly spaced ultra-broadband frequency comb when the initial comb is offset-free
Generic two-loop results for trilinear and quartic scalar self-interactions
No full textReconstructing the shape of the Higgs potential realised in Nature is a central part of the physics programme at the LHC and future colliders. In this context, accurate theoretical predictions for trilinear and quartic Higgs couplings are becoming increasingly important. In this paper, we present results that enable significant progress in the automation of these calculations at the two-loop level in a wide range of models. Specifically, we calculate the generic two-loop corrections for scalar -point functions with assuming that all external scalars are identical. Working in the zero-momentum approximation, we express the results in terms of generic couplings and masses. Additionally, by exploiting permutation invariances, we reduce the number of Feynman diagrams appearing to a substantially smaller set of basis diagrams. To ease the application of our setup, we also provide routines that allow to map our generic results to scalar two-loop amplitudes generated with the package FeynArts. We perform a series of calculations to cross-check our results with existing results in the literature. Moreover, we present new two-loop results for the trilinear Higgs coupling in the general singlet extension of the Standard Model. We also present the public Python package Tintegrals, which allows for fast and stable evaluations of all relevant two-loop integrals with vanishing external momenta