National Institute of Chemical Physics and Biophysics (NICPB; Estonian Keemilise ja Bioloogilise Füüsika Instituut, or KBFI) is public non-profit research institute that carries out fundamental and applied research and engages in the development of the novel directions in material sciences, physics, chemistry, gene- and biotechnology, environmental technology, and computer science. in Estonia, Tallinn at the address Akadeemia tee 23..
Combining geometrical frustration and one-dimensional magnetism boosts quantum fluctuations and leads to unusual states of quantum matter. We report the magnetic behavior of a well-separated S = 52 sawtooth spin chain compound CaFe2O(PO4)2 (CFPO). Magnetic susceptibility, heat capacity, and 31P nuclear magnetic resonance measurements show evidence of strong magnetic frustration in the compound. Despite a relatively large antiferromagnetic Curie-Weiss temperature of about-1073 K, the compound exhibits multiple magnetic transitions at low temperatures at 15.5, 10.4, and 7.8 K, respectively, with a frustration parameter (f approximate to |BCW|/TN) about 70. The Knight shift shows a broad maximum around 70 K for P1 and P2 sites. The spin-lattice relaxation rate 1/T1 follows temperature-independent behavior well above the long-range order (LRO). First-principles calculations capture the strong antiferromagnetic interactions in this quasi-one-dimensional sawtooth lattice, providing a microscopic explanation for the experimentally observed frustration, low dimensionality, and the onset of LRO at low temperatures. Our results indicate that CFPO exhibits the presence of short-range correlations and persistent spin dynamics characteristics above the LRO, which probably stem from the S = 52 sawtooth spin chain model.
We analyse a variety of Euclidean saddles in the gravitational path integral, with asymptotic AdS boundary conditions, in a class of Einstein-Scalar-Maxwell models. These include single boundary solutions, usual and wineglass wormholes, as well as more exotic (quasi)-oscillatory saddles. Our construction shows how an unbound number of oscillations gets tamed, when flat directions of the potential get lifted. We find several interesting phase transitions between these solutions. The Euclidean wormhole backgrounds can be analytically continued to Lorentzian FLRW universes. Some of them contain an early period of inflation. We delineate the conditions under which they can be the dominant saddles in the gravitational path integral and use them to estimate ratios of probabilities for different cosmological outcomes.
We derive quantum gravity contributions to the beta functions of the gauge and Yukawa couplings of a matter theory using the Schwinger proper-time flow equation. Working in the Einstein-Hilbert truncation, we investigate the gauge-fixing and regulator dependence of the corresponding renormalization group equations. We quantify the sensitivity of our results on unphysical parameters by evaluating the gravitational correction to the running matter couplings at the interactive fixed point of gravity and we compare our findings with existing determinations in alternative schemes. We finally confront the derived contributions with the typical size they should assume to generate observable low-scale predictions in the Standard Model and in several scenarios of new physics.
We examine single-field inflationary models for the formation of primordial black holes (PBHs). By analyzing the latest observations from the Atacama Cosmology Telescope [J. Cosmol. Astropart. Phys. 11 (2025) 062., J. Cosmol. Astropart. Phys. 11 (2025) 063.], we demonstrate that the observed preference for positive running (alpha s) of the scalar spectral index ns imposes significant restrictions on the parameter space for a large class of ultra-slow-roll (USR) models. This tension becomes progressively pronounced for more massive PBHs, posing substantial challenges for USR models to yield a detectable PBH abundance, especially in the mass range probed by ongoing and future gravitational-wave experiments such as LIGOVirgo-KAGRA and the Einstein Telescope. However, this discrepancy is minimal for asteroid-mass PBHs, which are still capable of feasibly constituting the entirety of dark matter. To numerically probe the sixdimensional parameter space of the models, we adapted a Markov Chain Monte Carlo approach to efficiently scan over the viable configurations. Our results further indicate that, in nonminimally coupled polynomial inflation, a viable cosmic microwave background (CMB) spectrum is best obtained at an inflection point for which second-order slow-roll approximation is necessary for precise CMB predictions.
The LZ experiment reported one anomalous event with nuclear recoil energy of 248 keV. Galactic halo dark matter (DM) cannot produce such a large energy unless heavier than 74 GeV, and heavy DM with spin-independent interactions would have produced unseen recoils at lower energy. Inelastic DM has been proposed as a way out. We consider, instead, an elastic collision of a dark sector particle with a momentum of at least 123 MeV and mass in the range 1-74 GeV as deuteron break-up in SNO disfavors sub-GeV masses. The absence of accompanying lower-energy recoils favours interactions whose rate grows with the momentum transfer, such as a pseudoscalar-pseudoscalar nucleon operator. This implies no leading-order signal in argon, an annual modulation below 1
