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Latest articles for Reports on Progress in Physics
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Review on physics of Higgs– R 2 ...
Higgs inflation, identifying the standard model (SM) Higgs boson as the, causes a unitarity issue during the preheating epoch after inflation in its simplest form, calling for a UV completion. Higgs– inflation serves as a natural candidate for the UV completion of Higgs inflation, providing a consistent framework to describe the inflationary dynamics till the end of reheating. Higgs– inflation contains a new scalar degree of freedom, the scalaron, which unitarizes the theory in the same way that the Higgs boson unitarizes the electroweak gauge boson scatterings in the SM. In this short review, we summarize the physics of Higgs– inflation. A particular emphasis is put on its particle physics aspects, such as the unitarity structure, frame-independence, and the renormalization group evolution.
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Grey-body factors of black holes *
Grey-body factors describe the frequency-dependent transmission of fields through the effective potential generated by a black hole or another compact object. They convert the idealized thermal spectrum of Hawking radiation into the spectrum measured by an observer, determine absorption and scattering cross sections, and provide real-frequency observables complementary to quasinormal modes. In this review, we present a unified account of grey-body factors in black-hole physics and related systems. We formulate the scattering problem for asymptotically flat, de Sitter, and anti-de Sitter spacetimes, and discuss the connections between transmission coefficients, absorption cross sections, Hawking radiation, and ringdown. We also review methods for their computation and survey recent developments, including the correspondence between grey-body factors and quasinormal modes, their stability under deformations of the effective potential, wormhole transmission and superradiance, and their behaviour in modified theories of gravity. Finally, we discuss the appearance of grey-body factors in gauge/gravity duality, where absorption probabilities in the bulk are related to correlation functions and transport coefficients in the boundary theory.
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Van der Waals superconducting electronics: materials, devices and circuit integration
Van der Waals (vdW) superconductors (SCs)—atomically thin crystalline materials that can be stacked into more complex heterostructures—have opened a promising avenue for superconducting electronics thanks to their properties that are otherwise difficult to obtain in other superconducting materials. These properties include strong resilience to high in-plane magnetic fields, electrostatic tuneability, and non-reciprocal transport rooted in inversion-symmetry breaking and strong spin–orbit coupling. In addition to highlighting the importance of these properties for superconducting electronics, this review gives an overview of the physical mechanisms that govern and influence superconductivity in vdW materials including Ising pairing, band inversion, and proximity effects at SC/ferromagnet interfaces that do not have an equivalent in thin-film systems. This overview then sets the basis to survey the wide range of functionalities enabled by superconducting vdW devices including gate-controlled devices, superconducting diodes, and circuit elements for readout and control of quantum bits. The review concludes with a forward look at wafer-scale growth and deterministic assembly of vdW devices, highlighting concrete pathways that can enable the transition from vdW device prototypes to deployable components for cryogenic electronics and quantum technologies.
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Higher-order corrections to the field shift in atomic systems
Differences in nuclear charge distributions between isotopes lead to small changes in atomic spectra known as the field shift (FS). While largely proportional to the change in the mean-square nuclear radius, the FS also contains higher-order contributions with different dependencies on nuclear moments. Their knowledge is required in searches for new physics using King plots, since they contribute to deviations from King-plot linearity observed experimentally in recent studies. We present a systematic expansion of the field-shift energies in terms of nuclear parameters and test its validity against direct numerical calculations for H-like ions. We also compute leading- and higher-order field-shift corrections for alkali-like systems from Li-like to Rb-like ions, and find that their ratios are nearly independent of the ionic charge state, agreeing with the corresponding hydrogenic ratios on a sub-percent level. Motivated by these findings, we introduce an approximation in which these ratios are assumed to be independent of the electronic configuration. It is shown that, within this approximation, higher-order field-shift corrections do not induce King-plot nonlinearities. We conclude that only the small contributions beyond this approximation can contribute to the nonlinearities observed experimentally.
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Collective excitations in quantum gravity condensates
A central open problem in quantum gravity is to understand how continuum spacetime emerges from quantum-geometric degrees of freedom in a background-independent setting. A many-body perspective suggests that spacetime emerges as a hydrodynamic phase of many atoms of quantum geometry. This idea underlies several approaches to quantum gravity, and it has been explicitly realised in the group field theory formalism. However, quantum fluctuations beyond the mean-field regime remain largely unexplored. We fill this gap by importing Bogolyubov theory to quantum gravity condensates, showing that leading beyond-mean-field effects manifest as collective excitations, in direct analogy with phonons in laboratory Bose–Einstein condensates. We implement the construction in a tractable group field theory model, where condensates of quantum-geometric atoms reproduce nonsingular expanding cosmologies, and derive the leading beyond-mean-field corrections to the emergent Friedmann dynamics. These results identify a new class of quantum-gravity excitations and establish a controlled bridge between microscopic quantum-gravitational dynamics, many-body collective phenomena, and signatures of spacetime emergence.