Abstract: In this talk, I introduce two complementary approaches to study the thermodynamics of horizons perturbatively away from stationarity in arbitrary diffeomorphism-invariant theories of gravity with non-minimal matter couplings. (1) Light-ray focusing: on the dynamical horizon, we prove a generalised focusing theorem encoding horizon thermodynamics: under positive null energy flux, light rays converge when their expansion is measured by the Wall entropy density rather than the area element. Wall entropy extends Bekenstein–Hawking and Wald entropies and satisfies the first and second laws. With higher-spin fields, the theorem and laws persist subject to a “higher-spin focusing condition”, proposed as a consistency constraint. (2) Symmetry: near-stationary horizons possess a perturbatively broken boost symmetry whose improved Noether charge defines the Hollands–Wald–Zhang dynamical entropy, which offers another dynamical generalisation of Wald entropy. We extend this from pure gravity to general theories with arbitrary bosonic matter couplings, analyse horizon temperature variations, and treat charged black objects—strings, rings, and branes, etc.—with p-form charges in one framework, deriving the associated first and second laws. Finally, the two approaches unify: the event-horizon dynamical entropy equals the Wall entropy of the generalised apparent horizon.

Abstract: In this informal internal seminar I will report on our ongoing work on isometry-invariant states of non-conformal, strongly coupled matter in de Sitter space using a class of bottom-up holographic models. We find that these models admit multiple de Sitter–symmetric states at a fixed Hubble expansion rate. We observe that, for certain choices of model parameters, such multiple states exist even at arbitrarily small curvatures, with a finite energy density gap between them. This minimum curvature depends exponentially on the model parameters. While gravity is treated as nondynamical in our analysis, the presence of multiple low-curvature states leads to  self-consistent de Sitter solutions of the Friedmann equation governing the cosmology of a universe filled with this matter.
Finally, we argue that these solutions act as natural attractors for the late-time evolution of deeply overcooled matter, which supports thermal inflation while near equilibrium and evolves toward the attractor solutions as it becomes far from equilibrium.

Abstract: The Cosmological Lithium Problem (CLP) is a well-known issue in astrophysics. It refers to an overestimation of the primordial 7Li abundance in the standard Big Bang nucleosynthesis (BBN) model predictions relative to astrophysical observations. Our research focuses on experimental nuclear physics to address the CLP. In particular, we aim to constrain the reaction rate of the 7Be(d, p)8Be reaction by measuring its cross section. The majority of 7Li nuclei were produced by the electron capture decay (T1/2= 53.22 days = 4.6 × 106 seconds) of 7Be. 7Be nuclei were produced in several hundred seconds during the BBN, leading to a timescale difference of more than 104 between the production time of 7Li and 7Be. This significant timescale difference implies that if more 7Be nuclei were destroyed during the BBN, it could result in a lower abundance of 7Li, potentially resolving the discrepancy.

Our study focuses on the 7Be(d, p)8Be reaction based on a theoretical suggestion that this reaction played a significant role in the destruction of 7Be nuclei during the BBN [1]. The measurement of the absolute cross section in the Big Bang energy region (Ec.m.=0.1−0.4 MeV) was crucial for understanding the nuclear reactions in the primordial universe. We produced a radioactive 7Be target and measured the 7Be(d, p)8Be reaction cross section at the tandem facility of Kobe University in Japan. A distinctive feature of this experiment was the production of an unstable nucleus 7Be as a target. The thick-target analysis method was applied to determine the cross sections. The cross section at the lowest energy of Ec.m.=0.12 MeV was measured with the highest sensitivity compared to the available data [2, 3, 4]. We confirmed that the measured 7Be(d, p)8Be cross sections have a limited impact on resolving the CLP.

This talk will outline the key details and discuss future perspectives, including a new project aimed at addressing the CLP.

References

[1] S. Q. Hou et al., Phys. Rev. C 91, 055802 (2015).

[2] R. Kavanagh, Nucl. Phys. 18, 492-501 (1960).

[3] C. Angulo et al., ApJ 630, L105 (2005).

[4] N. Rijal et al., PRL 122, 182701 (2019).

Abstract: The background of the formulation of the Simple Effective Interaction (SEI) is discussed. The systematics of its parameter fixation protocol is outlined that could account for the divergent trends on the density and momentum dependence of the isovector part of the nucleonic mean field predictions by different model calculations. 

The r-mode oscillation as a possible mechanism for the spin-down feature of newborn neutron stars is discussed. The ability of the bulk viscosity due to direct Urca processes in dissipating the large oscillations produced in the merger remnant in the event of two neutron star merger is examined where the equation of state of hot neutron star matter of neutron-proton-electron-muon composition is built upon it’s zero-temperature predictions.  

The predictions of SEI in different areas of finite nuclei properties is discussed. The correlation between the finite nuclei properties and the constraints resulting from neutron star phenomenology is examined using the charge radii differences in mirror nuclei pairs as observable.

Abstract: The progress in realising ultracold atomic mixtures has greatly revitalised the interest in studying impurities immersed in quantum mediums [1]. Following these developments, and motivated by the possibility of trapping ultracold atoms in optical lattices [2], the theoretical study of impurities in lattice configurations has emerged as a new platform for studying polaron physics. In this direction, recent studies of impurities interacting with bosonic baths have revealed intriguing features across the superfluid-to-Mott insulator transition [3,4].

In this talk  I will first present a numerical study of an impurity interacting with a bosonic bath and immersed in a harmonically confined optical lattice [5]. We reveal that the impurity can form a correlated counterflow state with the bath. This counterflow state [6] shows long-range anti-pair order and displays non-trivial features, including a sudden orthogonality. Then, I will briefly present a related study of an impurity interacting with a spin-1/2 fermonic bath in small lattices, where we show

[1] F. Grusdt, N. Mostaan, E. Demler and L. A. Peña Ardila, Rep. Prog. Phys. 88, 066401 (2025).

[2] I. Bloch, Nat. Phys. 1, 23 (2005).

[3] V. E. Colussi, F. Caleffi, C. Menotti, and A. Recati, Phys. Rev. Lett. 130, 17, 3002  (2023).

[4] R. Alhyder, V. E. Colussi, M. Čufar, J. Brand, A. Recati, G. M. Bruun, SciPost Phys. 19, 002 (2025).

[5] F. Isaule, A. Rojo-Francàs, L. Morales-Molina, and B. Juliá-Díaz, Phys. Rev. Lett. 135, 023404 (2025).

[6] A. B. Kuklov and B. V. Svistunov, Phys. Rev. Lett. 90, 100401 (2003).

Abstract: Since the prediction of the meson in 1935, facilities and institutions across the world have contributed to the discovery of over 200 distinct types, some of those being the well-known pions, kaons and J/Ψ. Understanding the properties of the mesons, including their spin, lifetime and mass, allows for the classification of this vast family of hadrons to be improved. This is particularly important in the case of the discovery of new or exotic mesons. In this endeavour, determining the spin is vitally important. A set of quantities known as moments of angular distributions relate the spin of a meson to the angular distributions of its decay products; furthermore, these quantities can be extracted unambiguously and directly from experimental data. The Thomas Jefferson National Accelerator Facility, also known as Jefferson Lab, located in Virginia, is home to the Continuous Electron Beam Accelerator Facility (CEBAF), which is capable of producing a high-luminosity 12 GeV electron beam. When this beam impinges on a supercooled liquid hydrogen target, electron-proton interactions result in the production of various mesons, which are then detected by the CEBAF Large Acceptance Spectrometer at 12 GeV (CLAS12). The purpose of this research is to use CLAS12 at Jefferson Lab to obtain the moments of angular distributions of mesons that decay into pairs of oppositely charged kaons.