Papers

We study the collision dynamics of localized oscillons in two classes of $(1+1)$-dimensional scalar field theories with metastable false vacua, a normal class with a positive quartic self-interaction term and an inverted class with a negative quartic term. We construct small-amplitude oscillon solutions around the false vacuum using the Fodor {et al.} expansion, and show that the force between oscillons decays exponentially at large separation, with a strength modulated by their relative phase. Numerical simulations of two-oscillon collisions exhibit reflection, crossing, and formation of excited oscillons. Resonance windows occur, similar to those found in kink-antikink collisions. In the normal theory, if the oscillons have sufficient energy, the field can pass over a sphaleron barrier and evolve into a kink-antikink pair, initiating a phase transition to the true vacuum. We also simulate the collision of oscillons evolved from a slightly perturbed sphaleron.

In this work, we investigate the thermodynamic geometry of Reissner-Nordstrom Anti-de Sitter (RN-AdS) black holes with quintessence in the grand canonical ensemble. The analysis employs the Ruppeiner curvature scalar to elucidate the microscopic interactions and critical phenomena in the extended phase space. Divergence of the scalar curvature signal phase transitions, while its sign characterizes the nature of the underlying interactions; negative for attractive and positive for repulsive type interactions. The analysis reveals that attractive interactions dominate at low electric potentials, whereas repulsive interactions prevail at higher potentials unlike the usual charged black holes. Finally, the interaction strength is fairly constant during the phase transition, providing a greater understanding of the quintessence influenced microscopic attributes of RN-AdS black holes.

We study quantum chaos in $\textrm{T}\overline{\textrm{T}}$-deformed two-dimensional conformal field theories with gravitational anomaly and their holographic dual description in topologically massive gravity. Using pole-skipping and shock-wave analysis, we extract the Lyapunov exponent and butterfly velocity and analyze the interplay between irrelevant deformation and parity-violating dynamics. We find that the chaos bound remains saturated, while the butterfly velocity exhibits nontrivial dependence on the deformation parameter and anomaly. We also identify a Hagedorn regime in which the chaotic response becomes complex valued, signaling a breakdown of the physical branch of the deformed theory.

We study gauging interfaces and their defect descendants in lattice models with generalized symmetries in higher dimensions. We construct explicit interface Hamiltonians for gauging a $\mathbb Z_2^{(0)}$ symmetry in $(2+1)d$ and a $\mathbb Z_2^{(1)}$ symmetry in $(3+1)d$. In higher dimensions, and especially in the presence of higher-form symmetries, the topological nature of gauging interfaces is obscured by the fact that the constrained Hilbert space depends on the location of the interface. We resolve this by introducing movement operators acting on a common unconstrained Hilbert space, which transport both the interface Hamiltonians and the associated constraints. As applications, we analyze condensation defects obtained from finite-region gauging and reconstruct the gauging map from movement operators. Finally, we apply the same framework to subgroup gauging, focusing on the example of gauging $\mathbb Z_2\subset \mathbb Z_4$. This produces a dual symmetry carrying a mixed anomaly, which we diagnose on the lattice through symmetry fractionalization on condensation defects. Our results provide an explicit lattice framework for studying topological interfaces, condensation defects, and the associated anomalies arising from gauging in higher-dimensional systems.

Center one-form symmetries in consistent quantum gravity theories are expected to be either broken or gauged, thereby determining the global form of the gauge group. We shed light on this expectation from the perspective of distinguished extended objects, which we denote by faithful string probes, for which the gauge symmetry is realized as a holomorphic current algebra. We argue that the worldsheet counterpart of gauged center one-form symmetries is the existence of chiral simple currents extending the current algebra. Accordingly, we show that the consistency condition for such extensions reproduce and generalize known field theoretic and geometric obstructions to the gauging of center one-form symmetries in six and eight dimensions. We verify this picture in a number of examples arising from heterotic string compactifications, and apply it to infer the gauge group topology of a recently identified class of six-dimensional models with no known F-theoretic realization. In 6d supergavity, our results also clarify an observation of Kim and Vafa on the existence of BPS particles required for consistency upon circle reduction: these particles arise from worldsheet simple currents whose existence is dictated by the presence of a gauged center one-form symmetry. Intriguingly, in several models across different dimensions we find composite higher-spin chiral currents beyond the current algebra, hinting at a stringy generalization of center one-form symmetries in the bulk.

We consider a model of 3d quantum gravity defined by $n$ copies of a rational Virasoro TQFT with central charge $1/2$, summed over all 3d topologies. This theory is holographically dual to an ensemble of all 2d CFTs with central charge $c=n/2$ and chiral algebra that includes $Vir_{1/2}^n$. We perform the sum over topologies and evaluate the partition function of the bulk theory. We then confirm the holographic duality by matching it to the boundary ensemble for small $n$. We proceed to consider the limit of a large central charge, in which the bulk theory simplifies and condenses to an Abelian phase. In this regime, the model manifests many features expected in semiclassical 3d quantum gravity. In particular, inclusion of all 3d topologies in the bulk sum cures the negativity of the density of states evaluated by the torus partition function. The model also exhibits a Hawking-Page transition, an exponentially suppressed wormhole amplitude, and provides a toy example of the holographic code. We discuss these aspects in detail and conclude with lessons for semiclassical quantum gravity.

The inflationary Lyth bound relates the primordial tensor amplitude to the inflaton field excursion. In ekpyrotic, bouncing and cyclic cosmologies there is no analogous universal tensor-to-field-distance relation because scalar and tensor perturbations depend on entropy conversion, matching through the bounce, and the specific mechanism that violates or evades the null energy condition. Here we propose a phase-resolved criterion for the accumulated scalar field trajectory length in a non-inflationary smoothing history. The quantity constrained in this study is not, in general, the geodesic distance between the initial and final field-space points. Rather, it is the invariant path length accumulated along the actual cosmological trajectory. Therefore, the resulting inequalities should be understood as sufficient, conservative trajectory length criteria for small-field control, not as model-independent necessary exclusions based on geodesic distance swampland reasoning. We also impose BKL (Belinski-Khalatnikov-Lifshitz) anisotropy suppression as an additional constraint on the ekpyrotic phase. In the canonical phase of the ekpyrotic contraction, we recover the known small-field scaling and embed it in a total trajectory length budget inequality. We impose three requirements: a BKL anisotropy suppression that is parameterized separately, a phenomenological cutoff-corrected distance budget inspired by tower of states logic, and observational conversion windows from residual isocurvature and non-Gaussianity. Furthermore, we propose a new master formula that provides a conditional lower limit on the value of the parameter $\epsilon_{\rm ek}$ that depends on the remaining distance available after conversion and the cosmological bounce.

Neural network field theory (NN-FT) formulates field theory in terms of a network architecture and a density on its parameters. We derive Schwinger–Dyson equations and Ward identities in NN-FT and utilize them to study anomalies. The equations depend on a conserved parameter space current that characterizes symmetries and how they break. It is relevant even in non-local NN-FTs, but can recover local currents in the case of a local Lagrangian by an appropriate fiber-wise average. In machine learning, this formalism is applied to feedforward networks and the attention mechanism. In physics, we use this machinery to study $U(1)$ symmetry for a complex scalar, the scale anomaly in $4d$ massless $\phi^4$ theory, the Weyl anomaly for the bosonic string (including a new computation of the critical dimension), and examples involving discrete topological data, such as winding numbers and T-duality. Since the results are obtained in network parameter space rather than the standard field space, they represent a new way to understand symmetries in quantum field theories.

Following Veltman's approach, we formulate and discuss a general cutting equation for QED in a plane-wave background. We apply the corresponding cutting rules to justify the connection between the two-loop radiative corrections to elastic electron scattering and the rate of the trident process in a constant crossed field. Among other terms generated by cuttings, some field-induced radiation corrections also emerge, which contain UV-finite contributions from loop insertions into external legs. As a byproduct, we compare the previously published results for the trident process in a constant crossed field and present a complete analytical expression for direct and exchange contributions to its rate, which is resolved in the spin of the initial electron. Our findings establish that although total rates can be reliably extracted from higher-loop by applying the cutting rules, reconstruction of differential rates requires additional care. The cutting rules apply to any loop order and may be extended to nonperturbative regimes.

We discuss various forms of refinements of Vogel's universality in Chern-Simons theory. While the original universality applies to arbitrary simple Lie groups, its counterpart in refined Chyrn-Simons theory is restricted to simply laced Lie groups.

It was recently proven that, in contrast to their matrix analogues, the moments of a real Gaussian tensor of size N do not in general factorize over their connected components in the asymptotic large N limit. While the original proof of this rather surprising result was not constructive, explicit examples of non-factorizing moments, which are expectation values of trace-invariants, have since then been discovered. We explore further aspects of this problem, with a focus on Haar-distributed (or Gaussian) complex random tensors, which are more directly relevant to quantum information. We start out by exhibiting an explicit example of non-factorizing trace-invariant, thereby filling a gap in the recent literature. We then turn to the opposite question: that of finding interesting families of trace-invariants that do in fact factorize at large N. We establish three main theorems in this regard. The first one provides a sufficient combinatorial bound ensuring large N factorization, that is also simple enough to be applicable to various cases of practical relevance. Our second main result shows that the expectation value of any compatible trace-invariant is dominated by certain tree-like combinatorial structures at large N, which we refer to as tree-like dominant pairings. Our third main theorem establishes that any trace-invariant admitting tree-like dominant pairings does actually factorize at large N. In this way, we are able to prove that various families of trace-invariants that have been previously studied in the literature do factorize at large N. We apply our findings to the theory of multipartite quantum entanglement: to any trace-invariant is associated a multipartite generalization of Rényi entanglement entropy, whose typical expectation value in the uniform random quantum state can be explicitly computed assuming large N factorization.

The Galactic Center gamma-ray excess (GCE) – a surplus of gamma-ray radiation around SgrA$^{\star}$ – has remained without a consensus interpretation for more than fifteen years. Dark-matter annihilation and unresolved millisecond-pulsar populations remain the leading candidates, yet neither connects the excess to the past activity of SgrA$^{\star}$ traced by the Fermi and eROSITA bubbles. We propose a common-origin scenario in which a contribution to the GCE arises as a fossil hadronic imprint of the same SgrA$^{\star}$ outburst associated with the bubbles. We develop a model of SgrA$^{\star}$ with a precessing paraboloidal Blandford-Znajek (BZ) jet launched from a tilted, magnetically arrested accretion disc during a ~ 7.5 Myr active phase ending ~2.6 Myr ago. In this picture, the jet drives the bipolar expansion of the Fermi/eROSITA bubbles – contributing, alongside wider-angle outflows, to their observed extent – and injects hadronic cosmic rays at the Galactic Center. We couple the analytic BZ injection to a two-zone diffusion numerical solver to compute the resulting GCE surface brightness and verify internal consistency: the proton Larmor radius remains small compared to the jet coherence scale, ensuring magnetic confinement of the cosmic-ray population, while attenuation of the produced $\gamma$ rays in the interstellar medium is negligible, leaving the medium effectively transparent. Isolating the jet contribution alone yields a spin-dependent, irreducible hadronic floor: for a SgrA$^{\star}$ spin of a$^{\star} = 0.9$, we find a robust floor at the few-percent to $\sim 10\%$ level of the observed GCE surface brightness across the inner ten degrees, highlighting a previously unexplored component relevant for comprehensive models of the GCE.

Curvature expansion for the heat kernel trace and the one-loop effective action is built for the wave operator of the theory in the quasi-thermal setup of a nonvacuum quantum state. This setup implies a non-static and non-stationary Euclidean gravitational background with periodic boundary conditions of the period $\beta=1/T$, where $T$ plays the role of effective global temperature to be locally rescaled by the metric gravitational potential. The results are obtained in the approximation quadratic in metric perturbations on top of flat Euclidean space and covariantized in terms of spacetime curvature. Covariantization includes a special vector field $\xi^\mu(x)$ which generalizes the Killing vector of static geometries with time translation isometry to the case of a generic arbitrarily inhomogeneous metric subject to timelike periodicity condition. This vector field is obtained as a covariant metric functional to quadratic order in metric perturbations and gives rise to the local function $T/\sqrt{\xi^2(x)}$, $\xi^2(x)=g_{\mu\nu}(x)\xi^\mu(x)\xi^\nu(x)$, reducing to Tolman temperature $T/\sqrt{g_{00}(\boldsymbol{x})}$ on stationary manifolds with Killing symmetry. High “temperature” asymptotic behavior of the nonlocal form factors—operator coefficients of the curvature tensor structures in the heat kernel and effective action—are obtained and possible cosmological applications of these results are discussed.

Null strings, strings with $2d$ null worldsheets, have about half a century of literature and are relevant in many physically interesting cases, especially when strings probe cosmological or black hole horizons. We observe that the null string action possesses a previously overlooked local symmetry, the consideration of which is necessary for the consistency of null string analyses. By correctly accounting for this symmetry, we show that the number of physical propagating degrees of freedom of null strings in $D$ dimensional target space is $D-3$, in contrast to $D-2$ that one finds in the literature. In other words, null strings probe a codimension-1 null surface on a $D$ dimensional target space. The existence of this overlooked symmetry calls for a thorough revision of results in the null string literature. We briefly mention some of its physical consequences.

We review the construction of higher-form symmetries for supersymmetric theories using a supergeometry framework. This reveals an enlarged set of topological conserved supercurrents, including Chern-Weil symmetries and new geometric Chern-Weil symmetries built from invariant supermanifold forms. In N=1 super-Maxwell theory in three dimensions, we construct the corresponding operators and charged defects, with charges determined by a super-linking number between their supporting hypersurfaces. At the end we provide as an original unpublished contribution some hints on how to construct super-symTFT for Chern-Weil and geometric Chern-Weil symmetries directly from supergravity.

In this paper, we draw a parallel between solutions of pure three-dimensional gravity with a negative cosmological constant and classical double copies in four dimensions. In the former case, topological solutions, such as the BTZ black hole, deficit angles, and naked singularities, emerge from identifying points in AdS using elements from its isometry algebra $so(2,2)$. The type of solution corresponds one-to-one with the orbits of $so(2,2)$. We demonstrate how various double copies of four-dimensional AdS gravity similarly arise from the $so(2,3)$ isometry elements, which also correspond one-to-one with their orbits through a Penrose-type transform. We classify all such elements and generate the corresponding double copies, which include AdS black holes, black branes, and many others. The double-copy isometries originate from the centralizer of a given AdS isometry, allowing us to define canonical coordinates associated with its Abelian part. Additionally, the two Casimir invariants of $so(2,3)$ feature in the metrics. Our classification naturally extends to higher spins, providing nonequivalent multicopies at the linearized level.

In this work, we provide a novel method to constrain the causal parameter space of a relativistic hydrodynamic system exclusively from its linear stability analysis at non-zero momenta. Our approach exploits the Lorentz-invariant stability property of causal theories. In boosted frames, the dispersion relation exhibits a feature that we call “$\gamma$-suppression,” whereby the higher-order terms in the wavenumber expansion are increasingly suppressed beyond leading order at large boosts. As a consequence, at near-luminal values of Lorentz boost, stability criteria at the spatially homogeneous limit are sufficient to identify the region of the parameter space that satisfies the necessary conditions of causality, even at non-zero momenta. After presenting the general hydrodynamic framework, we test the method in conformal Müller-Israel-Stewart theory and show that it provides an efficient way of deriving the necessary conditions of causality while remaining within the low-energy regime of hydrodynamic validity.

We extend the worldline quantum field theory formalism to include a direct diagrammatic method of computing the total flux of angular momentum from a black hole scattering event in the post-Minkowskian regime. Remarkably, except for subtle zero-frequency gravitons, the diagrammatic and integrational challenge is in a one-to-one correspondence with the analogous calculation of the black hole impulses – and the well-developed WQFT methodologies for the impulse may thus be directly imported to this problem. Zero-frequency gravitons appear in this calculation as a "static" integration region in addition to the "dynamical" region usually encountered for the impulse. We show that a large class of static contributions can be organized systematically by introducing $n$-point functions referred to as "static correlators". They reduce to a simple one-loop integral family which we compute explicitly using integration-by-parts relations and the method of differential equations. In passing, our analysis shows that static contributions disappear in space-time dimensions $D>4$. As a concrete application of our new method, we compute explicitly the $\mathcal{O}(G^3)$ total flux of angular momentum reproducing known results. Further, we apply the same method to electromagnetism where we compute the analogous $\mathcal{O}(\alpha^3)$ result.

In this work, Podolsky theory, a second-order, Lorentz- and gauge-invariant extension of classical electrodynamics, is considered. The effects of Podolsky's modification on fundamental phenomena such as the Stefan-Boltzmann law and the Casimir effect for the electromagnetic field are investigated. The Thermo Field Dynamics (TFD) formalism is employed to describe quantum fields at finite temperature and under spatial confinement through its topological structure.

We explicitly present all coupling conditions required for tree-level unitarity (tree unitarity) in theories with a finite number of massive and massless particles of spin up to 1. They allow us to diagnose tree unitarity of a system using only its particle content in the mass basis, without reconstructing the full Lagrangian. We show that all four-point amplitudes whose high-energy growth is canceled by tree unitarity conditions are on-shell constructible, thereby motivating the recursive construction of four-point amplitudes. By examining their high-energy growth, we derive tree unitarity conditions for four-point amplitudes. Imposing these conditions to simplify the Lagrangian structure, we use the Stückelberg formulation to derive the tree unitarity conditions arising from all higher-point amplitudes. We show that all tree unitarity conditions are fully captured up to five-point amplitudes, ensuring no necessity of examining higher-point ones. We apply our results to systematically examine tree unitarity conditions in the dark sector with a massive dark photon and dark matter particles of spin up to 1, and extract the essential features for mass generation in the massive dark photon case. In addition, we show that our results allow us to conclude that theories without scalars require an infinite tower of vectors and fermions for tree unitarity. Finally unitarity and related issues in the Higgs portal VDM are discussed in brief.

We show that the dissipation of small-scale perturbations through diffusion damping after neutrino decoupling lowers the present-day neutrino temperature compared to the expected value of $1.96\,{\text{K}}$. This reduces the relic neutrino abundance by an amount controlled by the integral of the primordial curvature power spectrum $\Delta_{\cal R}^2(k)$. We find that a relic neutrino detection by PTOLEMY can set limits $\Delta_{\cal R}^2(k) \lesssim {\cal O}(0.1)$ on scales $k \lesssim 3 \times 10^5\,{\text{Mpc}^{-1}}$, complementary to limits from Big Bang Nucleosynthesis, spectral distortions, pulsar timing arrays, and future dark ages 21-cm observations.

We study T-duality of $(p,q)$-hermitian geometries in backgrounds with non-Abelian gauge fields $A$ in heterotic string theories. We introduce a gauge-dressed complex geometry characterized by a shifted metric $\bar{g} = g + \frac{1}{2} \mathrm{Tr}(A^2)$, the closed 2-form $\omega$ and a quasi complex structure satisfying $\bar{J}^2 < 0$, but not necessarily $\bar{J}^2 = -1$. Utilizing the positive and negative chirality half generalized complex-like structures constructed by $(\bar{g}, \bar{J})$, we derive a heterotic Buscher-like rule for geometric quantities. We also demonstrate that the gauge-dressed structures can be used to construct an extended Born geometry that satisfies algebras of hypercomplex numbers.

We present a study of cubic surfaces from the novel perspective of positive geometry. Our positive geometries have dimension two (the surface minus its 27 lines), dimension three (its complement in 3-space), and dimension four (the moduli space). In each case we explore the positive arrangement, its combinatorial rank, and the canonical forms.

We investigate the renormalization group flow of a gravity–matter system in which a scalar field is minimally coupled to Einstein gravity and its kinetic term is given by a scale-dependent form factor $f_\Lambda(-\Box)$. Employing the Wilsonian proper-time flow equation, we derive a closed integro-differential equation that encodes the dependence of the form factor on the UV cutoff $\Lambda$. We solve the resulting fixed-point problem with a pseudospectral discretization and find a non-trivial fixed point for which $f_\ast(-\Box)$ departs from the canonical $-\Box$ behavior. Linearizing the flow about this solution yields a discrete spectrum of perturbations and a corresponding set of critical exponents, indicating a non-trivial scaling structure in this non-local sector compatible with asymptotic safety. We also observe that the form factor becomes local once the UV cutoff is removed, suggesting that the bare action associated with this fixed point is local in the scalar two-point sector.

The dipolar universality class describes the phase transition in 3D ferromagnets with strong dipolar interactions, as first discussed by Aharony and Fisher in the 1970s. While this universality class has been studied theoretically using renormalization group methods, as well as experimentally, little is known about it from Monte Carlo simulations. In this paper, we aim to bridge this gap. We introduce a lattice model that faithfully implements the transverse constraint on the order parameter. We introduce a Markov Chain Monte Carlo algorithm which involves a combination of local Metropolis updates preserving the constraint, and a global update of the zero mode. We perform simulations on cubic lattices up to volume $48\times 48 \times 48$. We observe a continuous phase transition between the disordered and ordered phases. We obtain estimates of the critical exponent $\nu$ and the critical Binder ratio, and compare them with results from other techniques. We also study whether rotational invariance emerges at the critical point, and discuss the influence of the toroidal geometry on this question.

In this paper, we determine the relativistic bound-state solutions for the Dirac oscillator (DO) in the curved spacetime of a cloud of strings in $(3+1)$-dimensions, where such solutions are given by the four-component normalized Dirac spinor and by the relativistic energy spectrum. However, unlike in literature, here, we work with the spacetime in two different forms/configurations, that is, both in its original form and in its modified form. To achieve our objective, we work with the curved DO in spherical coordinates, where we use the tetrad formalism. So, by defining a stationary ansatz for the spinor, we obtain two coupled first-order differential equations, and by substituting one equation into the other, we obtain a second-order differential equation. To analytically and exactly solve this differential equation, we use a change of function and of variable. From this, we obtain the well-known Whittaker equation, whose solution is the Whittaker function. Consequently, we obtain the energy spectrum, which is quantized in terms of the radial quantum number $n$ and the angular quantum number $\kappa$, and explicitly depends on the angular frequency $\omega$ (describes the DO), curvature parameter $a$ (describes the cloud of strings), and on the effective rest mass $m_{\text{eff}}$ (describes the rest mass modified by the curvature of spacetime). Besides, we graphically analyze the behavior of the spectrum as a function of $\omega$ and $a$ for three different values of $n$ and $\kappa$, as well as the behavior of the radial probability density for four different values of $\kappa$, $\omega$, and $a$ (with $n=0$).

The Aharonov-Casher (AC) effect describes the geometric phase acquired by a neutral particle carrying a magnetic dipole moment moving in an external electric field. In supersymmetric gauge theories it is often argued that exact supersymmetry enforces the vanishing of anomalous magnetic dipole moments, suggesting that the AC interaction may be incompatible with unbroken supersymmetry in four dimensions. In this work we show that this conclusion is model-dependent. We construct an $N=1$, $D=4$ supersymmetric gauge model in which a Lorentz-violating Kalb-Ramond background induces dynamically the dipole interaction responsible for the AC effect while leaving the supersymmetry algebra intact. The model couples a chiral superfield to an Abelian gauge superfield through a Chern-Simons-type interaction supplemented by a Fayet–Iliopoulos term. A duality identification between the symmetric combination $S+S^\dagger$ of the chiral superfield and the Kalb-Ramond superfield strength allows the antisymmetric tensor background to enter the supersymmetric dynamics without breaking supersymmetry. Integrating out the auxiliary $D$ field generates dynamically an effective dipole interaction of the form $\bar{\psi}\sigma^{\mu\nu}F_{\mu\nu}\psi$. In the nonrelativistic limit the resulting equation of motion reproduces the Aharonov-Casher Hamiltonian for a neutral fermion. The effective magnetic dipole moment is expressed in terms of the parameters of the model and can be mapped onto tensor coefficients of the fermion sector of the Standard Model Extension. Our results therefore provide an explicit realization of a four-dimensional supersymmetric theory in which the Aharonov–Casher interaction emerges dynamically while supersymmetry remains exact in the presence of Lorentz violation.

Rigidity conditions for a body considered as a discrete system of relativistic particles are proposed. They by themselves do not yet determine an evolution of the system, and some second-order equations must be added to them. Poincaré-covariant equations of motion compatible with these rigidity conditions are proposed and discussed. The resulting theory has the expected six dynamical degrees of freedom, allowing for more general motions than in Born's theory. Therefore, treating a relativistic body as a discrete system of particles could be a promising alternative to the standard approach based on Born's rigidity conditions.

We review recent theoretical and experimental developments in spin dynamics and polarization phenomena in relativistic systems, with a particular focus on heavy-ion collisions. The large angular momentum and magnetic field generated in non-central collisions induce vorticity in the quark-gluon plasma, leading to observable spin polarization of emitted hadrons. We discuss the theoretical foundations of spin polarization arising from spin-vorticity coupling, including formulations based on relativistic hydrodynamics, kinetic theory, and quantum statistical approaches such as the Zubarev density operator. A central theme of the review is the role of pseudo-gauge freedom and its implications for defining energy-momentum and spin tensors, which can influence theoretical predictions of polarization observables. We further examine different formulations of spin hydrodynamics, emphasizing the impact of gradient expansions, spin chemical potential, and entropy-current analysis on the structure of the theory and associated transport coefficients. In addition, we discuss the recent developments in heavy flavor spin dynamics within the framework of rotational Brownian motion, where spin degrees of freedom undergo stochastic evolution due to interactions with the medium. This framework provides a complementary perspective on spin relaxation and diffusion by incorporating the effects of strong initial magnetic fields and establishes connections between spin polarization and the initial geometry through the definition of polarization harmonics. This review provides a comprehensive overview of relativistic spin hydrodynamics as well as non-equilibrium spin dynamics, and outlines future directions toward a consistent and predictive description of spin phenomena in strongly interacting matter.

We develop a potential-independent cosmographic framework, in which cosmographic parameters are promoted to dynamical variables within a closed autonomous system. Although the cosmographic hierarchy is formally infinite, we achieve closure by mapping potential slow-roll parameters onto the kinematic phase space within General Relativity with a minimally coupled scalar field. Within this framework, we perform a stability analysis and show that inflationary (quasi-de Sitter) solutions arise as natural attractors, while stiff-fluid configurations act as repellers without invoking the slow-roll approximation. To describe the transition to standard Big Bang evolution, we extend the system to include a radiation component and a phenomenological decay term. This leads to a generalized, potential-independent description of reheating characterized by an effective equation of state $w_{\rm eff}$. We demonstrate that the radiation-dominated phase is the late-time attractor of the extended system. These results provide a unified kinematical description of the expansion history from inflation through reheating, bridging cosmography and scalar field dynamics.