Papers

We study correlation functions of light local operators and defect changing operators on the conformal line set by the 1/2 BPS Wilson line of $\mathcal N=4$ super Yang-Mills. We consider the defect changing operators associated with geometrical and internal cusp angles, which at strong coupling have a large scaling dimension and back-react on the dual $AdS_2$ world-sheet. We set up a holographic computation of correlation functions, in which the light operators are described by fluctuations around the cusped classical string solution, so that correlators of two defect changing operators and an arbitrary number of light protected operators are obtained from the on-shell action of these fluctuations. We implement this prescription in detail for the case of certain 4-point functions, with two light and two defect changing operators. Finally, since for small cusp angles the defect changing operators become light, we manage to derive relations satisfied by integrated correlators of light operators, valid at any coupling. We verify these relations at strong coupling for both internal and geometrical cusps.

We develop the post-Newtonian framework for the near-zone dynamics of a binary in de Sitter and anti-de Sitter spacetime. We consider a binary interacting via a free scalar field in a fixed (A)dS background in $D+1$ spacetime dimensions, with $D\ge3$ and odd. Using multipole expansion and re-summation techniques, we solve for the field degrees of freedom to obtain an effective particle description in the form of a Fokker action. We derive the equations of motion for the binary up to second post-Newtonian (2PN) order and obtain the corresponding 2PN Hamiltonian and conserved charges in phase space. We show that the conformal algebra, corresponding to the isometry algebra of the (A)dS background, is realised in phase space as a curvature-dependent deformation of the Poincare algebra at each PN order. Our results provide a systematic extension of post-Newtonian effective dynamics to finite-curvature backgrounds. This could serve as a useful framework for studying bound-state dynamics in (A)dS as well as in the corresponding holographic CFT.

We present a study of thermal two-point functions from Witten diagrams in thermal AdS$_{d+1}$, defined with the conformal boundary $S_\beta^1 \times \mathbb{R}^{d-1}$, with an aim to establish a connection between thermal CFT data and perturbative bulk dynamics. We analyze one-loop tadpole and bench diagrams arising from the cubic $\phi\phi\chi$ interaction in the bulk, segregating the different relative thermal winding sectors for the bench, and also extend the analysis to include quartic scalar contact diagrams with and without derivative interactions. We also analyze the spinning exchange thermal two-point function. Utilizing the split representation of bulk propagators and the method of images we reorganize the thermal Witten diagrams into the standard AdS integrals and obtain spectral and image-sum representations that make KMS periodicity of the correlators manifest. Additionally, we show possible position dependent effective one-point vertices of scalar and spinning fields in the bulk arising from the reduction of the coincident- point thermal bulk to bulk propagator loop, allowing tadpole-type diagrams to be reconstructed from effective local bulk interactions. The bench diagram however retains an intrinsically bi-local structure. We further investigate the thermal one-point coefficients and perturbative OPE data encoded in these thermal correlators, including contributions associated with anomalous dimensions. Finally, we examine their relation to thermal dispersion relations and the role of contributions that are not determined by discontinuity data alone. Our results provide a set of explicit bulk constructions for exploring the analytic structure of thermal CFT correlators and their connection to the thermal conformal bootstrap.

We study large-k symmetric and antisymmetric Wilson loops in N=4 super-Yang-Mills theory. We represent their generating functions as Fredholm determinants built from the Hermite kernel weighted by a symbol function that encodes the representation. Using the integrable structure of the kernel, we systematically apply the Tracy-Widom approach to derive a closed system of integro-differential equations. The equations are then solved order by order in 1/N by a WKB ansatz, while keeping the symbol function general. We find a closed-form expression for the leading and subleading order contributions to the generating functions. Finally, specializing to the two representations, we perform the large-k saddle-point analysis and find the subleading contribution to the Wilson loop. Our results confirm the previously observed discrepancies with the dual D-brane description of giant Wilson loops.

We establish topological recursion for the spin enumeration of hypermaps, or, in the dual language, spin dessins d'enfants. This problem has remarkable features distinguishing it from other applications of topological recursion to enumerative combinatorics. First, the spectral curve is elliptic rather than rational, as in most cases studied before. Second, it contains degenerate ramification points, and one has to apply a version of degenerate topological recursion. Finally, the meromorphic correlator differentials have "moving" poles on the antidiagonals between pairs of distinct arguments, and one has to adjust the loop equations to this kind of degeneracy as well. The computations involve concepts of different kinds, such as BKP integrability, Gaussian integrals, the x-y swap, and symplectic duality.

We present the first analytic computation of the time-domain multipoles of the gravitational waveform from hyperbolic black-hole scattering at leading order in the post-Minkowskian expansion, to all orders in velocity. We perform the partial-wave projection as a cut loop integral, which enables the use of dimensional regularization and associated integration techniques. As opposed to the frequency domain, the time-domain multipoles are logarithmic and do not contain Bessel-like functions. Our results pave the way for the incorporation of post-Minkowskian fluxes in waveform models for binary mergers.

We obtain a systematic understanding of the time-domain gravitational waveform of hyperbolic black-hole scattering at first order in the self-force expansion and all orders in the post-Newtonian/post-Minkowskian (PN/PM) expansion. The continuous frequency spectrum of unbound orbits makes the inverse Fourier transform to the time domain diverge order by order; we introduce a dimensional-regularization-inspired prescription that cures this uniformly. We show that the full waveform then follows, at any PM and PN order, from a single family of integrals, generated by the Lauricella function $F_D^{(3)}$, which we calculate using strategies familiar from the study of Feynman integrals. As a proof of principle, we use this understanding to compute the quadrupolar 1SF waveform through relative 10PM-20PN, that is to order ${\cal O}(G^{10} v^{42})$, the full 1SF waveform to 10PM-10PN, as well as the asymptotic fluxes and the dissipative scattering angle at the corresponding accuracy.

QCD calculations that use multihadron fragmentation functions usually involve multiple invariant mass scales simultaneously, with only one being the hard scale associated with an overall hard process. The other scales are associated with relative internal motion intrinsic to the fragmenting parton and the multihadron system. Nonperturbative contributions to this later type of dependence attract interest for their association with intrinsic partonic structures, but care is needed in disentangling the truly nonperturbative effects from perturbative behavior and relating the former to universal nonperturbative matrix elements. To this end, we show how to evolve collinear multihadron fragmentation functions in a way that accounts for the simultaneous presence of these extra scales. The general multihadron fragmentation functions evolve in the same way as ordinary single hadron fragmentation functions, with the dependence on the extra scales separated out. We use this to unify treatments of perturbative and nonperturbative effects in multihadron systems in a way that optimizes for interpretations focused on partonic structure.

We review the role of relative entropy in quantum field theories, where the local von Neumann algebras are generically of type III. Consequently, only few exact results are known, and even bounds are difficult to obtain. As a new result, we prove that the relative entropy between a locally squeezed state and the Minkowski vacuum is finite for free fermions.

In Inflation without an Inflaton (IWI), a de Sitter (dS) background drives inflation, and the graviton bilinear generates scalar perturbations at second order, with no inflaton or additional fundamental scalar field. We investigate how this scenario can account for the observed scalar spectral tilt. The tensor-mode dependence of the scalar power spectrum gives the consistency relation $n_s-1=2n_T$, since it contains four tensor mode functions. The scalar spectral tilt $n_s\simeq0.9649$ at CMB scales therefore gives $n_T\simeq-0.0175$, independent of the tensor-to-scalar ratio $r$, hence different from the standard single-field slow-roll prediction $n_T=-r/8$. A full time-dependent calculation of $\phi_2$ in exact dS leads to an almost scale-invariant scalar power spectrum, with a small blue infrared residual on the order of $n_s-1\simeq+4\times10^{-4}$. In order to account for the observed red tilt, we introduce a slow drift in the Hubble rate, parametrized by $\varepsilon=-\dot H/H^2$. The tensor tilt is then given by $n_T=-2\varepsilon$, implying $n_s-1\simeq-4\varepsilon$, at leading order. The observed tilt requires $\varepsilon_\ast\simeq0.0088$, far exceeding the drift that can be sustained by the classical graviton backreaction, for which we find $|\varepsilon_{\rm self}|\lesssim10^{-11}$. Therefore, we investigate the quantum break-time of dS as the origin of the background evolution. In this picture, the scalar tilt becomes $n_s-1=-4C_qN_{sp}(H/m_{pl})^2$, where $C_q$ is an order-one depletion coefficient, and the tilt is directly connected to the particle content of dS, $N_{sp}$. The evolution of the drift itself further predicts a positive running of $\alpha_s=+\tfrac12(1-n_s)^2\simeq+6\times10^{-4}$. These results conclude the distinctive observational predictions of the IWI scenario, establishing it as a falsifiable alternative to standard inflaton-driven models.

Kemp and Ramgoolam proposed a basis of monomials for a commutative semisimple algebra with generators \(C_1,\ldots, C_L\), constructed from a degeneracy graph which records how the eigenspaces of \( C_1\) are successively split by \( C_2,\ldots, C_L\). They showed that the basis property is equivalent to the non-vanishing of the determinant of the matrix of values of these monomials on the projector basis, and conjectured a factorised formula for this determinant, as a product of powers of eigenvalue differences. We prove this formula for any number of generators. The proof uses graph analogues of Newton polynomials. Their evaluation matrix is not triangular in general, but expanding the rows of the children of each node of the penultimate layer in a Newton basis of their eigenvalues makes it block triangular, with diagonal blocks given by smaller degeneracy graphs in which the final layer is removed. The formula then follows by induction on the number of layers. We show that the exponents in the determinant are overlap volumes of higher-dimensional Young diagrams attached to the nodes of the graph: intervals, ordinary Young diagrams, plane partitions and their higher analogues. Finally, the block triangular structure gives an explicit recursive inversion of the evaluation matrix, expressing the projectors in the monomial basis.

We systematically investigate BPS cohomologies of $\mathcal{N}=4$ super-Yang-Mills (SYM) theory with gauge group SU$(N)$ with $N=2, 3, 4$, focusing primarily on the BMN sector. We find non-Coulomb graviton cohomologies for $N>2$. For $N>2$, the lightest black hole cohomology in the BMN sector always carries non-trivial $R$-charge and corresponds to the brane-fused type. Therefore, the `core' black holes without hair are `heavier'. We also find that a family of brane-fused cohomologies in $N=3$ is not lifted at the first quantum order. At a fixed charge sector, gravitons carry definite parity under charge conjugation. Up to the levels we have tested, every black hole cohomology either has opposite parity to that of gravitons or is lifted by quantum corrections. We conjecture that black hole cohomologies always carry parity opposite to gravitons in the same charge sector.

It is conventionally believed that the Stochastic Gravitational-Wave Background (SGWB) from inflation provides information about the earliest universe. However, in this Letter, we present a different picture. Our analysis starts from the observation that the inflation-predicted spectrum implies gravitons reside in high-occupation states, which significantly enhances their self-interactions and triggers rapid thermalization. We show that approximately $80\%$ of the primordial gravitons participate in this thermalization, forming a Bose–Einstein distribution and thereby erasing the primordial information. Evaluated using typical inflation parameters, this thermalized spectrum yields a present-day peak frequency of $f_{0, \text{peak}}^{(\text{th})} \sim 1.4 \times 10^8 \, \mathrm{Hz}$ in the hundred-megahertz band with a peak amplitude of $\Omega_{0, \text{peak}}^{(\text{th})} \sim 3.5 \times 10^{-13}$. Due to the sharp drop-off away from the peak, the resulting spectrum lies beyond the reach of low-frequency observatories like PTAs, LISA, and LIGO, but remains uniquely accessible to high-frequency detectors such as microwave cavity resonators and dielectric haloscopes.

String theory is widely regarded as the only plausible candidate for a consistent UV-complete theory of quantum gravity. Cosmological observations suggest that our universe is undergoing accelerated expansion, pointing towards the presence of a small positive cosmological constant. Since de Sitter space is the maximally symmetric solution of Einstein's equations with a positive cosmological constant, understanding whether four-dimensional de Sitter space can be realized within string theory has become one of the central questions. Following a series of works that realize de Sitter space as an excited state—namely, as a Glauber–Sudarshan (GS) state in type IIB string theory—our goal has been to extend such a construction to heterotic string theories. Realizing de Sitter space as an excited state over a time-independent supersymmetric Minkowski background provides a mechanism for evading the vacuum-based no-go theorems that obstruct de Sitter solutions in string theory. Starting from a generic M-theory configuration, we obtain four-dimensional de Sitter space in the late-time limit of flat-slicing coordinates in both heterotic $SO(32)$ and heterotic $E_8 \times E_8$ theories through appropriate dynamical duality sequences. The corresponding GS state is constructed by evaluating the expectation value of the metric operator in M-theory using path-integral techniques. We analyse the conditions required for the existence of a well-defined effective field theory description of the setup and find that these conditions are equivalent to satisfying the null energy condition in a 3+1-dimensional FLRW cosmology. Furthermore, the de Sitter GS states are found to lie well within the temporal bound imposed by the Trans-Planckian Censorship Conjecture, rendering them as transient states. In the case of $E_8\times E_8$ theory, we also investigate implications arising from axion cosmology.

Using the open solid torus as a finite parent, we revisit modular flow for spherical regions in conformal field theory. Its nonsingular angular evolution gives finite modular generators in a very simple form, while an exact conformal map to a cavity frame recovers the Rindler, CHM, and stationary-source ball constructions as singular limits. The same finite parent also provides a regular completion of the center obstruction in the complexified ball flow. Charged, Dirac, and inhomogeneous scalar examples are given.

A Lagrangian submanifold in an almost Calabi-Yau manifold is called positive if the real part of the holomorphic volume form restricted to it is positive. It is called $\epsilon$-positive if the ratio of the restrictions of the imaginary and real parts of the holomorphic volume form is bounded by $\frac{1}{\epsilon}.$ An exact isotopy class of positive Lagrangian submanifolds admits a natural Riemannian metric. We prove that the Riemannian metric restricted to the subset of $\epsilon$-positive Lagrangians induces a path metric when the relative Kähler class of the ambient Calabi-Yau manifold lies on a line of rational slope. The proof relies on the construction of a sequence of quantization maps from a circle bundle over the space of positive Lagrangians to the dual of the space of holomorphic sections of powers of a prequantum line bundle. The rationality condition for the relative Kähler class allows us to reduce to the case of Bohr-Sommerfeld Lagrangians. Building on ideas of Tian and Nirenberg-Wells, Hörmander estimates are used to show that functions on a Bohr-Sommerfeld Lagrangian can be approximated by holomorphic sections of a sufficiently high power of the prequantum line bundle. Consequently, the quantization maps eventually separate fibers of the circle bundle.

We point out that for black holes (BH) of the same mass, despite of arising from two entirely different physical arguments, the peak frequency of the coarse-grained gravitational wave (GW) spectrum of gravitons $f_\text{peak}^\text{graviton}$ is very close to the peak frequency of the GW spectrum produced from binary BH mergers $f_\text{peak}^\text{merger}$. In particular, we find that $f_\text{peak}^\text{graviton}/f_\text{peak}^\text{merger}\approx 2.3$ independent from BH mass or population. If BHs are still evaporating, the peak frequencies scale as $\propto M_i^{-1}$ with $M_i$ is the initial BH mass. If BHs evaporated in the radiation (matter) dominated era, the peak frequencies scale as $\propto M_i^{1/2}$ ($\propto M_i$) respectively after taking into account redshift effect. Any deviation from the aforementioned magical ratio would indicate new BH physics. The sweetest frequency ballpark to look for this correlation is around $10^{14}\ \rm Hz-10^{20}\ \rm Hz$ where both GW spectra are allowed to have maximum amplitude. As a demonstration of what the new physics could be, we consider a phenomenological self-similar regular BH model of Hayward featuring a single hair parameter. The observed ratio of peak frequencies can be used to directly infer the hair parameter, along with crucial properties of the novel BH solution such as Hawking temperature, horizon size, and innermost stable circular orbit. We also comment on the pros and cons of correlating frequencies among other GW sources such as formation, population fluctuation, and sudden transition of adiabatic perturbation.

Higher-order curvature corrections to general relativity arise naturally in many fundamental theories and provide phenomenologically interesting low-energy effective field theories. However, higher-derivative terms can introduce ghost modes, which call the validity of such models into question. Here, we thoroughly investigate the classical linear stability of the most general second-order scalar-tensor theory, namely the Horndeski theory of gravity, augmented by a Weyl-squared term in the action. We consider shift-symmetric de Sitter and power-law FLRW backgrounds and study the evolution of linear perturbations. Vector perturbations are free of gradient and tachyonic instabilities for a positive Weyl-induced mass squared. Tensor perturbations necessarily contain a ghost; their superhorizon branches are bounded, while a frozen-background calculation identifies a separate finite-momentum stability condition. The scalar sector instead contains a growing long-wavelength branch for all expanding backgrounds we consider, which is inherited by at least one of the gauge-invariant Bardeen potentials. We show that this growth enters the Bardeen potentials through an inverse-gradient factor $a^2/k^2$: the dynamical scalar fields remain bounded on the inflationary backgrounds, the direct contribution of the growing shear to the clock-matched tidal field cancels, and the electric part of the Weyl tensor decays. We discuss the implications of our results for perturbative control and for the phenomenological viability of theories including quadratic curvature corrections.

We study the relation between the exact-WKB Delabaere–Dillinger–Pham Stokes jumps and the multi-instanton expansion of a one-dimensional potential with $N$ equal-depth minima. For a single barrier this relation is the Bogomolny–Zinn-Justin cancellation between the instanton–anti-instanton ambiguity and the Borel ambiguity of perturbation theory, and we extend it to every consecutive barrier interval and to the integration contours themselves. In the dilute large-$T$ regime at fixed nonperturbative grade, we derive the quasi-zero mode integral over the instanton separations from the Euclidean path integral and reduce it to Gamma and Hankel periods. With the local Weber level function of each well and one normalization per well fixed by the local Weber connection matrix, these periods reproduce the two lateral connected exact-WKB coefficients. The two lateral contours of each instanton–anti-instanton separation differ by exactly one Hankel cycle, and this linear Picard–Lefschetz relation reproduces the Stokes jump of the connected coefficient. A numerical solution of the Schrödinger equation for a symmetric triple well confirms the resulting two-barrier level splitting. At higher fixed grade, the map from ordered event sequences to normalized scalar coefficient products is not one-to-one. At leading dilute order the scalar weight of a closed event sequence depends only on the numbers of barrier crossings, $\mathcal I\bar{\mathcal I}$ pairs, and $\mathcal I\mathcal I$/$\bar{\mathcal I}\bar{\mathcal I}$ pairs. We construct two inequivalent grade-six triple-well event sequences with the same product of local Weber amplitudes, which embed in every potential with $N\ge3$ wells. Our results hold within the regular dilute, one-loop, local Weber approximation.

We study the linear energetic stability of non-Abelian vortices in an $SO(3)$ gauge-Higgs theory with residual gauge group $A_4$. In our previous work, we identified two families of such vortices associated with order-two and order-three elements of $A_4$, and found Bogomol'nyi–Prasad–Sommerfield-like behavior at special ratios of the Higgs and gauge-boson mass scales. Here, we investigate their stability against $SO(3)$ gauge and Higgs perturbations by analyzing the second order variation of the vortex tension using analytical and numerical methods. In particular, when all relevant mass scales are equal, we prove linear stability for all vortices in the order-three family. By contrast, at the same mass point, we prove that a vortex in the order-two family is unstable. Thus, although both vortex families exhibit Bogomol'nyi–Prasad–Sommerfield-like behavior in their reduced equations at this mass point, their stability properties in the full $SO(3)$ theory are qualitatively different.

This special issue brings together a collection of original research articles and review papers addressing topics directly related to the MoEDAL-MAPP experiment at the Large Hadron Collider (LHC). The experiment is designed to search for (meta-)stable, anomalously ionising particles predicted by theoretical extensions of the Standard Model. Several contributions explore the theoretical and phenomenological aspects of models of particular relevance to the experiment, including scenarios involving magnetic monopoles, highly electrically charged particles, and millicharged particles. Other contributions focus on experimental developments, highlighting novel detection techniques and technological advances aimed at identifying these unconventional signatures and probing new phenomena beyond the Standard Model.

By means of $W$-representation, we investigate the Wishart-Laguerre $\beta$-ensemble and present a compact expression for Catalan polynomials. For a special Nekrasov partition function associated with the Wishart-Laguerre $\beta$-ensemble, we show that it can be expressed as a exponential form of the special Catalan polynomials. Furthermore, we make a rule to calculate the Catalan polynomials by means of Feynman diagrams and present another expression for Catalan polynomials. We also establish the connection between certain Catalan polynomials and knot theory.

We compute the static quadrupole Love number $k_2$ and the dimensionless tidal deformability $\Lambda$ of cold white dwarfs in Eddington-inspired Born-Infeld (EiBI) gravity. Matter couples to the physical metric while perturbation equations are solved in an auxiliary metric, so the physical tidal field near the surface depends on derivatives of the equation of state. This dependence is regular for a surface polytropic index $1<\Gamma_{\rm env}<3/2$, but not for the $\Gamma = 5/3$ Chandrasekhar equation of state. The mechanism, an algebraic map between the metric that carries perturbations and the metric that matter feels, is common to Palatini-type theories, so the same type of surface condition should apply to tidal calculations in this wider class. We use thermodynamically consistent envelopes that exactly reach zero enthalpy. At five masses from \(0.6\) to \(1.3\,\Msun\) and five sampled Born-Infeld couplings \(\kappa\), with $|\kappa|\le5\times10^6\,\mathrm{m^2}$, the EiBI-GR differences are approximately linear in $\kappa$. The largest absolute fractional shifts are \(3.89\times 10^{-5}\) in the stellar radius $R$, \(4.09\times 10^{-5}\) in $k_2$, and \(2.36\times 10^{-4}\) in $\Lambda$. Across nine envelope models, half the spread of each quantity relative to the baseline envelope is at most \(0.0186\) in $R$ and \(0.0857\) in \(k_2\), but only \(3.02\times 10^{-5}\) in \(\Lambda\) as the changes in \(k_2\) and \(R^5\) largely cancel. A high-precision calculation shows that the envelope dependence of the EiBI-GR difference in \(\Lambda\) is small. Half the spread of this difference ranges from \(1.067\times 10^{-12}\) to \(6.208\times 10^{-11}\) over the 20 nonzero mass-coupling points.

We propose that the necessary conditions for the existence of inflation could be explained by a quantum probabilistic approach. We interpret physical states $\psi$ obtained via the path integral formulation as probability density amplitudes for the Universe to be measured at a particular geometric configuration. First, we examine the problem of ordering ambiguities in the Wheeler-DeWitt (WDW) equation. We develop a formalism to handle ambiguities in the canonical quantization of a $1d$ minisuperspace by defining ambiguity functions within the WDW equation. We define a Hilbert space inner product for calculating physical observables, and using an argument from the hermiticity of the Hamiltonian, we obtain an expression for its measure $\mu$ in addition to constraints on the ambiguity functions. By defining a new quantum state $\Psi =\sqrt{\mu} \psi$ and using the path integral formalism, we are able to resolve ambiguities and prove the theory is universal. We then generalize for any $M$-dimensional minisuperspace system, for which we can prove universality in the semi-classical approximation for a large class of models. We also show that this universality extends to all orders of quantum theory if the target space manifold of the theory is flat. We calculate probability amplitudes for various cosmological scenarios involving Starobinsky inflation. We summarize the Hartle-Hawking no-boundary proposal for GR and we comment on the distinct possibilities of defining a contour of integration: the sign choice of Hartle-Hawking vs that of Linde-Vilenkin. We make an analogous calculation for $R^{2}$ gravity and find that for the Linde- Vilenkin choice it is statistically more likely for the Universe to emerge in its inflationary stage. Finally, we calculate transition amplitudes when the kinetic energy of the inflaton field $\phi$ takes non-zero values.

We perform a comprehensive analysis of a radion/dilaton portal freeze-in dark matter in models of stabilized warped extra-dimensions. We show that the relic abundance of a generic dark matter particle (scalars, vectors, or fermions) is obtained via the conformal coupling of the radial mode in a consistent model stabilized warped extra- dimensions; our calculations show that in scenarios where the reheating temperature is much smaller than the radion mass, keV-TeV scale dark matter particles can saturate the relic density. We perform a comprehensive analysis of a radion/dilaton portal freeze-in dark matter in models of stabilized warped extra-dimensions. We show that the relic abundance of a generic dark matter particle (scalars, vectors, or fermions) is obtained via the conformal coupling of the radial mode in a consistent model stabilized warped extra- dimensions; our calculations show that in scenarios where the reheating temperature is much smaller than the radion mass, keV-TeV scale dark matter particles can saturate the relic density. Furthermore, we show that the model is subject to Lyman-alpha constraints in the keV-GeV range, providing a unique, model-independent probe of this sector. Our calculations extend previous attempts to calculate the freeze-in relic abundance in extra-dimensional portals by providing a consistent theoretical calculation of matrix elements, clearly laying out the underlying motivation and assumptions and providing a comprehensive account of the cosmological constraints on the model.

In this article we present a new view on string theory that is rooted in quantum foundations extended to the domain of quantum gravity in the form of gravitized quantum theory, in which the canonical probability measure captured by the Born rule of quantum theory, turns out to be dynamical and contextual. We claim that this gravitization of quantum theory is the essence of string theory. String theory, according to this view, originates in foundations of quantum theory and Nambu's dynamics, which features in the non-perturbative definition of string theory in terms of a T-duality covariant and non-commutative formulation, called the metastring. Nambu's dynamics and the associated cubic and hypercubic objects also appear as the natural language for exploring the new observables and phenomena implied by a dynamical Born rule, including triple and higher order quantum interference, that can be investigated in experiments involving massive quantum probes, and that are also needed for direct empirical tests of the Born rule, a cornerstone of quantum theory.

The gradient flow exact renormalization group (GFERG) is a formulation of the exact renormalization group for gauge theories that provides a renormalization group flow preserving the gauge Ward–Takahashi identity exactly. In this paper, we nonperturbatively solve the GFERG flow equation for the simplest nontrivial gauge-invariant Wilson action, introduced in a previous paper, for $D$-dimensional quantum electrodynamics with~$N_f$ flavors (for all~$D$, flavors are counted in units of four-component spinors). For $D=3$ and~$D=2$, a nontrivial infrared fixed point exists even for~$N_f=1$, and the structure of the critical exponents at the fixed point is qualitatively the same as that in the large-$N_f$ limit. We also obtain the gauge-field propagator in the continuum limit; for~$D=2$, it reproduces the dynamical mass of the Schwinger model within a few percent. To the best of our knowledge, apart from the large-$N_f$ approximation, this is the first example in which the Wilson renormalization group in a gauge theory is solved nonperturbatively while manifestly preserving gauge symmetry.

Grand Unified models of particle physics inevitably give rise to magnetic monopoles. Often the model will also contain a weakly broken discrete symmetry that leads to the formation of biased domain walls that survive for a limited period in cosmology. For a range of the discrete symmetry breaking parameter, domain walls can collapse to form magnetically charged extremal black holes lighter than $\simeq 1\, {\rm kg}$ but these are not expected to survive until the present epoch due to Hawking evaporation and Schwinger pair production of monopoles. If the parameter is smaller still, the black holes may be astrophysical, with mass greater than $10^{15}\, {\rm g}$ and with sub-extremal magnetic charge: $Q \simeq 10^8$ (for our canonical choice of parameters). The cosmological energy density in residual magnetic monopoles depends on the discrete symmetry breaking parameter and for sufficiently small values of the parameter, the magnetic monopole density can satisfy all observational constraints.

Lyapunov exponents characterize the average rate at which nearby trajectories in phase space converge or diverge and therefore provide a useful criterion for dynamical stability. In this work, we develop a general framework for analyzing Lyapunov exponents in stationary spacetimes and extend previous studies beyond circular orbits. For a generic stationary spacetime described by $g_{\mu\nu}(r,\theta)$, we show that the phase space relevant to linear perturbations is spanned by $(r,p_r,\theta,p_\theta)$ and the corresponding linear stability matrix has rank four. When the spacetime admits a rank-2 Killing tensor, the linear stability matrix can be reduced to a block-diagonal form, allowing the Lyapunov exponents to be obtained analytically. By imposing the appropriate constraint conditions, the formalism further yields the linear stability matrices and Lyapunov exponents for circular and spherical orbits. The validity of the method is illustrated by several representative examples, including the (inverted) harmonic oscillator, planar Kepler motion, and particle motion in Schwarzschild and Kerr spacetimes. These results provide a unified framework for investigating the stability properties of particle orbits in both classical and relativistic dynamical systems.

The mutual information of measurement of a local operator between two spatial regions characterizes the reduction in the uncertainty of measurement outcomes in one region given the outcome in the other. We study the Rényi-Shannon mutual information of measurement in conformal field theories (CFTs). Explicit calculations for scalar primaries and descendants in large $N$ CFTs are performed in the two extreme limits of the intervals being adjacent or largely separated. The results depend on only the cross ratio and the scaling dimension $\Delta$ of the operator being measured, with striking similarities to the mutual information of entanglement. We find a surprising quadratic dependence as $(\Delta-1/2)^2$ for adjacent intervals. This dependence superficially seems to violate the information processing inequality, which we discuss and resolve. We also offer a holographic interpretation of the mutual information of measurement.