It was shown that the Lie algebra underlying higher-spin holography admits a contraction including a Poincaré subalgebra in any space-time dimensions. The associated curvatures, however, do not reproduce upon linearization those that are usually employed to formulate the equations of motion of free massless particles in Minkowski space. We show that, despite this mismatch, the new linearized curvatures can also be used to describe massless higher-spin fields. This suggests a new way to build interacting higher-spin gauge theories in Minkowski space that may admit a holographic description.

We show that viable electroweak baryogenesis can be realized without a first-order phase transition if plasma is heated inhomogeneously by nongravitational structure formation in some particle species. Yukawa interactions can mediate relatively long-range attractive forces in the early Universe. This creates an instability and leads to growth of structure in some species even during the radiation dominated era. At temperatures below the electroweak scale, the collapsing and annihilating halos can heat up plasma in fireballs that expand and create the out-of-equilibrium high-temperature environment suitable for generating the baryon asymmetry. The plasma temperature at the time of baryogenesis can be as low as a few MeV, making it consistent with both standard and low-reheat cosmologies.

Based on a dynamical model on particle production, the production and fraction of exotic components in neutron star matter are analyzed. It is found that there exists a small fraction of strangeness in twice saturation density matter. For five times saturation density matter, the fraction of strange baryons can be as high as 25%–50%, depending on the equation of state used. The neutron-proton asymmetry of dense matter does not significantly impact the strangeness fraction in neutron star matter. This research provides new insights into the strange components in neutron stars.

Given a model for self-dual nonlinear electrodynamics in four spacetime dimensions, any deformation of this theory which is constructed from the duality-invariant energy-momentum tensor preserves duality invariance. In this work we present new proofs of this known result and also establish a previously unknown converse: any parametrized family of duality-invariant Lagrangians, all constructed from an Abelian field strength $F_{\mu \nu }$ but not its derivatives, is related by a generalized stress tensor flow, in a sense which we make precise. We establish this and other properties of stress tensor deformations of theories of nonlinear electrodynamics using both a conventional Lagrangian representation and using two auxiliary field formulations. We analyze these flows in several examples of duality-invariant models including the Born-Infeld and ModMax theories, and we derive a new auxiliary field representation for the two-parameter family of ModMax-Born-Infeld theories. These results suggest that the space of duality-invariant theories may be characterized as a subspace of theories of electrodynamics with the property that all tangent vectors to this subspace are operators constructed from the stress tensor.

We consider the strong-coupling phase in a model of $O(N)$ spin-2 field theory in de Sitter spacetime and the effective mass of spin-2 fields therein. In the strong-coupling phase, the Higuchi bound limits the mass parameter in the theory. The analysis using the large $N$ approximation finds the critical value of the mass parameter with numerical calculation.

We calculate the Schwinger pair-production rates in ${\mathbb{R}}^{3,1}$ as well as in the positively curved space $S^2\times {\mathbb{R}}^{1,1}$ for both spin-0 and spin-$\frac{1}{2}$ particles under the influence of an external $SU(2)\times U(1)$ gauge field producing an additional uniform non-Abelian magnetic field besides the usual uniform Abelian electric field. To this end, we determine and subsequently make use of the spectrum of the gauged Laplace and Dirac operators on both the flat and the curved geometries. We find that there are regimes in which the purely non-Abelian and the Abelian parts of the gauge field strength have either a counterplaying or reinforcing role, whose overall effect may be to enhance or suppress the pair-production rates. Positive curvature tends to enhance the latter for spin-0 and suppress it for spin-$\frac{1}{2}$ fields, while the details of the couplings to the purely Abelian and the non-Abelian parts of the magnetic field, which are extracted from the spectrum of the Laplace and Dirac operators on $S^2$, determine the cumulative effect on the pair-production rates. These features are elaborated in detail.

We study Unruh phenomena for a qudit detector coupled to a quantized scalar field, comparing its response to that of a standard qubit-based Unruh-DeWitt detector. We show that there are limitations to the utility of the detailed balance condition as an indicator for Unruh thermality of higher-dimensional qudit detector models. This can be traced to the fact that a qudit has multiple possible transition channels between its energy levels, in contrast to the 2-level qubit model. We illustrate these limitations using two types of qutrit detector models based on the spin-1 representations of $SU(2)$ and the non-Hermitian generalization of the Pauli observables (the Heisenberg-Weyl operators).

This paper reports calculations and analysis of the effects of a perfect conducting wall of a very large spherical shell on the stable thermodynamic equilibrium of a black hole sitting at the center of the shell that is filled with electromagnetic blackbody radiation. A parallel is drawn with the case where electromagnetic radiation is replaced by scalar blackbody radiation with Dirichlet or Neumann boundary conditions on the wall. It is found that the value of the shell radius above which only blackbody radiation remains in stable thermodynamic equilibrium can be considerably affected by vacuum polarization due to the presence of the wall.

We study the tidal problem and the resulting $I$-Love-$Q$ approximate universal relations for rotating superfluid neutron stars in the Hartle-Thorne formalism. Superfluid stars are described in this work by means of a two-fluid model consisting of superfluid neutrons and all other charged constituents. We employ a stationary and axisymmetric perturbation scheme to second order around a static and spherically symmetric background. Recently, we used this scheme to study isolated rotating superfluid stars. In this paper it is applied to analyze the axially symmetric sector of the tidal problem in a binary system. We show that a consistent use of perturbative matching theory amends the original two-fluid formalism for the tidal problem to account for the possible nonzero value of the energy density at the boundary of the star. This is exemplified by building numerically different stellar models spanning three equations of state. Significant departures from universality are found when the correct matching relations are not taken into account. We also present an augmented set of universal relations for superfluid neutron stars which includes the contribution to the total mass of the star at second order, $\delta M$. Therefore, our results complete the set of universal relations for rotating superfluid stars, generalizing our previous findings in the perfect fluid case.

We study phenomenological features and stability of boson stars in massless and massive scalar-tensor theory of gravity with Damour-Esposito-Farèse coupling. This coupling between the tensor and scalar sectors of the theory leads to a phenomenon called spontaneous scalarization, the onset of which we investigate by numerically computing families of boson-star models using shooting and relaxation algorithms. We systematically explore the effects of the theory’s coupling, the mass of the gravitational scalar and the choice of the bosonic potential on the structure of weakly and strongly scalarized solutions. Scalarized boson-star models share many common features with neutron stars in the same scalar-tensor theory of gravity. In particular, scalarization can result in boson stars with significantly larger radii and masses, which tend to be energetically favored over their weakly or nonscalarized counterparts. Overall, we find that boson stars are not quite as susceptible to scalarization as neutron stars.

As the existing techniques to directly detect dark matter particles in laboratory experiments continue to produce negative signals, the research community considers novel approaches including those relying on condensed matter systems with nontrivial quantum properties. For example, finding signatures of dark matter in transport characteristics of solids would be an important step on the road to detect this illusive component of the mass of our Universe. As a first step in this direction we have recently derived the modified kinetic equation taking into account two coupled $U(1)$-gauge fields, one being the standard Maxwell electromagnetic field and other corresponding to the dark sector. The resulting Boltzmann kinetic equation is modified by the Berry curvature which couples to both visible and dark sector gauge fields. The linear and nonlinear longitudinal and/or Hall currents in topological matter may signal the existence of dark particle induced electromagnetic fields. The usage of appropriately designed resonant cavity to enhance the electric field may help to reach the goal. The conservative estimates show that the technique should have the sensitivity of the order of ${10}^{-9}$ or better and may help to partially fill the gap between XENON1T and haloscope experiments.

Isocurvature perturbations with a blue power spectrum are one of the natural targets for the future large scale structure observations which are probing shorter length scales with greater accuracy. We present a Fisher forecast for the Euclid and MegaMapper (MM) experiments in their ability to detect blue isocurvature perturbations. We construct the theoretical predictions in the EFTofLSS and bias expansion formalisms at quartic order in overdensities which allows us to compute the power spectrum at one loop order and bispectrum at tree level and further include theoretical error at the next to leading order for the covariance determination. We find that Euclid is expected to provide at least a factor of few improvement on the isocurvature spectral amplitude compared to the existing Planck constraints for large spectral indices while MM is expected to provide about 1 to 1.5 order of magnitude improvement for a broad range of spectral indices. We find features that are specific to the blue isocurvature scenario including the leading parametric degeneracy being with the Laplacian bias and a UV sensitive bare sound speed parameter.

False-vacuum eternal inflation can be described as a random walk on the network of vacua of the string landscape. In this paper we show that the problem can be mapped naturally to a problem of directed percolation. The mapping relies on two general and well-justified approximations for transition rates: (1) the downward approximation, which neglects “upward” transitions, as these are generally exponentially suppressed; and (2) the dominant decay channel approximation, which capitalizes on the fact that tunneling rates are exponentially staggered. Lacking detailed knowledge of the string landscape, we model the network of vacua as random graphs with arbitrary degree distribution, including Erdös-Rényi and scale-free graphs. As a complementary approach, we also model regions of the landscape as regular lattices, specifically Bethe lattices. We find that the uniform-in-time probabilities proposed in our previous work favor regions of the landscape poised at the directed percolation phase transition. This raises the tantalizing prospect of deriving universal statistical distributions for physical observables, characterized by critical exponents that are insensitive to the details of the underlying landscape. We illustrate this with the cosmological constant, and show that the resulting distribution peaks as a power-law for small positive vacuum energy, with a critical exponent uniquely determined by the random graph universality class.

Quantum cosmology based on Lorentzian path integrals is a promising avenue. However, many previous works allow non-Lorentzian configurations by integrating the squared scale factor over the whole real line. Here we show that restricting the minisuperspace path integral to Lorentzian configurations with positive squared scale factor can significantly change the expectation values. In addition, this enables the study of causal horizons and their quantum fluctuations, and achieves singularity avoidance trivially by excluding singular minisuperspace geometries as non-Lorentzian. The results indicate that semiclassical saddle point approximation is not always valid in truly Lorentzian quantum cosmology. As a consequence, related works on the tunneling and no-boundary proposals, bouncing cosmology, and the quantum origin of inflation etc. need to be reexamined.

Cosmological bounds on neutrinos and additional hypothetical light thermal relics, such as QCD axions, are currently among the most restrictive ones. These limits mainly rely on cosmic microwave background temperature anisotropies. Nonetheless, one of the largest cosmological signatures of thermal relics is that on gravitational lensing, due to their free-streaming behavior before their nonrelativistic period. We investigate late-time only hot-relic mass constraints, primarily based on recently released lensing data from the Atacama Cosmology Telescope, both alone and in combination with lensing data from the Planck satellite. Additionally, we consider other local probes, such as baryon acoustic oscillations measurements, shear-shear, galaxy-galaxy, and galaxy-shear correlation functions from the dark energy survey, and distance moduli measurements from Type-Ia Supernovae. The tightest bounds we find are $\sum m_{\nu }<0.43\mathrm{eV}$ and $m_a<1.1\mathrm{eV}$, both at 95% CL Interestingly, these limits are still much stronger than those found on e.g., laboratory neutrino mass searches, reassessing the robustness of the extraction of thermal relic properties via cosmological observations. In addition, when considering lensing-only data, the significance of the Hubble constant tension is considerably reduced, while the clustering parameter ${\sigma }_8$ controversy is completely absent.

We show that the IceCube observation of the Galactic neutrino-flux component confirms the hint of detection of neutrinos from the Galactic ridge (the inner part of the Milky Way disk within the Galactic longitude $|l|<30°$), previously reported by the ANTARES Collaboration. This confirmation indicates that the bulk of the high-energy flux from the Galactic ridge in multi-TeV band is produced by interactions of high-energy protons and atomic nuclei, rather than electrons. We show that both ANTARES and IceCube measurements agree with the Fermi-LAT telescope measurements of the gamma-ray emission from the ridge. The multimessenger (neutrino plus gamma-ray) spectrum of the ridge over a broad energy range from 10 GeV to 10 TeV is consistent with a model of pion decay emission produced by a power-law distribution of protons with a slope $\mathrm{\Gamma }\simeq 2.5$, harder than that of the locally observed cosmic ray spectrum. This provides a multimessenger demonstration of the variability of the spectrum of cosmic rays across the Galactic disk.

In this paper we analyze the exclusive photoproduction of the $D$-meson pairs with large invariant mass. We perform evaluations in the collinear factorization framework and in the leading order of the strong coupling ${\alpha }_s$, expressing the cross section in terms of generalized parton distributions (GPDs) of different parton flavors in the proton. We focus on the photoproduction of the pseudoscalar-vector pairs, like, e.g., $D^{\pm }{D}^{*\mp }$, $D^0{\overline{D}}^{*0}$, $D_s^{+}{D}_s^{*-}$, which gets the dominant contribution from the chiral even GPDs of the target, and estimate the cross section in the kinematics of the future Electron Ion Collider. In all channels the amplitude of the process obtains comparable contributions from gluons and only one of the light quark flavors. This finding signals that the process potentially could be used to single out the contributions of the individual chiral even GPDs of light flavors. We found that the process is mostly sensitive to the behavior of GPDs in the so-called Efremov-Radyushkin-Brodsky-Lepage region. Numerically, the cross section of the process is sufficiently large for experimental studies and thus can be used as a complementary probe for studies of the GPDs.

The one- and two-boson momentum spectra are derived in the quantum local-equilibrium canonical ensemble of noninteracting bosons with a fixed particle number constraint. We define the canonical ensemble as a subensemble of events associated with the grand-canonical ensemble. Applying simple hydro-inspired parametrization with parameter values that correspond roughly to the values at the system’s breakup in $p+p$ collisions at the LHC energies, we compare our findings with the treatment which is based on the grand-canonical ensembles where mean particle numbers coincide with fixed particle numbers in the canonical ensembles. We observe a significantly greater sensitivity of the two-particle momentum correlation functions to fixed multiplicity constraint compared to one-particle momentum spectra. The results of our analysis may be useful for interpretation of multiplicity-dependent measurements of $p+p$ collision events.

We propose a novel method to find local plane-wave solutions of the linearized equations of motion of relativistic hydrodynamics in inhomogeneous equilibrium configurations, i.e., when a fluid in equilibrium is rigidly moving with nonzero thermal vorticity. Our method is based on extending the conserved currents to the tangent bundle, using a type of Wigner transformation. The Wigner-transformed conserved currents can then be Fourier-transformed into the cotangent bundle to obtain the dispersion relations for the space-time dependent eigenfrequencies. We show that the connection between the stability of hydrodynamics and the evolution of plane waves is not as straightforward as in the homogeneous case, namely, it is restricted to the equilibrium-preserving directions in the cotangent bundle. We apply this method to Müller-Israel-Stewart (MIS) theory and show that the interplay between the bulk viscous pressure and the shear-stress tensor with acceleration and rotation leads to novel modes, as well as modifications of the already known ones. We conclude that, within the domain of applicability, i.e., when boundary effects are negligible and the vorticity is not too large, MIS theory is stable and causal, with the same stability and causality conditions as for homogeneous equilibrium configurations.

Within the two Higgs doublet model (2HDM) with $\mathcal{C}P$ conservation and a softly broken $Z_2$ symmetry, we analyze the flavor changing Higgs decays $h\to bs$ ($bs$ refers jointly to the two decay channels $b\overline{s}$ and $\overline{b}s$), where $h$ is identified with the SM-like Higgs boson discovered at the LHC. We provide a comprehensive study of the decay width $\mathrm{\Gamma }(h\to bs)$ with particular focus on the most relevant effects from the triple Higgs coupling ${\lambda }_{h{H}^{+}{H}^{-}}$. Furthermore, we consider all the relevant theoretical and experimental constraints to determine which predictions for the $\mathrm{BR}(h\to bs)$ are still allowed by the current data. We find that the predictions for $\mathrm{BR}(h\to bs)$ in types II and III can be several orders of magnitude smaller compared to the SM value. In contrast, in type I and IV we find that the predicted enhancements in the decay rates with respect to the SM of up to about 70% and 50%, respectively, are still allowed. We discuss how these deviations from the SM are caused by interference effects controlled by the coupling ${\lambda }_{h{H}^{+}{H}^{-}}$ which can be large for very heavy $H^{\pm }$. To better understand the role of ${\lambda }_{h{H}^{+}{H}^{-}}$ in the $h\to bs$ decay we derive and analyze here the analytical results for the $hbs$ one-loop effective vertex that is generated by integrating out the heavy $H^{\pm }$.