It was recently pointed out that some precise photon-Galileon couplings in four dimensions (4D)—inspired by a higher dimensional reduction—are enough to obtain a Horndeski theory that is less constrained by the stringent experimental bounds on the speed of gravitational waves. They imply the constancy of the ratio of speed of gravity to light throughout cosmic evolution. This holds even if we include the general scalar potentials $G_4(\pi ,X)$ and $G_5(\pi )$. In this paper we go into the details of this 4D luminal extension of Horndeski theory including its scalar sector. We also present the complete action including the general $G_5(\pi ,X),G_6(\pi ,X)$ scalar potentials. Thus we show all the $U(1)$ gauge invariant vector Galileons in 4D that result from a Kaluza-Klein dimensional reduction from 5D Horndeski. They provide a consistent coupling of a higher derivative vector to scalar modifications of gravity—namely, without inducing Ostrogradsky ghosts and keeping gauge invariance—in the aim to explore more universal couplings of dark energy to other matter, such as vectors and in particular the photon.

First order phase transitions (FOPTs) constitute an active area of contemporary research as a promising cosmological source of observable gravitational waves. The spacetime dynamics of the background scalar field undergoing the phase transition can also directly produce quanta of particles that couple to the scalar, which has not been studied as extensively in the literature. This paper provides the first careful examination of various aspects of this phenomenon, which is important for understanding the dynamics of the phase transition, the generation of gravitational waves, and various high energy and beyond the Standard Model phenomena. In particular, the contributions from various stages of FOPTs (bubble nucleation, expansion, collision, postcollision) are disentangled, and conceptual aspects of the associated underlying physics relevant for particle production are clarified. Subtleties related to nonuniversality of particle interactions and masses in different vacua are discussed, and the suppression of nonperturbative effects such as tachyonic instability and parametric resonance due to the inhomogeneous nature of the process is examined.

While first order phase transitions (FOPTs) have been extensively studied as promising cosmological sources of gravitational waves, the phenomenon of particle production from the dynamics of the background field during FOPTs has received relatively little attention in the literature, where it has only been studied with semianalytic estimates in some simplified settings. This paper provides improved numerical studies of this effect in more realistic frameworks, revealing important qualitative details that have been missed in the literature. We also provide easy to use analytic formulas that can be used to calculate particle production in generic FOPT setups.

Recent observations from the James Webb Space Telescope (JWST) have uncovered massive galaxies at high redshifts, with their abundance significantly surpassing expectations. This finding poses a substantial challenge to both galaxy formation models and our understanding of cosmology. Additionally, discrepancies between the Hubble parameter inferred from high redshift cosmic microwave background (CMB) observations and those derived from low redshift distance ladder methods have led to what is known as the “Hubble tension.” Among the most promising solutions to this tension are early dark energy (EDE) models. In this study, we employ an axionlike EDE model in conjunction with a universal Salpeter initial mass function to fit the luminosity function derived from JWST data, as well as other cosmological probes, including the CMB, baryon acoustic oscillations, and the SH0ES local distance ladder. Our findings indicate that JWST observations favor a high energy fraction of EDE, $f_{\mathrm{EDE}}\sim 0.2\pm 0.03$, and a high Hubble constant value of $H_0\sim 74.6\pm 1.2\mathrm{km}/\mathrm{s}/\mathrm{Mpc}$, even in the absence of SH0ES data. This suggests that EDE not only addresses the $H_0$ tension but also provides a compelling explanation for the observed abundance of massive galaxies identified by JWST.

The expected improvements in the precision of inflationary physics observables including the scalar spectral index $n_s$ and the tensor-to-scalar ratio $r$ will reveal more than just the viability of a particular model of inflation. In the presence of a curvaton field $\chi$, supposedly dead models of inflation can be resurrected, as these observables are affected by curvaton perturbations. For currently successful models, improved constraints will enable us to constrain the properties of extra decaying scalar degrees of freedom produced during inflation. In this work, we demonstrate these diverse uses of a curvaton field with the most recent constraints on ($n_s,r$) and two exemplary inflation models, a Starobinsky-like model and a model of new inflation. The specific models used as examples can be derived in the context of supergravity. Our analysis invokes three free parameters: the curvaton mass $m_{\chi }$, its decay rate ${\mathrm{\Gamma }}_{\chi }$, and the reheating temperature $T_{\mathrm{RH}}$ produced by inflaton decays. We systematically analyze possible postinflationary era scenarios of a curvaton field. By projecting the most recent cosmic microwave background (CMB) data on ($n_s,r$) into this parameter space, we can either set constraints on the curvaton parameters from successful models of inflation (so that the success is not spoiled) or determine the parameters that are able to save a model for which $n_s$ is predicted to be below the experimental data. We emphasize that the initial value of $⟨{\chi }^2⟩\propto H^4/m_{\chi }^2$ produced during inflation is determined from a stochastic approach and thus not a free parameter in our analysis. We also investigate the production of local non-Gaussianity $f_{\mathrm{NL}}^{(\mathrm{loc})}$ and apply current CMB constraints to the parameter space. Intriguingly, we find that a large value of $f_{\mathrm{NL}}^{(\mathrm{loc})}$ of $\mathcal{O}(1)$ can be produced for both of the two representative inflation models.

While photons and gravitons do not interact significantly, photons can be converted to gravitons in a background magnetic field—a phenomenon known as the Gertsenshtein effect. In this paper, we investigate whether chiral electromagnetic waves can be converted to chiral gravitational waves (GW) in the presence of primordial magnetic fields during the radiation-dominated epoch of the early Universe. We consider two situations wherein chirality is either present in the propagating electromagnetic waves or it exists in the background magnetic field. Our analysis shows that while the conversion probability increases with stronger magnetic fields, it remains insensitive to the chiral nature of the background magnetic field. Consequently, the net chirality parameter is independent of the chirality of the background field in both cases. Finally, we demonstrate that the present-day energy density of the produced chiral GWs peaks at a frequency of $\sim 100\mathrm{GHz}$, and the corresponding characteristic strain can be sensitive to current and future missions designed to detect high-frequency GWs.

It has been proposed that the accelerated expansion of the Universe can be explained by the merging of our Universe with baby universes, resulting in dark energy with a phantomlike equation of state. However, the evidence in favor of it did not include the full set of cosmological observables. Here we examine the implications of this model for both early and late universe cosmology using data from Planck collaboration, DESI 2024 and other experiments. We find that the pure baby universe model gives a poor fit to current data. Extending it to include a contribution from the cosmological constant, we find two allowed regions of parameter space: one close to $\mathrm{\Lambda }\mathrm{CDM}$, and another with $\mathrm{\Lambda }<0$ plus the exotic dark energy component. The two regions can be significantly favored over $\mathrm{\Lambda }\mathrm{CDM}$, depending on the choice of supernova datasets, and they can ameliorate the Hubble tension to the level of $2\sigma$, depending on the supernova dataset. The model with $\mathrm{\Lambda }<0$ features an equation of state $w(a)$ with a pole singularity at early times.

It has been suggested that Centaurus A (Cen A) could make a contribution to the observed ultrahigh-energy cosmic-ray (UHECR) flux. We calculate the flux of astrophysical neutrinos produced by UHECRs accelerated in the jet of Cen A, a close-by jetted active galactic nucleus. We use a bottom-up approach, in which we follow the energization of protons and heavier elements in a magnetohydrodynamic simulation of a relativistic jet with proper parameters of Cen A, also accounting for attenuation losses based on the observed photon fields. We compare the expected neutrino flux with the sensitivity of current and planned neutrino detectors. We find that the detection of $\sim {10}^{17}–{10}^{18}\mathrm{eV}$ neutrinos from Cen A would require ultimate neutrino detectors that reach a point source sensitivity of $\sim \mathrm{a}\mathrm{few}\times {10}^{-13}\mathrm{erg}{\mathrm{cm}}^{-2}{\mathrm{s}}^{-1}$. Successful detection, though challenging, would be useful in constraining the Cen A contribution to the UHECRs.

We compute the flux of relic neutrino background ($\mathrm{R}\nu \mathrm{B}$) up-scattered by ultrahigh-energy (UHE) cosmic rays (CRs) in clusters that act as CR-reservoirs. The long trapping times of UHECRs make this flux larger than that of $\mathrm{R}\nu \mathrm{B}$ up-scattered by UHECRs on their way to Earth, which we also compute. We find that IceCube excludes $\mathrm{R}\nu \mathrm{B}$ weighted overdensities larger than ${10}^{10}$ in clusters, and that PUEO, RNO-G, GRAND, and IceCube-Gen2 will test values down to ${10}^8$. Our treatment incorporates the momentum transfer dependence of the neutrino-nucleus cross section, deep inelastic scattering, a mixed UHECR composition, and flavor information on the up-scattered $\mathrm{R}\nu \mathrm{B}$ fluxes for both cases of neutrino mass spectrum with normal and inverted ordering, providing new handles to possibly disentangle the up-scattered $\mathrm{R}\nu \mathrm{B}$ from cosmogenic neutrinos.

Space-based gravitational wave detectors have the capability to detect signals from very high redshifts. It is interesting to know if such capability can be used to study the global structure of the cosmic space. In this paper, we focus on one particular question: if there exists a reflective cosmic boundary at the high redshift ($z>15$), is it possible to find it? We find that, with the current level of technology: (1) gravitational waves appear to be the only means through which signatures from the cosmic boundary can possibly be detected; (2) a large variety of black holes, with masses roughly in the range $\mathcal{O}({10}^3–{10}^6)M_{\odot }$, can be used for the task; (3) in the presumably rare but physically possible case that two merger events from the growth history of a massive black hole are detected coincidentally, a detector network like $\mathrm{TianQin}+\mathrm{LISA}$ is essential to help improve the chance to determine the orientation of the cosmic boundary; and (4) the possibility to prove or disprove the presence of the cosmic boundary largely depends on how likely one can detect multiple pairs of coincident gravitational wave events.

We investigated a plasma system with kinematic viscosity $\nu =0.006$ and magnetic diffusivity $\eta =0.006$, driven by helical kinetic energy, to study the dynamics of energy and helicity in magnetic diffusion. Using the numerical data obtained, we explored methods to determine the $\alpha$ and $\beta$ coefficients that linearize the nonlinear electromotive force and the dynamo process. Initially, we applied conventional statistical approaches such as mean field theory, direct interaction approximation, and eddy-damped quasinormal Markovian closure. We then proposed a simpler alternative method using large scale magnetic data and turbulent kinetic data to calculate $\alpha$ and $\beta$. Our findings show that, while $\alpha$ qualitatively aligns with theoretical predictions, $\beta$ remains negative, indicating an inverse cascade of energy through magnetic diffusion. This deviates from conventional models and was further analyzed using a recursive method in the second moment identity, revealing that small scale kinetic helicity couples with large scale current density to transport energy inversely. We validated our method by reproducing the numerically calculated data. The consistency between our method and direct numerical simulations suggests that the negative diffusion process in plasma has a physical basis.

A magnetic monopole is a well-motivated class of beyond-Standard-Model particles that could provide insights into the long-standing puzzle of the quantization of electric charge. These hypothetical particles are likely to be super heavy ($\sim {10}^{15}\mathrm{GeV}$) and may have been produced during the very early stages of the Universe’s evolution. We propose a novel detection scenario for the search for such cosmic magnetic monopoles, utilizing a hybrid approach that combines radio-frequency atomic magnetometers and plastic scintillators. Such a setup allows one to detect both the induction and scintillation signals of monopoles with velocities larger than about ${10}^{-6}$ light speed (assuming a signal-to-noise ratio of $\sim 4$) and their masses larger than approximately ${10}^7\mathrm{GeV}$ (at $\beta \sim {10}^{-3}$). The proposed detector design has the potential to be scaled up to large areas, enabling the exploration of the parameter space of the cosmic magnetic monopoles beyond the current experimental and astrophysical constraints. It is estimated that such a detector can reach the current most stringent limits on the flux set by previous searches, with a signal-to-noise ratio of the induction signal larger than about 4.5, assuming an effective exposure being $20,000\mathrm{year}·{\mathrm{m}}^2$ and at least three coil layers.

Einstein Telescope (ET) is a third-generation gravitational-wave (GW) detector project which aims to reach a sensitivity $\sim 10$ times larger than current GW detectors such as Advanced LIGO and Advanced Virgo. The high rate of GW signals expected in the data will pose several data analysis challenges, such as the ability to disentangle overlapping signals, or the computational resources required to treat all the candidate events. We explore the behavior and the performances of pystampas, a data analysis pipeline designed to search for unmodeled GW signals with duration $\sim 1–1000\mathrm{s}$ on a mock dataset that consists of 1 month of data following ET design sensitivity on top of which is added a realistic distribution of compact binary coalescence (CBC) signals. Unmodeled searches are intrinsically less sensitive to CBC signals than template-based searches, but are computationally cheaper and more robust to uncertainties in the waveforms. This search recovers 38% of the total number of injected binary black hole (BBH) signals, including 89% of the systems with a total mass above $100M_{\odot }$, as well as the majority of binary neutron star (BNS) signals closer than 850 Mpc ($z=0.17$). It is also able to estimate the chirp mass of the recovered BNS with an average precision of 1.3%. Therefore, we show that this unmodeled search is able to detect a substantial amount of CBC events at a relatively low computational cost, which makes it interesting for low-latency analyses and independent validation of detections made by matched filtering pipelines. We also find that the presence of many CBC signals only marginally impacts the sensitivity of the search to other kinds of unmodeled long-duration transient signals, by $\sim 3\%$ in average.

We consider the process of electron-positron pair production in the presence of strong electric backgrounds being rapidly switched on and off and examine the total particle yield. For sufficiently sharp field profiles, the particle number can be substantially enhanced. It is demonstrated that this enhancement is quite similar to the phenomenon of dynamical assistance by a weak high-frequency field superimposed on a strong background. Both these mechanisms are analyzed by means of exact numerical computations, worldline instanton approach, and the locally constant field approximation. We identify the timescale of the switching profile leading to the pair-production enhancement and argue that the particle yield is highly unlikely to be increased by shaping the switch on and off of realistic laser pulses. On the other hand, we confirm that it is feasible to observe the dynamically assisted Schwinger effect by adding a rapidly oscillating field to a strong electric background.

In this paper, the dimensional reduction is applied to the Lee-Wick electrodynamics in which the classical sources are confined on a spatial plane. As result, the Lee-Wick pseudoelectrodynamics is achieved as a nonlocal electromagnetism defined in $1+2$ dimensions. The Abelian Anderson-Higgs mechanism is so introduced in the Lee-Wick pseudo-electrodynamics through a complex scalar sector in $1+2$ dimensions, breaking spontaneously the $U(1)$-gauge symmetry of the nonlocal theory. As consequence, the pseudo-Lee-Wick field acquires a light mass, beyond the usual heavy Lee-Wick mass, that is a natural mass parameter of the theory. After the spontaneous symmetry breaking takes place, classical features of the theory are discussed, as the pseudo-Proca-Lee-Wick electrodynamics, with the field equations and conservation laws. The introduction of Lee-Wick fermions also is proposed, in which it opens the discussion of a viable pseudo-Proca-Lee-Wick quantum electrodynamics in $1+2$ dimensions. The unitarity at the tree level of the Lee-Wick pseudo-electrodynamics is discussed through the optical theorem.

In this work, the equations of dissipative relativistic spin hydrodynamics based on quantum kinetic theory are derived. Employing the inverse-Reynolds dominance approach, a resummation scheme based on a power counting in Knudsen and inverse Reynolds numbers is constructed, leading to hydrodynamic equations that are accurate to second order. It is found that the spin dynamics can be characterized by 11 equations: six of them describe the evolution of the components of the spin potential, while the remaining five provide the equation of motion of a dissipative irreducible rank-two tensor. For a simple truncation, the first- and second-order transport coefficients are computed explicitly.

We exploit the complete complementarity relations (CCR) to fully characterize various aspects of quantumness in quantum electrodynamics (QED) scattering processes at tree level. As a paradigmatic example, we consider Bhabha scattering in two different configurations: in the first case, the initial state is factorized in the spin and we study the generation of entanglement due to the scattering. Then we consider the most general case in which the initial state can be entangled: we find that the scattering generates and distributes quantum information in a nontrivial way among the spin degrees of freedom of the particles, with CCR relations being preserved. An important outcome of our analysis is that maximal entanglement is conserved in the scattering process involving only fermions as input and output states, with a more complex situation if photons are present.

In this paper, we study the single production of doubly charged Higgs $H^{\pm \pm }$ in the type-II seesaw at the high energy muon collider. Compared with the pair production channel ${\mu }^{+}{\mu }^{-}\to H^{++}{H}^{--}$, the single production channel ${\mu }^{+}{\mu }^{-}\to {\mu }^{\mp }{\ell }^{\mp }{H}^{\pm \pm }$ in principle could probe the mass region above the threshold $m_{H^{\pm \pm }}>\sqrt{s}/2$. The single production channel depends on the Yukawa coupling $h$, which is related to the neutrino oscillation parameters. We show that the Majorana phases ${\varphi }_1$ and ${\varphi }_2$ have great impact on the individual cross section of the single production. We find that the same sign dilepton signature from $H^{\pm \pm }\to {\ell }^{\pm }{\ell }^{\pm }$ could probe $m_{H^{\pm \pm }}\lesssim 2.6(7.1)\mathrm{TeV}$ at the 3 (10) TeV muon collider when the triplet VEV $v_{\mathrm{\Delta }}\lesssim 3\mathrm{eV}$.

A dark sector with a very large number of massive degrees of freedom is generically constrained by radiative corrections to Newton’s constant. However, there are caveats to this statement, especially if the degrees of freedom are light or massless. Here, we examine in detail and update a number of constraints on the possible number of dark degrees of freedom, including from black hole evaporation, from perturbations to systems including an evaporating black hole, from direct gravitational production at colliders, from high-energy cosmic rays, and from supernovae energy losses.

Neutral triple gauge couplings (nTGCs) are a manifestation of new physics beyond the Standard Model (SM), as they are absent in the SM and are first generated by dimension-8 operators in the SM effective field theory (SMEFT). We study the UV completion of nTGCs in a renormalizable model with vectorlike heavy fermions. We compute the one-loop heavy fermion contributions to nTGC vertices by matching them to dimension-8 operators in the low energy limit. Such fermion loops contain either heavy fermions only or mixture of heavy fermions with light SM fermions. We find that their contributions can induce dimension-8 nTGC effective operators containing two SM Higgs-doublet fields, which are formulated with a complete set of 7 dimension-8 operators generating off-shell $CP$-even nTGCs. We present the results in terms of SMEFT coefficients and in terms of nTGC vertices (form factors) with two on-shell gauge bosons. In the heavy-light mixing case there appear terms that cannot be accommodated by conventional parametrizations of form factors due to extra logarithmic corrections. We further discuss the implications for probing such UV dynamics via nTGCs at high-energy colliders.