Primordial black holes formed in the early Universe via gravitational collapse of over-dense regions may contribute a significant amount to the present dark matter relic density. Inflation provides a natural framework for the production mechanism of primordial black holes. For example, single field inflation models with a fine-tuned scalar potential may exhibit a period of ultra-slow roll, during which the curvature perturbation may be enhanced to become seeds of the primordial black holes formed as the corresponding scales reenter the horizon. In this work, we propose an alternative mechanism for the primordial black hole formation. We consider a model in which a scalar field is coupled to the Gauss-Bonnet term and show that primordial black holes may be seeded when a scalar potential term and the Gauss-Bonnet coupling term are nearly balanced. Large curvature perturbation in this model not only leads to the production of primordial black holes, but it also sources gravitational waves at the second order. We calculate the present density parameter of the gravitational waves and discuss the detectability of the signals by comparing them with sensitivity bounds of future gravitational wave experiments.

The type-I seesaw mechanism provides a natural explanation for tiny neutrino masses. The right-handed neutrino masses it requires are, however, too large to keep the Higgs boson mass at its measured value. We show that vector spinors, singlet leptons that are like right-handed neutrinos, generate tiny neutrino masses naturally through the exchange of spin-$1/2$ and spin-$3/2$ components. This one-step seesaw mechanism, which we call the type-$3/2$ seesaw, keeps the Higgs boson mass unchanged at one loop and gives cause therefore to no fine-tuning problem. If the on-shell vector spinor is a pure spin-$3/2$ particle, then it becomes a potential candidate for hidden dark matter which gets diluted due only to the expansion of the Universe. The type-$3/2$ seesaw provides a natural framework for the neutrino, Higgs boson, and dark matter sectors, with overall agreement with current experiments and observations.

We present a major update on our investigations of SU(2) gauge theory with one Dirac flavor in the adjoint representation on the lattice. In particular, we consider larger volumes as well as four different values of the gauge coupling. We provide results for the spectrum including gluonic, fermionic, and hybrid observables; Polyakov loops; and the anomalous dimension of the fermionic condensate from the Dirac mode number. These data confirm that the theory is close to the lower boundary of the conformal window for adjoint fermions. Our investigations provide important insights regarding the realization of different infrared scenarios that have been conjectured for this theory.

In the deconfined regime of a non-Abelian gauge theory at nonzero temperature, previously it was argued that if a (gauge invariant) source is added to generate nonzero holonomy, that this source must be linear for small holonomy. The simplest example of this is the second Bernoulli polynomial. However, then there is a conundrum in computing the free energy to $\sim g^3$ in the coupling constant $g$, as part of the free energy is discontinuous as the holonomy vanishes. In this paper we investigate two ways of generating the second Bernoulli polynomial dynamically; as a mass derivative of an auxiliary field, and from two-dimensional ghosts embedded isotropically in four dimensions. Computing the holonomous hard-thermal loop in the gluon self-energy, we find that the limit of small holonomy is only well behaved for two dimensional ghosts, with a free energy which to $\sim g^3$ is continuous as the holonomy vanishes.

We investigate the impact of finite volume and the corresponding restrictions on long-range correlations on the location of the critical endpoint in the QCD phase diagram. To this end, we employ a sophisticated combination of lattice Yang–Mills theory and a (truncated) version of Dyson–Schwinger equations in Landau gauge for $2+1$ quark flavors that has been studied extensively in the past. In the infinite-volume limit, this system predicts a critical endpoint at moderate temperature and large chemical potential. We study this system at small and intermediate volumes and determine the dependence of the location of the critical endpoint on the boundary conditions and the volume of a three-dimensional cube with edge length $L$. We demonstrate that noticeable volume effects of more than five percent occur only for $L\lesssim 5\mathrm{fm}$ and that volumes as large as $L^3\gtrsim (8\mathrm{fm}{)}^3$ are very close to the infinite-volume limit.

We revisit constraints on annihilating dark matter based on the cosmological global 21 cm signature observed by EDGES. For this purpose, we used the numerical data of the latest $N$-body simulation for the first time performed by state-of-the-art standard in order to estimate the boost factor at high redshifts ($z=10–100$), which enhances the annihilation of dark matter in course of structure formations. By taking into account to what fraction injected energy from dark matter annihilation contributes to ionization, excitation, and heating of intergalactic medium during dark ages, we estimated how large the global 21 cm absorption can be. In the thermal freeze-out scenario, we find that the dark matter masses $m_{\mathrm{DM}}<15\mathrm{GeV}$ and $m_{\mathrm{DM}}<3\mathrm{GeV}$ have been excluded at 95% C.L. for the modes into $b\overline{b}$ and $e^{+}{e}^{-}$, respectively, which are obtained independently of any uncertainties in local astrophysics such as observationally-fitted density profiles of dark matter halos.

We study the compatibility of the quantum homogeneitiy and isotropy hypothesis (QHIH), proposed by Ashtekar and Gupt to restrict the choice of vacuum state for the cosmological perturbations in loop quantum cosmology (LQC), with the requirement that the selected vacuum should lead to a power spectrum that does not oscillate. We inspect in close detail the procedure that these authors followed to construct a set of states satisfying the QHIH, and how a preferred vacuum can be determined within this set. We find a step that is not univocally specified in this procedure, in relation with the replacement of the set of states that was originally allowed by the QHIH with an alternative set that is more manageable. In fact, the first of these sets does not contain the state that has been used in most of the implementations of the QHIH to the analysis of the power spectrum of the perturbations in LQC. We focus our attention on the original set picked out by the QHIH and investigate whether some of its elements may display a nonoscillatory behavior. We show that, to the extent to which the techniques used in this paper apply, this possibility is feasible. Thus, the two aforementioned criteria for the physical restriction of the vacuum state in LQC are compatible with each other and not exclusive.

We present a new technique for observing low energy neutrinos with the aim of detecting the cosmic neutrino background using ion storage rings. Utilizing high energy targets exploits the quadratic increase in the neutrino capture cross section with beam energy, and with sufficient beam energy, enables neutrino capture through inverse-beta decay processes from a stable initial state. We also show that there exist ion systems admitting resonant neutrino capture, capable of achieving larger capture cross sections at lower beam energies than their nonresonant counterparts. We calculate the neutrino capture rate and the optimal experimental runtime for a range of different resonant processes and target ions and we demonstrate that the resonant capture experiment can be performed with beam energies as low as $\mathcal{O}(10\mathrm{TeV})$ per target nucleon. Unfortunately, none of the ion systems discussed here can provide sufficient statistics to discover the cosmic neutrino background with current technology. We address the challenges associated with realizing this experiment in the future, taking into account the uncertainty in the beam and neutrino momentum distributions, synchrotron radiation, as well as the beam stability.

Unlike ground-based gravitational wave detectors, space-based gravitational wave detectors can detect the ringdown signals from massive black hole mergers with large signal-to-noise ratios, help to localize sources and extract their parameters. To reduce the computation time in the Fisher information matrix analysis, we derive the analytical formulas of frequency-domain ringdown signals for both heliocentric and geocentric detectors by considering the effects of the harmonic phases, the rotation period of the geocentric detector, and the detector’s arm length. We explore median errors of the parameter estimation and source localization with ringdown signals from binaries with different masses and different redshifts. Using a binary source with the total mass $M={10}^7{M}_{\odot }$ at the redshift $z=1$, we analyze the dependence of these errors on the sky position. We find that the network of space-based gravitational wave detectors can significantly improve the source localization at the ringdown stage. The results of the Fisher matrix approximation are also checked by Bayesian inference method.

We comprehensively study the effects of bubble wall thickness and speed on the gravitational wave emission spectrum of collisions of two vacuum bubbles. We numerically simulate a large dynamical range, making use of symmetry to reduce the dimensionality. The high-frequency slope of the gravitational wave spectrum is shown to depend on the thickness of the bubble wall, becoming steeper for thick-wall bubbles, in agreement with recent fully $3+1$ dimensional lattice simulations of many-bubble collisions. This dependence is present, even for highly relativistic bubble wall collisions. We use the reduced dimensionality as an opportunity to investigate dynamical phenomena which may underlie the observed differences in the gravitational wave spectra. These phenomena include “trapping,” which occurs most for thin-wall bubbles, and oscillations behind the bubble wall, which occur for thick-wall bubbles.

We estimate the strong coupling constants of charmed and bottom mesons $D_{(s)}^{*}$, $D_{(s)1}$, $B_{(s)}^{*}$, and $B_{(s)1}$ with light vector mesons $\rho$, $\omega$, $K^{*}$, and $\varphi$ within the framework of light-cone QCD sum rules. We take into account the contributions of two- and three-particle distribution amplitudes of light vector mesons of twist-2, -3, and -4, and determine the values of the couplings between heavy vector (axial vector) mesons and light vector mesons. These couplings can play an essential role in understanding the charmonium absorption cross section in quark-gluon plasma. Moreover, we compare our estimations to the ones predicted by other approaches.

We analyze the exclusive $\varphi$-meson photoproduction on both hydrogen and deuterium targets based on the published data of CLAS, SAPHIR and LEPS collaborations. A dipole-form scalar gravitational form factor is applied to describe the $|t|$-dependence of the differential cross section. Based on the average of all the near-threshold data from CLAS, SAPHIR and LEPS, we find that the proton and deuteron mass radii are $0.75\pm 0.02\mathrm{fm}$ and $1.95\pm 0.19\mathrm{fm}$ respectively. The coherent and near-threshold quarkonium photoproduction seems to be sensitive to the radius of the hadronic system. The vector-meson-dominance model together with a low-energy QCD theorem well describe the data of near-threshold $\varphi$ photoproduction on the hadronic systems.

The width $J/\psi \to \gamma {\eta }_c$ is often determined from the photon spectrum line shape of the $J/\psi \to \gamma {\eta }_c\to \gamma X$ decay process. We study this line shape in a nonrelativistic effective field theory framework of quantum chromodynamics including the finite width of the ${\eta }_c$ and include $\mathcal{O}(v^2)$ corrections. We observe that the photon spectrum line shape is divergent at large energies due to polynomially and logarithmically divergent terms, and, therefore, a subtraction and renormalization scheme is needed to integrate over the photon energies in order to obtain the decay width. We propose to subtract these divergences at the line-shape level in a manner consistent with the calculation of the width in dimensional regularization and $\overline{\mathrm{MS}}$ scheme. We analyze CLEO’s data with the proposed subtracted line shape and find that the discrepancy between the theoretical prediction and the experimental result is resolved.

We present the results of semi-inclusive neutrino-nucleus cross sections within the plane wave impulse approximation (PWIA) for three nuclear models: relativistic Fermi gas, independent-particle shell model, and natural orbital shell model in comparison with the available $\mathrm{CC}0\pi$ measurements from the T2K, $\mathrm{MINER}\nu \mathrm{A}$, and MicroBooNE collaborations where a muon and at least one proton are detected in the final state. Results are presented as a function of the momenta and angles of the final particles, as well as in terms of the imbalances between proton and muon kinematics. The present semi-inclusive formalism is based on fully relativistic microscopic calculations and numerical integrations to produce both lepton and hadron kinematics without relying on further approximations. The analysis reveals that contributions beyond PWIA are crucial to explain the experimental measurements and that the study of correlations between final-state proton and muon kinematics can provide valuable information on relevant nuclear effects such as the Fermi motion and final-state interactions.

We develop a new phenomenological model that addresses current tensions between observations of the early and late Universe. Our scenario features: (i) a decaying dark energy fluid (DDE) with a transition at $z\sim 5,000$, to raise today’s value of the Hubble parameter, and (ii) an ultralight axion (ULA), which starts oscillating at $z\gtrsim {10}^4$, to suppress the matter power spectrum. Our Markov chain Monte Carlo analyses show that such a dark sector model fits a combination of cosmic microwave background (CMB), baryon acoustic oscillations, and Large Scale Structure (LSS) data slightly better than the $\mathrm{\Lambda }\mathrm{CDM}$ model, while importantly reducing both the $H_0$ and $S_8$ tensions with late universe probes ($\lesssim 3\sigma$). Combined with measurements from cosmic shear surveys, we find that the discrepancy on $S_8$ is reduced to the $1.4\sigma$ level. Adding local supernovae measurements, we find that the $H_0$ and $S_8$ tensions are reduced to the $1.4\sigma$ and $1.2\sigma$ levels respectively, with a significant improvement $\mathrm{\Delta }{\chi }^2\simeq -18$ compared to the $\mathrm{\Lambda }\mathrm{CDM}$ model. With this complete dataset, the DDE and ULA are detected at $\simeq 4\sigma$ and $\simeq 2\sigma$, respectively. We discuss a possible particle physics realization of this model, with a dark confining gauge sector and its associated axion, although embedding the full details within microphysics remains an urgent open question. Our scenario will be decisively probed with future CMB and LSS surveys.

We propose a novel codimension-$n$ holography, called cone holography, between a gravitational theory in ($d+1$)-dimensional conical spacetime and a conformal field theory (CFT) on the $(d+1-n)$-dimensional defects. Similar to wedge holography, the cone holography can be obtained by taking the zero-volume limit of holographic defect CFT. Remarkably, it can be regarded as a holographic dual of the edge modes on the defects. For one class of solutions, we prove that the cone holography is equivalent to $\mathrm{AdS}/\mathrm{CFT}$, by showing that the classical gravitational action and thus the CFT partition function in large $N$ limit are the same for the two theories. In general, cone holography and $\mathrm{AdS}/\mathrm{CFT}$ are different due to the infinite towers of massive Kaluza-Klein modes on the branes. We test cone holography by studying Weyl anomaly, entanglement/Rényi entropy, and correlation functions and find good agreement between the holographic and the CFT results. In particular, the $c$-theorem is obeyed by cone holography. These are strong supports for our proposal. We discuss two kinds of boundary conditions, the mixed boundary condition and Neumann boundary condition, and find that they both define a consistent theory of cone holography. We also analyze the mass spectrum on the brane and find that the larger the tension is, the more continuous the mass spectrum is. The cone holography can be regarded as a generalization of the wedge holography, and it is closely related to the defect CFT, entanglement/Rényi entropy, and AdS/BCFT(dCFT). Here BCFT(dCFT) means a conformal field theory defined in a manifold with a boundary (defect). Thus, it is expected to have a wide range of applications.

We compute holographic complexity for the nonsupersymmetric Janus deformation of ${\mathrm{AdS}}_5$ according to the volume conjecture. The result is characterized by a power-law ultraviolet divergence. When a ball-shaped region located around the interface is considered, a subleading logarithmic divergent term and a finite part appear in the corresponding subregion volume complexity. Using two different prescriptions to regularize the divergences, we find that the coefficient of the logarithmic term is universal.

We suggest a new spin-4 self-dual model (parity singlet) and a new spin-4 parity doublet in $D=2+1$. They are of higher order in derivatives and are described by a totally symmetric rank-4 tensor without extra auxiliary fields. Despite the higher derivatives they are ghost free. We find gauge invariant field combinations which allow us to show that the canonical structure of the spin-4 (spin-3) models follows the same pattern of its spin-2 (spin-1) counterpart after field redefinitions. For $s=1$, 2, 3, 4, the spin-$s$ self-dual models of order $2s-1$ and the doublet models of order $2s$ can be written in terms of three gauge invariants. The cases $s=3$ and $s=4$ suggest a restricted conformal higher spin symmetry as a principle for defining linearized topologically massive gravity and linearized “new massive gravity” for arbitrary integer spins. A key role in our approach is played by the fact that the Cotton tensor in $D=2+1$ has only two independent components for any integer spin.

We formulate positivity bounds for scattering amplitudes including exchange of massless particles. We generalize the standard construction through dispersion relations to include the presence of a branch cut along the real axis in the complex plane for the Maldestam variable $s$. In general, validity of these bounds requires the cancellation of divergences in the forward limit of the amplitude, proportional to $t^{-1}$ and $\log (t)$. We show that this is possible in the case of gravitons if one assumes a Regge behavior of the amplitude at high energies below the Planck scale, as previously suggested in the literature, and that the concrete UV behavior of the amplitude is uniquely determined by the structure of IR divergences. We thus extend previous results by including a subleading logarithmic term, which we show to be universal. The bounds that we present here have the potential of constraining very general models of modified gravity and effective field theories of matter coupled to gravitation.