In an axiverse with numerous axions, the cosmological moduli problem poses a significant challenge because the abundance of axions can easily exceed that of dark matter. The well-established stochastic axion scenario offers a simple solution, relying on relatively low-scale inflation. However, axions are typically subject to mixing due to mass and kinetic terms, which can influence the solution using stochastic dynamics. Focusing on the fact that the QCD axion has a temperature-dependent mass, unlike other axions, we investigate the dynamics of the QCD axion and another axion with mixing. We find that the QCD axion abundance is significantly enhanced and becomes larger than that of the other axion for a certain range of parameters. This enhancement widens the parameter regions accounting for dark matter. In addition, we also find a parameter region in which both axions have enhanced abundances of the same order, which result in multicomponent dark matter.

We revisit the various measures of practical naturalness for models of weak-scale supersymmetry (SUSY) including: 1. electroweak (EW) naturalness; 2. naturalness via sensitivity to high-scale (HS) parameters [Ellis-Enquist-Nanopoulos-Zwirner/Barbieri-Giudice (EENZ/BG)]; 3. sensitivity of Higgs soft terms due to high-scale radiative corrections; and 4. stringy naturalness (SN) from the landscape. The EW measure is most conservative and seems unavoidable. We debut a new numerical routine for calculating the EENZ/BG measure from any SUSY Les Houches Accord file. We implement a careful analysis and comparison of these measures in the mSUGRA/CMSSM and NUHMi model parameter spaces and via parameter-space scans. We demonstrate the reasoning behind why—and the extent to which—the EENZ/BG and HS measures overestimate the degree of fine-tuning. We find the overestimation can range up to a factor of over 1000. While EENZ/BG and HS have ambiguities when applied to models such as anomaly- and mirage-mediation, the EW measure has no such ambiguity and so we display the natural parameter space regions of these models. SN depends on the landscape distribution of soft terms, but is closely related to EW naturalness via the atomic principle.

Nelson-Barr models solve the strong $CP$ problem based on spontaneous $CP$ violation and generically require vectorlike quarks (VLQs) mixing with standard quarks to transmit the $CP$ violation. We devise an explicit parametrization for the case of two VLQs of either down or up type and quantitatively study several aspects including the hierarchy of the VLQ Yukawas and their irreducible contribution to $\overline{\theta }$. In particular, with the use of the parametrization, we show that a big portion of the parameter space for two up-type VLQs at the TeV scale is still allowed by the constraint on $\overline{\theta }$, although this case had been previously shown to be very restricted based on estimates.

We determine the axial, scalar and tensor isovector charges of the nucleon, sigma and cascade baryons as well as the difference between the up and down quark masses, $m_u-m_d$. We employ gauge ensembles with $N_f=2+1$ nonperturbatively improved Wilson fermions at six values of the lattice spacing in the range $a\approx (0.039–0.098)\mathrm{fm}$, generated by the coordinated lattice simulations (CLS) effort. The pion mass $M_{\pi }$ ranges from around 430 MeV down to a near physical value of 130 MeV and the linear spatial lattice extent $L$ varies from $6.5M_{\pi }^{-1}$ to $3.0M_{\pi }^{-1}$, where $L{M}_{\pi }\ge 4$ for the majority of the ensembles. This allows us to perform a controlled interpolation/extrapolation of the charges to the physical mass point in the infinite volume and continuum limit. Investigating SU(3) flavor symmetry, we find moderate symmetry breaking effects for the axial charges at the physical quark mass point, while no significant effects are found for the other charges within current uncertainties.

We discuss the chiral fermion in the Hamiltonian formalism of lattice gauge theory. Although the naive chiral charge operator does not commute with the Hamiltonian, the commutable one can be defined for the overlap fermion. The eigenvalues of the energy and the chiral charge can be defined simultaneously. We study how the eigenvalue spectrum reflects chiral properties of systems, such as a chiral chemical potential and the axial anomaly. We also show that the Wilson fermion is a chiral fermion in one dimension.

I consider the frame dependence of QCD bound states in the presence of a confining, spatially constant gluon field energy density. The states are quantized at equal time in $A^0=0$ (temporal) gauge. I derive the frame dependence of the wave functions, and demonstrate the Lorentz covariance of the electromagnetic (transition) form factors for states of any spin. The wave functions of $J^{PC}=0^{-+}$ states with CM momentum $\mathit{P}\ne 0$ are considered in some detail, verifying their local normalizability and the expected frame dependence of the bound state energy.

In this study, we examine closely the impact of the post-CT18 LHC Drell-Yan data on parton distribution functions (PDFs) in the general CTEQ-TEA global analysis framework. We compare the two main theoretical predictions, the MCFM fixed order calculations at next-to-next-to-leading order (NNLO) and the ResBos2 NNLO matched to $q_T$ resummation up to next-to-next-to-next-to-leading logarithmic (N3LL) level. We find that the overall inclusive cross sections agree well but the fiducial distributions can differ at a percent level. We mainly discuss the result of the ResBos2 resummation calculation which yields a smaller Monte Carlo uncertainty, and a better description to the post-CT18 LHC Drell-Yan data. We find that the majority of post-CT18 LHC Drell-Yan data are consistent with the ATLAS 7 TeV $W$, $Z$ data, which were included in the CT18A, but not CT18, fit and increases the strange-quark distribution at the small $x$ region. The noticeable exception is that the ATLAS and LHCb 8 TeV $W$ data pull $d(\overline{d})$ quark PDFs to the opposite direction with respect to the ATLAS 7 TeV $W$, $Z$ data. The inclusion of these post-CT18 LHC Drell-Yan datasets in the CTEQ-TEA global analysis is to update the CT18 PDFs following similar trends as CT18Z PDFs. The parton luminosities and a few phenomenological implications with the fiducial $W^{\pm },Z$ and inclusive $H,t\overline{t},t\overline{t}H$ productions at the 14 TeV LHC, as examples, are presented.

Parton distribution functions (PDFs) play a central role in calculations for the LHC. To gain a deeper understanding of the emergence and interplay of constraints on the PDFs in the global QCD analyses, it is important to examine the relative significance and mutual compatibility of the experimental datasets included in the PDF fits. Toward this goal, we discuss the $L_2$ sensitivity, a convenient statistical indicator for exploring the statistical pulls of individual datasets on the best-fit PDFs and identifying tensions between competing datasets. Unlike the Lagrange multiplier method, the $L_2$ sensitivity can be quickly computed for a range of PDFs and momentum fractions using the published Hessian error sets. We employ the $L_2$ sensitivity as a common metric to study the relative importance of datasets in the recent ATLAS, CTEQ-TEA, MSHT, and reduced PDF4LHC21 PDF analyses at next-to-next-to-leading-order and approximate next-to-next-to-next-to-leading-order. We illustrate how this method can aid the users of PDFs to identify datasets that are important for a PDF at a given kinematic point, to study quark flavor composition and other detailed features of the PDFs, and to compare the data pulls on the PDFs for various perturbative orders and functional forms. We also address the feasibility of computing the sensitivities using Monte Carlo error PDFs. Together with the article, we present a companion interactive website with a large collection of plotted $L_2$ sensitivities for eight recent PDF releases and a C++ program to plot the $L_2$ sensitivities.

Recently, Jacobson and Visser [Partition Function for a Volume of Space, Phys. Rev. Lett. 130, 221501 (2023).] calculated the quantum partition function of a fixed, finite volume of a region with the topology of a ball in the saddle point approximation within the context of Einstein’s gravity with or without a cosmological constant. The result can be interpreted as the dimension of Hilbert space of the theory. Here we extend their computation to a theory defined in principle with infinitely many powers of curvature in three dimensions. We confirm their result: The partition function of a spatial region in the leading saddle point approximation is given as the exponential of the Bekenstein-Hawking or the Wald entropy of the boundary of the finite spatial region both in the case of zero and finite cosmological constant. In the latter case, the effective Newton’s constant appears in the entropy formula. The calculations lend support to the holographic nature of gravity for finite regions of space with a boundary.

We present the one-loop radiative corrections to the muon decay in ${\mathrm{U}(1)}_z$ extensions of the standard model. We compute the mass of the $W$ boson using those corrections and compare it to an approximation of the complete one-loop prediction implemented in automated computational tools. We point out that the truncation of the complete formulas become unreliable if the mass of the $Z^{\prime }$ boson, corresponding to the new ${\mathrm{U}(1)}_z$ gauge group, is larger than about 1 TeV.

The Hodge dual operator, recently introduced for supermanifolds, is used to reformulate super Yang-Mills and supergravity in $d=4$. We first recall the definition of the Hodge dual operator for flat and curved supermanifolds. Then we show how to recover the usual super-Yang-Mills equations of motion for $N=1,2$ supersymmetry, and the obstacles (as seen from the Hodge dual point of view) in the case $N\ge 3$. We reconsider several ingredients of supergeometry, relevant for a superspace formulation of supergravity, in terms of the Hodge dual operator. Finally we discuss how $d=4$ and $N=1$ supergravity is obtained in this framework.

We present a duality between a particle detector model coupled to the amplitude of a scalar field and one coupled to the field’s derivative in the limit of large energy gaps. We show that the results of the models can be mapped to each other in a one-to-one fashion modulo a rescaling by the detector’s gap. Our analysis is valid for arbitrary scalar fields in curved spacetimes and requires minimal assumptions regarding the detectors. The duality also applies to the case where more than one detector is coupled to the field. This shows that many examples of entanglement harvesting with amplitude coupled Unruh-DeWitt detectors give exactly the same result as derivative coupled detectors that interact with the field in the same region of spacetime.

In the realm of astrophysics, black holes exist within nonvacuum cosmological backgrounds, making it crucial to investigate how these backgrounds influence the properties of black holes. In this work, we first introduce a novel static spherically-symmetric exact solution of Einstein field equations representing a surrounded hairy black hole. This solution represents a generalization of the hairy Schwarzschild solution recently derived using the extended gravitational decoupling method. Then, we discuss how the new induced modification terms attributed to the primary hairs and various background fields affect the geodesic motion in comparison to the conventional Schwarzschild case. Although these modifications may appear insignificant in most cases, we identify specific conditions where they can be comparable to the Schwarzschild case for some particular background fields.

In this work we study the gravitational radiation produced by a Keplerian binary system within the context of very special linear gravity (VSLG), a novel theory of linearized gravity in the framework of very special relativity allowing for a gauge-invariant mass $m_g$ of the graviton. For this task, we exploit effective field theory’s techniques, which require, among others, the calculation of the squared amplitude of the emission process and therefore the polarization sum for VSLG gravitons. Working in the radiation zone and using the standard energy-momentum tensor’s expression for Keplerian binaries, we derive and study the properties of the VSLG energy-loss and period-decrease rates, also verifying they reduce to the correct General Relativity limit when sending $m_g\to 0$. Finally, using astronomical data from the Hulse-Taylor binary and the double pulsar J0737-3039, we obtain an upper bound on the VSLG graviton mass of $m_g\sim {10}^{-21}\mathrm{eV}$ that, while being comparable to bounds obtained in this same way for other massive gravity models, is still weaker than the kinematical bound $\sim {10}^{-22}\mathrm{eV}$ obtained from the combined observation of the astronomical events GW170817 and GRB170817A, which should still hold in VSLG.

Among all the different techniques to derive the Hawking effect, the approach based on gravitational anomaly by Robinson and Wilczek provides a simple and satisfactory origin of the black hole radiation. In this picture, the effective near horizon physics becomes chiral and contains gravitational anomaly. Nevertheless, the underlying description must be generally covariant, and therefore we require a compensating energy-momentum flux whose divergence cancels the anomaly at the horizon. Remarkably, the energy flux associated with the Hawking emission from the horizon exactly cancels the gravitational anomaly and restores the general covariance at the quantum level. In this work, we present a generalization of the original derivation for a stationary axisymmetric black hole solution of any gravity theory which differs perturbatively from general relativity. The crucial input of the calculation is a remarkable simplification of the near horizon geometry and the validity of the zeroth law of black hole mechanics.

A novel generalization of photon surfaces to the case of massive charged particles is given for spacetimes with at least one isometry, including stationary ones. A related notion of glued massive particle surfaces is also defined. These surfaces join worldlines parametrized by a family of independent conserved quantities and naturally arise in integrable spacetimes. We describe the basic geometric properties of such surfaces and their relationship to slice-reducible Killing tensors, illustrating all concepts with a number of examples. Massive particle surfaces have potential applications in the context of uniqueness theorems, Penrose inequalities, integrability, and the description of black-hole shadows in streams of massive charged particles or photons in a medium with an effective mass and charge.

I study the balance law equation of surface charges in the presence of background fields. The construction allows a unified description of Noether’s theorem for both global and local symmetries. From the balance law associated with some of these symmetries, I will discuss generalizations of Wald’s Noether entropy formula and general entropy balance laws on null hypersurfaces based on the null energy conditions, interpreted as an entropy creation term. The entropy is generally the so-called improved Noether charge, a quantity that has recently been investigated by many authors, associated to null future-pointing diffeomorphisms. These local and dynamical definitions of entropy on the black hole horizon differ from the Bekenstein-Hawking entropy through terms proportional to the first derivative of the area along the null geodesics. Two different definitions of the dynamical entropy are identified, deduced from gravity symplectic potentials providing a suitable notion of gravitational flux which vanish on nonexpanding horizons. The first one is proposed as a definition of the entropy for dynamical black holes by Wald and Zhang, and it satisfies the physical process first law locally. The second one vanishes on any cross section of Minkowski’s light cone. I study general properties of its balance law. In particular, I look at first order perturbations around a nonexpanding horizon. Furthermore, I show that the dynamical entropy increases on the event horizon formed by a spherical symmetric collapse between the two stationary states of vanishing flux, i.e., the initial flat light cone and the final stationary black hole. I compare this process to a phase transition, in which the symmetry group of the stationary black hole phase is enlarged by the supertranslations.

In the present work, we study the radial and nonradial perturbative stability of neutron stars in which the matter is disformally coupled to the metric. First, we derive the gravitational and the fluid equations of the neutron star in a static and spherically symmetric background. Then, we calculate the second-order expansion of the action that describes the dynamics of both axial and polar modes. From the resulting expressions, we derive the conditions to avoid gradient and ghost instabilities at the center of the star and at spatial infinity. In addition, a numerical analysis is performed to investigate the stability of a particular model with a constant disformal function denoted as $\mathrm{\Lambda }$ in the whole spacetime. We found that the chosen model is stable against the gradient instability in a small range of the constant $\mathrm{\Lambda }$.

Recently, it has been demonstrated by Comisso and Asenjo that magnetic reconnection processes in the ergosphere of a Kerr black hole can provide us with a promising mechanism for extracting the rotational energy from it. In this paper, we study the energy extraction from the newly proposed rotating regular black holes via this Comisso-Asenjo mechanism. This novel rotating regular black hole has an exponential convergence factor $e^{-k/r}$ on the mass term characterized by the regular parameter $k$ in the exponent. We explore the effects of this regular parameter on the magnetic reconnection as well as other critical parameters determining the Comisso-Asenjo process. The parameter spaces allowing energy extraction to occur are investigated. The power, efficiency, and the power ratio to the Blandford-Znajek mechanism are studied. The results show that the regularity of the rotating black hole has significant effects on the energy extraction via the Comisso-Asenjo mechanism.

The weak gravity conjecture indicates that extremal black holes in the low-energy effective field theory should be able to decay. This criterion gives rise to nontrivial constraints on the coefficients of higher-order derivative corrections to gravity. In this paper, we investigate the tidal deformability of neutral black holes due to higher-order derivative corrections. As a proof of concept, we consider a correction of cubic order in the Riemann curvature tensor. The tidal Love numbers of neutral black holes receive leading-order corrections from higher-order derivative terms, since black holes in pure General Relativity have vanishing tidal Love number. We conclude that the interplay between the tidal deformability of black holes and the weak gravity conjecture provides useful information about the effective field theory.