A modification of the Skyrme model has been recently proposed, which admits an exact self-dual sector by the introduction of six scalar fields assembled in a symmetric, positive, and invertible $3\times 3$ matrix $h$. In this paper we study soft manners of breaking the self-duality of that model. The crucial observation is that the self-duality equations impose distinct conditions on the three eigenvalues of $h$, and on the three fields lying in the orthogonal matrix that diagonalizes $h$. We keep the self-duality equations for the latter, and break those equations associated to the eigenvalues. We perform the breaking by the addition of kinetic and potential terms for the $h$ fields, and construct numerical solutions using the gradient flow method to minimize the static energy. It is also shown that the addition of just a potential term proportional to the determinant of $h$ leads to a model with an exact self-dual sector and with self-duality equations differing from the original ones by just an additional coupling constant.

This work continues the investigation of radiation phenomena from emitter-field interactions, extending our earlier study [J.-T. Hsiang and B. L. Hu, Physics 1, 430 (2019).] of quantum radiation from a stationary emitter’s internal degree of freedom, modeled by a harmonic oscillator, to the emittance of classical radiation. By assuming that the emitter interacts with a quantum scalar field initially in a coherent state, we show how a stochastic component of the internal dynamics of the emitter arises from the vacuum fluctuations of the field, resulting in the emittance of quantum radiation, whose reaction induces quantum dissipation in the internal dynamics. We also show how the deterministic mean field drives the internal classical mean component to emit classical radiation and receive classical radiation reaction. Both components are statistically distinct and fully decoupled. It is clearly seen that the effects of the vacuum fluctuations of the field are matched with those of quantum radiation reaction, not with classical radiation reaction, as the folklore goes. In contrast to the quantum component of the emitter’s internal dynamics, which always equilibrates, the relaxation dynamics of the classical component largely depends on the late-time behavior of the mean field. For the values of the parameters defining the coherent state of the field much greater than unity, if the mean field remains periodic, then the internal dynamics of the emitter will appear classical and periodic. If the mean field diminishes with time, then the classical component of the emitter’s internal dynamics subsides but the quantum component will abide and dynamically equilibrate. This also explains why quantum radiation from a stationary emitter is not observed, and a probe located far away only sees classical radiation. Our analysis therefore paints a continuum landscape starting from vacuum fluctuations in the quantum field to classical radiation and radiation reaction.

We study the structure of the higher-curvature gravitational densities that are induced from holographic renormalization in ${\mathrm{AdS}}_{d+1}$. In a braneworld construction, such densities define a $d$-dimensional higher-curvature gravitational theory on the brane, which in turn is dual to a ($d-1$)-dimensional CFT living at its boundary. We show that this ${\mathrm{CFT}}_{d-1}$ satisfies a holographic $c$-theorem in general dimensions (different than the $g$-theorem of holographic boundary CFTs), since at each and every order the higher-curvature densities satisfy $c$-theorems on their own. We find that, in these densities, the terms that affect the monotonicity of the holographic $c$-function are algebraic in the curvature, and do not involve covariant derivatives of the Riemann tensor. We examine various other features of the holographically induced higher-curvature densities, such as the presence of reduced-order traced equations, and their connection to Born-Infeld-type gravitational Lagrangians.

Toward understanding of dark energy, we propose a novel method to directly produce a chameleon particle and force its decay under controlled gas pressure in a laboratory-based experiment. Chameleon gravity, characterized by its varying mass depending on its environment, could be a source of dark energy, which is predicted in modified gravity. A remarkable finding is a correspondence between the varying mass and a characteristic pressure dependence of a stimulated photon-photon scattering rate in a dilute gas surrounding a focused photon-beam spot. By observing a steep pressure dependence in the scattering rate, we can directly extract the characteristic feature of the chameleon mechanism. As a benchmark model of modified gravity consistent with the present cosmological observations, a reduced $F(R)$ gravity is introduced in the laboratory scale. We then demonstrate that the proposed method indeed enables a wide-ranging parameter scan of such a chameleon model with the varying mass around $(0.1-1)(\mu \mathrm{eV})$ by controlling pressure values.

Both the fluctuations of the onboard lasers and clocks in a space-based gravitational wave interferometer can significantly decrease the sensitivity of the detector to an unacceptable performance level. Implementing a self-referenced optical frequency comb (OFC) driven by the onboard laser can establish the relationship between these two phase fluctuations. This makes a modification of the time-delay interferometry (TDI) combinations, which is originally used to reduce the larger laser phase noise, to simultaneously reduce the phase noises of the onboard lasers and clocks. At present, only a few typically modified combinations with an OFC have been constructed. In this work, we develop a general method obtaining all of the modified TDI combinations, the core of which is a skillful substitution of the time-delay operator. More specifically, with a skillful substitution, one can directly derive the modified TDI combination from an arbitrary TDI combination. This method avoids studying how to reconstruct the modified TDI combination with an OFC.

We explore the possibility of a scalar field driving ekpyrotic contraction through a noncanonical kinetic energy density rather than a negative potential. We find that this kinetically driven ekpyrosis (“k-ekpyrosis”) can be achieved in a variety of models, including scalar field theories with power-law, polynomial, or Dirac-Born-Infeld (DBI-)like kinetic terms in the action. Of these examples, the ekpyrotic phase is best sustained in power-law models, which can generate large and constant equation-of-state parameters, followed by DBI-like models, which can exhibit dynamical attractors toward similarly large equations of state. We show that for a broad class of theories including these examples, phases of k-ekpyrosis are accompanied by preceding or concurrent phases of superluminality.

We investigate the flow around a black hole moving through a cloud of self-interacting scalar dark matter. We focus on the large scalar mass limit, with quartic self-interactions, and on the subsonic regime. We show how the scalar field behaves as a perfect gas of adiabatic index ${\gamma }_{\mathrm{ad}}=2$ at large radii while the accretion rate is governed by the relativistic regime close to the Schwarzschild radius. We obtain analytical results thanks to large-radius expansions, which are also related to the small-scale relativistic accretion rate. We find that the accretion rate is greater than for collisionless particles, by a factor $c/c_s\gg 1$, but smaller than for a perfect gas, by a factor $c_s/c\ll 1$, where $c_s$ is the speed of sound. The dynamical friction is smaller than for a perfect gas, by the same factor $c_s/c\ll 1$, and also smaller than Chandrasekhar’s result for collisionless particles, by a factor $c_s/(cC)$, where $C$ is the Coulomb logarithm. It is also smaller than for fuzzy dark matter, by a factor $v_0/c\ll 1$.

We use redshift-space galaxy clustering data from the BOSS survey to constrain local primordial non-Gaussianity (LPNG). This is of particular importance due to the consistency relations, which imply that a detection of LPNG would rule out all single-field inflationary models. Our constraints are based on the consistently analyzed redshift-space galaxy power spectra and bispectra, extracted from the public BOSS data with optimal window-free estimators. We use a complete perturbation theory model including all one-loop power spectrum corrections generated by LPNG. Our constraint on the amplitude of the local non-Gaussian shape is $f_{\mathrm{NL}}^{\text{local}}=-33\pm 28$ at 68% C.L., yielding no evidence for primordial non-Gaussianity. The addition of the bispectrum tightens the $f_{\mathrm{NL}}^{\text{local}}$ constraints from BOSS by 20%, and allows breaking of degeneracies with non-Gaussian galaxy bias. These results set the stage for the analysis of future surveys, whose larger volumes will yield significantly tighter constraints on LPNG.

We study the redshift-space fluctuations induced by a stochastic gravitational wave background (SGWB) via the Sachs-Wolfe effect. The redshift-space fluctuations can be encapsulated in a line-of-sight integral that is useful for studying the imprint of short-wavelength gravitational waves on the cosmic microwave background (CMB) anisotropy. We thus derive constraints on the SGWB from small-scale CMB anisotropy measurements. Our results reproduce the constraint on the short-wavelength SGWB, previously derived from the Planck and BICEP/Keck array CMB data with a CMB Boltzmann numerical code. Furthermore, we improve the constraint and extend it to shorter wavelengths by using the CMB measurements made by the Atacama Cosmology Telescope and the South Pole Telescope. Also, the integral provides us with a precise redshift fluctuation correlation between a pair of pulsars in pulsar timing measurements, which conveniently incorporates the effect of the pulsar term into a small-angle correlation. We further discuss the observation of pulsar pairs in globular clusters to look for this small-angle correlation.

Gravitational-wave observations of binary neutron star mergers and their electromagnetic counterparts provide an independent measurement of the Hubble constant, $H_0$, through the standard-sirens approach. Current methods of determining $H_0$, such as measurements from the early Universe and the local distance ladder, are in tension with one another. If gravitational waves are to break this tension, a thorough understanding of systematic uncertainties of gravitational-wave observations is required. To accurately estimate the properties of gravitational-wave signals measured by LIGO and Virgo, we need to understand the characteristics of the detector noise. Non-Gaussian transients in the detector data and rapid changes in the instrument, known as nonstationary noise, can both add a systematic uncertainty to inferred results. We investigate how nonstationary noise affects the estimation of the luminosity distance of the source and therefore of $H_0$. Using a population of 100 simulated binary neutron star signals, we show that nonstationary noise can bias the estimation of the luminosity distance by up to 6.8%. However, only $\sim 15\%$ of binary neutron star signals would be affected around their merger time with nonstationary noise at a similar level to that seen in the first half of LIGO-Virgo’s third observing run. Comparing the expected bias to other systematic uncertainties, we argue that nonstationary noise in the current generation of detectors will not be a limiting factor in resolving the tension on $H_0$ using standard sirens. Although, evaluating nonstationarity in gravitational-wave data will be crucial to obtain accurate estimates of $H_0$.

We provide a linear analysis on normal modes of the spin Boltzmann equation proposed by Weickgenannt et al. [Phys. Rev. D 104, 016022 (2021)], where the nondiagonal or polarized part of the transition rate is neglected to ensure the Hermitian property of a linearized collision operator. As an instrumental element of spin kinetic theory, the conservation of total angular momentum is explicitly considered; thus, our analysis is relevant to the recent investigation on the issue of local spin polarization. By treating the linearized collision operator as an evolution operator, solving the normal modes turns out to be a degenerate perturbation problem in quantum mechanics. The dispersion relations of spinless modes are in accordance with well-known calculations, while the frequencies of spin modes are also determined up to second-order in wave vectors; the second-order expressions are only formal solutions to be further determined. Moreover, the relaxation of spin density is related to our linear mode analysis, which shall play a big role in investigating the issues of the local spin polarization in the relativistic heavy-ion collisions.

We study the geometric structure of the physical region of neutrino mixing matrices as part of the unit ball of the spectral norm. Each matrix from the geometric region is a convex combination of unitary PMNS matrices. The disjoint subsets corresponding to a different minimal number of additional neutrinos are described as relative interiors of faces of the unit ball. We determined the Carathéodory’s number showing that at most four unitary matrices of dimension three are necessary to represent any matrix from the neutrino geometric region. For matrices which correspond to scenarios with one and two additional neutrino states, the Carathéodory’s number is two and three, respectively. Further, we discuss the volume associated with different mathematical structures, particularly with unitary and orthogonal groups, and the unit ball of the spectral norm. We compare the obtained volumes to the volume of the region of physically admissible mixing matrices for both the $CP$-conserving and $CP$-violating cases in the present scenario with three neutrino families and scenarios with the neutrino mixing matrix of dimension higher than three.

The CDF Collaboration at Fermilab has recently reported a new precision measurement of the $W$ boson mass showing a substantial $7\sigma$ deviation from the Standard Model prediction. Moreover, Fermilab has recently confirmed the longstanding tension in the $(g-2{)}_{\mu }$ measurement. We propose a unified solution to these deviations within the simplest radiative neutrino mass model; the Zee model. Our analysis establishes nontrivial links between the origin of neutrino mass, the $(g-2{)}_{\mu }$ anomaly, and the $W$ boson mass shift while being consistent with lepton flavor violation and all other experimental constraints. We find that the mass spectrum of the physical scalars must be hierarchical to be consistent with the $W$ boson mass shift; remarkably, this is also the key to resolving the $(g-2{)}_{\mu }$ tension. Furthermore, this mass splitting offers a unique same-sign dimuon signal through which our model can be tested at the LHC.

We present the differential predictions for the rapidity distribution of a pair of leptons through the Drell-Yan (DY) process at the LHC taking into account the soft-virtual (SV) as well as next-to-soft-virtual (NSV) resummation effects in QCD perturbation theory to next-to-next-to-leading-order plus next-to-next-to-leading-logarithmic ($\mathrm{NNLO}+\overline{\mathrm{NNLL}}$) accuracy. We perform the resummation in two-dimensional Mellin space using our recent formalism [A. H. Ajjath et al., Phys. Rev. D 103, L111502 (2021)] by limiting ourselves to contributions only from quark-antiquark ($q\overline{q}$) initiated channels. The resummed corrections to the fixed-order results are computed through a matched formula using the minimal prescription procedure. We find that the resummation at next-to-leading-logarithmic (next-to-next-to-leading-logarithmic) level brings about 3.98% (1.24%) corrections. We also observe that the sensitivity to the renormalization scale gets improved substantially by the inclusion of NSV resummed predictions at $\overline{\mathrm{NNLL}}$ accuracy. Further, the lack of quark gluon ($qg$) initiated contributions to the NSV part in the $\overline{\mathrm{NNLL}}$ resummed predictions leaves large factorization scale dependence, indicating their importance at NSV level as we go to higher orders in perturbation theory.

We calculate the $W$-exchange contribution to the ${\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+(\prime )}{\pi }^{+}$ decay using light-cone sum rules. The two-particle light-cone distribution amplitudes of the pion are used as nonperturbative input for the sum rules calculation, and the perturbative kernel is calculated at the leading order. We obtain the corresponding decay branching fractions by combining our $W$-exchange amplitudes with the factorizable amplitudes given by various theoretical methods from the literature. It is shown that with the factorizable amplitudes from heavy quark effective theory, we obtain the branching fraction ratio $\mathcal{B}({\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+\prime }{\pi }^{+})/\mathcal{B}({\mathrm{\Xi }}_{cc}^{++}\to {\mathrm{\Xi }}_c^{+}{\pi }^{+})=1.42\pm 0.78$, which is consistent with the experimental value of $1.41\pm 0.17\pm 0.1$.

We perform a global fit of electroweak data within the Standard Model, using state-of-the art experimental and theoretical results, including a determination of the electromagnetic coupling at the electroweak scale based on recent lattice calculations. In addition to the posteriors for all parameters and observables obtained from the global fit, we present indirect determinations for all parameters and predictions for all observables. Furthermore, we present full predictions, obtained using only the experimental information on Standard Model parameters, and a fully indirect determination of Standard Model parameters using only experimental information on electroweak data. Finally, we discuss in detail the compatibility of experimental data with the Standard Model and find a global p-value of 0.5.

The recently released images of the supermassive black holes in the M87 galaxy and the galaxy of our own make probing black hole spacetimes and testing general relativity (GR) possible. The violation of equatorial reflection symmetry of black hole spacetimes is clearly a smoking gun of physics beyond GR. In this paper, we place constraints on the violation of black hole reflection symmetry using the bounds on the ring size of the $\mathrm{Sgr}{\mathrm{A}}^{*}$ black hole images, which are consistent with the critical curve radius predicted in GR within $\sim 10\%$. Adopting a theory-agnostic framework, we consider a Kerr-like metric in which the violation of reflection symmetry is parametrized by a single parameter, without altering the multipoles of the black hole. The critical curves are always vertically symmetric due to the existence of hidden symmetry associated with the Killing tensor, even though the spacetime is reflection asymmetric. We find that the size of critical curves is sensitive to the amount of reflection symmetry being violated, and place the first constraints on the parameter space of the model using the $\mathrm{Sgr}{\mathrm{A}}^{*}$ images.

We investigate the effects ultralight bosonic field dark matter may have on the dynamics of unstable differentially rotating neutron stars prone to the bar-mode instability. To this aim we perform numerical simulations in general relativity of rotating neutron stars accreting an initial spherically symmetric bosonic field cloud, solving the Einstein-(complex, massive) Klein-Gordon-Euler and the Einstein-(complex) Proca-Euler systems. We find that the presence of the bosonic field can critically modify the development of the bar-mode instability of neutron stars, depending on the total mass of the bosonic field and on the boson particle mass. In some cases, the accreting bosonic field can even quench the dominant $\ell =m=2$ mode of the bar-deformation by dynamically forming a mixed (fermion-boson) star that retains part of the angular momentum of the original neutron star. However, the mixed star undergoes the development of a mixed bar that leads to significant gravitational-wave emission, substantially different to that of the isolated neutron star. Our results indicate that dark-matter accretion in neutron stars could change the frequency of the expected emission of the bar-mode instability, which would have an important impact on ongoing searches for continuous gravitational waves.