It is well known that the flat Friedmann-Robertson-Walker metric is a special case of Bianchi type I spacetime. In this paper, we use 38 Hubble parameter, $H(z)$, measurements at intermediate redshifts $0.07\le z\le 2.36$ and its joint combination with the latest “joint light curves” (JLA) sample, comprising 740 type Ia supernovae in the redshift range of $z\epsilon [0.01,1.30]$ to constrain the parameters of the Bianchi type I dark energy model. We also use the same datasets to constrain flat a $\mathrm{\Lambda }\mathrm{CDM}$ model. In both cases, we specifically address the expansion rate $H_0$ as well as the transition redshift $z_t$ determinations out of these measurements. In both models, we found that using joint combination of datasets gives rise to lower values for model parameters. Also to compare the considered cosmologies, we have made Akaike information criterion and Bayes factor ($\mathrm{\Psi }$) tests.

The axionlike particle (ALP)-photon mixing in the magnetic field around $\gamma$-ray sources or along the line of sight could induce oscillation between photons and ALPs, which then causes irregularities in the $\gamma$-ray spectra. In this work we search for such spectral irregularities in the spectrum of PKS $2155-304$ using 8.6 years of data from the Fermi Large Area Telescope (Fermi-LAT). No significant evidence for the presence of ALP-photon oscillation is obtained, and the parameter space of ALPs is constrained. The exclusion region sensitively depends on the poorly known magnetic field of the host galaxy cluster of PKS $2155-304$. If the magnetic field is as high as $\sim 10\mu \mathrm{G}$, the “holelike” parameter region allowed in Ref. [1] can be ruled out.

During a de Sitter stage of expansion, the spectator fields of different spin are constrained by the critical density bound and by further requirements determined by their specific physical nature. The evolution of spectator electric fields in conformally flat background geometries is occasionally concocted by postulating the existence of ad hoc currents, but this apparently innocuous trick violates the second law of thermodynamics. Such a problem occurs, in particular, for those configurations (customarily employed for the analysis of the Schwinger effect in four-dimensional de Sitter backgrounds) leading to an electric energy density which is practically unaffected by the expansion of the underlying geometry. The obtained results are compared with more mundane situations where Joule heating develops in the early stages of a quasi-de Sitter phase.

With developing a scheme to determine the thermal width of a pion in a medium, we investigate the shear and bulk viscosities and their ratios to entropy density. We calculate the temperature ($T$)-dependence of the pion mass and decay constant via the Dyson-Schwinger equations of QCD and get the pion thermal width with the QCD approach. We obtain then the $T$-dependence of the viscosities, especially a novel feature of the bulk viscosity, via the continuum QCD approach. The novel concavo-convex behavior of the bulk viscosity to entropy density ratio against the temperature is a demonstration of the QCD phase transitions.

Dark matter that interacts with the Standard Model by exchanging photons through higher multipole interactions occurs in a wide range of both strongly and weakly coupled hidden sector models. We study the collider detection prospects of these candidates, with a focus on Majorana dark matter that couples through the anapole moment. The study is conducted at the effective field theory level with the mono-$Z$ signature incorporating varying levels of systematic uncertainties at the high-luminosity LHC. The projected collider reach on the anapole moment is then compared to the reach coming from direct detection experiments like LZ. Finally, the analysis is applied to a weakly coupled completion with leptophilic dark matter.

We analyze neutrino mass matrices having one texture zero, assuming that the neutrino mixing matrix has either its first (${\mathrm{TM}}_1$) or second (${\mathrm{TM}}_2$) column identical to that of the tribimaximal mixing matrix. We found that all six possible one texture-zero neutrino mass matrices are compatible with the present neutrino oscillation data when combined with ${\mathrm{TM}}_1$ or ${\mathrm{TM}}_2$ mixing. These textures have interesting predictions for the presently unknown parameters such as the effective Majorana neutrino mass, the Dirac $CP$ violating phase, and the neutrino mass scale. We also present a way to theoretically realize some of these textures using $A_4$ symmetry within the framework of the type-$\mathrm{I}+\mathrm{II}$ seesaw mechanism.

The LEP experiment at CERN provided accurate measurements of the $Z$ neutral gauge boson properties. Although all measurements agree well with the standard model (SM) predictions, the forward backward asymmetry of the bottom-quark remains almost $3\sigma$ away from the SM value. We proposed that this anomaly may be explained by the existence of a new $U(1{)}_D$ gauge boson, which couples with opposite charges to the right-handed components of the bottom and charm quarks. Cancellation of gauge anomalies demands the presence of a vector-like singlet charged lepton as well as a neutral Dirac (or Majorana) particle that provides a dark matter candidate. Constraints from precision measurements imply that the mass of the new gauge boson should be around 115 GeV. We discuss the experimental constraints on this scenario, including the existence of a di-jet resonance excess at an invariant mass similar to the mass of this new gauge boson, observed in boosted topologies at the CMS experiment.

In the general Higgs portal-like models, the extra neutral scalar, $S$, can mix with the Standard Model (SM) Higgs boson, $H$. We perform an exploratory study focusing on the direct search for such a light singlet $S$ at the Large Hadron Collider (LHC). After careful study of the SM background, we find the process $pp\to t\overline{t}S$ followed by $S\to b\overline{b}$ can be used to investigate $S$ with mass in the $20<M_S<100\mathrm{GeV}$ range, which has not been well explored at the LHC. The signal significance becomes meaningful with a luminosity around a few ${\text{ab}}^{-1}$. Also, we study the prospects of finding the light scalar at the future 100 TeV $pp$ collider, the $Z$ and Higgs factories. With similar luminosity, the current Large Electron-Positron Collider (LEP) limits on the mixing between $S$ and $H$ can be improved by at least one or two order of magnitudes.

We point out that 7 keV axino dark matter (DM) in the R-parity violating (RPV) supersymmetric (SUSY) Dine-Fischler-Srednicki-Zhitnitsky axion model can simultaneously reproduce the 3.5 keV x-ray line excess and evade stringent constraints from the $\mathrm{Ly}\text{−}\alpha$ forest data. Peccei-Quinn symmetry breaking naturally generates both the TeV-scale $\mu$ term and the MeV-scale RPV term. The RPV term introduces a tiny axino-neutrino mixing and provides axino DM as a variant of the sterile neutrino DM explaining the 3.5 keV x-ray line excess. Axinos are produced by freeze-in processes via the $\mu$ term. The resultant phase space distribution tends to be colder than the Fermi-Dirac distribution. The inherent entropy production from late-time saxion decay makes axinos even colder than those without saxion decay. The resultant axino DM takes the correct relic density and is compatible even with the latest and strongest constraint from the Ly-$\alpha$ forest data.

Using Monte Carlo simulations with overrelaxation, we have equilibrated lattices up to $\beta =2.928$, size $60^4$, for pure SU(2) lattice gauge theory with the Wilson action. We calculate topological charges with the standard cooling method and find that they become more reliable with increasing $\beta$ values and lattice sizes. Continuum limit estimates of the topological susceptibility $\chi$ are obtained of which we favor ${\chi }^{1/4}/T_c=0.643(12)$, where $T_c$ is the SU(2) deconfinement temperature. Differences between cooling length scales in different topological sectors turn out to be too small to be detectable within our statistical errors.

We study the semileptonic decays of the $B_c$ meson into final charmonium states within the standard model and beyond. The relevant hadronic transition form factors are calculated in the framework of the covariant confined quark model developed by us. We focus on the tau mode of these decays, which may provide some hints of new physics effects. We extend the standard model by assuming a general effective Hamiltonian describing the $b\to c\tau \nu$ transition, which consists of the full set of the four-fermion operators. We then obtain experimental constraints on the Wilson coefficients corresponding to each operator and provide predictions for the branching fractions and other polarization observables in different new physics scenarios.

We present a strong coupling constant extraction at next-to-leading order QCD accuracy using ATLAS $Z+2$,3,4 jets data. This is the first extraction using processes with a dependency on high powers of the coupling constant. We obtain values of the strong coupling constant at the $Z$ mass compatible with the world average and with uncertainties commensurate with other next-to-leading order extractions at hadron colliders. Our most conservative result for the strong coupling constant is ${\alpha }_S(M_Z)=0.1178_{-0.0043}^{+0.0051}$.

We elucidate that the phase diagram of massless $N$-flavor QCD under a ${\mathbb{Z}}_N$ flavor-twisted boundary condition (massless ${\mathbb{Z}}_N$-QCD) is constrained by a ’t Hooft anomaly involving two-form gauge fields. As a consequence, massless ${\mathbb{Z}}_N$-QCD turns out to realize persistent order at any temperature and quark chemical potential; namely, the symmetric and gapped phase is strictly forbidden. This is the first result on the finite-$(T,\mu )$ phase diagram in QCD-type theories based on anomaly matching related to center and discrete axial symmetries.

By analyzing a data sample of $2.93{\mathrm{fb}}^{-1}$ collected at $\sqrt{s}=3.773\mathrm{GeV}$ with the BESIII detector operated at the BEPCII storage rings, we measure the branching fractions $\mathcal{B}(D^0\to \omega \eta )=(2.15\pm 0.17_{\mathrm{stat}}\pm 0.15_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to \eta {\pi }^0)=(0.58\pm 0.05_{\mathrm{stat}}\pm 0.05_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to {\eta }^{\prime }{\pi }^0)=(0.93\pm 0.11_{\mathrm{stat}}\pm 0.09_{\mathrm{sys}})\times {10}^{-3}$, $\mathcal{B}(D^0\to \eta \eta )=(2.20\pm 0.07_{\mathrm{stat}}\pm 0.06_{\mathrm{sys}})\times {10}^{-3}$ and $\mathcal{B}(D^0\to {\eta }^{\prime }\eta )=(0.94\pm 0.25_{\mathrm{stat}}\pm 0.11_{\mathrm{sys}})\times {10}^{-3}$. We note that $\mathcal{B}(D^0\to \omega \eta )$ is measured for the first time and that $\mathcal{B}(D^0\to \eta \eta )$ is measured with much improved precision.

The electrical neutrality of the neutron is linked to the electric charge quantization. It is not understood yet if the electric charge is quantized or not. Since the discovery of the neutron, many attempts have been made to measure its electric charge $q_n$ directly and indirectly. We present a method to search for a possible $q_n$ by means of an optical setup using ultracold neutrons. In a first run, a statistical sensitivity of $\delta q_n=2.4\times {10}^{-20}e/\sqrt{\mathrm{day}}$ is achieved. Possible improvements to increase this sensitivity down to $\delta q_n\approx 1\times {10}^{-21}e/\sqrt{\mathrm{day}}$ are found and discussed.

We clarify the relation between the Noether charge associated to an arbitrary vector field and the equations of motion by revisiting Wald formalism. For a timelike Killing vector, aspects of the Noether charge suggest that it is dual to the heat current in the boundary for general holographic theories. For a spacelike Killing vector, we interpret the Noether charge (at the transverse direction) as shear stress of the dual fluid so we can compute the ratio of shear viscosity to entropy density by simply using the infrared data on the black hole event horizon. We test the new method for Einstein gravity and Gauss-Bonnet gravity and find that it produces correct results for both cases even in the presence of additional matter fields.

General Relativity is known to produce singularities in the potential generated by a point source. Our universe can be modeled as a de Sitter (dS) metric and we show that ghost-free infinite derivative gravity (IDG) produces a nonsingular potential around a dS background, while returning to the GR prediction at large distances. We also show that although there are an apparently infinite number of coefficients in the theory, only a finite number actually affect the predictions. By writing the linearized equations of motion in a simplified form, we find that at distances below the Hubble length scale, the difference between the IDG potential around a flat background and around a de Sitter background is negligible.

Motivated by multiple phenomenological considerations, we perform the first search for the existence of a $\overline{b}\overline{b}bb$ tetraquark bound state with a mass below the lowest noninteracting bottomonium-pair threshold using the first-principles lattice nonrelativistic QCD methodology. We use a full $S$-wave color/spin basis for the $\overline{b}\overline{b}bb$ operators in the three $0^{++}$, $1^{+-}$ and $2^{++}$ channels. We employ four gluon field ensembles at multiple lattice spacing values ranging from $a=0.06–0.12\mathrm{fm}$, all of which include $u$, $d$, $s$ and $c$ quarks in the sea, and one ensemble which has physical light-quark masses. Additionally, we perform novel exploratory work with the objective of highlighting any signal of a near threshold tetraquark, if it existed, by adding an auxiliary potential into the QCD interactions. With our results we find no evidence of a QCD bound tetraquark below the lowest noninteracting thresholds in the channels studied.

We present an improved study of the electromagnetic form factors of the nucleon and of the Roper-nucleon transition using an extended version of the effective action of soft-wall AdS/QCD. We include novel contribution from additional nonminimal terms, which do not renormalize the charge and do not change the normalization of the corresponding form factors, but the inclusion of these terms results in an important contribution to the momentum dependence of the form factors and helicity amplitudes.