In this paper, we investigate the braneworld scenario in $f(T)$ gravity with a $K$-field as the background field. We consider various different specific forms of $f(T)$ gravity and $K$-field and find a general way to construct the braneworld model. Based on our solutions, the split of branes is investigated. In addition, the stability of the braneworld is studied by investigating the tensor perturbation of the vielbein.

We analyze the evolution of a Friedmann-Robertson-Walker spacetime within the framework of $f(R)$ metric gravity using an exponential model. We show that $f(R)$ gravity may lead to a vanishing effective cosmological constant in the far future (i.e., $R\to 0$) and yet produce a transient accelerated expansion at present time with a potentially viable cosmological history. This property is reminiscent of quintessence dark energy but contrasts with several $f(R)$ models in that most of them produce a nonvanishing effective cosmological constant asymptotically in time ($R\to 4{\mathrm{\Lambda }}_{\mathrm{eff}}$). We also show that relativistic stars in asymptotically flat spacetimes can be supported within this framework without encountering any singularity, notably in the Ricci scalar $R$.

We show how the basic idea of parabolic Jacobi relaxation can be modified to obtain a new class of hyperbolic relaxation schemes that are suitable for the solution of elliptic equations. Some of the analytic and numerical properties of hyperbolic relaxation are examined. We describe its implementation as a first order system in a pseudospectral evolution code, demonstrating that certain elliptic equations can be solved within a framework for hyperbolic evolution systems. Applications include various initial data problems in numerical general relativity. In particular we generate initial data for the evolution of a massless scalar field, a single neutron star, and binary neutron star systems.

We present a novel theory of gravity by considering an extension of symmetric teleparallel gravity. This is done by introducing, in the framework of the metric-affine formalism, a new class of theories where the nonmetricity $Q$ is nonminimally coupled to the matter Lagrangian. More specifically, we consider a Lagrangian of the form $L\sim f_1(Q)+f_2(Q)L_M$, where $f_1$ and $f_2$ are generic functions of $Q$, and $L_M$ is the matter Lagrangian. This nonminimal coupling entails the nonconservation of the energy-momentum tensor, and consequently the appearance of an extra force. The formulation of the gravity sector in terms of the $Q$ instead of the curvature may result in subtle improvements of the theory. In the context of nonminimal matter couplings, we are therefore motivated to explore whether the new geometrical formulation in terms of the $Q$, when implemented also in the matter sector, would allow more universally consistent and viable realizations of the nonminimal coupling. Furthermore, we consider several cosmological applications by presenting the evolution equations and imposing specific functional forms of the functions $f_1(Q)$ and $f_2(Q)$, such as power-law and exponential dependencies of the nonminimal couplings. Cosmological solutions are considered in two general classes of models, and found to feature accelerating expansion at late times.

We apply the Lagrangian perturbation theory with time-dependent growth functions at second and third order of perturbation with the aim to model the effect of dynamical dark energy on redshift-space distortions. Our fiducial galaxy redshift surveys are modeled after the upcoming SKA and DESI redshift surveys. We include PLANCK CMB priors and the 20% uncertainty on the linear bias parameter, incorporating the unknown instrumentation noise. After the marginalizing, our results show that the constraints on the density parameter could potentially get better than $\sim 1\%$, while the constraints on $w_0$ and $w_{\mathrm{a}}$ could be better than $\sim 5\%$ and $\sim 60\%$, respectively, consistent with works done before. However, the inclusion of time-dependent growth functions would alter the nonlinear power spectrum by as much as $\sim 10\%$. The inclusion of the time-dependent growth functions become crucial as the precision gets better.

We study the extent to which the decay of cold dark matter axions can be probed with forthcoming radio telescopes such as the Square Kilometer Array (SKA). In particular, we focus on signals arising from dwarf spheroidal galaxies, where astrophysical uncertainties are reduced and the expected magnetic field strengths are such that signals arising from axion decay may dominate over axion-photon conversion in a magnetic field. We show that with $\sim 100\mathrm{hr}$ of observing time, SKA could improve current sensitivity by 2–3 orders of magnitude—potentially obtaining sufficient sensitivity to begin probing the decay of cold dark matter axions.

The gauged $U(1{)}_{L_{\mu }-L_{\tau }}$ model can provide for additional contributions to the muon anomalous magnetic moment by means of a loop involving the $Z^{\prime }$ gauge boson. However, the parameter space of such models is severely constrained if one combines the latest muon ($g-2$) data with various neutrino experiments, such as neutrino trident production, $\nu -e$ and $\nu -q$ elastic scattering, etc. In a supersymmetric $U(1{)}_{L_{\mu }-L_{\tau }}$ model, a larger region of parameter space opens up, thus enabling one to explore otherwise forbidden regions of parameter space in nonsupersymmetric models involving the new gauge coupling ($g_X$) and the mass of the $Z^{\prime }$ gauge boson ($M_{Z^{\prime }}$). We show that the minimal model with the minimal supersymmetric Standard Model (MSSM) field content is strongly disfavored from $Z$-boson decay and neutrino data. We also show that the nonminimal model with two extra singlet superfields can lead to correct neutrino masses and mixing involving both tree-level and one-loop contributions. We find that, in this model, both muon ($g-2$) and neutrino data may be simultaneously explained in a parameter region consistent with experimental observations. In addition, we observe that the muon ($g-2$) anomaly can be accommodated even with higher values of electroweak sparticle masses compared to the MSSM. Charged lepton-flavor-violating processes (like $\mu \to e\gamma$, $\tau \to \mu \gamma$, etc.) may have potentially large branching ratios in this scenario. Depending on the magnitude of the supersymmetry contribution to these processes, they may constrain hitherto unconstrained regions of the $M_{Z^{\prime }}-g_X$ parameter space. However, we find that these branching fractions never exceed their upper bounds in a region where both muon ($g-2$) and neutrino oscillation data can be simultaneously accommodated.

A simple regularity in anticipating P-wave excitation energies of states with heavy quarks is noted. It can apply to systems such as the negative-parity ${\mathrm{\Sigma }}_c$, ${\mathrm{\Sigma }}_b$, and ${\mathrm{\Omega }}_c$, $\overline{Q}Q$ quarkonia, and the bottom-charmed meson $B_c$. When one subtracts a term accounting for phenomenological energies of heavy quarks binding with one another in S-waves, the residual excitation energies display an approximately linear behavior in the reduced mass of constituents, all the way from the $\mathrm{\Lambda }$ to the $\mathrm{\Upsilon }$.

Heavy flavor measurements in high multiplicity proton-proton and proton-nucleus collisions at collider energies enable unique insights into their production and hadronization mechanism because experimental and theoretical uncertainties cancel in ratios of their cross sections relative to minimum bias events. We explore such event engineering using the color glass condensate (CGC) effective field theory to compute short-distance charmonium cross sections. The CGC is combined with heavy-quark fragmentation functions to compute $D$-meson cross sections; for the $J/\psi$, hadronization is described employing nonrelativistic QCD (NRQCD) and an improved color evaporation model. Excellent agreement is found between the CGC computations and the LHC heavy flavor data in high multiplicity events. Event engineering in this $\mathrm{CGC}+\mathrm{NRQCD}$ framework reveals a very rapid growth in the fragmentation of the ${}^3{S}_1^{[8]}$ state in rare events relative to minimum bias events.

Statistical average of the axial current is evaluated on the basis of the covariant Wigner function. In the resulting formula, chemical potential $\mu$, angular velocity $\mathrm{\Omega }$ and acceleration $|\mathit{a}|$ enter in combination $\mu \pm (\mathrm{\Omega }\pm i|\mathit{a}|)/2$. The limiting cases of zero mass and zero temperature are investigated in detail. In the zero-mass limit, the axial current is described by a smooth function only at temperatures higher than the Unruh temperature. At zero temperature, the axial current, as a function of the angular velocity and chemical potential, vanishes in a two-dimensional plane region.

Despite the tremendous success of general relativity so far, modified theories of gravity have received increased attention lately, motivated from both theoretical and observational aspects. In particular, gravitational wave observations opened new possibilities for testing the viability of such theories in the dynamical and strong-field regime. One could test each modified theory of gravity against observed data one at a time, though perhaps a more efficient approach would be to first probe gravity in a theory-agnostic way and map such information to that on specific theories afterward. One example of such model-independent tests of gravity with gravitational waves is the parametrized post-Einsteinian formalism, in which one introduces generic parameters in the amplitude and phase that capture non-Einsteinian effects. In this paper, we derive gravitational waveforms from inspiraling compact binaries in various modified theories of gravity that violate at least one fundamental pillar in general relativity, such as the strong equivalence principle, Lorentz and parity invariance, and commutativity of spacetime. We achieve this by first deriving relations between corrections to the waveform amplitude/phase and those to the frequency evolution and Kepler’s third law, since the latter two have already been (or can easily be) derived in several example modified theories of gravity. In particular, such an analysis allows us to derive corrections to the waveform amplitude, which extends many of previous works that focused on deriving phase corrections only. Moreover, we derive modified gravitational waveforms in theories with a varying gravitational constant. In particular, we extend the previous work by introducing two different gravitational constants (the conservative one entering in the binding energy and the dissipative one entering in the gravitational wave luminosity) and allowing masses of binary constituents to also vary with time. We also correct some errors in the previous literature. Our results can be used to improve current analyses of testing general relativity with available gravitational wave data as well as to achieve new projected constraints on various modified theories of gravity with future gravitational wave observations.

The vacuum solution of Einstein’s theory of general relativity provides a rotating metric with a ring singularity, which is covered by the inner and outer horizons and an ergo region. In this paper, we will discuss how ghost-free, quadratic curvature, infinite derivative gravity (IDG) may resolve the ring singularity. In IDG the nonlocality of the gravitational interaction can smear out the delta-Dirac source distribution by making the metric potential finite everywhere including at $r=0$. We show that the same feature also holds for a rotating metric. We can resolve the ring singularity such that no horizons are formed in the linear regime by smearing out a delta-source distribution on a ring. We will also show that the Kerr metric does not solve the full nonlinear equations of motion of ghost-free quadratic curvature IDG.

The exact axisymmetric and static solution of the Einstein equations coupled to the axisymmetric and static gravitating scalar (or phantom) field is presented. The spacetimes modified by the scalar field are explicitly given for the so-called $\gamma$-metric and the Erez-Rosen metric with quadrupole moment $q$, and the influence of the additional deformation parameters ${\gamma }_{*}$ and $q_{*}$ generated by the scalar field is studied. It is shown that the null energy condition is satisfied for the phantom field, but it is not satisfied for the standard scalar field. The test particle motion in both the modified $\gamma$-metric and the Erez-Rosen quadrupole metric is studied; the circular geodesics are determined, and near-circular trajectories are explicitly presented for characteristic values of the spacetime parameters. It is also demonstrated that the parameters ${\gamma }_{*}$ and $q_{*}$ have no influence on the test particle motion in the equatorial plane.

Scalar-tensor gravity, with the screening mechanisms to avoid the severe constraints of the fifth force in the Solar System, can be described with a unified theoretical framework, the so-called screened modified gravity (SMG). Within this framework, in this paper we calculate the waveforms of gravitational-waves (GWs) emitted by inspiral compact binaries, which include four polarization modes, the plus $h_{+}$, cross $h_{\times }$, breathing $h_b$, and longitudinal $h_L$ modes. The scalar polarizations $h_b$ and $h_L$ are both caused by the scalar field of SMG, and satisfy a simple linear relation. With the stationary phase approximations, we obtain their Fourier transforms, and derive the correction terms in the amplitude, phase, and polarizations of GWs, relative to the corresponding results in general relativity. The corresponding parametrized post-Einsteinian parameters in the general SMG are also identified. Imposing the noise level of the ground-based Einstein Telescope, we find that GW detections from inspiral compact binaries composed of a neutron star and a black hole can place stringent constraints on the sensitivities of neutron stars, and the bound is applicable to any SMG theory. Finally, we apply these results to some specific theories of SMG, including chameleon, symmetron, dilaton and $f(R)$.

Gamma-ray searches for new physics such as dark matter are often driven by investigating the composition of the extragalactic gamma-ray background (EGB). Classic approaches to EGB decomposition manifest in resolving individual point sources and dissecting the intensity spectrum of the remaining unresolved component. Furthermore, statistical methods have recently been proven to outperform the sensitivity of classic source detection algorithms in finding point-source populations in the unresolved flux regime. In this article, we employ the 1-point photon count statistics of eight years of Fermi-LAT data to resolve the population of extragalactic point sources and to decompose the diffuse isotropic background contribution for Galactic latitudes $|b|\ge 30°$. We use three adjacent energy bins between 1 and 10 GeV. For the first time, we extend the analysis to incorporate a potential contribution from annihilating dark matter smoothly distributed in the Galaxy. We investigate the sensitivity reach of 1-point statistics for constraining the thermally-averaged self-annihilation cross section $⟨\sigma v⟩$ of dark matter, using different template models for the Galactic foreground emission. Given the official Fermi-LAT interstellar emission model, we set upper bounds on the dark matter self-annihilation cross section $⟨\sigma v⟩$ that are comparable with the constraints obtained by other indirect detection methods, in particular by the stacking analysis of several dwarf spheroidal galaxies.

The MiniBooNE collaboration has recently reported evidence for a light sterile neutrino with large mixing angles, thus corroborating the measurement by LSND twenty years ago. Such a state would be directly in conflict with Planck measurement of big bang nucleosynthesis $N_{\mathrm{eff}}$ unless there is self-interaction in the sterile sector. Our objective is to investigate if such interactions could result in resonant absorption in the cosmogenic neutrino spectrum and its consequences for the IceCube experiment. We show that it is possible to give independent bounds on sterile neutrino parameter space from IceCube observations with the dips in the spectrum corresponding to the neutrino masses.

Axions are a potential dark matter candidate, which may condense and form self-gravitating compact objects, called axion stars (ASs). In this work, we study for the first time head-on collisions of relativistic ASs with black holes (BHs) and neutron stars (NSs). In the case of BH-AS mergers we find that, in general, the largest scalar clouds are produced by mergers of low compactness ASs and spinning BHs. Although in most of the cases which we study the majority of the mass is absorbed by the BH within a short time after the merger, in favorable cases the remaining cloud surrounding the final BH remnant can be as large as 30% of the initial axion star mass, with a bosonic cloud mass of $\mathcal{O}({10}^{-1})M_{\mathrm{BH}}$ and peak energy density comparable to that obtained in a superradiant buildup. This provides a dynamical mechanism for the formation of long lived scalar hair, which could lead to observable signals in cases where the axion interacts with baryonic matter around the BH, or where it forms the seed of a future superradiant buildup in highly spinning cases. Considering NS-AS collisions we find two possible final states: (i) a BH surrounded by a (small) scalar cloud, or (ii) a stable NS enveloped in an axion cloud of roughly the same mass as the initial AS. While for low mass ASs the NS is only mildly perturbed by the collision, a larger mass AS gives rise to a massive ejection of baryonic mass from the system, purely due to gravitational effects. Therefore, even in the absence of a direct axion coupling to baryonic matter, NS-AS collisions could give rise to electromagnetic observables in addition to their gravitational wave signatures.

The strong and radiative decays of the low-lying $\lambda$-mode $D$-wave ${\mathrm{\Lambda }}_{c(b)}$, ${\mathrm{\Sigma }}_{c(b)}$, ${\mathrm{\Xi }}_{c(b)}$, ${\mathrm{\Xi }}_{c(b)}^{\prime }$, and ${\mathrm{\Omega }}_{c(b)}$ baryons are studied in a constituent quark model. Our calculation shows the following: (i) The missing $\lambda$-mode $D$-wave ${\mathrm{\Omega }}_{c(b)}$, ${\mathrm{\Lambda }}_b$, and ${\mathrm{\Xi }}_b$ baryons have a relatively narrow decay width of a few MeV or a few tens of MeV and their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiments. (ii) The $\lambda$-mode $1D$-wave excitations in the ${\mathrm{\Sigma }}_{c(b)}$ and ${\mathrm{\Xi }}_{c(b)}^{\prime }$ families appear to have a relatively broad width of $\sim 50–200\mathrm{MeV}$. Most of the $1D$-wave states have large decay rates into the $1P$-wave heavy baryons via the pionic or kaonic strong decay processes, which should be taken seriously in future observations. (iii) Both ${\mathrm{\Lambda }}_c(2860)$ and ${\mathrm{\Xi }}_c(3050)$ seem to favor the $J^P=3/2^{+}$ excitation $|{{}^{2}D}_{\lambda \lambda }{\frac{3}{2}}^{+}⟩$ of ${\overline{\mathbf{3}}}_F$, while both ${\mathrm{\Lambda }}_c(2880)$ and ${\mathrm{\Xi }}_c(3080)$ may be assigned as the $J^P=5/2^{+}$ excitation $|{{}^{2}D}_{\lambda \lambda }{\frac{5}{2}}^{+}⟩$ of ${\overline{\mathbf{3}}}_F$, The nature of ${\mathrm{\Xi }}_c(3050)$ and ${\mathrm{\Xi }}_c(3080)$ could be tested by the radiative transitions ${\mathrm{\Xi }}_c(3055{)}^0\to {\mathrm{\Xi }}_c(2790{)}^0\gamma$ and ${\mathrm{\Xi }}_c(3080{)}^0\to {\mathrm{\Xi }}_c(2815{)}^0\gamma$, respectively.

We derive fermionic Green’s functions in the background of the Euclidean solitons describing false vacuum decay in a prototypal Higgs-Yukawa theory. In combination with appropriate counterterms for the masses, couplings and wave-function normalization, these can be used to calculate radiative corrections to the soliton solutions and transition rates that fully account for the inhomogeneous background provided by the nucleated bubble. We apply this approach to the archetypal example of transitions between the quasidegenerate vacua of a massive scalar field with a quartic self-interaction. The effect of fermion loops is compared with those from additional scalar fields, and the loop effects accounting for the spacetime inhomogeneity of the tunneling configuration are compared with those where gradients are neglected. We find that scalar loops lead to an enhancement of the decay rate, whereas fermion loops lead to a suppression. These effects get relatively amplified by a perturbatively small factor when gradients are accounted for. In addition, we observe that the radiative corrections to the solitonic field profiles are smoother when the gradients are included. The method presented here for computing fermionic radiative corrections should be applicable beyond the archetypal example of vacuum decay. In particular, we work out methods that are suitable for calculations in the thin-wall limit, as well as others that take account of the full spherical symmetry of the solution. For the latter case, we construct the Green’s functions based on spin hyperspherical harmonics, which are eigenfunctions of the appropriate angular momentum operators that commute with the Dirac operator in the solitonic background.

A new vector dark matter (DM) scenario in the context of the gauge-Higgs unification (GHU) is proposed. The DM particle is identified with an electric-charge neutral component in an $SU(2{)}_L$ doublet vector field with the same quantum number as the Standard Model Higgs doublet. Since such an $SU(2{)}_L$ doublet vector field is incorporated in all models of the GHU scenario, it is always a primary and model-independent candidate for the DM in the scenario. The observed relic density is reproduced through DM pair annihilations into the weak gauge bosons with a TeV-scale DM mass, which is nothing but the compactification scale of extra dimensions. Due to the higher-dimensional gauge structure of the GHU scenario, a pair of the DM particles has no direct coupling with a single $Z$-boson/Higgs boson, so that the DM particle evades the severe constraint from the current direct DM search experiments.