We show that the equation of null geodesics in spherically symmetric spacetimes in isotropic coordinates is identical to the equation of light ray trajectories in isotropic media in flat spacetime. Based on this analogy we introduce an exact simulation of the light ray trajectories both in these spacetimes and in their metamaterial analogs in terms of the spacetime index of refraction. As unstable light trajectories, the photon spheres form in these metamaterial analogs at exactly the same radial distances as expected from the corresponding black hole geometries. Using the same ray-tracing simulation we find the analog of a simple black hole shadow formed by the metamaterial analog of a Schwarzschild black hole, eclipsing a line of light sources near its analog horizon. Designing such a metamaterial could provide a laboratory setting to explore this recently observed phenomenon.

Color-sextet scalars could have an array of possible couplings to the Standard Model beyond their well-known renormalizable couplings to quark pairs. The next-largest couplings these scalars might enjoy have mass dimension six, and some include electroweak fields and can therefore produce highly distinctive signals at hadron colliders. Here we study the single production of color-sextet scalars in association with a hard lepton, which results from a dimension-six coupling to leptons in addition to quarks and gluons. We identify parameter space in which these scalars decay promptly and propose a search for such particles in final states with two jets and an opposite-charge lepton pair, one member of which has high momentum. We then impose our selection criteria on the proposed signal and its leading backgrounds to project the discovery potential and exclusion limits during the next runs of the LHC. We compare our search with existing searches for leptoquarks, and we find we achieve much higher sensitivity with our tailored approach due to the unique kinematics of leptonic sextet events.

The chiral quark soliton model has been successfully applied to describe the heavy baryon spectrum, both for charm and bottom, leading to the conclusion that the heavy quark has no effect on the soliton. This suggests that replacing a heavy quark by a heavy antidiquark $\overline{Q}\overline{Q}$ in color triplet should give a viable description of heavy tetraquarks. We follow this strategy to compute tetraquark masses. To estimate heavy diquark masses, we use the Cornell potential with appropriately rescaled parameters. The lightest charm tetraquark is 70 MeV above the $D{D}^{*}$ threshold. On the contrary, both nonstrange and strange bottom tetraquarks are bound by approximately 140 and 60 MeV, respectively.

Using a data sample of $(448.1\pm 2.9)\times {10}^6\psi (3686)$ decays collected at an $e^{+}{e}^{-}$ center-of-mass energy of 3.686 GeV by the BESIII detector at Beijing Electron Positron Collider II, we report an observation of the hindered electromagnetic Dalitz decay $\psi (3686)\to e^{+}{e}^{-}{\eta }_c$ with a significance of $7.9\sigma$. The branching fraction is determined to be $\mathcal{B}(\psi (3686)\to e^{+}{e}^{-}{\eta }_c)=(3.77\pm 0.40_{\mathrm{stat}}\pm 0.18_{\mathrm{syst}})\times {10}^{-5}$, agreeing well with the prediction of the vector meson dominance model. This is the first measurement of the electromagnetic Dalitz transition between the $\psi (3686)$ and the ${\eta }_c$, which provides new insight into the electromagnetic properties of this decay, and offers new opportunities to measure the absolute branching fractions of ${\eta }_c$ decays.

It was shown a few years back that for a stationary regular black hole or star solution in the Brans-Dicke theory with a positive cosmological constant $\mathrm{\Lambda }$, endowed with a de Sitter or cosmological event horizon in the asymptotic region, not only there exists no nontrivial field configurations, but also the inverse Brans-Dicke parameter ${\omega }^{-1}$ must be vanishing. This essentially reduces the theory to Einstein’s general relativity. The assumption of the existence of the cosmological horizon was crucial for this proof. However, since the Brans-Dicke field $\varphi$, couples directly to the $\mathrm{\Lambda }$-term in the energy-momentum tensor as well as $\mathrm{\Lambda }$ acts as a source in $\varphi$’s equation of motion, it seems reasonable to ask: can $\varphi$ become strong instead and screen the effect of $\mathrm{\Lambda }$, at very large scales, so that the asymptotic de Sitter structure is replaced by some alternative, yet still acceptable boundary condition? In this work we analytically argue that no such alternative exists, as long as the spacetime is assumed to be free of any naked curvature singularity. We further support this result by providing explicit numerical computations. Thus we conclude that in the presence of a positive $\mathrm{\Lambda }$, irrespective of whether the asymptotic de Sitter boundary condition is imposed or not, a regular stationary black hole or even a star solution in the Brans-Dicke theory always necessitates ${\omega }^{-1}=0$, and thereby reducing the theory to general relativity. The qualitative differences of this result with that of the standard no hair theorems are also pointed out.

We show a possible way to build the $\mathrm{AdS}/\mathrm{CFT}$ correspondence starting from the quantum field theory side based on renormalization group approach. An extra dimension is naturally introduced in our scheme as the renomalization scale. The holographic wave equations are derived, with the potential term being determined by the QFT properties. We discover that only around the fixed point, i.e., the conformal limit, the potential in the bulk equations can be fully constrained, and upon this foundation, the correspondence is build. We demonstrate this fact using a 3D scalar theory in which, besides the trivial fixed point, there exists the Wilson-Fisher fixed point. From the energy scalings around those fixed points, we determine the behavior of the potential in the bulk equations.

The phenomenology of primordial black hole (PBH) physics and the associated PBH abundance constraints can be used to probe the physics of the early universe. In this work, we investigate the PBH formation during the standard radiation-dominated era by studying the effect of an early $F(R)$ modified gravity phase with a bouncing behavior which is introduced to avoid the initial spacetime singularity problem. In particular, we calculate the energy density power spectrum at horizon crossing time, and then we extract the PBH abundance in the context of peak theory as a function of the parameter $\alpha$ of our $F(R)$ gravity bouncing model at hand. Interestingly, we find that to avoid gravitational-wave overproduction from an early PBH dominated era before big bang nucleosynthesis, $\alpha$ should lie within the range $\alpha \le {10}^{-19}{M}_{\mathrm{Pl}}^2$. This constraint can be translated to a constraint on the energy scale at the onset of the hot big bang phase, $H_{\mathrm{RD}}\sim \sqrt{\alpha }/2$, which can be recast as $H_{\mathrm{RD}}<{10}^{-10}{M}_{\mathrm{Pl}}$.

We present a systematic study of the dynamics and gravitational-wave emission of head-on collisions of spinning vector boson stars, known as Proca stars. To this aim we build a catalog of about 800 numerical-relativity simulations of such systems. We find that the wavelike nature of bosonic stars has a large impact on the gravitational-wave emission. In particular, we show that the initial relative phase $\mathrm{\Delta }\epsilon ={\epsilon }_1-{\epsilon }_2$ of the two complex fields forming the stars (or, equivalently, the relative phase at merger) strongly impacts both the emitted gravitational-wave energy and the corresponding mode structure. This leads to a nonmonotonic dependence of the emission on the frequency of the secondary star ${\omega }_2$, for fixed frequency ${\omega }_1$ of the primary. This phenomenology, which has not been found for the case of black-hole mergers, reflects the distinct ability of the Proca field to interact with itself in both constructive and destructive manners. We postulate this may serve as a smoking gun to shed light on the possible existence of these objects.

We examine the Chandrasekhar limit for white dwarfs in $f(R)$ gravity, with a simple polytropic equation of state describing stellar matter. We use the most popular $f(R)$ gravity model, namely the $f(R)=R+\alpha R^2$ gravity, and calculate the parameters of the stellar configurations with polytropic equation of state of the form $p=K{\rho }^{1+1/n}$ for various values of the parameter $n$. In order to simplify our analysis we use the equivalent Einstein frame form of $R^2$-gravity which is basically a scalar-tensor theory with well-known potential for the scalar field. In this description one can use simple approximations for the scalar field $\varphi$ leaving only the potential term for it. Our analysis indicates that for the nonrelativistic case with $n=3/2$, discrepancies between the $R^2$-gravity and general relativity can appear only when the parameter $\alpha$ of the $R^2$ term, takes values close to maximal limit derived from the binary pulsar data namely ${\alpha }_{\max }=5\times {10}^{15}{\mathrm{cm}}^2$. Thus, the study of low-mass white dwarfs can hardly give restrictions on the parameter $\alpha$. For relativistic polytropes with $n=3$ we found that Chandrasekhar limit can in principle change for smaller $\alpha$ values. The main conclusion from our calculations is the existence of white dwarfs with large masses $\sim 1.33M_{\odot }$, which can impose stricter limits on the parameter $\alpha$ for the $R^2$ gravity model. Specifically, our estimations on the parameter $\alpha$ of the $R^2$ model is $\alpha \sim {10}^{13}{\mathrm{cm}}^2$.

The flavor evolution of neutrinos in environments with large neutrino number densities is an open problem at the nexus of astrophysics and neutrino flavor physics. Among the many unanswered questions pertaining to this problem, it remains to be determined whether neutrino-neutrino coherent scattering can give rise to nontrivial quantum entanglement among neutrinos, and whether this can affect the flavor evolution in a meaningful way. To gain further insight into this question, here we study a simple system of two interacting neutrino beams and obtain the exact phase space explored by this system using the Husimi quasiprobability distribution. We observe that the entanglement induced by the coupling leads to strong delocalization in phase-space with largely non-Gaussian quantum fluctuations. The link between the neutrino entanglement and quantum fluctuations is illustrated using the one- and two-neutrino entropy. In addition, we propose an approximate phase-space method to describe the interacting neutrinos problem, where the exact evolution is replaced by a set of independent mean-field evolutions with a statistical sampling of the initial conditions. The phase-space approach provides a simple and accurate method to describe the gross features of the neutrino entanglement problem. Applications are shown using time-independent and time-dependent Hamiltonians in the nonadiabatic regime.

TXS $0506+056$, source of the extreme energy neutrino event, IceCube-170922A, has an interesting environment to study the lepto-hadronic emissions. The Fermi-LAT detector reported high energy (HE) $\gamma$-ray flare between 100 MeV and 100 GeV starting from 15 September 2017 from this source. Several follow-ups to trace the very high energy (VHE) gamma-ray counterparts around the IceCube-170922A resulted in no success around 22 September 2022. Only after 28 September, the Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) telescopes observed the first VHE gamma rays from the blazar above 100 GeV. The $\sim 41\mathrm{h}$ survey resulted in VHE $\gamma$-ray activity until 31 October 2017, nearly 45 days after the HE flare. Here we propose the extended GeV $\gamma$ rays can be explained by taking two production channels, electron synchrotron self Compton and proton synchrotron for HE and VHE emissions, respectively. The 45 days of VHE emission from the peak of the HE flare can be explained with $L_p^{\prime }\simeq {10}^{47}\mathrm{erg}/\sec$ in the jet frame and magnetic field of 2.4 G, consistent with the ${\mathrm{L}}_{\mathrm{Edd}}$ for a blackhole mass $5\times {10}^9{\mathrm{M}}_{\odot }$. With the same luminosity of accelerated protons, we explained the observed neutrino flux with proton-varying-ambient interaction.

The concept of the modulation potential being utilized to describe the solar modulation of galactic cosmic rays is calculated based on the full three-dimensional Parker transport equation. This is in sharp contrast to the force-field approach, which is based on a series of approximations of this equation and where traditionally all the physical processes are condensed into a single parameter without knowing their relative contribution. In our comprehensive approach to the modulation potential, the contribution of all the different physical processes is given explicitly as derived directly from the parameters of Parker’s transport equation. We use the stochastic differential equations approach to study the effects of each of these different physical modulation processes thoroughly and then also determine the rigidity and mass-to-charge-ratio ($A/Z$) of these processes for the first time in the context of a modulation potential. It is found that: (1) This comprehensive modulation potential for galactic cosmic particles with a given rigidity at the Earth is a random variable, which can be fit by an inverse Gaussian distribution; (2) the rigidity and $A/Z$ dependence of this modulation potential can be divided into three categories based on the index value of power law diffusion; (3) the modulation caused by convection becomes weaker with increased rigidity and eventually dissipates, leading to a larger modulation potential for particles with a larger $A/Z$; (4) particle drift significantly reduces this modulation potential and its variation with changes in the tilt angle of the heliospheric current sheet has a distinct pattern for each of the two solar magnetic field polarities.

We explore the possible phases of a condensed dark matter (DM) candidate taken to be in the form of a fermion with a Yukawa coupling to a scalar particle, at zero temperature but at finite density. This theory essentially depends on only four parameters, the Yukawa coupling, the fermion mass, the scalar mediator mass, and the DM density. At low-fermion densities we delimit the Bardeen-Cooper-Schrieffer (BCS), Bose-Einstein condensate (BEC), and crossover phases as a function of model parameters using the notion of scattering length. We further study the BCS phase by consistently including emergent effects such as the scalar-density condensate and superfluid gaps. Within the mean-field approximation, we derive the consistent set of gap equations, retaining their momentum dependence, and valid in both the nonrelativistic and relativistic regimes. We present numerical solutions to the set of gap equations, in particular when the mediator mass is smaller and larger than the DM mass. Finally, we discuss the equation of state and possible astrophysical implications for asymmetric DM.

The CDF Collaboration has recently reported an updated result on the $W$-boson mass measurement, showing a $7\sigma$ deviation from the standard model prediction. The discrepancy may indicate new contributions to the Fermi coupling constant. We study simple extensions of the standard model by introducing an extra scalar, fermion, or vector field. It is found that the tension implies the new physics existing in multi-TeV scales if the new coupling to the electron and/or muon is of order unity.

By making use of the hybrid collinear and high-energy factorization, where the Balitsky-Fadin-Kuraev-Lipatov (BFKL) resummation of leading and next-to-leading energy logarithms is combined with the standard description in terms of collinear parton densities, we compare predictions for Mueller-Navelet jet rapidity and angular differential rates with data collected by CMS at $\sqrt{s}=7\mathrm{TeV}$. We provide an evidence that the study of azimuthal distributions, calculated as a Fourier sum of correlation moments and embodying the high-energy signal coming from all conformal-spin modes, permits us to overcome the well-known issues emerging in the description of Mueller-Navelet final states at natural values of the renormalization scale. We come out with a clear indication that the next-to-leading BFKL description of these observables at natural scales is valid when the rapidity interval between the two jets is large, and it allows us to catch the core high-energy dynamics emerging from data.

We report a branching fraction measurement of the singly Cabibbo-suppressed decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}^{+}$ using a data sample collected with the BESIII detector at the BEPCII storage ring. The data span center-of-mass energies from 4.599 to 4.950 GeV and correspond to an integrated luminosity of $6.44{\mathrm{fb}}^{-1}$. The branching fraction of ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}^{+}$ relative to that of the Cabibbo-favored decay ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}$ is measured to be $\mathcal{R}=\frac{\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}^{+})}{\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+})}=(4.78\pm 0.34\pm 0.20)\%$. Combining with the world-average value of $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+})$, we obtain $\mathcal{B}({\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{K}^{+})=(6.21\pm 0.44\pm 0.26\pm 0.34)\times {10}^{-4}$. Here the first uncertainties are statistical, the second systematic, and the third comes from the uncertainty of the ${\mathrm{\Lambda }}_c^{+}\to \mathrm{\Lambda }{\pi }^{+}$ branching fraction. This result, which is more precise than previous measurements, does not agree with theoretical predictions, and suggests that nonfactorizable contributions have been underestimated in current models.

We discuss some aspects of the metric configuration space in quantum gravity in the background field formalism. We give a necessary and sufficient condition for the parametrization of Euclidean metric fluctuations such that (i) the signature of the metric is preserved in all configurations that enter the gravitational path integral, and (ii) the parametrization provides a bijective map between full Euclidean metrics and metric fluctuations about a fixed background. For the case of foliatable manifolds, we show how to parametrize fluctuations in order to preserve foliatability of all configurations. Moreover, we show explicitly that preserving the signature on the configuration space for the Lorentzian quantum gravitational path integral is most conveniently achieved by inequality constraints. We discuss the implementation of these inequality constraints in a nonperturbative renormalization group setup.

It is known that the spectrum of quasinormal modes of potential barriers is related to the spectrum of bound states of the corresponding potential wells. This property has been widely used to compute black hole quasinormal modes, but it is limited to a few “approximate” potentials with certain transformation properties for which the spectrum of bound states must be known analytically. In this work we circumvent this limitation by proposing an approach that allows one to make use of potentials with similar transformation properties, but where the spectrum of bound states can also be computed numerically. Because the numerical calculation of bound states is usually more stable than the direct computation of the corresponding quasinormal modes, the new approach is also interesting from a technical point of view. We apply the method to different potentials, including the Pöschl-Teller potential for which all steps can be understood analytically, as well as potentials for which we are not aware of analytic results but provide independent numerical results for comparison. As a canonical test, all potentials are chosen to match the Regge-Wheeler potential of axial perturbations of the Schwarzschild black hole. We find that the new approximate potentials are more suitable to approximate the exact quasi-normal modes than the Pöschl-Teller potential, particularly for the first overtone. We hope this work opens new perspectives to the computation of quasinormal modes and finds further improvements and generalizations in the future.

We address the notorious metastability of the Standard Model (SM) and promote it to a model building task: What are the new ingredients required to stabilize the SM up to the Planck scale without encountering sub-Planckian Landau poles? Using the SM extended by vectorlike fermions, we chart out the corresponding landscape of Higgs stability. We find that the gauge portal mechanism, triggered by new SM charge carriers, opens up sizable room for stability in a minimally invasive manner. We also find models with Higgs criticality and Yukawa portals opening up at stronger coupling. Several models allow for vectorlike fermions in the TeV range, which can be searched for at the LHC. For nontrivial flavor structure, severe flavor-changing neutral current constraints arise that complement those from stability and push lower fermion masses up to $\mathcal{O}({10}^3\mathrm{TeV})$.

We study quark and lepton mass matrices derived from magnetized $T^2/{\mathbb{Z}}_2$ orbifold models. Quark and lepton masses have a large hierarchy. In addition, mixing angles are large in the lepton sector, while those are small in the quark sector. We find that this structure can be realized in certain flavor models, which are identified by the zero points of the zero-mode wave functions of fermions and Higgs modes. We classify such realistic flavor models. Fixed points $\tau =i$, $e^{2\pi i/3}$ and $i\infty$ of the modulus $\tau$ play a role in realizing a large mass hierarchy through our scenario, where residual $S$, $ST$, and $T$ symmetries remain and the lightest Higgs modes can correspond to eigenstates of residual symmetries at the leading order. As a result, we find that there are 24 flavor models in total which can be realistic in a vicinity of $S$-symmetric vacuum but no flavor models for $ST$- and $T$-symmetric vacua.