Dark matter is poorly constrained by direct detection experiments at masses below 1 MeV. This is an important target for the next generation of experiments, and several methods have been proposed to probe this mass range. One class of such experiments will search for dark matter–electron recoils. However, simplified models with new light degrees of freedom coupled to electrons face significant pressure from cosmology, and the extent of these restrictions more generally is poorly understood. Here, we perform a systematic study of cosmological constraints on models with a heavy mediator in the context of an effective field theory. We include constraints from (i) disruption of primordial nucleosynthesis, (ii) overproduction of dark matter, and (iii) the effective number of neutrino species at recombination. We demonstrate the implications of our results for proposed electron recoil experiments, and highlight scenarios which may be amenable to direct detection.

The steady advance in core-collapse supernova simulations requires a more precise description of neutrino processes in hot and dense matter. In this work, we study the rates of charged-current (CC) weak processes with (anti)muons in supernova matter. At the relativistic mean field level, we derive results for the rates of CC neutrino-nucleon reactions, taking into account full kinematics, weak magnetism and pseudoscalar terms, and $q^2$-dependent nucleon form factors in the hadronic current. In addition to muonic semileptonic processes we also consider purely leptonic processes. In particular, we show that inverse muon decay can dominate the opacities for low energy ${\nu }_{\mu }$ and ${\overline{\nu }}_e$ at densities $\gtrsim {10}^{13}\mathrm{g}{\mathrm{cm}}^{-3}$.

New physics close to the electroweak scale is well motivated by a number of theoretical arguments. However, colliders, most notably the Large Hadron Collider, have failed to deliver evidence for physics beyond the Standard Model. One possibility for how new electroweak-scale particles could have evaded detection so far is if they carry only electroweak charge, i.e., are color neutral. Future $e^{+}{e}^{-}$ colliders are prime tools to study such new physics. Here, we investigate the sensitivity of $e^{+}{e}^{-}$ colliders to scalar partners of the charged leptons, known as sleptons in supersymmetric extensions of the Standard Model. In order to allow such scalar lepton partners to decay, we consider models with an additional neutral fermion, which in supersymmetric models corresponds to a neutralino. We demonstrate that future $e^{+}{e}^{-}$ colliders would be able to probe most of the kinematically accessible parameter space, i.e., where the mass of the scalar lepton partner is less than half of the collider’s center-of-mass energy, with only a few days of data. Besides constraining more general models, this would allow to probe some well motivated dark matter scenarios in the Minimal Supersymmetric Standard Model, in particular the incredible bulk and stau coannihilation scenarios.

We present a novel perspective to characterize the chiral magnetic and related effects in terms of angular decomposed modes. We find that the vector current and the chirality density are connected through a surprisingly simple relation for all the modes and any mass, which defines the mode decomposed chiral magnetic effect in such a way free from the chiral chemical potential. The mode decomposed formulation is useful also to investigate properties of rotating fermions. For demonstration, we give an intuitive account for a nonzero density emerging from a combination of rotation and magnetic field as well as an approach to the chiral vortical effect at finite density.

Opaque detectors are a recently proposed novel detector concept where an opaque scintillator aligned with wavelength-shifting fibers is used to enable the discrimination of electron neutrinos and antineutrinos with a rather low energy threshold. In this work, we investigate the potential effects of the enhanced detection capabilities of the opaque detectors in accelerator neutrino experiments. Focusing on the energy threshold, energy resolution, detection efficiency and background suppression in the analysis of electron-like events, we determine whether using opaque detectors could lead to improvements in the $CP$ violation and light sterile neutrino searches in the future accelerator neutrino experiments. We also identify the minimum requirements for the opaque detectors to reach the designated physics goals in the simulated experiments. We find that a 75.6% fraction of ${\delta }_{CP}$ values could be reached for $CP$ violation discovery by $3\sigma$ confidence level or better when opaque detectors of 120 kton and 130 kton fiducial masses are used together with neutrino beams from J-PARC and MOMENT, respectively, whereas near detectors placed about 250 m from sources are sufficient to exclude the gallium anomaly at $2\sigma$ confidence level.

In this paper, we investigate the correlation functions of the conformal field theory (CFT) with the $T\overline{T}$ deformation on a torus in terms of the perturbative CFT approach, which is the extension of the previous investigations on correlation functions defined on a plane. We systematically obtain the first-order correction to the correlation functions of the CFTs with a $T\overline{T}$ deformation in both operator formalism and path integral language. As a consistency check, we compute the deformed partition function, namely, the zero-point correlation function, up to the first order, which is consistent with results in the literature. Moreover, we obtain a new recursion relation for correlation functions with multiple $T$’s and $\overline{T}$’s inserted in generic CFTs on a torus. Based on the recursion relations, we study some correlation functions of stress tensors up to the first order under $T\overline{T}$ deformation.

Recently, a new path integral formulation of loop quantum gravity (LQG) has been derived in M. Han and H. Liu, Phys. Rev. D 101, 046003 (2020). from the reduced phase space formulation of the canonical LQG. This paper focuses on the semiclassical analysis of this path integral formulation. We show that dominant contributions of the path integral come from solutions of semiclassical equations of motion (EOMs), which reduce to Hamilton’s equations of holonomies and fluxes $h(e)$, $p^a(e)$ in the reduced phase space ${\mathcal{P}}_{\gamma }$ of the cubic lattice $\gamma$: $\frac{\mathrm{d}h(e)}{\mathrm{d}\tau }=\{h(e),\mathbf{H}\}$, $\frac{\mathrm{d}{p}^a(e)}{\mathrm{d}\tau }=\{p^a(e),\mathbf{H}\}$, where $\mathbf{H}$ is the discrete physical Hamiltonian. The semiclassical dynamics from the path integral becomes an initial value problem of Hamiltonian time evolution in ${\mathcal{P}}_{\gamma }$. Moreover when we take the continuum limit of the lattice $\gamma$, these Hamilton’s equations reproduce correctly classical reduced phase space EOMs of gravity coupled to dust fields in the continuum, as far as initial and final states are semiclassical. Our result proves that the new path integral formulation has the correct semiclassical limit and indicates that the reduced phase space quantization in LQG is semiclassically consistent. Based on these results, we compare this path integral formulation and the spin foam formulation, and show that this formulation has several advantages including the finiteness, the relation with canonical LQG, and the freedom from cosine and flatness problems.

The static traversable wormhole should be made out of some type of exotic matter which satisfies the Morris-Thorne conditions. Although the characteristic size of the region with the exotic matter can be made arbitrary small, the calculations performed so far suggest that the Morris-Thorne conditions are quite restrictive and it is hard to find the matter with the desired properties. Traditionally, the quantized fields are considered as the best candidates because they can violate the weak-energy condition. In this paper we employ the Schwinger-DeWitt expansion to construct and examine the approximate stress-energy tensor of the quantized massive scalar (with an arbitrary curvature coupling), spinor and vector field in the spacetime of the Damour-Solodukhin wormhole. We find that for the scalar field there is a region in a parameter space in which the stress-energy tensor has the desired properties. That means that of the twenty-one cases considered so far (the seven types of the wormhole geometries and the three types of the massive fields) only in the four cases (for certain values of the parameters) the stress-energy tensor does satisfy the Morris-Thorne conditions.

We point out that the standard formulation of the cosmological constant problem itself is problematic since it is trying to apply the very large scale homogeneous cosmological model to very small (Planck) scale phenomenon. At small scales, both the spacetime and the vacuum stress energy are highly inhomogeneous and wildly fluctuating. This is a version of Wheeler’s “spacetime foam.” We show that this “foamy” structure would produce a large positive contribution to the average macroscopic spatial curvature of the Universe. In order to cancel this contribution to match the observation, the usually defined effective cosmological constant ${\lambda }_{\mathrm{eff}}={\lambda }_B+8\pi G⟨\rho ⟩$ has to take a large negative value. The spacetime dynamics sourced by this large negative ${\lambda }_{\mathrm{eff}}$ would be similar to the cyclic model of the universe in the sense that at small scales every point in space is a “microcyclic universe” which is following an eternal series of oscillations between expansions and contractions. Moreover, if the bare cosmological constant ${\lambda }_B$ is dominant, the size of each “microuniverse” would increase a tiny bit at a slowly accelerating rate during each microcycle of the oscillation due to the weak parametric resonance effect produced by the fluctuations of the quantum vacuum stress energy tensor. In this way, the large cosmological constant generated at small scales is hidden at observable scale and no fine-tuning of ${\lambda }_B$ to the accuracy of ${10}^{-122}$ is needed. This at least resolves the old cosmological constant problem and suggests that it is the quantum vacuum fluctuations serve as the dark energy which is accelerating the expansion of our Universe.

The ratio of the number of muons with a threshold of 1 GeV and charged particles at a distance of 600 m from the axis is analyzed. Air showers with energies above 5 EeV and zenith angles with less than 60 degrees are considered. Comparison of experimental data with calculations by the QGSJETII-04 model for various primary nuclei, including a gamma ray, showed that the mass composition of cosmic rays up to energies of $\sim 10\mathrm{EeV}$ mainly consists of protons and helium nuclei, with a small number of heavy nuclei. Data include air showers with a very low muon content, which are assumed to be produced by primary gamma rays.

Most of the exotic resonances observed in the past decade appear as a peak structure near some threshold. These near-threshold phenomena can be interpreted as genuine resonant states or enhanced threshold cusps. Apparently, there is no straightforward way of distinguishing the two structures. In this work, we employ the strength of deep feed-forward neural network in classifying objects with almost similar features. We construct a neural network model with scattering amplitude as input and the nature of a pole causing the enhancement as output. The training data is generated by an S-matrix satisfying the unitarity and analyticity requirements. Using the separable potential model, we generate a validation data set to measure the network’s predictive power. We find that our trained neural network model gives high accuracy when the cutoff parameter of the validation data is within 400–800 MeV. As a final test, we use the Nijmegen partial wave and potential models for nucleon-nucleon scattering and show that the network gives the correct nature of the pole.

We present a simple modification of the Altarelli-Feruglio $A_4$ flavor symmetry model using a minimal number of parameters congruous with the symmetries of the original theory. The resulting model is consistent with all presently known data on neutrino masses and mixings. Furthermore, it makes testable tight predictions for future experiments aimed at improving the measurements of ${\sin }^2{\theta }_{12}$, ${\sin }^2{\theta }_{13}$, ${\delta }_{\mathrm{CP}}$ and the neutrinoless double-beta decay parameter $|m_{ee}|$. Our model exploits the unique possibility of multiple allowed, yet qualitatively different, contractions of fields charged under the $A_4$ discrete symmetry.

Decays $D\to {\pi }^{+}{\pi }^{-}{e}^{+}{\nu }_e$ and $D_s\to {\pi }^{+}{\pi }^{-}{e}^{+}{\nu }_e$ serve as probes that check the existence of constituent $q\overline{q}$ components in the wave functions of scalar mesons decaying into ${\pi }^{+}{\pi }^{-}$. There exists a great deal of concrete evidence in favor of the exotic four-quark nature of light scalars. At the same time, the further expansion of the area of the $q^2{\overline{q}}^2$ model validity for light scalars on ever new processes seems extremely interesting and important. We analyze the BESIII and CLEO data on the decays $D^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}{\nu }_e$ and $D_s^{+}\to {\pi }^{+}{\pi }^{-}{e}^{+}{\nu }_e$ and show that the results of these experiments together can be interpreted in favor of the four-quark nature of light scalar mesons $\sigma (500)$ and $f_0(980)$. Our approach can also be applied to the description of other similar decays involving light scalars.

We perform an analysis on the ${\chi }_{cJ}$ polarization in the ${\psi }^{\prime }$ radiative transition and propose to use it to probe the mechanism of ${\chi }_{cJ}$ decay to the baryon-antibaryon pairs in experiment. To start with the unpolarized $e^{+}{e}^{-}$ collisions, we follow the polarization transfer to the ${\chi }_{cJ}$ states, and estimate the degree of ${\chi }_{cJ}$ polarization. We show that the $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ pair has rich spin configurations, which are beneficial for us to study its decay asymmetry parameter and measure the helicity amplitudes. The experimental observables to reveal the ${\chi }_{cJ}$ and $\mathrm{\Lambda }\overline{\mathrm{\Lambda }}$ spin polarization are presented.

If the neutrino is a Majorana particle, low-energy lepton-number-violating (LNV) processes, such as neutrinoless double-beta ($0\nu \beta \beta$) decay, are possible. It may also be possible to observe high-energy $0\nu \beta \beta$-like LNV processes at the LHC. These are distinguished by the presence of same-sign dileptons in the final state (e.g., $\overline{u}d\to t\overline{b}{e}^{-}{\mu }^{-}$). In this paper, we show that $CP$-violating triple products (TPs) may be present in the process, and may be measurable at the LHC. If a nonzero TP were observed, it would give us much information about the underlying new physics (NP). We would know that there are (at least) two interfering NP amplitudes, with different weak phases and different Lorentz structures. And if we had some knowledge of the NP, e.g., by direct production of NP particles, we could get information about the magnitudes and relative phases of its couplings.

We study the deconfinement transition line in QCD for quark chemical potentials up to ${\mu }_q\sim 5\mathrm{T}$ (${\mu }_B\sim 15\mathrm{T}$). To circumvent the sign problem we use the complex Langevin equation with gauge cooling. The plaquette gauge action is used with two flavors of naive Wilson fermions at a relatively heavy pion mass of roughly 1.3 GeV. A quadratic dependence describes the transition line well on the whole chemical potential range.

The single longitudinal spin asymmetry $A_{UL}^{\sin (2{\varphi }_h-2{\varphi }_R)}$ of dihadron production in semi-inclusive deep inelastic scattering (SIDIS) is examined through helicity-dependent dihadron fragmentation function (DiFF) $G_1^{\perp }$. The correlation of the longitudinal polarization of a fragmenting quark with the transverse momenta of the produced hadron pair is illustrated by this DiFF. The experimental investigation for this azimuthal asymmetry in dihadron SIDIS by the COMPASS Collaboration has lately yielded a very small signal. Here, the unknown T-odd dihadron fragmentation function $G_1^{\perp }$ utilizing a spectator model is computed. The model has been successfully used to describe the dihadron production in both the unpolarized and the single polarized processes to access the asymmetry and clarify why the signal is very small. The transverse momentum dependent factorization method, in which the transverse momentum of the final state hadron pair is left unintegrated, has been considered. The $\sin (2{\varphi }_h-2{\varphi }_R)$ asymmetry at the COMPASS kinematics is estimated and we compare it with the data. Besides, the predictions on the same asymmetry are also made at the HERMES and Electron Ion Collider.

A Poincaré-covariant $\mathrm{quark}+\mathrm{diquark}$ Faddeev equation, augmented by a statistical implementation of the Schlessinger point method for the interpolation and extrapolation of smooth functions, is used to compute nucleon elastic form factors on $0\le Q^2\le 18m_N^2$ ($m_N$ is the nucleon mass) and elucidate their role as probes of emergent hadronic mass in the Standard Model. The calculations expose features of the form factors that can be tested in new generation experiments at existing facilities, e.g., a zero in $G_E^p/G_M^p$, a maximum in $G_E^n/G_M^n$, and a zero in the proton’s $d$-quark Dirac form factor, $F_1^d$. Additionally, examination of the associated light-front-transverse number and anomalous magnetization densities reveals inter alia: a marked excess of valence $u$ quarks in the neighborhood of the proton’s center of transverse momentum, and that the valence $d$ quark is markedly more active magnetically than either of the valence $u$ quarks. The calculations and analysis also reveal other aspects of nucleon structure that could be tested with a high-luminosity accelerator capable of delivering higher beam energies than are currently available.

We develop an algorithm based on an interaction network to identify high-transverse-momentum Higgs bosons decaying to bottom quark-antiquark pairs and distinguish them from ordinary jets that reflect the configurations of quarks and gluons at short distances. The algorithm’s inputs are features of the reconstructed charged particles in a jet and the secondary vertices associated with them. Describing the jet shower as a combination of particle-to-particle and particle-to-vertex interactions, the model is trained to learn a jet representation on which the classification problem is optimized. The algorithm is trained on simulated samples of realistic LHC collisions, released by the CMS Collaboration on the CERN Open Data Portal. The interaction network achieves a drastic improvement in the identification performance with respect to state-of-the-art algorithms.