Conventional lore from Tremaine and Gunn excludes fermionic dark matter lighter than a few hundred eV, based on the Pauli exclusion principle. We highlight a simple way of evading this bound with a large number of species that leads to numerous nontrivial consequences. In this scenario there are many distinct species of fermions with quasidegenerate masses and no couplings to the standard model. Nonetheless, gravitational interactions lead to constraints from measurements at the LHC, of cosmic rays, of supernovae, and of black hole spins and lifetimes. We find that the LHC constrains the number of distinct species, bosons or fermions lighter than $\sim 500\mathrm{GeV}$, to be $N\lesssim {10}^{62}$. This, in particular, implies that roughly degenerate fermionic dark matter must be heavier than $\sim {10}^{-14}\mathrm{eV}$, which thus relaxes the Tremaine-Gunn bound by $\sim 16$ orders of magnitude. Slightly weaker constraints applying to masses up to $\sim 100\mathrm{TeV}$ exist from cosmic ray measurements while various constraints on masses $\lesssim {10}^{-10}\mathrm{eV}$ apply from black hole observations. We consider a variety of phenomenological bounds on the number of species of particles. Finally, we note that there exist theoretical considerations regarding quantum gravity which could impose more severe constraints that may limit the number of physical states to $N\lesssim {10}^{32}$.

The interactions between two octet baryons are studied at low energies using lattice quantum chromodynamics (LQCD) with larger-than-physical quark masses corresponding to a pion mass of $m_{\pi }\sim 450\mathrm{MeV}$ and a kaon mass of $m_K\sim 596\mathrm{MeV}$. The two-baryon systems that are analyzed range from strangeness $S=0$ to $S=-4$ and include the spin-singlet and triplet $NN$, $\mathrm{\Sigma }N$ ($I=3/2$), and $\mathrm{\Xi }\mathrm{\Xi }$ states, the spin-singlet $\mathrm{\Sigma }\mathrm{\Sigma }$ ($I=2$) and $\mathrm{\Xi }\mathrm{\Sigma }$ ($I=3/2$) states, and the spin-triplet $\mathrm{\Xi }N$ ($I=0$) state. The corresponding $s$-wave scattering phase shifts, low-energy scattering parameters, and binding energies when applicable are extracted using Lüscher’s formalism. While the results are consistent with most of the systems being bound at this pion mass, the interactions in the spin-triplet $\mathrm{\Sigma }N$ and $\mathrm{\Xi }\mathrm{\Xi }$ channels are found to be repulsive and do not support bound states. Using results from previous studies of these systems at a larger pion mass, an extrapolation of the binding energies to the physical point is performed and is compared with available experimental values and phenomenological predictions. The low-energy coefficients in pionless effective field theory (EFT) relevant for two-baryon interactions, including those responsible for $SU(3)$ flavor-symmetry breaking, are constrained. The $SU(3)$ flavor symmetry is observed to hold approximately at the chosen values of the quark masses, as well as the $SU(6)$ spin-flavor symmetry, predicted at large $N_c$. A remnant of an accidental $SU(16)$ symmetry found previously at a larger pion mass is further observed. The $SU(6)$-symmetric EFT constrained by these LQCD calculations is used to make predictions for two-baryon systems for which the low-energy scattering parameters could not be determined with LQCD directly in this study, and to constrain the coefficients of all leading $SU(3)$ flavor-symmetric interactions, demonstrating the predictive power of two-baryon EFTs matched to LQCD.

Preparing strongly coupled particle states on quantum computers requires large resources. In this work, we show how classical sampling coupled with projection operators can be used to compute Minkowski matrix elements without explicitly preparing these states on the quantum computer. We demonstrate this for the $2+1\mathrm{d}$ ${\mathbb{Z}}_2$ lattice gauge theory on small lattices with a quantum simulator.

Using the framework of nonrelativistic effective field theory, the finite-volume ground-state energy shift is calculated up to and including $O(L^{-6})$ for the system of three pions in the channel with the total isospin $I=1$. The relativistic corrections are included perturbatively, up to the same order in the inverse of the box size $L$. The obtained explicit expression, together with the known result for the system with maximal isospin $I=3$, can be used for the extraction of two independent effective three-body couplings from the measured ground-state spectrum of three pions.

We study spontaneous chiral-symmetry breaking in SU(3) QCD in terms of the dual superconductor picture for quark confinement in the maximally Abelian (MA) gauge, using lattice QCD Monte Carlo simulations with four different lattices of ${16}^4$, ${24}^4$, ${24}^3\times 6$ at $\beta =6.0$ (i.e., the spacing $a\simeq 0.1\mathrm{fm}$), and ${32}^4$ at $\beta =6.2$ (i.e., $a\simeq 0.075\mathrm{fm}$), at the quenched level. First, in the confinement phase, we find Abelian dominance and monopole dominance in the MA gauge for the chiral condensate in the chiral limit, using the two different methods of (i) the Banks-Casher relation with the Dirac eigenvalue density and (ii) finite quark-mass calculations with the quark propagator and its chiral extrapolation. In the high-temperature deconfined phase, the chiral restoration is observed also for the Abelian and the monopole sectors. Second, we investigate local correlation between the chiral condensate and monopoles, which topologically appear in the MA gauge. We find that the chiral condensate locally takes a quite large value near monopoles. As an interesting possibility, the strong magnetic field around monopoles is responsible to chiral symmetry breaking in QCD, similarly to the magnetic catalysis.

We propose the approach for a lattice investigation of light cone distribution amplitudes (LCDA) of heavy-light mesons, such as the $B$ meson, using the formalism of parton pseudodistributions. A basic ingredient of the approach is the study of short-distance behavior of the $B$-meson Ioffe-time distribution amplitude (ITDA), which is a generalization of the $B$-meson LCDA in coordinate space. We construct a reduced ITDA for the $B$ meson, and derive the matching relation between the reduced ITDA and the LCDA. The reduced ITDA is ultraviolet finite, which guarantees that the continuum limit exists on the lattice.

The newly observed hidden-charm tetraquark state $Z_{cs}(3985)$, together with $Z_c(3900)$ and $X(4020)$, are studied in the combined theoretical framework of the effective range expansion, compositeness relation, and the decay width saturation. The elastic effective-range-expansion approach leads to sensible results for the scattering lengths, effective ranges, and the compositeness coefficients, i.e., the probabilities to find the two-charm-meson molecule components in the tetraquark states. The coupled-channel formalism by including the $J/\psi \pi$ and $D{\overline{D}}^{*}/\overline{D}{D}^{*}$ to fulfill the constraints of the compositeness relation and the decay width confirms the elastic effective-range-expansion results for the $Z_c(3900)$, by using the experimental inputs for the ratios of the decay widths between $D{\overline{D}}^{*}/\overline{D}{D}^{*}$ and $J/\psi \pi$. With the results from the elastic effective-range-expansion study as input for the compositeness, we generalize the discussions to the $Z_{cs}(3985)$ by including the $J/\psi K^{-}$ and $D_s^{-}{D}^{*0}/D_s^{*-}{D}^0$ and predict the partial decay widths of the $J/\psi K^{-}$. Similar calculations are also carried out for the $X(4020)$ by including the $h_c\pi$ and $D^{*}{\overline{D}}^{*}$, and the partial decay widths of the $h_c\pi$ is predicted. Our results can provide useful guidelines for future experimental measurements.

We discuss whether the bound nature of multiquark states in quark models could benefit from relativistic effects on the kinetic energy operator. For mesons and baryons, relativistic corrections to the kinetic energy lead to lower energies, and thus call for a retuning of the parameters of the model. For multiquark states, as well as their respective thresholds, a comparison is made of the results obtained with nonrelativistic and relativistic kinetic energy. It is found that the binding energy is lower in the relativistic case. In particular, $QQ\overline{q}\overline{q}$ tetraquarks with double heavy flavor become stable for a larger ratio of the heavy to light quark masses; the all-heavy tetraquarks $QQ\overline{Q}\overline{Q}$ that are not stable in standard nonrelativistic quark models remain unstable when a relativistic form of kinetic energy is adopted.

The electric charge renormalization constant, as defined in the Thomson limit, is expressed in terms of self-energies of the photon–Z-boson system in an arbitrary $R_{\xi }$ gauge to all perturbative orders. The derivation as carried out in the Standard Model holds in all spontaneously broken gauge theories with the ${\mathrm{SU}(2)}_{\mathrm{w}}\times {\mathrm{U}(1)}_Y$ gauge group in the electroweak sector and is based on the application of charge universality to a fake fermion with infinitesimal weak hypercharge and vanishing weak isospin, which effectively decouples from all other particles. Charge universality, for instance, follows from the known universal form of the charge renormalization constant as derived within the background-field formalism. Finally, we have generalized the described procedure to gauge theories with gauge group ${\mathrm{U}(1)}_Y\times G$ with any Lie group $G$, only assuming that electromagnetic gauge symmetry is unbroken and mixes with ${\mathrm{U}(1)}_Y$ transformations in a nontrivial way.

A measurement is reported of differential top quark pair ($t\overline{t}$) production cross sections, where top quarks are produced at large transverse momenta. The data collected with the CMS detector at the LHC are from $pp$ collisions at a center-of-mass energy of $13\mathrm{TeV}$ corresponding to an integrated luminosity of $35.9{\mathrm{fb}}^{-1}$. The measurement uses events where at least one top quark decays as $t\to Wb\to q{\overline{q}}^{\prime }b$ and is reconstructed as a large-radius jet with transverse momentum in excess of 400 GeV. The second top quark is required to decay either in a similar way or leptonically, as inferred from a reconstructed electron or muon, a bottom quark jet, and missing transverse momentum due to the undetected neutrino. The cross section is extracted as a function of kinematic variables of individual top quarks or of the $t\overline{t}$ system. The results are presented at the particle level, within a region of phase space close to that of the experimental acceptance, and at the parton level and are compared to various theoretical models. In both decay channels, the observed absolute cross sections are significantly lower than the predictions from theory, while the normalized differential measurements are well described.

Experiments looking for a lepton-flavor-violating decay ${\mu }^{+}\to e^{+}{X}^0$ are reviewed in light of present-day germanium detector technology, with an eye on scenarios where a long-lived, slow-moving massive boson $X^0$ might have a cosmological impact. A broad swath of interesting, unexplored parameter space very close to the kinematic limit of the decay is found to be within the reach of a new proposed search. A number of possible roles for $X^0$ in past and present epochs can be investigated.

Recently, several studies have pointed out that gravitational-wave detectors are sensitive to ultralight vector dark matter and can improve the current best constraints given by the equivalence principle tests. While a gravitational-wave detector is a highly precise measuring tool for the length difference of its arms, its sensitivity is limited because the displacements of its test mass mirrors caused by vector dark matter are almost common. In this paper, we point out that the sensitivity is significantly improved if the effect of finite light-traveling time in the detector’s arms is taken into account. This effect enables advanced LIGO to improve the constraints on the $U(1{)}_{B-L}$ gauge coupling by an order of magnitude compared with the current best constraints. It also makes the sensitivities of the future gravitational-wave detectors overwhelmingly better than the current ones. The factor by which the constraints are improved due to the new effect depends on the mass of the vector dark matter, and the maximum improvement factors are 470, 880, 1600, 180, and 1400 for advanced LIGO, Einstein Telescope, Cosmic Explorer, DECIGO, and LISA, respectively. Including the new effect, we update the constraints given by the first observing run of advanced LIGO and improve the constraints on the $U(1{)}_B$ gauge coupling by an order of magnitude compared with the current best constraints.

We investigate the gravitational perturbations of the Schwarzschild black hole in the nonlocal gravity model recently proposed by Deser and Woodard. The analysis is performed in the localized version in which the nonlocal corrections are represented by some auxiliary scalar fields. We find that the nonlocal corrections do not affect the axial gravitational perturbations, and hence the axial modes are completely identical to those in general relativity (GR). However, the polar modes become different from their GR counterparts when the scalar fields are excited at the background level. In such a case the polar modes are sourced by an additional massless scalar mode and, as a result, the isospectrality between the axial and the polar modes breaks down. We also perform a similar analysis for the predecessor of this model and arrive at the same conclusion for it.

We give a formal treatment of the “correlated worldline” theory of quantum gravity. The generating functional is written as a product over multiple copies of the coupled matter and gravitational fields; paths for fields are correlated via gravity itself. In the limit where the gravitational coupling $G\to 0$, conventional quantum field theory is recovered; in the classical limit $\hslash \to 0$, general relativity is recovered. A formal loop expansion is derived, with all terms up to one-loop order $\sim O(l_P^2)$ given explicitly, where $l_P$ is the Planck length. We then derive the form of a perturbation expansion in $l_P^2$ around a background field, with the correlation functions given explicitly up to $\sim O(l_P^2)$. Finally, we explicitly demonstrate the on shell gauge independence of the theory, to order $l_P^2$ in gravitational coupling and to all orders in matter loops, and derive the relevant Ward identities.

Primordial non-Gaussianity (PNG) is a key probe of the origins of primordial fluctuations in the early universe. It has been shown that multitracer measurements of large-scale structure can produce high-precision measurements of PNG. Future line intensity mapping surveys are well suited to these measurements owing to their ability to rapidly survey large volumes and access the large scales at which PNG becomes important. In this paper, we explore for the first time how multitracer PNG measurements with intensity mapping surveys depend on the sub-galactic scale physics which drives line emission. We consider an example cross-correlation between CO maps, and quantify the impact varying the astrophysical model has on $f_{\mathrm{NL}}$ measurements. We find a nontrivial coupling between horizon-scale PNG measurements and the molecular cloud-scale interstellar medium that can have order unity effects on $f_{\mathrm{NL}}$ constraints with near-future experimental sensitivities. We discuss how these effects depend on noise level and survey design. We further find that the cross-correlation shot noise, an effect nearly unique to intensity mapping measurements, can play an important role in multi-tracer analyses and should not be neglected.

We demonstrate that next-generation cosmic microwave background spectral distortion and pulsar timing array experiments can either detect signatures of primordial black holes in the mass range $\mathcal{O}(0.1–{10}^{12})M_{\odot }$, which are sourced from primordial overdensities within the standard thermal history of the universe, or constrain their existence to a negligible abundance, ruling them out as super-massive black hole seeds. Our conclusions are robust to changes in (i) the statistical properties of primordial density fluctuations, (ii) primordial black hole merger and accretion history and (iii) clustering statistics.

Macroscopic dark matter (macros) is a broad class of alternative candidates to particle dark matter. These candidates would transfer energy to matter primarily through elastic scattering. A sufficiently large macro passing through the atmosphere would produce a straight channel of ionized plasma. If the cross section of the macro is ${\sigma }_x⪆6\times {10}^{-9}{\mathrm{cm}}^2$, then under atmospheric conditions conducive to lightning (e.g., a thunderstorm) the plasma channel would be sufficient to seed a lightning strike with a single leader. This is entirely unlike ordinary bolt lightning in which a long sequence of hundreds or thousands of few-meter-long leaders are strung together. This macro-induced lightning would be extremely straight and thus highly distinctive. Neither wind shear nor magnetohydrodynamic instabilities would markedly spoil its straightness. The only photographically documented case of a straight lightning bolt is probably not straight enough to have been macro-induced. We estimate the region of macro parameter space that could be probed by a search for straight lightning from the number of thunderstorms happening on Earth at any time. We also estimate the parameter space that can be probed by carefully monitoring Jupiter, e.g., using a Jupiter probe. All code and data are available at https://github.com/cwru-pat/macro_lightning.

The presence of an excess $\gamma$-ray signal toward the Galactic Center (GC) has now been well established, and is known as the GC excess. Leading explanations for the signal include mismodeling of the Galactic diffuse emission along the line of sight, an unresolved population of millisecond pulsars, and/or the annihilation of dark matter (DM). Recently, evidence for another excess $\gamma$-ray signal has been reported toward the outer halo of M31. In this work we interpret the excess signals from both the GC and outer halo of M31 in the framework of DM annihilation, and show that the two spectra are consistent with a DM origin once $J$-factors are taken into account. We further compare the excesses to models of DM annihilation, and determine the corresponding best-fit parameters. We find good fits to the spectrum both in two body and four body annihilation modes.

We study the heavy dark matter produced around the temperature of the phase transition. Meanwhile domain walls can be formed after the breakdown of a ${\mathbb{Z}}_3$ discrete symmetry induced by the first-order phase transition. The generated gravitational waves by domain wall decay are found to be able to probed by the pulsar timing arrays, and the future square kilometer array.

We investigate nucleon decays to light invisible fermion mediated by the colored scalar ${\overline{S}}_1=(\overline{3},1,-2/3)$ and compare them with the results coming from the mediation of $S_1=(\overline{3},1,1/3)$. In the case of ${\overline{S}}_1=(\overline{3},1,-2/3)$ uplike quarks couple to the invisible fermion, while in the case of $S_1=(\overline{3},1,1/3)$ the downlike quarks couple to the invisible fermion. For the mass of invisible fermion smaller than the mass $m_p-m_K$, proton (neutron) can decay to $K$ and invisible fermion and the masses of ${\overline{S}}_1$ and $S_1$ are in the region $\sim {10}^{15}\mathrm{GeV}$. The decays of nucleons to pions and invisible fermion can occur at the tree level, but in the case of ${\overline{S}}_1$ they come from a dimension-nine operator and are therefore suppressed by several orders of magnitude compared to the decays into kaons. For the invisible fermion mass in the range (937.8, 938.8 MeV), decay of neutron $n\to \chi \gamma$ induced by ${\overline{S}}_1$ is possible at the loop level, while the proton remains stable. The branching ratio of such decay is $\le {10}^{-6}$, which does not explain neutron decay anomaly, but is in agreement with the Borexino experiment bound. We comment on low-energy processes with the nucleonlike mass of $\chi$ in the final state as $\mathrm{\Lambda }\to \chi \gamma$ and heavy hadron decays to invisibles.