Eternally inflating universes lead to an infinite number of Boltzmann brains but also an infinite number of ordinary observers. If we use the scale factor measure to regularize these infinities, the ordinary observers dominate the Boltzmann brains if the vacuum decay rate of each vacuum is larger than its Boltzmann brain nucleation rate. Here, we point out that nucleation of small black holes should be counted in the vacuum decay rate, and this rate is always larger than the Boltzmann brain rate, if the minimum Boltzmann brain mass is more than the Planck mass. We also discuss nucleation of small, rapidly inflating regions, which may also have a higher rate than Boltzmann brains. This process also affects the distribution of the different vacua in eternal inflation.

Dwarf spheroidal galaxies are dark matter dominated systems, and as such, ideal for indirect dark matter searches. If dark matter decays into high-energy photons in the dwarf galaxies, they will be a good target for current and future generations of x-ray and gamma-ray telescopes. By adopting the latest estimates of density profiles of dwarf galaxies in the Milky Way, we revise the estimates dark matter decay rates in dwarf galaxies; our results are more robust, but weaker than previous estimates. Applying these results, we study the detectability of dark matter decays with x-ray and very-high-energy gamma-ray telescopes, such as eROSITA, XRISM, Athena, HAWC, and CTA. Our projection shows that all of these x-ray telescopes will be able to critically assess the claim of the 7 keV sterile neutrino decays from stacked galaxy clusters and nearby galaxies. For TeV decaying dark matter, we can constrain its lifetime to be longer than $\sim {10}^{27}–{10}^{28}\mathrm{s}$. We also make projections for future dwarf galaxies that would be newly discovered with the Vera Rubin Observatory Legacy Survey of Space and Time, which will further improve the expected sensitivity to dark matter decays both in the keV and PeV mass ranges.

Dark matter might be made of “warm” particles, such as sterile neutrinos in the keV mass range, which can decay into photons through mixing and are consequently detectable by x-ray telescopes. Axionlike particles (ALPs) are detectable by x-ray telescopes, too, when coupled to standard model particles and decay into photons in the keV range. Both particles could explain the unidentified 3.5 keV line, and, interestingly, XENON1T observed an excess of electron recoil events most prominent at 2–3 keV. One explanation could be an ALPs origin, which is not yet excluded by x-ray constraints in an anomaly free symmetry model in which the photon production is suppressed. We study the diffuse emission coming from the Galactic halo and calculate the sensitivity of all-sky x-ray survey performed by eROSITA to identify a sterile neutrino or ALP dark matter. We estimate bounds on the mixing angle of the sterile neutrinos and coupling strength of the ALPs. After four years of data taking by eROSITA, we expect to set stringent constraints, and in particular, we expect to firmly probe mixing angle ${\sin }^2(2\theta )$ up to nearly 2 orders magnitude below the best-fit value for explaining the unidentified 3.5 keV line. Moreover, with eROSITA, we will be able to probe the ALP parameter space of couplings to photons and electrons and potentially confirm an ALP origin of the XENON1T excess.

In this paper we analyze in detail the production of strangeness in proton-proton collisions in the kinematics of large transverse momenta $p_T$ of produced hadrons. Using the color dipole framework, we estimate the production cross sections for kaons and demonstrate that the shapes of the $p_T$ dependence are in agreement with available experimental data. We also analyze the self-normalized yields of strange hadrons as a function of multiplicity of coproduced hadrons, and find that the predictions are in agreement with the faster-than-linear growth seen in experimental data. Our description is largely parameter free and extends our previous studies dedicated to the explanation of multiplicity enhancement of quarkonia, as well as open heavy flavor $D$ and $B$ mesons.

In non-Hermitian random matrix theory there are three universality classes for local spectral correlations: the Ginibre class and the nonstandard classes ${\mathrm{AI}}^{†}$ and ${\mathrm{AII}}^{†}$. We show that the continuum Dirac operator in two-color QCD coupled to a chiral U(1) gauge field or an imaginary chiral chemical potential falls in class ${\mathrm{AI}}^{†}$ (${\mathrm{AII}}^{†}$) for fermions in pseudoreal (real) representations of SU(2). We introduce the corresponding chiral random matrix theories and verify our predictions in lattice simulations with staggered fermions, for which the correspondence between representation and universality class is reversed. Specifically, we compute the complex eigenvalue spacing ratios introduced recently. We also derive novel spectral sum rules.

We investigate general properties of the eigenvalue spectrum for improved staggered quarks. We introduce a new chirality operator $[{\gamma }_5\otimes 1]$ and a new shift operator $[1\otimes {\xi }_5]$, which respect the same recursion relation as the ${\gamma }_5$ operator in the continuum. Then we show that matrix elements of the chirality operator sandwiched between two eigenstates of the staggered Dirac operator are related to those of the shift operator by the Ward identity of the conserved $U(1{)}_A$ symmetry of staggered fermion actions. We perform a numerical study in quenched QCD using HYP staggered quarks to demonstrate the Ward identity. We introduce a new concept of leakage patterns which collectively represent the matrix elements of the chirality operator and the shift operator sandwiched between two eigenstates of the staggered Dirac operator. The leakage pattern provides a new method to identify zero modes and nonzero modes in the Dirac eigenvalue spectrum. This method is as robust as the spectral flow method but requires much less computing power. Analysis using a machine learning technique confirms that the leakage pattern is universal, since the staggered Dirac eigenmodes on normal gauge configurations respect it. In addition, the leakage pattern can be used to determine a ratio of renormalization factors as a by-product. We conclude that it might be possible and realistic to measure the topological charge $Q$ using the Atiya-Singer index theorem and the leakage pattern of the chirality operator in the staggered fermion formalism.

The compact tetraquark states with fully heavy quark contents $QQ\overline{Q}\overline{Q}$ are studied as the bound states of the diquark-antidiquark within the Bethe-Salpeter framework. The (anti)diquark masses and form factors used are the same as we calculated the doubly heavy baryons in a previous work. Under the instantaneous approximation, the three-dimensional (Bethe-)Salpeter equation of the tetraquarks is derived and solved numerically to obtain the corresponding mass spectra and wave functions of the tetraquarks with $J^{PC}=0^{++}$, $1^{+-}$, and $2^{++}$. Our results show that the three ground states of $cc\overline{c}\overline{c}$ locate in the mass range of 6.4–6.5 GeV, and the $bb\overline{b}\overline{b}$ states in mass range of 19.2–19.3 GeV. The obtained relativistic wave functions naturally include the mixing effects from the possible $D$ (or $G$) partial waves, and then can be further used to do precise calculations of the tetraquark decays. Based on the obtained results, the LHCb’s observation $X(6900)$ is less likely to be the ground states of compact $cc\overline{c}\overline{c}$ tetraquarks but might be the first or second excited states. In addition, a widely used propagatorlike form factor is also investigated and discussed.

The total cross section and differential cross sections for the production of $B_c^{\pm }$ mesons, times their branching fraction to $J/\psi {\pi }^{\pm }$, are measured relative to those for the production of $B^{\pm }$ mesons, times their branching fraction to $J/\psi K^{\pm }$. The data used for this study correspond to an integrated luminosity of $20.3{\mathrm{fb}}^{-1}$ of $pp$ collisions recorded by the ATLAS detector at the Large Hadron Collider in 2012 at a center-of-mass energy of $\sqrt{s}=8\mathrm{TeV}$. The measurement is performed differentially in bins of transverse momentum $p_{\mathrm{T}}$ for $13\mathrm{GeV}<p_{\mathrm{T}}(B_c^{\pm })<22\mathrm{GeV}$ and $p_{\mathrm{T}}(B_c^{\pm })>22\mathrm{GeV}$ and in bins of rapidity $y$ for $|y|<0.75$ and $0.75<|y|<2.3$. The relative cross section times branching fraction for the full range $p_{\mathrm{T}}>13\mathrm{GeV}$ and $|y|<2.3$ is $(0.34\pm 0.04_{\mathrm{stat}}{{}_{-0.02}^{+0.06}}_{\mathrm{sys}}\pm 0.01_{\text{lifetime}})\%$. The differential measurements suggest that the production cross section of the $B_c^{\pm }$ decreases faster with $p_{\mathrm{T}}$ than the production cross section of the $B^{\pm }$, while no significant dependence on rapidity is observed.

In this work we explicitly show that the perturbative unitarity of analytic infinite derivative scalar field theories can be achieved using a modified prescription for computing scattering amplitudes. The crux of the new prescription is the analytic continuation of a result obtained in the Euclidean signature to the Minkowski external momenta. We intensively elaborate an example of a nonlocal ${\varphi }^4$ model for various infinite derivative operators. General UV properties of amplitudes in nonlocal theories are discussed.

The construction of constraint-satisfying initial data is an essential element for the numerical exploration of the dynamics of compact-object binaries. While several codes have been developed over the years to compute generic quasiequilibrium configurations of binaries comprising either two black holes, or two neutron stars, or a black hole and a neutron star, these codes are often not publicly available or they provide only a limited capability in terms of mass ratios and spins of the components in the binary. We here present a new open-source collection of spectral elliptic solvers that are capable of exploring the major parameter space of binary black holes (BBHs), binary neutron stars (BNSs), and mixed binaries of black holes and neutron stars (BHNSs). Particularly important is the ability of the spectral-solver library to handle neutron stars that are either irrotational or with an intrinsic spin angular momentum that is parallel to the orbital one. By supporting both analytic and tabulated equations of state at zero or finite temperature, the new infrastructure is particularly geared toward allowing for the construction of BHNS and BNS binaries. For the latter, we show that the new solvers are able to reach the most extreme corners in the physically plausible space of parameters, including extreme mass ratios and spin asymmetries, thus representing the most extreme BNS computed to date. Through a systematic series of examples, we demonstrate that the solvers are able to construct quasiequilibrium and eccentricity-reduced initial data for BBHs, BNSs, and BHNSs, achieving spectral convergence in all cases. Furthermore, using such initial data, we have carried out evolutions of these systems from the inspiral to after the merger, obtaining evolutions with eccentricities $\lesssim {10}^{-4}-{10}^{-3}$, and accurate gravitational waveforms.

The objective of this work is to investigate the influence of the corrections to the spherical symmetrical accretion of an infinity gas cloud characterized by a polytropic equation into a massive object due to the post-Newtonian approximation. Starting with the steady state post-Newtonian hydrodynamic equations for the mass, mass-energy, and momentum densities, the post-Newtonian Bernoulli equation is derived. The post-Newtonian corrections to the critical values of the flow velocity, sound velocity and radial distance are obtained from the system of hydrodynamics equations in spherical coordinates. It was considered that the ratio of the sound velocity far the massive body and the speed of light was of order $a_{\infty }/c={10}^{-2}$. The analysis of the solution led to following results: the Mach number for the Newtonian and post-Newtonian accretion have practically the same values for radial distances of order of the critical radial distance; by decreasing the radial distance the Mach number for the Newtonian accretion is bigger than the one for the post-Newtonian accretion; the difference between the Newtonian and post-Newtonian Mach numbers when the ratio $a_{\infty }/c\ll {10}^{-2}$ is insignificant; the effect of the correction terms in post-Newtonian Bernoulli equation is more perceptive for the lowest values of the radial distance; the solutions for $a_{\infty }/c>{10}^{-2}$ does not lead to a continuous inflow and outflow velocity at the critical point; the comparison of the solutions with those that follow from a relativistic Bernoulli equation shows that the dependence of the Mach number with the radial distance of the former is bigger than the Newtonian and post-Newtonian Mach numbers.

The present epoch of accelerated cosmic expansion is supposed to be driven by an unknown constituent called dark energy, which in the standard model takes the form of a cosmological constant, characterized by a constant equation of state with $w=-1$. An interesting perspective over the role and nature of dark energy can be achieved by drawing a parallel with a previous epoch of accelerated expansion, inflation, which we assume to be driven by a single scalar field, the inflaton. Since the Planck satellite has constrained the value of the scalar spectral index $n_s$ away from 1, the inflaton cannot be identified with a pure cosmological constant, as is also suggested by the fact that inflation ended. Thus, it is interesting to verify whether a hypothetical observer would have been able to measure the deviation of the equation of state parameter of the inflaton from $-1$. To do so, we consider a class of single-field slow-roll inflationary models dubbed $\mathrm{HSR}\{i\}$, where the hierarchy of Hubble slow-roll parameters is truncated at the $i$th order. The models are tested through a Markov chain Monte Carlo analysis based on combinations of the latest Planck and BICEP2/Keck data sets, and the resulting chains are converted into sets of allowed evolution histories of $w$. $\mathrm{HSR}\{1\}$ is excluded observationally since it would predict that $n_s=1$, in contrast with the recent Planck constraints, while we find that $\mathrm{HSR}\{2\}$ would prefer $w>-1$, but is disfavored by the addition of the BICEP2/Keck data. The overall best description for the data is provided by $\mathrm{HSR}\{3\}$, which yields a 68% upper bound of $1+w<0.0014$. Therefore, if the current era of accelerated expansion happens to have the same equation of state as inflation during the observable epoch, then current and upcoming cosmological observations will not be able to detect that $w\ne -1$. This provides a cautionary tale for drawing conclusions about the nature of dark energy on the basis of the nonobservation of a deviation from $w=-1$.

Production of dark photons inside the Sun forms the basis for the most sensitive probes of such particles over a wide mass range. A small fraction of dark photons is emitted into gravitationally bound orbits, building up a “solar basin” population that survives for astrophysically long times. We show that this population could lead to signals in existing and proposed dark matter detection experiments, opening up significant new parameter space independent of whether dark photons make up the dark matter. Even with conservative assumptions, results from current dark matter experiments already constrain new parameter space; with fiducial assumptions, a solar basin population of dark photons could be responsible for excess events seen in XENON1T. Future low-threshold experiments could be sensitive to these Solar-System-bound dark photons down to sub-eV masses, at couplings orders of magnitude below current constraints.

A new physical phenomenon is described in detail: volumetric stellar emission into gravitationally bound orbits of weakly coupled particles such as axions, moduli, hidden photons, and neutrinos. While only a tiny fraction of the instantaneous luminosity of a star (the vast majority of the emission is into relativistic modes), the continual injection of these particles into a small part of phase space causes them to accumulate over astrophysically long timescales, forming what I call a “stellar basin,” in analogy with the geologic kind. The energy density of the solar basin will surpass that of the relativistic solar flux at Earth’s location after only a million years, for any sufficiently long-lived particle with mass near the solar core’s temperature, and which is produced through an emission process whose matrix elements are unsuppressed at low momentum. This observation has immediate and striking consequences for direct detection experiments—including new limits on axion parameter space independent of dark matter assumptions—and may also increase the prospects for indirect detection of weakly interacting particles around compact stars.

We report results of a search for an isotropic gravitational-wave background (GWB) using data from Advanced LIGO’s and Advanced Virgo’s third observing run (O3) combined with upper limits from the earlier O1 and O2 runs. Unlike in previous observing runs in the advanced detector era, we include Virgo in the search for the GWB. The results of the search are consistent with uncorrelated noise, and therefore we place upper limits on the strength of the GWB. We find that the dimensionless energy density ${\mathrm{\Omega }}_{\mathrm{GW}}\le 5.8\times {10}^{-9}$ at the 95% credible level for a flat (frequency-independent) GWB, using a prior which is uniform in the log of the strength of the GWB, with 99% of the sensitivity coming from the band 20–76.6 Hz; ${\mathrm{\Omega }}_{\mathrm{GW}}(f)\le 3.4\times {10}^{-9}$ at 25 Hz for a power-law GWB with a spectral index of $2/3$ (consistent with expectations for compact binary coalescences), in the band 20–90.6 Hz; and ${\mathrm{\Omega }}_{\mathrm{GW}}(f)\le 3.9\times {10}^{-10}$ at 25 Hz for a spectral index of 3, in the band 20–291.6 Hz. These upper limits improve over our previous results by a factor of 6.0 for a flat GWB, 8.8 for a spectral index of $2/3$, and 13.1 for a spectral index of 3. We also search for a GWB arising from scalar and vector modes, which are predicted by alternative theories of gravity; we do not find evidence of these, and place upper limits on the strength of GWBs with these polarizations. We demonstrate that there is no evidence of correlated noise of magnetic origin by performing a Bayesian analysis that allows for the presence of both a GWB and an effective magnetic background arising from geophysical Schumann resonances. We compare our upper limits to a fiducial model for the GWB from the merger of compact binaries, updating the model to use the most recent data-driven population inference from the systems detected during O3a. Finally, we combine our results with observations of individual mergers and show that, at design sensitivity, this joint approach may yield stronger constraints on the merger rate of binary black holes at $z\gtrsim 2$ than can be achieved with individually resolved mergers alone.

We analyze in detail the production of ${\chi }_c$ and ${\chi }_b$ mesons in $pp$ collisions. Using the color dipole framework, we estimate the cross sections in the kinematics of ongoing and forthcoming experiments and find that our estimates are in reasonable agreement with currently available experimental data. We also analyze the dependence on multiplicity of coproduced hadrons and find that it is significantly milder than that of $S$-wave quarkonia. We expect that an experimental confirmation of this result could constitute an important test of our understanding of multiplicity enhancement mechanisms in the production of different quarkonia states.

We present a complete list of the dimension-eight operator basis in the standard model effective field theory using group theoretic techniques in a systematic and automated way. We adopt a new form of operators in terms of the irreducible representations of the Lorentz group and identify the Lorentz structures as states in a $SU(N)$ group. In this way, redundancy from equations of motion is absent and that from integration by part is treated using the fact that the independent Lorentz basis forms an invariant subspace of the $SU(N)$ group. We also decompose operators into the ones with definite permutation symmetries among flavor indices to deal with subtlety from repeated fields. For the first time to our knowledge, we provide the explicit form of independent flavor-specified operators in a systematic way. Our algorithm can easily be applied to higher-dimensional standard model effective field theory and other effective field theories, making these studies more approachable.

We present a complete and independent list of the dimension-nine operator basis in the Standard Model effective field theory by an automatic algorithm based on the amplitude-operator correspondence. A complete basis ($Y$-basis) is first constructed by enumerating the Young tableau of an auxiliary $SU(N)$ group and the gauge groups, with the equation-of-motion and integration-by-part redundancies all removed. In the presence of repeated fields, another basis ($P$-basis) with explicit flavor symmetries among them is derived from the $Y$-basis, which further induces a basis of independent monomial operators through a systematic process called desymmetrization. Our form of operators has advantages over the traditional way of presenting operators constrained by flavor relations, in the simplicity of both eliminating flavor redundancies and identifying independent flavor-specified operators. We list the 90456 (560) operators for three (one) generations of fermions, all of which violate baryon number or lepton number conservation; among them we find new violation patterns as $\mathrm{\Delta }B=2$ and $\mathrm{\Delta }L=3$, which only appear at the dimensions $d\ge 9$.

Jets constructed via clustering algorithms (e.g., anti-$k_T$, soft-drop) have been proposed for many precision measurements, such as the strong coupling ${\alpha }_s$ and the nucleon intrinsic dynamics. However, the theoretical accuracy is affected by missing QCD corrections at higher orders for the jet functions in the associated factorization theorems. Their calculation is complicated by the jet clustering procedure. In this work, we propose a method to evaluate jet functions at higher orders in QCD. The calculation involves the phase space sector decomposition with suitable soft subtractions. As a concrete example, we present the quark-jet function using the anti-$k_T$ algorithm with $E$-scheme recombination at next-to-next-to-leading order.

Precise measurement of the survival probability $P_{ee}$ of solar electron neutrino (${\nu }_e$) as a function of its energy [$P_{ee}(E_{\nu e})$] is one of the key issues in neutrino physics. Current $P_{ee}$ data, due to their limited accuracy, still allow for nonstandard interactions (NSIs) to be alternatives to the standard one, which is based on the MSW-LMA prediction. In order to determine $P_{ee}$ values at several values of $E_{\nu e}$ with higher accuracy, we propose to use several target nuclei with different threshold energies for ${\nu }_e$ detection. We examined charged-current (CC) responses of various nuclei seeking the ones: (a) having large and concentrated Gamow-Teller (GT) transition strength in the low excitation-energy region, and (b) having appropriate and a variety of reaction $Q$ values, i.e., $\approx 1$ to 17 MeV, in the (${\nu }_e,e^{-}$) reaction. As a result, we found that systematic solar ${\nu }_e$ measurements with target nuclei ${}^6\mathrm{Li}$, ${}^7\mathrm{Li}$, ${}^{12}\mathrm{C}$, ${}^{18}\mathrm{O}$, ${}^{19}\mathrm{F}$, and ${}^{42}\mathrm{Ca}$ can put strong constraints on the $P_{ee}(E_{\nu e})$ curve and thus on these NSI models. In addition, we notice that three of these nuclei, ${}^6\mathrm{Li}$, ${}^7\mathrm{Li}$, and ${}^{12}\mathrm{C}$, have large and concentrated neutral-current (NC) responses with detection threshold-energies of 3.56, 0.48, and 15.11 MeV, respectively. Note that the NC measurement is flavor independent. Thus, the measured results should represent the original strength of ${\nu }_e$ from the Sun.