We investigate the use of data-driven likelihoods to bypass a key assumption made in many scientific analyses, which is that the true likelihood of the data is Gaussian. In particular, we suggest using the optimization targets of flow-based generative models, a class of models that can capture complex distributions by transforming a simple base distribution through layers of nonlinearities. We call these flow-based likelihoods (FBL). We analyze the accuracy and precision of the reconstructed likelihoods on mock Gaussian data, and show that simply gauging the quality of samples drawn from the trained model is not a sufficient indicator that the true likelihood has been learned. We nevertheless demonstrate that the likelihood can be reconstructed to a precision equal to that of sampling error due to a finite sample size. We then apply FBLs to mock weak lensing convergence power spectra, a cosmological observable that is significantly non-Gaussian (NG). We find that the FBL captures the NG signatures in the data extremely well, while other commonly used data-driven likelihoods, such as Gaussian mixture models and independent component analysis, fail to do so. This suggests that works that have found small posterior shifts in NG data with data-driven likelihoods such as these could be underestimating the impact of non-Gaussianity in parameter constraints. By introducing a suite of tests that can capture different levels of NG in the data, we show that the success or failure of traditional data-driven likelihoods can be tied back to the structure of the NG in the data. Unlike other methods, the flexibility of the FBL makes it successful at tackling different types of NG simultaneously. Because of this, and consequently their likely applicability across datasets and domains, we encourage their use for inference when sufficient mock data are available for training.

Spacecraft observations of cosmic ray antimatter intensities can potentially shed new light on previously unknown physics and hence play an essential role in the search for dark matter. At lower energies, however, these particles experience considerable modulation in the heliosphere. Since the advent of cosmic ray modulation studies, simplified approaches to solving the Parker transport equation have been used to glean insights from observations as to the behavior of these particles. We show, due to the inherent limitations imposed by the assumptions made in simplifying the Parker equation, that the use of these approaches can introduce unknown uncertainties into analyses based on them, and thus that these approaches should be used with caution, especially when novel insights into potentially new physics are sought.

The detection of binary neutron star mergers represents one of the most important and complex astrophysical discoveries of the recent years. One of the unclear aspects of the problem is the turbulent magnetic field amplification, initially triggered by the Kelvin-Helmholtz instability at much smaller scales than any reachable numerical resolution nowadays. Here we present numerical simulations of the first 10 milliseconds of a binary neutron star merger. First, we confirm in detail how the simulated amplification depends on the numerical resolution and is distributed on a broad range of scales, as expected from turbulent magnetohydrodynamics theory. We find that an initial large-scale magnetic field of ${10}^{11}\mathrm{G}$ inside each star is amplified in the remnant to root-mean-square values above ${10}^{16}\mathrm{G}$ within the first 5 milliseconds for our highest-resolution run. Then, we run large eddy simulations, exploring the performance of the subgrid-scale gradient model, already tested successfully in previous turbulent box simulations. We show that the addition of this model is especially important in the induction equation, since it leads to an amplification of the magnetic field comparable to a higher-resolution run, but with a greatly reduced computational cost. In the first 10 milliseconds, there is no clear hint for an ordered, large-scale magnetic field, which should indeed occur in longer timescales through magnetic winding and the magnetorotational instability.

Collective excitations in condensed matter systems, such as phonons and magnons, have recently been proposed as novel detection channels for light dark matter. We show that excitation of (i) optical phonon polaritons in polar materials in an $\mathcal{O}(1\mathrm{T})$ magnetic field (via the axion-photon coupling), and (ii) gapped magnons in magnetically ordered materials (via the axion wind coupling to the electron spin), can cover the difficult-to-reach $\mathcal{O}(1–100)\mathrm{meV}$ mass window of QCD axion dark matter with less than a kilogram-year exposure. Finding materials with a large number of optical phonon or magnon modes that can couple to the axion field is crucial, suggesting a program to search for a range of materials with different resonant energies and excitation selection rules; we outline the rules and discuss a few candidate targets, leaving a more exhaustive search for future work. Ongoing development of single photon, phonon, and magnon detectors will provide the key for experimentally realizing the ideas presented here.

In this paper we present a higher-dimensional seesaw mechanism. We consider a single, flat extra dimension, where a fat brane is localized and contains the standard model (SM) fields, similar to universal extra dimension models. There is only one Dirac fermion in the bulk, and in four dimensions it results in two towers of Kaluza-Klein (KK) Majorana sterile neutrinos, whose mass mixing with the SM neutrinos is suppressed due to a brane-localized kinetic term. The interaction between the sterile neutrinos and the SM is through the usual coupling with the Higgs boson, where the coupling depends upon the compactification radius $R^{-1}={10}^{-2}-1\mathrm{GeV}$ and the width of the fat brane $L^{-1}=2\mathrm{TeV}$, where the latter value is chosen to avoid LHC constraints. Due to this suppression mechanism the mass of the lightest sterile neutrinos can be of order $\mathcal{O}(1-10)\mathrm{TeV}$ while naturally explaining the small SM neutrino mass, which in turn is easily obtained for a large range of parameter choices. Furthermore, neutrino oscillations are not substantially influenced by the tower of sterile KK particles. Finally, leptogenesis is investigated in this setup, and it is viable for some values within the parameter space.

We propose a low-scale renormalizable trinification theory that successfully explains the flavor hierarchies and neutrino puzzle in the Standard Model (SM), as well as provides a dark matter candidate and also contains the necessary means for efficient leptogenesis. The proposed theory is based on the trinification $\mathrm{SU}(3{)}_{\mathrm{C}}\times \mathrm{SU}(3{)}_{\mathrm{L}}\times \mathrm{SU}(3{)}_{\mathrm{R}}$ gauge symmetry, which is supplemented with an additional flavor symmetry $\mathrm{U}(1{)}_{\mathrm{X}}\times {\mathbb{Z}}_2^{(1)}\times {\mathbb{Z}}_2^{(2)}$. In the proposed model the top quark and the exotic fermions acquire tree-level masses, whereas the lighter SM charged fermions gain masses radiatively at one-loop level. In addition, the light active neutrino masses arise from a combination of radiative and type-I seesaw mechanisms, with the Dirac neutrino mass matrix generated at one-loop level.

We show that the electron recoil excess around 2 keV claimed by the Xenon Collaboration can be fitted by dark matter (DM) or DM-like particles having a fast component with velocity of order $\sim 0.1$. Those particles cannot be part of the cold DM halo of our Galaxy, so we speculate about their possible nature and origin, such as fast-moving DM subhalos, semiannihilations of DM and relativistic axions produced by a nearby axion star. Feasible new physics scenarios must accommodate exotic DM dynamics and unusual DM properties.

A quantum algorithm is developed to calculate decay rates and cross sections using quantum resources that scale polynomially in the system size assuming similar scaling for state preparation and time evolution. This is done by computing finite-volume one- and two-particle Green’s functions on the quantum hardware. Particle decay rates and two-particle scattering cross sections are extracted from the imaginary parts of the Green’s function. A $0+1$ dimensional implementation of this method is demonstrated on IBM’s superconducting quantum hardware for the decay of a heavy scalar particle to a pair of light scalars.

This paper presents a method for alleviating sign problems in lattice path integrals, including those associated with finite fermion density in relativistic systems. The method makes use of information gained from some systematic expansion—such as perturbation theory—in order to accelerate the Monte Carlo computation. The method is exact, in the sense that no approximation to the lattice path integral is introduced. Thanks to the underlying systematic expansion, the method is systematically improvable, so that an arbitrary reduction in the sign problem can in principle be obtained. The Thirring model (in $0+1$ and $1+1$ dimensions) is used to demonstrate the ability of this method to reduce the finite-density sign problem.

The motivation and construction of the original quenched Eguchi-Kawai (QEK) model are reviewed, providing much greater detail than in the first, 1982 QEK paper. A 2008 article announced that QEK fails as a reduced model because the average over permutations of eigenvalues stays annealed. It is shown here that the original quenching logic naturally leads to a formulation with no annealed average over permutations.

Results of a lattice field theory simulation of the single-flavor Thirring model in $2+1$ spacetime dimensions are presented. The lattice model is formulated using domain wall fermions as a means to recover the correct U(2) symmetries of the continuum model in the limit where the wall separation $L_s\to \infty$. Simulations on ${12}^3,16^3\times L_s$, varying self-interaction strength $g^2$ and bare mass $m$, are performed with $L_s=8,\dots ,48$, and the results for the bilinear condensate $⟨\overline{\psi }\psi ⟩$ are fitted to a model equation of state assuming a $\mathrm{U}(2)\to \mathrm{U}(1)\otimes \mathrm{U}(1)$ symmetry-breaking phase transition at a critical $g_c^2$. First estimates for $g_c^{-2}a$ and critical exponents are presented, showing small but significant departures from mean-field values. The results confirm that a symmetry-breaking transition does exist and therefore the critical number of flavors for the Thirring model $N_c>1$. Results for both the condensate and associated susceptibility are also obtained in the broken phase on ${16}^3\times 48$, suggesting that here the $L_s\to \infty$ extrapolation is not yet under control. We also present results obtained with the associated $2+1\mathrm{D}$ truncated overlap operator $D_{\mathrm{OL}}$ demonstrating exponential localization, a necessary condition for the recovery of U(2) global symmetry, but that the recovery of the Ginsparg-Wilson condition as $L_s\to \infty$ is extremely slow in the broken phase.

The divergent part of the one-loop Vilkovisky unique effective action for quantum Einstein gravity is evaluated in the general parametrization of the quantum field, including the separated conformal factor. The output of this calculation explicitly demonstrates the parametrization and conformal gauge independence of the unique effective action with the configuration space metric chosen following Vilkovisky’s prescription.

We study two families of composite twisted Ramond fields (made by products of two operators) in the $\mathcal{N}=(4,4)$ supersymmetric D1-D5 ${\mathrm{SCFT}}_2$ deformed by a marginal modulus operator away from its $(T^4{)}^N/S_N$ free orbifold point. We construct the large-$N$ contributions to the four-point functions with two composite operators and two deformation fields. These functions allow us to derive short-distance operator product expansion limits and to calculate the anomalous dimensions of the composite operators. We demonstrate that one can distinguish two sets of composite Ramond states with twists $m_1$ and $m_2$: protected states, for which $m_1+m_2=N$, and “lifted” states for which $m_1+m_2<N$. The latter require an appropriate renormalization. We also derive the leading order corrections to their two-point functions, and to their three-point functions with the deformation operator.

Continuing our work on the nature and existence of fluctuation-dissipation relations (FDR) in linear and nonlinear open quantum systems [J.-T. Hsiang, B. L. Hu, and S.-Y. Lin, Phys. Rev. D 100, 025019 (2019); J.-T. Hsiang, B. L. Hu, S.-Y. Lin, and K. Yamamoto, Phys. Lett. B 795, 694 (2019); J.-T. Hsiang and B. L. Hu, Physics (Utrecht) 1, 430 (2019); J.-T. Hsiang and B. L. Hu, Phys. Rev. D 101, 125003 (2020)], here we consider such relations when a linear system is in a nonequilibrium steady state (NESS). With the model of two-oscillators (considered as a short harmonic chain with the two ends) each connected to a thermal bath of different temperatures we find that when the chain is fully relaxed due to interaction with the baths, the relation that connects the noise kernel and the imaginary part of the dissipation kernel of the chain in one bath does not assume the conventional form for the FDR in equilibrium cases. There exists an additional term we call the “bias current” that depends on the difference of the bath’s initial temperatures and the interoscillator coupling strength. We further show that this term is related to the steady heat flow between the two baths when the system is in an NESS. The ability to know the real-time development of the interheat exchange (between the baths and the end-oscillators) and the intraheat transfer (within the chain) and their dependence on the parameters in the system offers possibilities for quantifiable control, and in the design of quantum heat engines, or thermal devices.

We take into account two further physical models which play an utmost importance in the framework of analog gravity. We first consider Bose-Einstein condensates (BEC) and then surface gravity waves in water. Our approach is based on the use of the master equation we introduced in a previous work. A more complete analysis of the singular perturbation problem involved, with particular reference to the behavior in the neighborhood of the (real) turning point and its connection with the Wentzel-Kramers-Brillouin approximation, allows us to verify the thermal character of the particle production process. Furthermore, we can provide a simple scheme apt to calculate explicitly the gray-body factors in the case of BEC and surface waves. This corroborates the improved approach we proposed for studying the analog Hawking effect in the usual limit of small dispersive effects.

We consider further the problem of the analog Hawking radiation. We propose a fourth order ordinary differential equation, which allows us to discuss the problem of Hawking radiation in analog gravity in a unified way, encompassing fluids and dielectric media. In a suitable approximation, involving weak dispersive effects, Wentzel-Kramers-Brillouin solutions are obtained far from the horizon (turning point), and furthermore an equation governing the behavior near the horizon is derived, and a complete set of analytical solutions is obtained also near the horizon. The subluminal case of the original fluid model introduced by Corley and Jacobson and the case of dielectric media are discussed. We show that in this approximation scheme there is a mode which is not directly involved in the pair-creation process. Thermality is verified and a framework for calculating the gray-body factor is provided.

Cold dark stars made of self-gravitating fermions in the degenerate limit are constructed in general relativity and in R-square gravity, $f(R)=R+\alpha R^2$. The properties of the resulting cold dark stars in both theories of gravity are studied. It is found that the same gravitational potential is generated for different election of the parameters of the model, such as the mass of the fermion, the self-interacting strength, or the value of $\alpha$; thus, a possible confusion in the determination of the dark matter properties and the favored theory of gravity might arise.

The annihilation and decay of dark matter (DM) during the dark ages can leave imprints in the cosmic microwave background (CMB) radiation by altering the cosmic reionization process. CMB polarization anisotropy can be sensitive to such energy injection at higher redshift and therefore helps reducing degeneracy between spectral parameters in $\mathrm{\Lambda }\mathrm{CDM}$ and other astrophysical parameters. In light of several upcoming CMB polarization experiments, such as AdvACTPol, AliCPT, CLASS, Simons Observatory, Simons Array, SPT-3G, we forecast their prospective sensitivity in probing dark matter annihilation and decay signals. We find that future missions have 95% C.L. projected limits on DM decay and annihilation rates to orders of ${\mathrm{\Gamma }}_{\chi }({\tau }_{\chi }^{-1})\sim {10}^{-27}{\mathrm{s}}^{-1}$ and $⟨\sigma v⟩/m_{\chi }\sim {10}^{-29}{\mathrm{cm}}^3{\mathrm{s}}^{-1}{\mathrm{GeV}}^{-1}$, respectively, significantly improving the sensitivity to DM from current experimental bounds.

We revisit the signatures from collisions of cosmic rays on sub-GeV dark matter (DM) in the Milky Way. In addition to the upscattered DM component that can be probed by existing DM and neutrino experiments widely discussed, we examine the associated signals in $\gamma$ rays and neutrinos that span a wide energy range due to the inelastic scatterings. Assuming a simple vector portal DM model for illustration, we compute both the upscattered DM flux by cosmic-ray protons and the resulting emission of secondary $\gamma$ rays and high-energy neutrinos from proton excitation, hadronization, and the subsequent meson decay. We derive limits on coupling constants in the vector portal model using data from the $\gamma$-ray and high-energy neutrino telescopes including Fermi, H.E.S.S., and IceCube. These limits are compared to those obtained by considering the upscattered DM signals at the low-energy DM (neutrino) detectors XENON1T (MiniBooNE) and IceCube. For this particular model, the limits are set predominantly by nondetection of the upscattered DM events in XENON1T, for most of the DM mass range due to the large scattering cross section at low energies. Nevertheless, our study demonstrates that the $\gamma$-ray and neutrino signals, traditionally considered as indirect probes for DM annihilation and decay, can also be directly used to constrain the DM-nucleon interaction in complementary to the direct search experiments.