Cosmic strings that couple to neutrinos may account for a portion of the high-energy astrophysical neutrino (HEAN) flux seen by IceCube. Here, we calculate the observed spectrum of neutrinos emitted from a population of cosmic-string loops that contain quasicusps, quasikinks, or kink-kink collisions. We consider two broad neutrino emission models: one where these string features emit a neutrino directly, and one where they emit a scalar particle which then eventually decays to a neutrino. In either case, we find the spectrum of cosmic-string neutrinos to follow a two-parameter model described by a power law with a high-energy cutoff. While none of the models in question fully match the observed HEAN spectrum, we do find that the maximum contribution of cosmic-string neutrinos can still be an $\mathcal{O}(1)$ fraction of the observed flux in addition to producing a bump in the observed neutrino spectrum. Finally, for each of the models presented, we present the viable parameter space for neutrino emission.

Sources of high-energy cosmic rays are presently unknown, but can be constrained in various ways. Some of these constraints can be graphically presented on the so-called Hillas diagram. Previous versions of this diagram determined the range of geometrical sizes and magnetic fields of potential astrophysical accelerators, taking into account geometrical criteria and radiation losses. In this work, we update the Hillas diagram for protons, taking into account the losses associated with the $p\gamma$ and photopair interactions, relating the allowed regions to the source electromagnetic luminosity. The strongest constraints are obtained for bright compact sources such as the central regions of active galactic nuclei.

Numerical simulations of neutron star mergers represent an essential step toward interpreting the full complexity of multimessenger observations and constraining the properties of supranuclear matter. Currently, simulations are limited by an array of factors, including computational performance and input physics uncertainties, such as the neutron star equation of state. In this work, we expand the range of nuclear phenomenology efficiently available to simulations by introducing a new analytic parametrization of cold, beta-equilibrated matter that is based on the relativistic enthalpy. We show that the new enthalpy parametrization can capture a range of nuclear behavior, including strong phase transitions. We implement the enthalpy parametrization in the spectre code, simulate isolated neutron stars, and compare performance to the commonly used spectral and polytropic parametrizations. We find comparable computational performance for nuclear models that are well represented by either parametrization, such as simple hadronic equations of state. We show that the enthalpy parametrization further allows us to simulate more complicated hadronic models or models with phase transitions that are inaccessible to current parametrizations.

The problem of spontaneous vacuum decay in low-energy collisions of heavy nuclei is considered beyond the scope of the monopole approximation. The time-dependent Dirac equation is solved in a rotating coordinate system with $z$-axis directed along the internuclear line and the origin placed at the center of mass. The probabilities of electron-positron pair creation and the positron energy spectra are calculated in the approximation neglecting the rotational coupling. The two-center potential is expanded over spherical harmonics and the convergence with respect to the number of terms in this expansion is studied. The results show that taking into account the two-center potential instead of its spherically symmetric part preserves all the signatures of the transition to the supercritical regime that have been found in the framework of the monopole approximation and even enhances some of them.

We investigate the implications of one vanishing minor in the neutrino mass matrix using trimaximal mixing matrix. In this context, we analyze all six patterns of one vanishing minor zero in the neutrino mass matrix and present correlations of the neutrino oscillation parameters. All the six patterns are found to be phenomenologically viable with the present neutrino oscillation data. We also predict the values of effective Majorana mass, the effective electron antineutrino mass, and the total neutrino mass for all the patterns. The value obtained for the effective neutrino mass is within the reach future neutrinoless double $\beta$ decay experiments. We also propose a flavor model where such patterns can be generated within the seesaw model.

Baryon asymmetry of the Universe is evaluated in the model originally proposed by Aoki et al. [Phys. Rev. Lett. 102, 051805 (2009)], where Majorana masses of neutrinos are generated via three-loop diagrams composed of additional scalar bosons including the dark matter candidate which is odd under an unbroken $Z_2$ symmetry. In order for the model to include multiple $CP$-violating phases, we do not impose the softly broken $Z_2$ symmetry imposed in the original model to avoid the flavor-changing neutral current at tree level. Instead, for simplicity, we assume the flavor alignment structure in the Yukawa interactions. We also simply assume the alignment structure in the Higgs potential so that the Higgs couplings coincide with those in the standard model at tree level. Under these phenomenological simplifications, the model still contains multiple $CP$-violating phases. By using destructive interferences among them, it is compatible with the stringent constraint from the electric dipole moment measurements to generate the observed baryon asymmetry along with the scenario of electroweak baryogenesis. We show a benchmark scenario which can explain neutrino mass, dark matter, and baryon asymmetry of the Universe simultaneously and can satisfy all the other available experimental data. Some phenomenological predictions of the model are also discussed.

We study a bottom-up, holographic description of a field theory yielding the spontaneous breaking of an approximate $SO(5)$ global symmetry to its $SO(4)$ subgroup. The weakly coupled, six-dimensional gravity dual has regular geometry. One of the dimensions is compactified on a circle that shrinks smoothly to zero size at a finite value of the holographic direction, hence introducing a physical scale in a way that mimics the effect of confinement in the dual four-dimensional field theory. We study the spectrum of small fluctuations of the bulk fields carrying $SO(5)$ quantum numbers, which can be interpreted as spin-0 and spin-1 bound states in the dual field theory. This work supplements an earlier publication focused only on the $SO(5)$ singlet states. We explore the parameter space of the theory, paying particular attention to composite states that have the right quantum numbers to be identified as pseudo-Nambu-Goldstone bosons (PNGBs). We find that in this model the PNGBs are generally heavy, with masses of the same order as other bound states, indicating the presence of a sizeable amount of explicit symmetry breaking in the field-theory side. Nevertheless, we also find a qualitatively new, unexpected result. When the dimension of the field-theory operator inducing $SO(5)$ breaking is close to half the space-time dimensionality, there exists a region of parameter space in which the PNGBs and the lightest scalar are both parametrically light in comparison to all other bound states of the field theory. Although this region is known to yield metastable classical backgrounds, this finding might be relevant to model building in the composite Higgs context.

Nonstandard neutrino interactions (NSI) arising from light and heavy mediators probe different sectors of the parameter space of models focusing on phenomena that require the extension of the standard model. High-energy scattering experiments are not relevant on constraining the NSI hiding a light mediator at the fundamental level, while flavor-universal NSI cannot be probed with neutrino oscillation experiments. Currently the only way to measure flavor-universal NSI with a light mediator is to rely on coherent elastic neutrino-nucleon scattering experiments, which we use to derive bounds for light mediator flavor-universal NSI. For light NSI, we obtain ${ϵ}^u\in [-14.85,14.79]$ and ${ϵ}^d=[-13.19,13.84]$ (90% CL.). We also derive constraints on flavor-universal heavy NSI and find a $2\sigma$ tension. Finally, we discuss the implications of the experiments on the allowed parameter space of a specific example model, called superweak extension of the standard model.

I show that spontaneous breaking of vector flavor symmetry on the lattice is impossible in gauge theories with a positive functional-integral measure, for discretized Dirac operators linear in the quark masses, if the corresponding propagator and its commutator with the flavor symmetry generators can be bounded in norm independently of the gauge configuration and uniformly in the volume. Under these assumptions, any order parameter vanishes in the symmetric limit of fermions of equal masses. I show that these assumptions are satisfied by staggered, minimally doubled and Ginsparg-Wilson fermions for positive fermion mass, for any value of the lattice spacing, and so in the continuum limit if this exists. They are instead not satisfied by Wilson fermions, for which spontaneous vector flavor symmetry breaking is known to take place in the Aoki phase. The existence of regularizations unaffected by residual fermion doubling for which the symmetry cannot break spontaneously on the lattice establishes rigorously (at the physicist’s level) the impossibility of its spontaneous breaking in the continuum for any number of flavors.

We present a light-front model calculation of the pion parton distribution functions (PDFs) and the pion electromagnetic form factor. The pion state is modeled in terms of light-front wave functions (LFWFs) for the $q\overline{q}$, $q\overline{q}q\overline{q}$, $q\overline{q}g$, and $q\overline{q}gg$ components. We design the LFWFs so that the parameters in the longitudinal- and transverse-momentum space enter separately in the fit of the pion PDFs and the electromagnetic form factor, respectively. We extract the pion PDFs within the xFitter framework using available Drell-Yan and photon-production data. With the obtained parameters in the longitudinal-momentum space, we then fit the available experimental data on the pion electromagnetic form factor to constrain the remaining parameters in the transverse-momentum space. The results for the pion PDFs are compatible with existing extractions and lattice calculations, and the fit to the pion electromagnetic form factor data works quite successfully. The obtained parametrization for the LFWFs marks a step forward toward a unified description of different hadron distribution functions in both the longitudinal- and transverse-momentum space and will be further applied to a phenomenological study of transverse-momentum-dependent parton distribution functions and generalized parton distributions.

A dynamically constrained phase-space coalescence (dcpc) model was introduced to study the exotic state ${\chi }_{c1}(3872)$ yield for three possible structures: tetraquark state, nuclearlike state, and molecular state respectively, where the hadronic final states generated by the parton and hadron cascade model (paciae). The ${\chi }_{c1}(3872)/\psi (2S)$ cross-section ratio from beauty-hadron decays (nonprompt) based on the ${\chi }_{c1}(3872)$ or $\psi (2S)\to J/\psi {\pi }^{+}{\pi }^{-}$ bound state in the decay chains as a function of charged-particle multiplicity and transverse momentum in $pp$ collisions at $\sqrt{s}=8\mathrm{TeV}$ are calculated. A tetraquark state scenario from paciae$+$dcpc model shows better agreement with the LHCb and ATLAS measurements for the nonprompt ${\chi }_{c1}(3872)/\psi (2S)$ cross-section ratio distributions, indicating that the ${\chi }_{c1}(3872)$ is more likely to be a compact tetraquark state.

We explore the impact of strong classical color fields, which occur in the earliest stages of heavy-ion collisions and are known as the glasma, on the classical transport of hard probes, namely heavy quarks and jets. To achieve this, we simulate SU(3) color fields using classical real-time lattice gauge theory and couple them to an ensemble of test particles whose dynamics are described by Wong’s equations. We provide an overview of how classical color algebras are constructed and introduce a method to generate random classical SU(3) color charges. We extensively test our numerical particle solver in the limits of infinitely massive heavy quarks and ultrarelativistic lightlike jets and obtain excellent quantitative agreement with previous studies. Going towards realistic masses and initial momenta, we extract longitudinal and transverse momentum broadening for heavy quarks and jets. The resulting accumulated momenta and the anisotropy of these dynamical hard probes exhibit deviations from limiting scenarios, showing that the full dynamics have a significant effect.

We calculate radiative decay rates of mesons and glueballs in the top-down holographic Witten-Sakai-Sugimoto model with finite quark masses. After assessing to what extent this model agrees or disagrees with experimental data, we present its predictions for so far undetermined decay channels. Contrary to widespread expectations, we obtain sizeable two-photon widths of scalar, tensor, and pseudoscalar glueballs, suggesting in particular that the observed two-photon rate of the glueball candidate $f_0(1710)$ is not too large to permit a glueball interpretation, but could be even much higher. We also discuss the so-called exotic scalar glueball, which in the Witten-Sakai-Sugimoto model is too broad to match either of the main glueball candidates $f_0(1500)$ and $f_0(1710)$ but might be of interest with regard to the alternative scenario of the so-called fragmented scalar glueball. Employing the exotic scalar glueball for the latter, much smaller two-photon rates are predicted for the ground-state glueball despite a larger total width; relatively large two-photon rates would then apply to the excited scalar glueball described by the predominantly dilatonic scalar glueball. In either case, the resulting contributions to the muon $g-2$ from hadronic light-by-light scattering involving glueball exchanges are small compared to other single meson exchanges, of the order of $\lesssim {10}^{-12}$.

Exclusive heavy-vector meson photoproduction is a prominent signal in collider experiments with hadron beams. At the highest photon-hadron collision energies, this process is considered as a candidate to constrain the gluon parton distribution function (PDF) at small longitudinal momentum fractions. However, in the framework of collinear factorization, exclusive particle production is described in terms of generalized parton distributions (GPDs). In this contribution, we investigate the connection between GPDs and PDFs at the leading order in ${\alpha }_s$. Our main result is a proposal to quantify the systematic uncertainty inherent to this connection. We put our approach into context with respect to the Shuvaev transform. Our uncertainty estimate can be straightforwardly adapted to higher fixed orders and small-$x$ resummation. The question of extrapolating GPDs to vanishing skewness is paramount for the program of the Electron Ion Collider, notably for the extraction of the radial distributions of partons.

By analyzing $2.93{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ collision data taken at the center-of-mass energy of 3.773 GeV with the BESIII detector, the branching fractions of the inclusive decays $D^{+}\to K_S^{0}X$ and $D^0\to K_S^{0}X$ are measured to be $(33.11\pm 0.13\pm 0.36)\%$ and $(20.75\pm 0.12\pm 0.20)\%$, respectively, where the first uncertainties are statistical and the second are systematic. These results are consistent with the world averages of previous measurements, but with much improved precision.

The minimal-length paradigm, a possible implication of quantum gravity at low energies, is commonly understood as a phenomenological modification of Heisenberg’s uncertainty relation. We show that this modification is equivalent to a cut-off in the space conjugate to the position representation, i.e. the space of wave numbers, which does not necessarily correspond to momentum space. This result is generalized to several dim ensions and noncommutative geometries once a suitable definition of the wave number is provided. Furthermore, we find a direct relation between the ensuing bound in wave-number space and the minimal-length scale. For scenarios in which the existence of the minimal length cannot be explicitly verified, the proposed framework can be used to clarify the situation. Indeed, applying it to common models, we find that one of them does, against all expectations, allow for arbitrary precision in position measurements. In closing, we comment on general implications of our findings for the field. In particular, we point out that the minimal length is purely kinematical such that, effectively, it is not influenced by the overlying dynamics and the choice of Hamiltonian.

The propagation of perturbations is studied with generalized holonomy corrections in a fully consistent way, ensuring that the deformed algebra of constraints remains closed. The primordial cosmological power spectra are calculated. It is shown that, although the detailed form of the correction does unavoidably impact the observables, the main known results of loop quantum cosmology are robust in this respect.

We study a holographic model of quantum chromodynamics, which can describe a color superconductor and a dilute nucleon gas phase. The two phases are adjoined in the phase diagram at a critical value of the chemical potential. In other words, a first-order transition from the ordinary nucleon gas to the color superconductor is found by increasing the chemical potential. This model is suitable to investigate the possibility of a cold compact star with a color superconducting core. The equation of state of the star is given by the holographic model considered in this article, and we find that it is impossible in the present model to find a hybrid star of nuclear matter and the color superconductor core through the relation of mass and radius of the star by solving the Tolman-Oppenheimer-Volkoff equations. Several other interesting implications are given by using the equation of state.

We first present a consistent canonical formulation of the general (nonmarginal) Oppenheimer-Snyder model. The switching between comoving and stationary observer is achieved by promoting coordinate transformations between dust proper time and Schwarzschild-Killing time to canonical ones. This leads to a multivalued Hamiltonian, which is deparameterizable. We then discuss the quantization of comoving and stationary observers by employing the method of affine coherent state quantization (ACSQ). We thereby demonstrate that under certain conditions the quantum corrected trajectories can replace the classical singularity by a bounce. We then show that both comoving and stationary observers see this bouncing collapse behavior. We finally discuss a switching between these classes of observers at the quantum level.

We discuss the relationship between the Bogoliubov transformations, squeezed states, entanglement, and maximum violation of the Bell-Clauser-Horne-Shimony-Holt (Bell-CHSH) inequality. In particular, we point out that the construction of the four bounded operators entering the Bell-CHSH inequality can be worked out in a simple and general way, covering a large variety of models, ranging from quantum mechanism to relativistic quantum field theories. Various examples are employed to illustrate the above mentioned framework. We start by considering a pair of entangled spin-one particles and a squeezed oscillator in quantum mechanics, moving then to the relativistic complex quantum scalar field and to the analysis of the vacuum state in Minkowski space-time in terms of the left and right Rindler modes. In the latter case, the Bell-CHSH inequality turns out to be parametrized by the Unruh temperature.