We present a novel method for revealing the equation of state of high-density neutron star matter through gravitational waves emitted during the postmerger phase of a binary neutron star system. The method relies on a small number of detections of the peak frequency in the postmerger phase for binaries of different (relatively low) masses, in the most likely range of expected detections. From such observations, one can construct the derivative of the peak frequency vs the binary mass, in this mass range. Through a detailed study of binary neutron star mergers for a large sample of equations of state, we show that one can extrapolate the above information to the highest possible mass (the threshold mass for black hole formation in a binary neutron star merger). In turn, this allows for an empirical determination of the maximum mass of cold, nonrotating neutron stars to within $0.1M_{\odot }$, while the corresponding radius is determined to within a few percent. Combining this with the determination of the radius of cold, nonrotating neutron stars of $1.6M_{\odot }$ [to within a few percent, as was demonstrated in Bauswein et al. Phys. Rev. D 86, 063001 (2012)], allows for a clear distinction of a particular candidate equation of state among a large set of other candidates. Our method is particularly appealing because it reveals simultaneously the moderate and very high-density parts of the equation of state, enabling the distinction of mass-radius relations even if they are similar at typical neutron star masses. Furthermore, our method also allows us to deduce the maximum central energy density and maximum central rest-mass density of cold, nonrotating neutron stars with an accuracy of a few percent.

The ${}^7\mathrm{Li}$ abundance calculated in BBN with the baryon-to-photon ratio fixed from fits to the CMB power spectrum is inconsistent with the observed lithium abundances on the surface of metal-poor halo stars. Previous cosmological solutions proposed to resolve this ${}^7\mathrm{Li}$ problem include photon cooling (possibly via the Bose-Einstein condensation of a scalar particle) or the decay of a long-lived $X$ particle (possibly the next-to-lightest supersymmetric particle). In this paper we reanalyze these solutions, both separately and in concert. We also introduce the possibility of a primordial magnetic field (PMF) into these models. We constrain the $X$ particles and the PMF parameters by the observed light element abundances using a likelihood analysis to show that the inclusion of all three possibilities leads to an optimum solution to the lithium problem. We deduce allowed ranges for the $X$ particle parameters and energy density in the PMF that can solve ${}^7\mathrm{Li}$ problem.

Weinberg recently pointed out a flaw in the standard argument that large $N_c$ QCD with color-fundamental quarks [QCD(F)] cannot yield narrow tetraquark states. In particular, he observed that the argument does not rule out narrow tetraquarks associated with the leading-order connected diagrams; such tetraquarks would have a width scaling as $N_c^{-1}$. It is shown here, however, that while the standard analysis of tetraquarks does not rule them out, a more thorough analysis rules out quantum-number exotic tetraquarks associated with the leading-order connected diagrams. This analysis is based entirely on conventional assumptions used in large $N_c$ physics applied to the analytic properties of meson-meson scattering. Our result implies that one of three possibilities must be true: (i) quantum-number exotic tetraquarks do not exist at large $N_c$; (ii) quantum-number exotic tetraquarks exist, but are associated with subleading connected diagrams and have anomalously small widths that scale as $N_c^{-2}$ or smaller; or (iii) the conventional assumptions used in large $N_c$ analysis are inadequate.

The Higgs associated production cross section at an $e^{+}{e}^{-}$ collider is indirectly sensitive to the Higgs self-coupling, $h^3$, at next-to-leading order (NLO). Utilizing this, a new indirect method is proposed for constraining deviations in the self-coupling below the di-Higgs production threshold in certain models. Although this indirect constraint is model dependent, making it valid only under specific assumptions, meaningful indirect constraints on the self-coupling may be realized. Specific realistic scenarios where the indirect constraint applies are discussed and in particular it is shown that in the well-motivated class of two Higgs-doublet models there exist regions of parameter space in which the NLO effects from a modified self-coupling dominate over the leading order modifications, demonstrating a concrete scenario in which large modifications of the Higgs self-coupling may be indirectly constrained using the proposed method. Other models, such as strongly coupled scenarios, are also discussed. The indirect method would give valuable constraints on deviations in the Higgs self-coupling, and would be complementary to the direct measurements possible with di-Higgs production at other colliders, providing precious additional information in the effort to unravel the properties of the Higgs boson.

We calculate universal finite-size scaling functions for the order parameter and the longitudinal susceptibility of the three-dimensional $O(4)$ model. The phase transition of this model is supposed to be in the same universality class as the chiral transition of two-flavor QCD. The scaling functions serve as a testing device for QCD simulations on small lattices, where, for example, pseudocritical temperatures are difficult to determine. In addition, we have improved the infinite-volume limit parametrization of the scaling functions by using newly generated high statistics data for the three-dimensional $O(4)$ model in the high-temperature region on an $L=120$ lattice.

We study the spectrum of heavy-light mesons within a model with linear instantaneous confining potential. The single-quark Green function and spontaneous breaking of chiral symmetry are obtained from the Schwinger-Dyson (gap) equation. For the meson spectrum we derive a Bethe-Salpeter equation. We solve this equation numerically in the heavy-light limit and obtain effective restoration of chiral and $U(1{)}_A$ symmetries at large spins.

By considering semi-inclusive deep-inelastic scattering and the (complementary) $q_T$-spectrum for Drell-Yan lepton pair production we derive the QCD evolution for all the leading-twist transverse momentum dependent distribution and fragmentation functions. We argue that all of those functions evolve with $Q^2$ following a single evolution kernel. This kernel is independent of the underlying kinematics and it is also spin independent. Those features hold, in impact parameter space, to all values of $b_T$. The evolution kernel presented has all of its large logarithms resummed up to next-to-next-to leading logarithmic accuracy, which is the highest possible accuracy given the existing perturbative calculations. As a study case we apply this kernel to investigate the evolution of the Collins function, one of the ingredients that have recently attracted much attention within the phenomenological studies of spin asymmetries. Our analysis can be readily implemented to revisit previously obtained fits that involve data at different scales for other spin-dependent functions. Such improved fits are important to get better predictions—with the correct evolution kernel—for certain upcoming experiments aiming to measure the Sivers function, Collins function, transversity, and other spin-dependent functions as well.

Based on a general form of the effective vertex functions for the decays of $P$-wave charmonia ${\chi }_{cJ}$, angular distribution formulas for the subsequent decays ${\chi }_{cJ}\to J/\psi \gamma$ and $J/\psi \to {\mu }^{+}{\mu }^{-}$ are derived. The formulas are the same as those obtained in a different approach in the literature. Our formulas are expressed in a more general form, including parity violation effects and the full angular dependence of $J/\psi$ and muon in the cascade decay ${\chi }_{cJ}\to J/\psi \gamma \to {\mu }^{+}{\mu }^{-}\gamma$. The ${\chi }_{cJ}$ polarization observables are expressed in terms of rational functions of the spin density matrix elements of ${\chi }_{cJ}$ production. Generalized rotation-invariant relations for arbitrary integer-spin particles are also derived and their expressions in terms of observable angular distribution parameters are given in the ${\chi }_{c1}$ and ${\chi }_{c2}$. To complement our previous direct-$J/\psi$ polarization result, we also discuss the impact on the observable prompt-$J/\psi$ polarization. As an illustrative application of our angular distribution formulas, we present the angular distributions in terms of the tree-level spin density matrix elements of ${\chi }_{c1}$ and ${\chi }_{c2}$ production in several different frames at the Large Hadron Collider. Moreover, a reweighting method is also proposed to determine the entire set of the production spin density matrix elements of the ${\chi }_{c2}$, some of which disappear or are suppressed for vanishing higher-order multipole effects making the complete extraction difficult experimentally.

In this work, we study all the observed $a_2$ states and group them into the $a_2$ meson family, where their total and two-body Okubo-Zweig-Iizuka allowed strong decay partial widths are calculated via the quark pair creation model. Taking into account the present experimental data, we further give the corresponding phenomenological analysis, which is valuable to test whether each $a_2$ state can be assigned into the $a_2$ meson family. What is more important is that the prediction of their decay behaviors will be helpful for future experimental study of the $a_2$ states.

The LHCb experiment observed $B^{+}\to {\pi }^{+}{\mu }^{+}{\mu }^{-}$ decay with $1.0{\mathrm{fb}}^{-1}$ data, which is the first measurement of a flavor changing neutral current $b\to d{\ell }^{+}{\ell }^{-}$ decay ($\ell =e,\mu$). Based on QCD factorization, we give standard model predictions for the branching ratios, direct CP asymmetries, and isospin asymmetry for $B\to \pi {\ell }^{+}{\ell }^{-}$ decays, in the kinematic region where the dilepton invariant mass is small. We find that the contribution from weak annihilation enhances the direct CP asymmetry for low ${\ell }^{+}{\ell }^{-}$ pair mass. Anticipating improved measurements, we assess the utility of $B^{+}\to {\pi }^{+}{\ell }^{+}{\ell }^{-}$ observables, when combined with $B^0\to {\pi }^{-}{\ell }^{+}\nu$ and $B^{+}\to K^{+}{\ell }^{+}{\ell }^{-}$, for determining Cabibbo-Kobayashi-Maskawa matrix parameters in the future.

We propose a new model where the Dirac mass term for neutrinos, the Majorana mass term for right-handed neutrinos, and the other new fermion masses arise via the spontaneous breakdown of the $\mathrm{U}(1{)}_{\mathrm{B}-\mathrm{L}}$ gauge symmetry. The anomaly-free condition gives four sets of assignment of the $\mathrm{B}-\mathrm{L}$ charge to new particles, and three of these sets have an associated global $\mathrm{U}(1{)}_{\mathrm{DM}}$ symmetry which stabilizes dark matter candidates. The dark matter candidates contribute to generating the Dirac mass term for neutrinos at the one-loop level. Consequently, tiny neutrino masses are generated at the two-loop level via a type-I-seesaw-like mechanism. We show that this model can satisfy current bounds from neutrino oscillation data, the lepton flavor violation, the relic abundance of the dark matter, and the direct search for the dark matter. This model would be tested at future collider experiments and dark matter experiments.

We propose a possible explanation for the recent claim of an excess at 3.5 keV in the x-ray spectrum within a minimal extension of the standard model that explains dark matter and baryon abundance of the Universe. The dark matter mass in this model is $\mathcal{O}(\text{GeV})$ and its relic density has a nonthermal origin. The model includes two colored scalars of $\mathcal{O}(\text{TeV})$ mass ($X_{1,2}$), and two singlet fermions that are almost degenerate in mass with the proton ($N_{1,2}$). The heavier fermion $N_2$ undergoes radiative decay to the lighter one $N_1$ that is absolutely stable. Radiative decay with a lifetime $\sim {10}^{23}$ seconds can account for the claimed 3.5 keV line, which requires couplings $\sim {10}^{-3}–{10}^{-1}$ between $X_{1,2}$, $N_{1,2}$ and the up-type quarks. The model also gives rise to potentially detectable monojet, dijet, and monotop signals at the LHC.

Very recently, the IceCube Collaboration reported a flux of neutrinos in the energy range $50\mathrm{TeV}\lesssim E_{\nu }\lesssim 2\mathrm{PeV}$, which departs from expectations from atmospheric background at the $5.7\sigma$ level. This flux is in remarkable agreement with the expected diffuse flux of neutrinos from starburst galaxies, and the three highest energy events have uncertainty contours encompassing some of such systems. These events, all of which have well-measured energies above 1 PeV, exhibit shower topologies, for which the angular resolution is about 15°. Due to this angular uncertainty and the a posteriori nature of cuts used in our study, it is not possible to assign a robust statistical significance to this association. Using muon tracks, which have angular resolution $<1°$, we compute the number of observations required to make a statistically significant statement and show that in a few years of operation the upgraded IceCube detector should be able to confirm or refute this hypothesis. We also note that double bang topology rates constitute a possible discriminator among various astrophysical sources.

We consider the stellar oscillations of relativistic stars in the Eddington-inspired Born-Infeld gravity (EiBI). In order to examine the specific frequencies, we derive the perturbation equations governing the stellar oscillations in EiBI by linearizing the field equations and numerically determine the oscillation frequencies by changing the coupling parameter in EiBI, $\kappa$, and stellar models. As a result, we find that the frequencies depend strongly on the value of $\kappa$, where the frequencies in EiBI with negative $\kappa$ become higher and those with positive $\kappa$ become lower than the expectations in general relativity. We also find that, via the observation of the fundamental frequency, one could distinguish EiBI with $8\pi {\epsilon }_0|\kappa |\gtrsim 0.03$ from general relativity, independently of the equation of state for neutron star matter, where ${\epsilon }_0$ denotes the nuclear saturation density and ${\epsilon }_0\kappa$ becomes a dimensionless parameter. With the further constraints on equation of state, one might distinguish EiBI even with $8\pi {\epsilon }_0|\kappa |\lesssim 0.03$ from general relativity.