We perform a detailed study of a specific two Higgs doublet model with a $U(1)$ gauge symmetry, instead of a typical $Z_2$ discrete symmetry, containing a very light gauge boson $Z^{\prime }$ (GeV scale or below). The Standard Model (SM) fermions do not carry $U(1)$ charges, but induced couplings to the $Z^{\prime }$ (called the dark $Z$) are generated through mixing with the SM neutral gauge bosons. Such a light $Z^{\prime }$ could explain some astrophysical anomalies as well as the muon $g-2$ deviation, and has been the subject of great experimental interest. We consider the scenario in which the 125 GeV SM-like Higgs ($H$) is the heavier scalar state, and focus on the lighter neutral state ($h$) as well as charged Higgs. We analyze the constraints on the model from various experiments and predict novel channels to search for these Higgs scalars at the LHC. In particular, experiments looking for lepton jets are among potentially important searches.

It has been recently argued that some longstanding problems in semileptonic $B$ decays can be solved provided the branching ratio for the $B\to D^{\prime (*)}$ semileptonic decays are large enough. We have studied these decays in a constituent quark model, which has been successful in describing semileptonic and nonleptonic $B$ decays into orbitally excited charmed mesons. Our results do not confirm the hypothesis of large branching ratios for the $B\to D^{\prime (*)}$ semileptonic decays. In addition, we calculate the nonleptonic $B\to D^{\prime }\pi$ decays which can provide an independent test of the form factors involved in the $B\to D^{\prime (*)}$ reactions.

Binary neutron stars (BNSs) are the primary source of gravitational waves for the Laser Interferometer Gravitational-Wave Observatory (LIGO) and its international partners Virgo and KAGRA. Current BNS searches target field binaries whose orbits will have circularized by radiation reaction before their gravitational waves enter the advanced LIGO sensitive band at 15 Hz. It has been suggested that a population of BNSs may form by $n$-body interactions near supermassive black holes or in globular clusters and that these systems may have non-negligible eccentricity in the advanced LIGO band. We show that for BNS systems with total mass of $2.4M_{\odot }$ ($6M_{\odot }$), the effect of eccentricity $e\lesssim 0.02$ (0.05) is negligible and a circular search is effectual for these binaries. For eccentricities up to $e=0.4$, we investigate the selection bias caused by neglecting eccentricity in BNS searches. If such high eccentricity systems exist, searches that specifically target eccentric binaries will be needed in advanced LIGO and Virgo.

We investigate a holographic description of $k$-strings in higher representations via D5-branes with world volume fluxes. The D-brane configurations are embedded in supergravity backgrounds dual to confining field theories in three and four dimensions. We compute the tensions and find qualitative agreement for the totally symmetric and totally antisymmetric representations with the results of other methods such as lattice as well as the Hamiltonian approach of Karabali and Nair. A one-loop computation on the D-brane configurations yields the Lüscher term and allows us to confirm a previously proposed universal expression following from holography.

We construct a molecule of fractional vortices with fractional topological lump charges as a baby Skyrmion with the unit topological lump charge in the antiferromagnetic (or XY) baby Skyrme model, that is, an $O(3)$ sigma model with a four-derivative term and an antiferromagnetic or XY-type potential term quadratic in fields. We further construct configurations with topological lump charges $Q\le 7$ and find that bound states of vortex molecules constitute regular polygons with $2Q$ vertices as vortices, where the rotational symmetry $SO(2)$ in real space is spontaneously broken into a discrete subgroup ${\mathbf{Z}}_Q$. We also find metastable and arrayed bound states of fractional vortices for $Q=5$, 6. On the other hand, we find for $Q=7$ that the regular polygon is metastable and the arrayed bound state is stable. We calculate binding energies of all configurations.

It has been argued that the existence of old neutron stars excludes the possibility of nonannihilating light bosonic dark matter, such as that arising in asymmetric dark matter scenarios. If nonannihilating dark matter is captured by neutron stars, the density will eventually become sufficient for black hole formation. However, the dynamics of collapse is highly sensitive to dark matter self-interactions. Repulsive self-interactions, even if extremely weak, can prevent black hole formation. We argue that self-interactions will necessarily be present and estimate their strength in representative models. We also consider the coannihilation of dark matter with nucleons, which arises naturally in many asymmetric dark matter models and which again acts to prevent black hole formation. We demonstrate how the excluded region of the dark matter parameter space shrinks as the strength of such interactions is increased and conclude that neutron star observations do not exclude most realistic bosonic asymmetric dark matter models.

We study the equilibrium structures of white dwarfs with dark matter cores formed by non-self-annihilating dark matter (DM) particles with masses ranging from 1 GeV to 100 GeV, which are assumed to form an ideal degenerate Fermi gas inside the stars. For DM particles of mass 10 GeV and 100 GeV, we find that stable stellar models exist only if the mass of the DM core inside the star is less than $O({10}^{-3})M_{\odot }$ and $O({10}^{-6})M_{\odot }$, respectively. The global properties of these stars, and in particular the corresponding Chandrasekhar mass limits, are essentially the same as those of traditional white dwarf models without DM. Nevertheless, in the 10 GeV case, the gravitational attraction of the DM core is strong enough to squeeze the normal matter in the core region to densities above neutron drip, far above those in traditional white dwarfs. For DM with a particle mass of 1 GeV, the DM core inside the star can be as massive as $\sim 0.1M_{\odot }$ and affects the global structure of the star significantly. In this case, the radius of a stellar model with DM can be about two times smaller than that of a traditional white dwarf. Furthermore, the Chandrasekhar mass limit can also be decreased by as much as 40%. Our results may have implications on the extent to which type Ia supernovae can be regarded as standard candles—a key assumption in the discovery of dark energy.

Oscillons are long-lived, localized, oscillatory scalar field configurations. In this work we derive a condition for the existence of small-amplitude oscillons (and provide solutions) in scalar field theories with noncanonical kinetic terms. While oscillons have been studied extensively in the canonical case, this is the first example of oscillons in scalar field theories with noncanonical kinetic terms. In particular, we demonstrate the existence of oscillons supported solely by the noncanonical kinetic terms, without any need for nonlinear terms in the potential. In the small-amplitude limit, we provide an explicit condition for their stability in $d+1$ dimensions against long-wavelength perturbations. We show that for $d\ge 3$, there exists a long-wavelength instability which can lead to radial collapse of small-amplitude oscillons.

We perform a QCD sum rule analysis for the scalar $f_0(980)$ meson to investigate whether it can be described as a pure bound state of $K$ and $\overline{K}$ mesons. Based on the QCD sum rule with the operators of up to dimension 10 within the operator product expansion, we found that it is hard to treat the $f_0(980)$ as a simple $K\overline{K}$ bound state, which implies that the $f_0(980)$ scalar meson has more complicated structure being mixed states of various configurations.

Many beyond the standard model theories introduce light paraphotons, a hypothetical spin-1 field that kinetically mixes with photons. Microwave cavity experiments have traditionally searched for paraphotons via transmission of power from an actively driven cavity to a passive receiver cavity, with the two cavities separated by a barrier that is impenetrable to photons. We extend this measurement technique to account for two-way coupling between the cavities and show that the presence of a paraphoton field can alter the resonant frequencies of the coupled cavity pair. We propose an experiment that exploits this effect and uses measurements of a cavity’s resonant frequency to constrain the paraphoton-photon mixing parameter $\chi$. We show that such an experiment can improve the sensitivity to $\chi$ over existing experiments for paraphoton masses less than the resonant frequency of the cavity, and that it can eliminate some of the most common systematics for resonant cavity experiments.

Dark matter (DM) self-interactions have important implications for the formation and evolution of structure, from dwarf galaxies to clusters of galaxies. We study the dynamics of self-interacting DM via a light mediator, focusing on the quantum resonant regime where the scattering cross section has a nontrivial velocity dependence. While there are long-standing indications that observations of small scale structure in the Universe are not in accord with the predictions of collisionless DM, theoretical study and simulations of DM self-interactions have focused on parameter regimes with simple analytic solutions for the scattering cross section, with constant or classical velocity (and no angular) dependence. We devise a method that allows us to explore the velocity and angular dependence of self-scattering more broadly, in the strongly coupled resonant and classical regimes where many partial modes are necessary for achieving the result. We map out the entire parameter space of DM self-interactions—and implications for structure observations—as a function of the coupling and the DM and mediator masses. We derive a new analytic formula for describing resonant $s$-wave scattering. Finally, we show that DM self-interactions can be correlated with observations of Sommerfeld enhancements in DM annihilation through indirect detection experiments.

We present a method to evaluate on the lattice the leading isospin breaking effects due to both the small mass difference between the up and down quarks and the QED interaction. Our proposal is applicable in principle to any $\mathrm{QCD}+\mathrm{QED}$ gauge invariant hadronic observable that can be computed on the lattice. It is based on the expansion of the path integral in powers of the small parameters $({\widehat{m}}_d-{\widehat{m}}_u)/{\Lambda }_{\mathrm{QCD}}$ and ${\widehat{\alpha }}_{\mathrm{em}}$, where ${\widehat{m}}_f$ is the renormalized quark mass and ${\widehat{\alpha }}_{\mathrm{em}}$ the renormalized fine structure constant. In this paper we discuss in detail the general strategy of the method and the conventional, although arbitrary, separation of QCD from QED isospin breaking corrections. We obtain results for the pion mass splitting, $M_{{\pi }^{+}}^2-M_{{\pi }^0}^2=1.44(13)(16)\times {10}^3{\mathrm{MeV}}^2$, for the Dashen’s theorem breaking parameter ${\epsilon }_{\gamma }=0.79(18)(18)$, for the light quark masses, $[{\widehat{m}}_d-{\widehat{m}}_u](\overline{\mathrm{MS}},2\mathrm{GeV})=2.39(8)(17)\mathrm{MeV}$, $[{\widehat{m}}_u/{\widehat{m}}_d](\overline{\mathrm{MS}},2\mathrm{GeV})=0.50(2)(3)$, and for the flavor symmetry breaking parameters $R$ and $Q$. We also update our previous results for the QCD isospin breaking corrections to the $K_{\ell 2}$ decay rate and for the QCD contribution to the neutron-proton mass splitting. The numerical results of this paper have been obtained by using the gluon field configurations produced by the ETMC Collaboration with $n_f=2$ dynamical quarks. We treated the dynamical quarks as electrically neutral particles (electroquenched approximation) and neglected a disconnected diagram in the charged and neutral pion mass splitting. We provide all the formulas necessary to remove these approximations and discuss in detail the estimate of the associated systematic uncertainties.

Within the framework of the nonrelativistic quantum chromodynamics, we present a detailed discussion on the heavy quarkonium production at the leading order in ${\alpha }_s$ at a $e^{+}{e}^{-}$ collider with the collision energy around the $Z^0$ peak. Quarkonia are produced through the semi-exclusive channels $e^{+}{e}^{-}\to |H_{Q\overline{Q}}⟩+X$ with $X=Q\overline{Q}$ or $gg$, where $Q$ indicates a heavy quark (respectively, $b$ or $c$). It is noted that in addition to the color-singlet $1S$-level quarkonium states, the $2S$ and $1P$ color-singlet states and the color-octet $|(Q\overline{Q})[1{}^{3}S_1^{(\mathbf{8})}]g⟩$ state also provide sizable contributions. The heavy quarkonium transverse momentum and rapidity distributions for the $e^{+}{e}^{-}$ collision energy $E_{\mathrm{cm}}=m_Z$ are presented. For both charmonium and bottomonium production via the $Z^0$ propagator, there is approximate “spin degeneracy” between the spin-triplet and spin-singlet quarkonium states. Uncertainties for the total cross sections are estimated by taking $m_c=1.50\pm 0.15\mathrm{GeV}$ and $m_b=4.90\pm 0.15\mathrm{GeV}$. Around $E_{\mathrm{cm}}=m_Z$, due to the $Z^0$-boson resonance effect, total cross sections for the channels via the $Z^0$-propagator become much larger than the channels via the virtual photon propagator. We conclude that, in addition to the $B$ factories such as BABAR and Belle, and the hadronic colliders such as Tevatron and LHC, such a super $Z$ factory will present an excellent platform for studying the heavy quarkonium properties.

In this paper we study the three-point correlation functions of two scalar operators with large conformal dimensions and the $R$-current or stress-energy tensor at strong coupling with the help of the ${\mathrm{AdS}}_4/{\mathrm{CFT}}_3$ correspondence. The scalar operators are dual to semiclassical strings in ${\mathrm{AdS}}_4\times C{P}^3$, which are pointlike in AdS. We establish thorough concordance between string theory results at large coupling constant and general predictions coming from Ward identities in the dual three-dimensional superconformal gauge theory.

We find a regime in which a strongly coupled striped superconductor features a superconducting dome. This regime is signified by i) a modulating chemical potential that averages to zero, and ii) a superconducting order parameter that has a scaling dimension $3/2<\Delta \le 3$. We also find that in this regime, the order parameter exhibits a mild dependence on the modulation wavelength of the stripes.

Emergent gravity is based on the Darboux theorem or the Moser lemma in symplectic geometry, stating that the electromagnetic force can always be eliminated by a local coordinate transformation as far as $U(1)$ gauge theory is defined on a spacetime with symplectic structure. In this approach, the spacetime geometry is defined by $U(1)$ gauge fields on noncommutative (NC) spacetime. Accordingly, the topology of spacetime is determined by the topology of NC $U(1)$ gauge fields. We show that the topology change of spacetime is ample in emergent gravity and the subsequent resolution of spacetime singularity is possible in NC spacetime. Therefore, the emergent gravity approach provides a well-defined mechanism for the topology change of spacetime which does not suffer from any spacetime singularity, in sharp contrast to general relativity.

We consider the two-particle irreducible Cornwall-Jackiw-Tomboulis effective action at finite temperature for a noncommutative real scalar field theory in four dimensions, with noncommutativity among space and time variables. By means of a Rayleig-Ritz variation, we study the solutions of a stripe-type nonuniform background, which depends on space and time, and hence on temperature. The analysis in the first approximation shows that such solutions appear in the planar limit, as already known, but also under normal noncommutativity, in an anisotropic region which has not been considered. Further, we show that the transition from the uniform ordered phase to the nonuniform one is first order.

We investigate the creation of massless quasiparticle pairs from the vacuum state in graphene by the space homogeneous time-dependent electric field. For this purpose the formalism of ($2+1$)-dimensional quantum electrodynamics is applied to the case of a nonstationary background with arbitrary time dependence allowing the $S$-matrix formulation of the problem. The number of created pairs per unit of graphene area is expressed via the asymptotic solution at $t\to \infty$ of the second-order differential equation of an oscillator-type with a complex frequency satisfying some initial conditions at $t\to -\infty$. The obtained results are applied to the electric field with specific dependence on time admitting the exact solution of the Dirac equation. The number of created pairs per unit area is calculated analytically in a wide variety of different regimes depending on the parameters of the electric field. The investigated earlier case of the static electric field is reproduced as a particular case of our formalism. It is shown that the creation rate in a time-dependent field is often larger than in a static field.

We have investigated the features of the gauge vector field in a braneworld scenario built as a warped product between a 3-brane and a 2-cycle of the resolved conifold. This scenario allowed us to study how the gauge field behaves when the transverse manifold evolves upon a geometric flow that controls the singularity at the origin. Also, since the transverse manifold has a cylindrical symmetry according to the 3-brane, this geometry can be regarded as a near brane correction of the stringlike branes. Indeed, by means of a new warp function and the angular metric component of the resolved conifold, the braneworld can exhibit a conical form near the origin as well as a regular behavior in that region. The analysis of the gauge field in this background has been carried out for the $s$-wave state and a normalizable massless mode was found. For the massive modes, the resolution parameter avoids an infinite well on the brane and controls the depth of the well and the height of the barrier around the brane. The massive modes are slightly changed near the brane but they agree with the stringlike spectrum for large distances.