We have chosen the reactions $D_s^{+}\to {\pi }^{+}{\pi }^0{a}_0(980)(f_0(980))$ investigating the isospin violating channel $D_s^{+}\to {\pi }^{+}{\pi }^0{f}_0(980)$. The reaction was chosen because by varying the ${\pi }^0{a}_0(980)(f_0(980))$ invariant mass one goes through the peak of a triangle singularity emerging from $D_s^{+}\to {\pi }^{+}{\overline{K}}^{*}K$, followed by ${\overline{K}}^{*}\to \overline{K}{\pi }^0$ and the further merging of $K\overline{K}$ to produce the $a_0(980)$ or $f_0(980)$. We found that the amount of isospin violation had its peak precisely at the value of the ${\pi }^0{a}_0(980)(f_0(980))$ invariant mass where the singularity has its maximum, stressing the role of the triangle singularities as a factor to enhance the mixing of the $f_0(980)$ and $a_0(980)$ resonances. We calculate absolute rates for the reactions and show that they are within present measurable range. The measurement of these reactions would bring further information into the role of triangle singularities in isospin violation and the $a_0-f_0$ mixing, in particular, and shed further light into the nature of the low energy scalar mesons.

Using target space null reduction of the Polyakov action, we find a novel covariant action for strings moving in a torsional Newton-Cartan geometry. Sending the string tension to zero while rescaling the Newton-Cartan clock 1-form, so as to keep the string action finite, we obtain a nonrelativistic string moving in a new type of non-Lorentzian geometry that we call $U(1)$-Galilean geometry. We apply this to strings on ${\mathrm{AdS}}_5\times S^5$ for which we show that the zero tension limit is realized by the spin matrix theory limits of the AdS/CFT correspondence. This is closely related to limits of spin chains studied in connection to integrability in AdS/CFT. The simplest example gives a covariant version of the Landau-Lifshitz sigma-model.

The motion of time-like test particles in the Fisher/Janis-Newman-Winicour (F/JNW) spacetime is studied with the Hamiltonian formulation of the geodesic equations. The spacetime is characterized by its mass parameter $r_g$ and scalar field parameter $\nu$. The innermost bound and stable circular orbits are calculated and the effective potential is analyzed. Consistent with numerical results in earlier literature, for $\nu <\frac{1}{2}$, particles with nonzero angular momentum encounter an infinite potential barrier, preventing them from reaching the naked singularity at $r=r_g$. Periodic orbits in the spacetime are also obtained. Compared to the periodic orbits around the Schwarzschild black hole, it is found that typically lower energies are required for the same orbits in the F/JNW spacetime.

Studying the effects of dark energy and modified gravity on cosmological scales has led to a great number of physical models being developed. The effective field theory (EFT) of cosmic acceleration allows an efficient exploration of this large model space, usually carried out on a phenomenological basis. However, constraints on such parametrized EFT coefficients cannot be trivially connected to fundamental covariant theories. In this paper we reconstruct the class of covariant Horndeski scalar-tensor theories that reproduce the same background dynamics and linear perturbations as a given EFT action. One can use this reconstruction to interpret constraints on parametrized EFT coefficients in terms of viable covariant Horndeski theories. We demonstrate this method with a number of well-known models and discuss a range of future applications.

We investigate toroidal marginally outer trapped surfaces (MOTS) and marginally outer trapped tubes (MOTT) in closed Friedmann-Lemaître-Robertson-Walker (FLRW) geometries. They are constructed by embedding constant mean curvature (CMC) Clifford tori in a FLRW spacetime. This construction is used to assess the quality of certain isoperimetric inequalities, recently proved in axial symmetry. Similarly to spherically symmetric MOTS existing in FLRW spacetimes, the toroidal ones are also unstable.

We present a family of exact black-hole solutions on a static spherically symmetric background in second-order generalized Proca theories with derivative vector-field interactions coupled to gravity. We also derive nonexact solutions in power-law coupling models including vector Galileons and numerically show the existence of regular black holes with a primary hair associated with the longitudinal propagation. The intrinsic vector-field derivative interactions generally give rise to a secondary hair induced by nontrivial field profiles. The deviation from General Relativity is most significant around the horizon and hence there is a golden opportunity for probing the Proca hair by the measurements of gravitational waves (GWs) in the regime of strong gravity.

We study all translationally and rotationally invariant local theories involving massless spin 2 and spin 1 particles that mediate long range forces, allowing for general energy relations and violation of boost invariance. Although gauge invariance is not a priori required to describe non-Lorentz invariant theories, we first establish that locality requires soft gauge invariance. Then by taking the soft graviton limit in scattering amplitudes, we prove that in addition to the usual requirement of universal graviton couplings, the special relativistic energy-momentum relation is also required and must be exact. We contrast this to the case of theories with only spin $\le 1$ particles, where, although we can still derive charge conservation from locality, special relativity can be easily violated. We provide indications that the entire structure of relativity can be built up from spin 2 in this fashion.

Stellar-mass primordial black holes (PBH) have been recently reconsidered as a dark matter (DM) candidate after the aLIGO discovery of several binary black hole (BH) mergers with masses of tens of $M_{\odot }$. Matter accretion on such massive objects leads to the emission of high-energy photons, capable of altering the ionization and thermal history of the universe. This, in turn, affects the statistical properties of the cosmic microwave background (CMB) anisotropies. Previous analyses have assumed spherical accretion. We argue that this approximation likely breaks down and that an accretion disk should form in the dark ages. Using the most up-to-date tools to compute the energy deposition in the medium, we derive constraints on the fraction of DM in PBH. Provided that disks form early on, even under conservative assumptions for accretion, these constraints exclude a monochromatic distribution of PBH with masses above $\sim 2M_{\odot }$ as the dominant form of DM. The bound on the median PBH mass gets more stringent if a broad, log-normal mass function is considered. A deepened understanding of nonlinear clustering properties and BH accretion disk physics would permit an improved treatment and possibly lead to more stringent constraints.

We propose that there is a regime of quantum gravity phenomena, for the case that the cosmological constant is small and positive, which concerns physics at temperatures below the de Sitter temperature, or length scales larger than the horizon. We observe that the standard form of the equivalence principle does not apply in this regime; we consider instead that a weakened form of the equivalence principle might hold in which the ratio of gravitational to inertial mass is a function of environmental parameters. We consider possible principles to determine that function. These lead to behavior that, in the limit of $\hslash \to 0$ and $c\to \infty$, reproduces the modifications of Newtonian dynamics first proposed by Milgrom. Thus modified newtonian dynamics is elucidated as coding the physics of a novel regime of quantum gravity phenomena. We propose also an effective description of this regime in terms of a bimetric theory, valid in the approximation where the metric is static. This predicts a new effect, which modifies gravity for radial motions.

In this work we explore the effects of a weak magnetic field and a thermal bath on the decay process of a neutral scalar boson into two charged scalar bosons. Our findings indicate that a magnetic field inhibits pair production, while temperature enhances it. The employed formalism allows us to isolate the contribution of magnetic fields in vacuum, leading to a separate analysis of the effects of different ingredients. This is essential since the analytical computation of the decay width requires some approximation and the results that can be found in the literature are not always coincident. We perform the calculation in vacuum by two different weak-field approximations. The particle pair production in vacuum is found to coincide with finite-temperature behavior, which is opposite the results obtained by other authors in scenarios that involve neutral particles decaying into a pair of charged fermions. Among other differences between these scenarios, we find out that the analytical structure of the self-energy imposed by the spin of particles involved in the process is determinant in the behavior of the decay rate with the magnetic field.

We consider nontopological first-order solitons arising from a gauged $CP(2)$ model in the presence of the Maxwell term multiplied by a nontrivial dielectric function. We implement the corresponding first-order scenario by minimizing the total energy, thus introducing the corresponding energy lower bound; such a construction is only possible due to a differential constraint that includes the dielectric function itself and the self-interacting potential defining the model. We saturate the aforementioned bound by focusing our attention on those solutions fulfilling a particular set of two coupled first-order differential equations. Next, in order to solve these equations, we choose the dielectric function explicitly, and also calculate the corresponding self-interacting potential. We impose appropriate boundary conditions that support nontopological solitons, from which we verify that the energy of final structures is proportional to the magnetic flux they engender: both quantities are not quantized, as expected. We depict the new numerical solutions, while commenting on the main properties they present.

We consider the production at the LHC of exotic quarks $U^{+}$ of charge $Q=+(5/3)e$ and $D^{-}$ of charge $Q=-(4/3)e$ of mass $m_{*}$ arising in a composite fermion scenario characterized by a compositeness scale $\mathrm{\Lambda }$. Such states are predicted in composite models of higher isospin multiplets ($I_W=1$ or $I_W=3/2$). Given their exotic charges (such as $5/3$), their decays proceed through the electroweak interactions. We compute decay widths and rates for resonant production of the exotic quarks at the LHC. Partly motivated by the recent observation of an excess by the CMS collaboration in the $e{\cancel{p}}_{T}jj$ final state signature we focus on $pp\to U^{+}j\to W^{+}+jj\to {\ell }^{+}{\cancel{p}}_{T}jj$ and then perform a fast simulation of the detector reconstruction based on Delphes. We then scan the parameter space of the model ($m_{*}=\mathrm{\Lambda }$) and study the statistical significance of the signal against the relevant standard model background ($Wjj$ followed by leptonic decay of the $W$ gauge boson) providing the luminosity curves as function of $m_{*}$ for discovery at 3- and $5\text{−}\sigma$ level.

We revisit the static potential for the $QQ\overline{Q}\overline{Q}$ system using SU(3) lattice simulations, studying both the color singlets’ ground state and first excited state. We consider geometries where the two static quarks and the two antiquarks are at the corners of rectangles of different sizes. We analyze the transition between a tetraquark system and a two-meson system with a two by two correlator matrix. We compare the potentials computed with quenched QCD and with dynamical quarks. We also compare our simulations with the results of previous studies and analyze quantitatively fits of our results with Ansätze inspired in the string flip-flop model and in its possible color excitations.

We compute the slope and curvature, at vanishing four-momentum transfer squared, of the leading order hadronic vacuum polarization function, using lattice quantum chromodynamics. Calculations are performed with $2+1+1$ flavors of staggered fermions directly at the physical values of the quark masses and in volumes of linear extent larger than 6 fm. The continuum limit is carried out using six different lattice spacings. All connected and disconnected contributions are calculated, up to and including those of the charm.

In a matrix model of pure SU(2) Yang-Mills theory, boundaries emerge in the space of ${\text{Mat}}_3(\mathbb{R})$ and the Hamiltonian requires boundary conditions. We show the existence of edge localized glueball states that can have negative energies. These edge levels can be lifted to positive energies if the gluons acquire a London-like mass. This suggests a new phase of QCD with an incompressible bulk.

We outline a holographic recipe to reconstruct ${\alpha }^{\prime }$ corrections to anti–de Sitter (AdS) (quantum) gravity from an underlying CFT in the strictly planar limit ($N\to \infty$). Assuming that the boundary CFT can be solved in principle to all orders of the ’t Hooft coupling $\lambda$, for scalar primary operators, the ${\lambda }^{-1}$ expansion of the conformal dimensions can be mapped to higher curvature corrections of the dual bulk scalar field action. Furthermore, for the metric perturbations in the bulk, the $\mathrm{AdS}/\mathrm{CFT}$ operator-field isomorphism forces these corrections to be of the Lovelock type. We demonstrate this by reconstructing the coefficient of the leading Lovelock correction, also known as the Gauss-Bonnet term in a bulk AdS gravity action using the expression of stress-tensor two-point function up to subleading order in ${\lambda }^{-1}$.

We study the discretization of three-dimensional gravity with $\mathrm{\Lambda }=0$ following the loop quantum gravity framework. In the process, we realize that different choices of polarization are possible. This allows us to introduce a new discretization based on the triad as opposed to the connection as in the standard loop quantum gravity framework. We also identify the classical nontrivial symmetries of discrete gravity, namely the Drinfeld double, given in terms of momentum maps. Another choice of polarization is given by the Chern-Simons formulation of gravity. Our framework also provides a new discretization scheme of Chern-Simons, which keeps track of the link between the continuum variables and the discrete ones. We show how the Poisson bracket we recover between the Chern-Simons holonomies allows us to recover the Goldman bracket. There is also a transparent link between the discrete Chern-Simons formulation and the discretization of gravity based on the connection (loop gravity) or triad variables (dual loop gravity).