Flavor Quantum Numbers Research Articles

Entanglement in flavored scalar scattering

We investigate quantum entanglement in high-energy 2 → 2 scalar scattering, where the scalars are characterized by an internal flavor quantum number acting like a qubit. Working at the 1-loop order in perturbation theory, we build the final-state density matrix as a function of the scattering amplitudes connecting the initial to the outgoing state. In this construction, the unitarity of the S-matrix is guaranteed at the required order by the optical theorem. We consider the post-scattering entanglement between the momentum and flavor degrees of freedom of the final-state particles, as well as the entanglement of the two-qubit flavor subsystem. In each case we identify the couplings of the scalar potential that can generate, destroy, or transfer entanglement between different bipartite subspaces of the Hilbert space.

Inclusive Hadronic Decay Rate of the τ Lepton from Lattice QCD: The u[over ¯]s Flavor Channel and the Cabibbo Angle.

We present a lattice determination of the inclusive decay rate of the process τ↦X_{us}ν_{τ} in which the τ lepton decays into a generic hadronic state X_{us} with u[over ¯]s flavor quantum numbers. Our results have been obtained in n_{f}=2+1+1 isosymmetric QCD with full nonperturbative accuracy, without any operator product expansion approximation and, except for the presently missing long-distance isospin-breaking corrections, include a solid estimate of all sources of theoretical uncertainties. This has been possible by using the Hansen-Lupo-Tantalo method [M. Hansen etal., Phys. Rev. D 99, 094508 (2019)PRVDAQ2470-001010.1103/PhysRevD.99.094508] that we have already successfully applied [A. Evangelista etal., Phys. Rev. D 108, 074513 (2023)PRVDAQ2470-001010.1103/PhysRevD.108.074513] to compute the inclusive decay rate of the process τ↦X_{ud}ν_{τ} in the u[over ¯]d flavor channel. By combining our first-principles theoretical results with the presently available experimental data, we extract the Cabibbo-Kobayashi-Maskawa matrix element |V_{us}|, the Cabibbo angle, with a 0.9% accuracy, dominated by the experimental error.

Production of Strange and Charm Hadrons in Pb+Pb Collisions at sNN = 5.02 TeV

Using a quark combination model with the equal-velocity combination approximation, we study the production of hadrons with strangeness and charm flavor quantum numbers in Pb+Pb collisions at sNN= 5.02 TeV. We present analytical expressions and numerical results for these hadrons’ transverse momentum spectra and yield ratios. Our numerical results agree well with the experimental data available. The features of strange and charm hadron production in the quark–gluon plasma at the early stage of heavy ion collisions are also discussed.

Electroweak flavour unification

We propose that the electroweak and flavour quantum numbers of the Standard Model (SM) could be unified at high energies in an SU(4) × Sp(6)L× Sp(6)R anomaly-free gauge model. All the SM fermions are packaged into two fundamental fields, ΨL ∼ (4,6,1) and ΨR ∼ (4,1,6), thereby explaining the origin of three families of fermions. The SM Higgs, being electroweakly charged, necessarily becomes charged also under flavour when embedded in the UV model. It is therefore natural for its vacuum expectation value to couple only to the third family. The other components of the UV Higgs fields are presumed heavy. Extra scalars are needed to break this symmetry down to the SM, which can proceed via ‘flavour-deconstructed’ gauge groups; for instance, we propose a pattern Sp(6)L→ {prod}_{i=1}^3mathrm{SU}{(2)}_{L,i}to mathrm{SU}{(2)}_L for the left-handed factor. When the heavy Higgs components are integrated out, realistic quark Yukawa couplings with in-built hierarchies are naturally generated without any further ingredients, if we assume the various symmetry breaking scalars condense at different scales. The CKM matrix that we compute is not a generic unitary matrix, but it can precisely fit the observed values.

Consideration of Additive Quantum Numbers of Fermions and Their Conservations

Two new flavor quantum numbers D and U for down and up quarks, respectively, are introduced, and then quark quantum number H is proposed as the sum of the flavor quantum numbers of quarks. Moreover, lepton quark-like quantum number HL and finally fermion quantum number F are brought forward. Old and new additive quantum numbers are conserved at three different levels in weak interaction, and F builds up a clear relationship to the electric charge of fermions.

Freezing In with lepton flavored fermions

Dark, chiral fermions carrying lepton flavor quantum numbers are natural candidates for freeze-in. Small couplings with the Standard Model fermions of the order of lepton Yukawas are `automatic' in the limit of Minimal Flavor Violation. In the absence of total lepton number violating interactions, particles with certain representations under the flavor group remain absolutely stable. For masses in the GeV-TeV range, the simplest model with three flavors, leads to signals at future direct detection experiments like DARWIN. Interestingly, freeze-in with a smaller flavor group such as SU(2) is already being probed by XENON1T.

Vector mesons on the wall

A domain-wall configuration of the η′ meson bounded by a string (called a pancake or a Hall droplet) is recently proposed to describe the baryons with spin Nc/2. In order to understand its baryon number as well as the flavor quantum number, we argue that the vector mesons (the ρ and ω mesons) should play an essential role for the consistency of the whole picture. We determine the effective theory of large-Nc QCD with Nf massless fermions by taking into account a mixed anomaly involving the θ-periodicity and the global symmetry. The anomaly matching requires the presence of a dynamical domain wall on which a mathrm{U}{left({N}_fright)}_{-{N}_c} Chern-Simons theory is supported. We consider the boundary conditions that should be imposed on the edge of the domain wall, and conclude that there should be a boundary term that couples the mathrm{U}{left({N}_fright)}_{-{N}_c} gauge field to the vector mesons. We discuss the impact on physics of the chiral phase transition and the relation to the “duality” of QCD.

Systematic study of the muon-nucleus overlap integrals for various processes in muonic atoms

As it is known, the bound muon of a muonic atom can participate in many electroweak processes as the allowed channels of the ordinary ^""-capture by the atomic nucleus, μ~ •+- (A, Z) -» (A,Z — l) + νβ, and the muon decay in orbit, μ~ -» e~ + υμ ·+- ve, as well as the exotic channels of the muon-to-electron, μ~ + (A, Z) —> (.A, Z)* + e~, and muon-to-positron, μ~ + (A, Ζ) -» (A, Ζ — 2) + e+, conversions. The latter reactions have not been seen by experiments up to now, but they are predicted by various extensions of the standard model (they violate the flavor and/or lepton quantum numbers). For all the above muonic processes, the muon-nucleus overlap integrals are necessary in order to calculate the relevant rates. These integrals can be evaluated if, in addition to the nuclear states, the wave function of the bound muon (also that of the outgoinglepton) are known. In the present work, we perform precise calculations of the muon (and electron/positron) wave functions for both the Schrödinger and Dirac equations. We use modern neural network techniques to overcome the difficulties arising from the finite size of the nucléon and nuclear Coulomb potential. As some applications, the obtained muonnucleus integrals for various muonic atoms are going to be used for evaluating exclusive muon-capture rates and muon to electron/positron conversion branching ratios.

(Anti-)symmetrizing wave functions

The construction of fully (anti-)symmetric states with many particles, when the single particle state carries multiple quantum numbers, is a problem that seems to have not been systematically addressed in the literature. A quintessential example is the construction of ground state baryon wave functions where the color singlet condition reduces the problem to just two (flavor and spin) quantum numbers. In this paper, we address the general problem by noting that it can be re-interpreted as an eigenvalue equation and provide a formalism that applies to the generic number of particles and the generic number of quantum numbers. As an immediate result, we find a complete solution to the two quantum number case, from which the baryon wave function problem with an arbitrary number of flavors follows. As a more elaborate illustration that reveals complications not visible in the two quantum number case, we present the complete class of states possible for a system of five fermionic particles with three quantum numbers each. Our formalism makes systematic use of properties of the symmetric group and Young tableaux. Even though our motivations to consider this question have their roots in Sachdev-Ye-Kitaev-like tensor models and holography, the problem and its solution should have broader applications.

Exotic doubly charmed Ds0*(2317)D and Ds1*(2460)D* molecules

The $D_{s0}^*(2317) D$ and $D_{s1}^*(2460) D^*$ heavy meson systems can exchange a kaon that is emitted in S-wave owing to the opposite intrinsic parity of the $D_{s0}^*$($D_{s1}^*$) and $D$($D^*$) mesons. As a consequence of the mass difference of the $D_{s0}^*$($D_{s1}^*$) and $D$($D^*$) mesons, the range of the kaon exchange potential will be significantly longer than expected, corresponding to an effective mass of about $200\,{\rm MeV}$. The potential will be very strong: the strength of the interaction is proportional to $(m_{D_{s0}} - m_D)^2 / f_{\pi}^2$ and $(m_{D_{s1}} - m_{D^*})^2 / f_{\pi}^2$. This combination of range and strength almost guarantees the existence of $D_{s0}^*(2317) D$ and $D_{s1}^*(2460) D^*$ bound states with $J^P = 0^{-}$ and $J^P = 0^{-}, 2^{-}$ respectively. Concrete calculations indicate a binding energy of $5-15\,{\rm MeV}$ independently of $J^P$. The $D_{s0}^*(2317) D$ and $D_{s1}^*(2460) D^*$ molecules have manifestly exotic flavour quantum numbers: $C=2$, $S=1$ and $I=1/2$. We expect the existence of bottom counterparts composed of the $B B_{s0}$ and $B^* B_{s1}^*$ mesons, which will be more bound and have a richer spectrum that might include a shallow P-wave state and an excited S-wave state.

Testing a possible way of geometrization of the strong interaction by a Kaluza–Klein star

Geometrization of the fundamental interactions has been extensively studied during the century. The idea of introducing compactified spatial dimensions originated by Kaluza and Klein. Following their approach, several model were built representing quantum numbers (e.g. charges) as compactified space-time dimensions. Such geometrized theoretical descriptions of the fundamental interactions might lead us to get closer to the unification of the principle theories. Here, we apply a [Formula: see text] dimensional theory, which contains one extra compactified spatial dimension [Formula: see text] in connection with the flavor quantum number in Quantum Chromodynamics. Within our model the size of the [Formula: see text] dimension is proportional to the inverse mass-difference of the first low-mass baryon states. We used this phenomena to apply in a compact star model — a natural laboratory for testing the theory of strong interaction and the gravitational theory in parallel. Our aim is to test the modification of the measurable macroscopical parameters of a compact Kaluza–Klein star by varying the size of the compactified extra dimension. Since larger the [Formula: see text] the smaller the mass difference between the first spokes of the Kaluza–Klein ladder resulting smaller-mass stars. Using the Tolman–Oppenheimer–Volkov equation, we investigate the [Formula: see text]-[Formula: see text] diagram and the dependence of the maximum mass of compact stars. Besides testing the validity of our model we compare our results to the existing observational data of pulsar properties for constraints.

Skew-flavored dark matter

We explore a novel flavor structure in the interactions of dark matter with the Standard Model. We consider theories in which both the dark matter candidate, and the particles that mediate its interactions with the Standard Model fields, carry flavor quantum numbers. The interactions are skewed in flavor space, so that a dark matter particle does not directly couple to the Standard Model matter fields of the same flavor, but only to the other two flavors. This framework respects Minimal Flavor Violation, and is therefore naturally consistent with flavor constraints. We study the phenomenology of a benchmark model in which dark matter couples to right-handed charged leptons. In large regions of parameter space the dark matter can emerge as a thermal relic, while remaining consistent with the constraints from direct and indirect detection. The collider signatures of this scenario include events with multiple leptons and missing energy. These events exhibit a characteristic flavor pattern that may allow this class of models to be distinguished from other theories of dark matter.

Quark-flavored scalar dark matter

It is an intriguing possibility that dark matter (DM) could have flavor quantum numbers like the quarks. We propose and investigate a class of UV-complete models of this kind, in which the dark matter is in a scalar triplet of an SU(3) flavor symmetry, and interacts with quarks via a colored flavor-singlet fermionic mediator. Such mediators could be discovered at the LHC if their masses are $\sim 1$ TeV. We constrain the DM-mediator couplings using relic abundance, direct detection, and flavor-changing neutral-current considerations. We find that, for reasonable values of its couplings, scalar flavored DM can contribute significantly to the real and imaginary parts of the $B_s$-$\bar B_s$ mixing amplitude. We further assess the potential for such models to explain the galactic center GeV gamma-ray excess.

Model for two-channel Kondo effect in carbon nanotube quantum dots

The overscreened Kondo effect is shown to be feasible in a carbon nanotube quantum dot junction hosting a spin-$\frac{1}{2}$ atom with a single $s$-wave valence electron (e.g., Au). The idea is to use the two valleys $\ensuremath{\xi}=\mathbf{K},{\mathbf{K}}^{\ensuremath{'}}$ (located on two inequivalent corners of the first Brillouin zone) as two symmetry protected flavor quantum numbers. Exchange interaction between the itinerant electrons and the host atom is computed and shown to be antiferromagnetic, and it does not couple different flavors. Perturbative renormalization group analysis exposes a finite weak-coupling two-channel fixed point, where the Kondo temperature is estimated to be around $0.5--5$ K. Remarkably, occurrence of two different scaling regimes implies a nonmonotonic dependence of the conductance as a function of temperature. Consequently, in this system (unlike the ``standard'' two-channel Kondo effect), the physics of the overscreened Kondo effect is exposed already in the weak coupling regime.

Tetraquarks with exotic flavor quantum numbers at largeNcin QCD(AS)

It is shown that the large $N_c$ limit of QCD with quarks in the two-index antisymmetric color representation [QCD(AS)] has narrow tetraquark states with exotic flavor quantum numbers. They decay into mesons with a width that is parametrically $O(1/N_c^2)$. Tetraquarks with non-exotic quantum numbers mix at leading order with mesons of the same overall quantum numbers. QCD(AS) at $N_c=3$ corresponds to ordinary QCD; its large $N_c$ limit represents an alternative starting point for a $1/N_c$ expansion to the standard one with quarks in the fundamental color representation.

Flavored dark matter and R-parity violation

AbstractMinimal Flavor Violation offers an alternative symmetry rationale to R-parity conservation for the suppression of proton decay in supersymmetric extensions of the Standard Model. The naturalness of such theories is generically under less tension from LHC searches than R-parity conserving models. The flavor symmetry can also guarantee the stability of dark matter if it carries flavor quantum numbers. We outline general features of supersymmetric flavored dark matter (SFDM) models within the framework of MFV SUSY. A simple model of top flavored dark matter is presented. If the dark matter is a thermal relic, then nearly the entire parameter space of the model is testable by upcoming direct detection and LHC searches.

Dark matter within the minimal flavour violation ansatz

Minimal Flavour Violation hypothesis can provide an attractive framework for Dark Matter (DM). We consider scalar DM candidates carrying flavour quantum numbers and whose representation under the flavour group guarantees DM stability. They interact with the Standard Model fields through Higgs portal at renormalisable level and also to quarks through dimension-6 operators. We provide a systematic analysis of the viable parameter space for the DM fields, which are triplet of the flavour group, considering several DM-quark interactions. In this framework, we analyse in which cases the viable parameter space differs from Higgs portal models thanks to the underlying flavour structure. In contrast to minimal Higgs portal scenarios, we find that light DM in the GeV mass range as well as heavier candidates above Higgs resonance could be allowed by colliders, direct and indirect DM detection searches as well as flavour constraints. The large mass regime above mt could even be beyond the reach of future experiments such as Xenon 1T.

Too many X’s, Y’s and Z’s?

Heavy meson spectroscopy above open flavor thresholds has become a challenge both from the experimental and theoretical points of view. Experimentally, several signals have been interpreted as meson resonances with unusual properties; theoretically, such signals may be identified with meson-meson molecules or compact multiquark structures. We analyze the influence of thresholds on heavy meson spectroscopy comparing different flavor sectors and quantum numbers. The validity of a quark-model picture above open-flavor thresholds would severely restrict the number of channels that may lodge multiquark structures as meson-meson molecules.

Forward Tevatron top quarks and backward LHC top quarks with associates

The anomalous forward-backward asymmetry (${A}_{\mathrm{FB}}$) in $t\overline{t}$ production at the Tevatron is in apparent contradiction with the $t\overline{t}$ charge asymmetry (${A}_{\mathrm{C}}$) measurements at the LHC, which agree well with the standard model predictions. We argue that associated production of a state with $[u\overline{t}]$ flavor quantum numbers can lead to a sizable negative contribution to ${A}_{\mathrm{C}}$. Exchange of such a resonance in the $t$ channel would lead to positive contributions to ${A}_{\mathrm{FB}}$ and ${A}_{\mathrm{C}}$, as has been extensively discussed in the literature. Given the additional negative ${A}_{\mathrm{C}}$ contribution, both the Tevatron and LHC data can be naturally accommodated within this framework. A simple realization of this setup is the well known example of a ${Z}^{\ensuremath{'}}$ with flavor off-diagonal up-top couplings. We provide a detailed study of this model, demonstrating that it indeed reproduces the $t\overline{t}$ asymmetry data, and is compatible with other constraints, e.g., $t+\mathrm{\text{jet}}$ resonance searches, $t\overline{t}$ inclusive jet multiplicities, and atomic parity violation.

Flavored Dark Matter and its Laboratory Tests

In this talk, based on the paper 1109.3516, we consider theories where the dark matter particle carries lepton flavor quantum numbers, and has renormalizable contact interactions with the Standard Model fields. We find that the region of parameter space where dark matter has the right abundance to be a thermal relic is in general within reach of current direct detection experiments. In order to evaluate the collider prospects, we focus on a class of models where dark matter carries tau flavor, and show that the collider signals of these models include events with four or more isolated leptons and missing energy. A significant part of parameter space in these theories can be discovered above Standard Model backgrounds at the 14 TeV Large Hadron Collider. We also study the extent to which flavor and charge correlations among the final state leptons allows models of this type to be distinguished from theories where dark matter couples to leptons but does not carry flavor, similarly to a neutralino.