Quark States Research Articles

Presymmetry in the Standard Model with adulterated Dirac neutrinos

Recently we proposed a model for light Dirac neutrinos in which two right-handed (RH) neutrinos per generation are added to the particles of the Standard Model (SM), implemented with the symmetry of fermionic contents. The ordinary one is decoupled via the high scale type-I seesaw mechanism, while the extra pairs off with its left-handed (LH) partner. The symmetry of lepton and quark contents was merely used as a guideline to the choice of parameters because it is not a proper symmetry. Here we argue that the underlying symmetry to take for this correspondence is presymmetry, the hidden electroweak symmetry of the SM extended with RH neutrinos defined by transformations which exchange lepton and quark bare states with the same electroweak charges and no Majorana mass terms in the underlying Lagrangian. It gives a topological character to fractional charges, relates the number of families to the number of quark colors, and now guarantees the great disparity between the couplings of the two RH neutrinos. Thus, Dirac neutrinos with extremely small masses appear as natural predictions of presymmetry, satisfying the ’t Hooft’s naturalness conditions in the extended seesaw where the extra RH neutrinos serve to adulterate the mass properties in the low scale effective theory, which retains without extensions the gauge and Higgs sectors of the SM. However, the high energy threshold for the seesaw implies new physics to stabilize the quantum corrections to the Higgs boson mass in agreement with the naturalness requirement.

Diphoton decay of the Higgs boson and new bound states of top and antitop quarks

We consider the constraints, provided by the LHC results on Higgs boson decay into 2 photons and its production via gluon fusion, on the previously proposed Standard Model (SM) strongly bound state S of six top quarks and six antitop quarks. A correlation is predicted between the ratios [Formula: see text] and [Formula: see text] of the Higgs diphoton decay and gluon production amplitudes, respectively to their SM values. We estimate the contribution to these amplitudes from one-loop diagrams involving the 12 quark bound state S and related excited states using an atomic physics based model. We find two regions of parameter space consistent with the ATLAS and CMS data on [Formula: see text] at the three sigma level: a region close to the SM values [Formula: see text] with the mass of the bound state [Formula: see text][Formula: see text]GeV and a region with [Formula: see text] corresponding to a bound state mass of [Formula: see text][Formula: see text]GeV.

Strings from domain walls in supersymmetric Yang-Mills theory and adjoint QCD

We study strings between static quarks in QCD with ${n}_{f}$ adjoint fermions, including $\mathcal{N}=1$ supersymmetric Yang-Mills (SYM), in the calculable regime on ${\mathbb{R}}^{3}\ifmmode\times\else\texttimes\fi{}{\mathbb{S}}_{L}^{1}$, which shares many features with the XY-spin model. We find that they have many qualitatively new features not previously known. The difference from other realizations of Abelian confinement is due to the composite nature of magnetic bions, whose Dirac quantum with fundamental quarks is two, and to the unbroken part of the Weyl group. In particular we show that strings are composed of two domain walls, that quarks are not confined on domain walls, that strings can end on domain walls, and that ``Y'' or ``$\mathrm{\ensuremath{\Delta}}$'' baryons can form. By similar argumentation, liberation of vortices on domain walls in the condensed matter counterparts may have important implications in the physics of transport. In the gauge theory we briefly discuss the lightest modes of strings and the decompactification limit.

Hamiltonian approach to QCD in Coulomb gauge: Perturbative treatment of the quark sector

We study the static gluon and quark propagator of the Hamiltonian approach to quantum chromodynamics in Coulomb gauge in one-loop Rayleigh–Schrödinger perturbation theory. We show that the results agree with the equal-time limit of the four-dimensional propagators evaluated in the functional integral (Lagrangian) approach.

Y-stringlike behavior of a static baryon at finite temperature

We look into the signatures of the effective Y-bosonic strings in the gluonic profile due to a system of three static quarks on the lattice. The color field is calculated in pure SU(3) Yang-Mills lattice gauge theory at finite temperature with Polyakov loop operators. The analysis of the action density unveils a filled-$\mathrm{\ensuremath{\Delta}}$ distribution. However, we found that these $\mathrm{\ensuremath{\Delta}}$-shaped action density profiles are structured from three Y-shaped Gaussian-like flux tubes. The geometry of the Y-shaped Gaussian flux tubes changes according to the quark configuration and temperature. The lattice data for the mean-square width of the gluonic action density have been compared to the corresponding width calculated based on the string model at finite temperature. We assume Y-string configuration with minimal length. The growth pattern of the action density of the gluonic field fits to junction fluctuations of the Y-baryonic string model for large quark separation at the considered temperatures.

NeutralBmeson mixings andBmeson decay constants with static heavy and domain-wall light quarks

Neutral $B$ meson mixing matrix elements and $B$ meson decay constants are calculated. Static approximation is used for $b$ quark and domain-wall fermion formalism is employed for light quarks. The calculations are carried out on $2+1$ flavor dynamical ensembles generated by RBC/UKQCD Collaborations with lattice spacings $0.086$fm ($a^{-1}\sim 2.3$GeV) and $0.11$fm ($1.7$GeV), and a fixed physical spatial volume of about $(2.7{\rm fm})^3$. In the static quark action, link-smearings are used to improve the signal-to-noise ratio. We employ two kinds of link-smearings, HYP1 and HYP2, and their results are combined in taking the continuum limit. For the matching between the lattice and the continuum theory, one-loop perturbative $O(a)$ improvements are made to reduce discretization errors. As the most important quantity of this work, we obtain SU(3) breaking ratio $\xi=1.208(60)$, where the error includes statistical and systematic one. (Uncertainty from infinite $b$ quark mass is not included.) We also find other neutral $B$ meson mixing quantities $f_B\sqrt{\hat{B}_B}=240(22)$MeV, $f_{B_s}\sqrt{\hat{B}_{B_s}}=290(22)$MeV, $\hat{B}_B=1.17(22)$, $\hat{B}_{B_s}=1.22(13)$ and $B_{B_s}/B_B=1.028(74)$, $B$ meson decay constants $f_B=219(17)$MeV, $f_{B_s}=264(19)$MeV and $f_{B_s}/f_B=1.193(41)$, in the static limit of $b$ quark, which do not include infinite $b$ quark mass uncertainty.

Nucleon Structure Including High Fock States in AdS/QCD Models

We discuss a holographic soft-wall model that consider several Fock states in nucleon description. In our approach nucleon structure is a superposition of a three-valence quark state with high Fock states including an adjustable number of partons (quarks, antiquarks and gluons). With a minimal number of free parameters (dilaton scale parameter, mixing parameters of partial contributions of Fock states, coupling constants in the effective Lagrangian) we achieve a reasonable agreement with data.

On the holographic width of flux tubes

We investigate the width of the flux tube between heavy static quark charges. Using the gauge/gravity duality, we find the properties of the minimal connected surface related to the width of the bound state. We show that in the confining phase, the logarithmic broadening predicted by the effective string description and observed in lattice simulations is a generic property of all confining backgrounds. We also study the transverse fluctuations of the string connecting two static quarks in curved backgrounds. Our formalism is applied to AdS space where we compute the expectation value of the square of transverse deviations of the string, a quantity related to the width.

WIMPs at the galactic center

Simple models of weakly interacting massive particles (WIMPs) predict dark matter annihilations into pairs of electroweak gauge bosons, Higgses or tops, which through their subsequent cascade decays produce a spectrum of gamma rays. Intriguingly, an excess in gamma rays coming from near the Galactic center has been consistently observed in Fermi data. A recent analysis by the Fermi collaboration confirms these earlier results. Taking into account the systematic uncertainties in the modelling of the gamma ray backgrounds, we show for the first time that this excess can be well fit by these final states. In particular, for annihilations to (WW, ZZ, hh, tt̄), dark matter with mass between threshold and approximately (165, 190, 280, 310) GeV gives an acceptable fit. The fit range for bb̄ is also enlarged to 35 GeV ≲ mχ ≲ 165 GeV. These are to be compared to previous fits that concluded only much lighter dark matter annihilating into b, τ, and light quark final states could describe the excess. We demonstrate that simple, well-motivated models of WIMP dark matter including a thermal-relic neutralino of the MSSM, Higgs portal models, as well as other simplified models can explain the excess.

Transverse transport properties of a charged drop in an electric field

Transport properties of a charged droplet of weakly interacting particles in transverse electric field are investigated. Nonequilibrium, time-dependent distribution function which describes a process of the droplet transverse evolution with constant entropy in the field is calculated. With the help of this distribution function, shear viscosity coefficients in the transverse plane are calculated as well. They are found to be dependent on the ratio of the potential energy of the droplet in the electric field to the kinetic energy of the droplet; for weakly interacting particles, this parameter is small. Additionally, these coefficients are time-dependent and change during the hydrodynamical state of the droplet's expansion. Applicability of the results to the description of initial states of quark–gluon plasma (QGP) obtained in high-energy interactions of nuclei is also discussed.

K-strings as fundamental strings

It has been noticed that the k-string observables can be expressed in terms of the fundamental string ones. We identify a sufficient condition for a generic gravity dual background which when satisfied the mapping can be done. The condition is naturally related to a preserved quantity under the T-dualities acting on the Dp-brane describing the high representation Wilson loops. We also find the explicit relation between the observables of the heavy k-quark and the single quark states. As an application to our generic study and motivated by the fact that the anisotropic theories satisfy our condition, we compute the width of the k-string in these theories to find that the logarithmic broadening is still present, but the total result is affected by the anisotropy of the space.

How and Why the Universe Is Natural

In previous paper, we showed that the elementary particles mass spectrum can be computed from theory using a resonance equation. The predicted H 0 mass agrees with the latest CERN publications. As a result, the H 0 acquires its mass exactly in the same geometry as the Z 0 and the W ± ; it is not a “purely scalar boson” and then quadratic divergences are inexistent. In this paper, we find an underlying structure of the field with 19 pure states, where 36 quark states (including color) and 3 or 6 neutrinos states are mixtures, and we show that the CKM and PMNS matrices elements come from the equation and the field structure. We conclude that the field is natural since over the 23 SM parameters, at least 19 are fully constrained by the field structure.

The Light-Front Schrödinger Equation and the Determination of the Perturbative QCD Scale from Color Confinement: A First Approximation to QCD

The valence Fock-state wavefunctions of the light-front QCD Hamiltonian satisfy a relativistic equation of motion with an effective confining potential $U$ which systematically incorporates the effects of higher quark and gluon Fock states. If one requires that the effective action which underlies the QCD Lagrangian remains conformally invariant and extends the formalism of de Alfaro, Fubini and Furlan to light front Hamiltonian theory, the potential $U$ has a unique form of a harmonic oscillator potential, and a mass gap arises. The result is a nonperturbative relativistic light-front quantum mechanical wave equation which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number $n$ and orbital angular momentum $L$. Only one mass parameter $\kappa$ appears. Light-front holography thus provides a precise relation between the bound-state amplitudes in the fifth dimension of AdS space and the boost-invariant light-front wavefunctions describing the internal structure of hadrons in physical space-time. We also show how the mass scale $\kappa$ underlying confinement and hadron masses determines the scale $\Lambda_{\overline{MS}} $ controlling the evolution of the perturbative QCD coupling. The relation between scales is obtained by matching the nonperturbative dynamics, as described by an effective conformal theory mapped to the light-front and its embedding in AdS space, to the perturbative QCD regime computed to four-loop order. The result is an effective coupling defined at all momenta. The predicted value $\Lambda_{\overline{MS}} = 0.328 \pm 0.034$ GeV is in agreement with the world average $0.339 \pm 0.010$ GeV. The analysis applies to any renormalization scheme.

Confinement and Chiral-Symmetry Breaking in the Covariant Spectator Theory

We show that in the framework of the covariant spectator theory (CST), the equations for the quark anti-quark bound state and for the quark mass function satisfy the requirement of chiral symmetry, incorporating spontaneous chiral symmetry breaking. We then present the results for the pion electromagnetic form factor obtained within a dynamical quark model formulated in Minkowski space and based on the CST.

Magnetic Moments of The Baryon Anti-decuplet and Octet Pentaquark States

The magnetic moments of the baryon anti-decuplet and octet-pentaquark states have been estimated in the framework of diquark-diquark-antiquark configuration using the composite fermion (CF) model of diquark suggested by us. The masses of the diquark have been estimated in the CF approach and subsequently used to estimate the magnetic moments of baryon antidecuplet and octet penta quark states. Results are compared with existing predictions.

Refined Lattice/Model Investigation of $u d \bar {b} \bar {b}$ Tetraquark Candidates with Heavy Spin Effects Taken into Account

We investigate four-quark systems consisting of two heavy anti-bottom quarks and two light up/down quarks. We propose to solve a coupled Schr\odinger equation for the anti-bottom-anti-bottom separation using potentials computed via lattice QCD in the limit of static anti-bottom quarks. This coupled Schr\odinger equation allows to incorporate effects due to the heavy anti-bottom spins. First exploratory numerical tests are discussed.

Dynamics of Quarks in a 2D Flux Tube

On the basis of a compactification of the (3+1) into (1+1) dimensional space-time [1], the quark states inside the 2D flux tube are studied for the case of a linear transverse confining potential. The derived states are classified by both the projections of the orbital momentum and the spin along the tube direction. The spectrum of the fermion states is evaluated. It is found that the energy eigenvalues of the quarks appear to be approximately related to the square root of the eigenvalues of the two-dimensional harmonic oscillator.

Angular analysis of polarized top quark decay intoBmesons in two different helicity systems

We calculate the ${\cal O}(\alpha_s)$ radiative corrections to the spin dependent differential decay rates of the process $t\rightarrow b+W^+$. These are needed to study the angular distribution of the energy of hadrons produced in polarized top quark decays at next-to-leading order (NLO). In our previous work, we studied the angular distribution of the scaled-energy of bottom-flavored hadrons (B) from polarized top quark decays, using a specific helicity coordinate system where the top quark spin was measured relative to the bottom momentum (system~1). Here, we study the angular distribution of the energy spectrum of B-hadron in a different helicity system, where the top spin is specified relative to the W-momentum (system~2). These energy distributions are governed by the polarized and unpolarized rate functions which are related to the density matrix elements of the decay $t\rightarrow W^++b$. Through this paper, we present our predictions of the B-hadron spectrum in the polarized and unpolarized top decay and shall compare the polarized results in two different helicity systems. These predictions can be used to determine the polarization states of top quarks and also provide direct access to the B-hadron fragmentation functions (FFs) and allow us to deepen our knowledge of the hadroniazation process.

Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic Center

The apparent gamma-ray excess in the Galactic center region and inner Galaxy has attracted considerable interest, notably because both its spectrum and its radial distribution are consistent with an interpretation in terms of annihilating dark matter particles with a mass of about 10--40 GeV. We confront such an interpretation with an updated compilation of various indirect dark matter detection bounds, which we adapt to the specific form required by the observed signal. We find that cosmic-ray positron data strongly rule out dark matter annihilating to light leptons, or ``democratically'' to all leptons, as an explanation of the signal. Cosmic-ray antiprotons, for which we present independent and significantly improved limits with respect to previous estimates, are already in considerable tension with dark matter (DM) annihilation to any combination of quark final states; the first set of AMS-02 data will thus be able to rule out or confirm the DM hypothesis with high confidence. For reasonable assumptions about the magnetic field in the Galactic center region, radio observations independently put very severe constraints on a DM interpretation of the excess, in particular for all leptonic annihilation channels.

Quarkonium measurements in the STAR experiment

Abstract Calculations of Quantum Chromodynamics on lattice showed that under conditions of high energy density or high temperature nuclear matter undergoes a phase transition from a state of quarks and gluons confined in hadrons to a deconfined state, the Quark–Gluon Plasma (QGP). Such conditions were present in first moments after the Big Bang and can be created in laboratory by colliding of heavy ions with sufficient energy. One of the most prominent signatures of QGP formation is the quarkonium suppression in central heavy-ion collisions arising from the Debye screening of the quark–antiquark potential in hot and dense nuclear matter. However, cold nuclear matter effects and heavy quark recombination could influence the measured quarkonium yields. Measurements of J / ψ at different collision energies can shed new light on understanding the interplay of these mechanisms for J / ψ production. The production mechanism of J / ψ is not well understood yet and the simultaneous measurement of J / ψ transverse momentum spectra and polarization in p + p collisions can significantly constrain possible production scenarios. In this proceedings, we report the recent STAR measurements of J / ψ production at mid-rapidity in p + p , d + Au , Au + Au at s NN = 200 GeV and in Au + Au collisions at s NN = 39 GeV and s NN = 62 GeV .