Featured Researches

High Energy Physics Phenomenology

Analyticity and Regge asymptotics in virtual Compton scattering on the nucleon

We test the consistency of the data on the nucleon structure functions with analyticity and the Regge asymptotics of the virtual Compton amplitude. By solving a functional extremal problem, we derive an optimal lower bound on the maximum difference between the exact amplitude and the dominant Reggeon contribution for energiesνabove a certain high valueνh(Q2). Considering in particular the difference of the amplitudes $T_1^\inel(\nu, Q^2)$ for the proton and neutron, we find that the lower bound decreases in an impressive way whenνh(Q2)is increased, and represents a very small fraction of the magnitude of the dominant Reggeon. While the method cannot rule out the hypothesis of a fixed Regge pole, the results indicate that the data on the structure function are consistent with an asymptotic behaviour given by leading Reggeon contributions. We also show that the minimum of the lower bound as a function of the subtraction constant $S_1^\inel(Q^2)$ provides a reasonable estimate of this quantity, in a frame similar, but not identical to the Reggeon dominance hypothesis.

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High Energy Physics Phenomenology

Angular Distributions, Polarization Observables, Spin Density Matrices and Statistical Tensors in Photoproduction of Two Pseudoscalar Mesons off a Nucleon

In two meson photoproduction off a nucleon, for the case in which two of the three final state hadrons are products of the decay of an intermediate resonance, general expressions for its decay distribution and for polarization observables are derived in a model independent way. These are functions of either the spin density matrix elements (SDME's) or statistical tensors of the resonance, and the angles of its decay products. The expressions are general enough that it also describes cases where more than one resonance of arbitrary quantum numbers contributes, including interference effects. They can therefore be used to extract the SDME's or statistical tensors of the resonances that contribute to the reaction.

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High Energy Physics Phenomenology

Angular analysis of bottom-flavored hadron production in semileptonic decays of polarized top quarks

We study the inclusive production of bottom-flavored hadrons from semileptonic decays of polarized top quarks at next-to-leading order in QCD using fragmentation functions recently determined from a global fit toe+e??data. We provide the relevant differential decay widths at parton level in analytic form. These results fill an important gap in the theoretical interpretation of recent measurements of the top-quark polarization and thett¯spin correlations using dilepton final states in proton-proton collisions at the CERN Large Hadron Collider. As an illustration, we study the distributions in the scaled bottom-hadron energy of the polarized-top-quark decay widths for differentW-boson helicities.

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High Energy Physics Phenomenology

Anomalies and parities for quintessential and ultra-light axions

We discuss the energy scales of the explicit breaking terms of the global symmetries \USW~ needed for the quinessential axion (QA) and the ultra-light axion (ULA). The appropriate scale of QA is about108GeV.

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High Energy Physics Phenomenology

Anomaly-free Abelian gauge symmetries with Dirac scotogenic models

We perform a systematic analysis of standard model extensions with an additional anomaly-free gaugeU(1)symmetry, to generate Dirac neutrino masses at one loop. Under such symmetry, standard model fields could either transform or be invariant, corresponding to an activeU(1)Xor a darkU(1)Dsymmetry, respectively. Having an anomaly-free symmetry imposes nontrivial conditions to the number and charges of the unavoidable new states. We perform an intensive scan, looking for non-anomalous solutions for given number of extra chiral fermions. In particular, we concentrate on solutions giving rise to scotogenic neutrino masses via the effective Dirac mass operator. We study the cases where the Dirac mass operator with dimension 5 or 6, is mediated by Dirac or Majorana states, and corresponds to an activeU(1)Xor a darkU(1)Dsymmetry. Finally, we comment on the solutions featuring no massless chiral fermions.

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High Energy Physics Phenomenology

Application of the Uniformized Mittag-Leffler Expansion to?(1405)

We study the pole properties of?(1405)in a model-independent manner by applying the Uniformized Mittag-Leffler expansion proposed in our previous paper. The resonant energy, width and residues are determined by expanding the observable as a sum of resonant-pole pairs under an appropriate parameterization which expresses the observable to be single-valued, and fitting it to experimental data of the invariant-mass distribution of?+Σ??,???Σ+,?0Σ0final states in the reaction,γp??K+?Σ, and the elastic and inelastic cross section,K??p??K??p,K¯0n,?+Σ??,???Σ+. As we gradually increase the number of pairs from one to three, the first pair converges while the second and third pairs emerge further and further away from the first pair, implying that the Uniformized Mittag-Leffler expansion with three pairs is almost convergent in the vicinity of the?(1405). The broad peak structure between the?ΣandK¯Nthresholds regarded to be?(1405)is explained by a single pair with a resonant energy of 1420±1 MeV, and a half width of 48±2 MeV, which is consistent with the single-pole picture of?(1405). We conclude that the Uniformized Mittag-Leffler expansion turns out to be a very powerful method to obtain resonance energy, width and residues from the near-threshold spectrum.

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High Energy Physics Phenomenology

Astrophysical neutrino oscillations accounting for neutrino charge radii

We derive for the first time an effective neutrino evolution Hamiltonian accounting for neutrino interactions with external magnetic field due to neutrino charge radii and anapole moment. The results are interesting for possible applications in astrophysics.

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High Energy Physics Phenomenology

Axi-Higgs Cosmology

If the electroweak Higgs vacuum expectation valuevin early universe is??%higher than its present valuev0=246GeV, the7Li puzzle in BBN and the CMB/?CDM tension with late-universe measurements on Hubble parameter are mitigated. We propose a model of an axion coupled to the Higgs field, named "axi-Higgs", with its massma??10??0??10??9eVand decay constantfa??1017??1018GeV, to achieve this goal. The axion initial valueainiyields an initial?vini/v0??.01throughout the BBN-recombination epoch and a percent level contribution to the total matter density today. Because of its very large de Broglie wavelength, this axion matter density?asuppresses the matter power spectrum, alleviating the CMB/?CDMS8/?8tension with the weak-lensing data. It also explains the recently reported isotropic cosmic birefringence by its coupling with photons. Adding the axion (m??10??2eV) in the fuzzy dark matter model to the axi-Higgs model allows bigger?vrecand?ato address the Hubble andS8/?8tensions simultaneously. The model predicts that?vmay be detected by the spectral measurements of quasars, while its oscillation may be observed in the atomic clock measurements.

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High Energy Physics Phenomenology

Axial meson exchange and theZc(3900)andZcs(3985)resonances as heavy hadron molecules

Early speculations about the existence of heavy hadron molecules were grounded on the idea that light-meson exchanges forces could lead to binding. In analogy to the deuteron, the light-mesons usually considered include the pion, sigma, rho and omega, but not the axial mesona1(1260). Though it has been argued in the past that the coupling of the axial meson to the nucleons is indeed strong, its mass is considerably heavier than that of the vector mesons and thus its exchange ends up being suppressed. Yet, this is not necessarily the case in heavy hadrons molecules: we find that even though the contribution to binding from the axial meson is modest, it cannot be neglected in the isovector sector where vector meson exchange cancels out. This might provide a natural binding mechanism for molecular candidates such as theZc(3900),Zc(4020)or the more recently observedZcs(3985). However theZcs(3985)is much more dependent on the nature of scalar meson exchange (in particular whether the sigma has a sizable coupling to the strange quark) than on the contribution of the axial mesons. This later observation might also be relevant for the strange hidden-charm pentaquarkPcs(4459).

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High Energy Physics Phenomenology

Axion Quality from Superconformal Dynamics

We discuss a possibility that a superconformal dynamics induces the emergence of a globalU(1)PQsymmetry to solve the strong CP problem through the axion. Fields spontaneously breaking theU(1)PQsymmetry couple to new quarks charged under the ordinary colorSU(3)Cand a newSU(N)gauge group. The theory flows into an IR fixed point where theU(1)PQbreaking fields hold a large anomalous dimension leading to the suppression ofU(1)PQ-violating higher dimensional operators. The spontaneous breaking of theU(1)PQmakes the new quarks massive. TheU(1)PQsymmetry is anomalous under theSU(3)Cbut not under theSU(N)so that the axion couples to only the colorSU(3)Cand the usual axion potential is generated. We also comment on a model that theU(1)PQbreaking fields are realized as meson superfields in a new supersymmetric QCD.

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