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preprint2016arXiv

The $S$-wave resonance contributions to the three-body decays $B^0_{(s)}\to η_c f_0(X)\to η_cπ^+π^-$ in perturbative QCD approach

In this paper, we study the three-body decays $B^0/B^0_s \to η_c f_0(X)\to η_c π^+π^-$ by employing the perturbative QCD (PQCD) factorization approach. We evaluate the $S$-wave resonance contributions by using the two-pion distribution amplitude $Φ_{ππ}^{\rm S}$. The Breit-Wigner formula for the $f_0(500)$, $f_0(1500)$, and $f_0(1790)$ resonances and the Flatté model for the $f_0(980)$ resonance are adopted to parameterize the time-like scalar form factors $F_{s}(ω^2)$. We also use the D.~V.~Bugg model to parameterize the $f_0(500)$ and compare the relevant theoretical predictions from different models. We found the following results: (a) the PQCD predictions for the branching ratios are ${\cal B}(B^0\to η_c f_0(500)[π^+π^-])= \left ( 1.53 ^{+0.76}_{-0.35} \right ) \times 10^{-6}$ for Breit-Wigner model and ${\cal B}(B^0\to η_c f_0(500)[π^+π^-])= \left ( 2.31 ^{+0.96}_{-0.48} \right ) \times 10^{-6}$ for D.~V.~Bugg model; (b) $ {\cal B}(B_s\to η_c f_0(X)[π^+π^-] ) =\left ( 5.02^{+1.49}_{-1.08} \right )\times 10^{-5}$ when the contributions from $f_0(X)=(f_0(980),f_0(1500),f_0(1790))$ are all taken into account; and (c) The considered decays could be measured at the ongoing LHCb exp

preprint2016arXiv

Mirror dark matter will be confirmed or excluded by XENON1T

Mirror dark matter, where dark matter resides in a hidden sector exactly isomorphic to the standard model, can be probed via direct detection experiments by both nuclear and electron recoils if the kinetic mixing interaction exists. In fact, the kinetic mixing interaction appears to be a prerequisite for consistent small scale structure: Mirror dark matter halos around spiral galaxies are dissipative - losing energy via dark photon emission. This ongoing energy loss requires a substantial energy input, which can be sourced from ordinary supernovae via kinetic mixing induced processes in the supernova's core. Astrophysical considerations thereby give a lower limit on the kinetic mixing strength, and indeed lower limits on both nuclear and electron recoil rates in direct detection experiments can be estimated. We show here that potentially all of the viable parameter space will be probed in forthcoming XENON experiments including LUX and XENON1T. Thus, we anticipate that these experiments will provide a definitive test of the mirror dark matter hypothesis.

preprint2016arXiv

Fermionic WIMPs and Vacuum Stability in the Scotogenic Model

We demonstrate that the condition of vacuum stability severely restricts scenarios with fermionic WIMP dark matter in the scotogenic model. The sizable Yukawa couplings that are required to satisfy the dark matter constraint via thermal freeze-out in these scenarios tend to destabilise the vacuum at scales below that of the heaviest singlet fermion, rendering the model inconsistent from a theoretical point of view. By means of a scan over the parameter space, we study the impact of these renormalisation group effects on the viable regions of this model. Our analysis shows that a fraction of more than 90% of the points compatible with all known experimental constraints - including neutrino masses, the dark matter density, and lepton flavour violation - is actually inconsistent.

preprint2016arXiv

Gravitational waves and Higgs boson couplings for exploring first order phase transition in the model with a singlet scalar field

We calculate the spectrum of gravitational waves originated from strongly first order electroweak phase transition in the extended Higgs model with a real singlet field. In order to calculate the bubble nucleation rate, we perform a two-field analysis to evaluate bounce solutions connecting the true and the false vacua using the one-loop effective potential at finite temperatures. Imposing the Sakharov condition of the departure from thermal equilibrium for baryogenesis, we survey allowed regions of parameters of the model. We then investigate the gravitational waves produced at electroweak bubble collisions in the early Universe, such as the sound wave, the bubble wall collision and the plasma turbulence. We find that the strength at the peak frequency can be large enough to be detected at future space-based gravitational interferometers such as eLISA, DECIGO and BBO. Predicted deviations in the various Higgs boson couplings are also evaluated at the zero temperature, and are shown to be large enough too. Therefore, in this model strongly first order electroweak phase transition can be tested by the combination of the precision study of various Higgs boson couplings at LHC, the me

preprint2015arXiv

Chiral symmetry restoration in static-light mesons: chiral restoration theorem, the quark running mass m(k) and first chiral restoration signals in the lattice QCD spectra

Chiral symmetry restoration high in the hadron spectra is expected but it remains to be confirmed both in lattice QCD computations and in experiments. Recently, a theorem was derived, relating chiral symmetry restoration high in the hadron spectra to the spontaneous generation of the dynamical quark mass in QCD. We refine the theorem in the case of static-light mesons. Utilizing chiral quark model computations and lattice QCD results for the spectrum of mesons composed by a static antiquark and a light quark, we explore chiral symmetry restoration in the spectrum and the quark running mass m(k).

preprint2016arXiv

Hadron Spectroscopy, exotics and $B_c^+$ physics at LHCb

The LHCb experiment is designed to study properties and decays of heavy flavored hadrons produced from $pp$ collisions at the LHC. During Run~1, it has recorded the world's largest data sample of beauty and charm hadrons, enabling precision spectroscopy studies of such particles. Several important results obtained by LHCb, such as the discovery of the first pentaquark states and the first unambiguous determination of the $Z_c(4430)^-$ as an exotic state, have dramatically increased the interest on spectroscopy of heavy hadrons. An overview of the latest LHCb results on the subject, including the discovery of four strange exotic states decaying as $X \to J/ψϕ$, is presented. LHCb has also made significant contributions to the field of $B_c^+$ physics, the lowest bound state of the heavy flavor $\bar{b}$ and $c$ quarks. A synopsis of the the latest results is given.

preprint2016arXiv

The Radiative Z2 Breaking Twin Higgs

In twin Higgs model, the Higgs boson mass is protected by a $Z_2$ symmetry. The $Z_2$ symmetry needs to be broken either explicitly or spontaneously to obtain misalignment between electroweak and new physics vacua. We propose a novel $Z_2$ breaking mechanism, in which the $Z_2$ is spontaneously broken by radiative corrections to the Higgs potential. Two twin Higgses with different vacua are needed, and vacuum misalignment is realized by opposite but comparable contributions from gauge and Yukawa interactions to the potential. Due to fully radiative symmetry breaking, the Higgs sector is completely determined by twin Higgs vacuum, Yukawa and gauge couplings. There are eight pseudo-Goldstone bosons: the Higgs boson, inert doublet Higgs, and three twin scalars. We show the 125 GeV Higgs mass and constraints from Higgs coupling measurements could be satisfied.

preprint2016arXiv

Quarkonium Production in an Improved Color Evaporation Model

We propose an improved version of the color evaporation model to describe heavy quarkonium production. In contrast to the traditional color evaporation model, we impose the constraint that the invariant mass of the intermediate heavy quark-antiquark pair to be larger than the mass of produced quarkonium. We also introduce a momentum shift between heavy quark-antiquark pair and the quarkonium. Numerical calculations show that our model can describe the charmonium yields as well as ratio of $ψ^\prime$ over $J/ψ$ better than the traditional color evaporation model.

preprint2017arXiv

Analytic structure of QCD propagators in Minkowski space

Analytical functions for the propagators of QCD, including a set of chiral quarks, are derived by a one-loop massive expansion in the Landau gauge, deep in the infrared. By analytic continuation, the spectral functions are studied in Minkowski space, yielding a direct proof of positivity violation and confinement from first principles.The dynamical breaking of chiral symmetry is described on the same footing of gluon mass generation, providing a unified picture. While dealing with the exact Lagrangian, the expansion is based on massive free-particle propagators, is safe in the infrared and is equivalent to the standard perturbation theory in the UV. By dimensional regularization, all diverging mass terms cancel exactly without including mass counterterms that would spoil the gauge and chiral symmetry of the Lagrangian. Universal scaling properties are predicted for the inverse dressing functions and shown to be satisfied by the lattice data. Complex conjugated poles are found for the gluon propagator, in agreement with the i-particle scenario.

preprint2016arXiv

Hadronic production of $D(2550)$, $D^(2600)$, $D(2750)$, $D^_1(2760)$ and $D^*_3(2760)$

Hadronic decays of radially excited $2D$ $D(2^3D_1)$, $D(2^3D_3)$, $D(2D_2)$ and $D(2D^\prime_2)$ have been studied in a $^3P_0$ model. All OZI-allowed decay channels of these $2D$ $D$ resonances have been given, and relevant decay widths have been calculated. $D(2550)$, $D^*(2600)$, $D(2750)$, $D^*_1(2760)$ and $D^*_3(2760)$ can be produced in hadronic decays of $D(2^3D_1)$, $D(2^3D_3)$, $D(2D_2)$ and $D(2D^\prime_2)$. In different assignments, hadronic decay widths and some relevant ratios from the $2D$ $D$ resonances to $D(2550)$, $D^*(2600)$, $D(2750)$, $D^*_1(2760)$ or $D^*_3(2760)$ final states have been predicted, which may provide some more information to identify these resonances in forthcoming experiments.

preprint2016arXiv

A Hydrodynamic Approach to the Study of Anisotropic Instabilities in Dissipative Relativistic Plasmas

We develop a purely hydrodynamic formalism to describe collisional, anisotropic instabilities in a relativistic plasma, that are usually described with kinetic theory tools. Our main motivation is the fact that coarse-grained models of high particle number systems give more clear and comprehensive physical descriptions of those systems than purely kinetic approaches, and can be more easily tested experimentally as well as numerically. In particular, we aim at developing a theory that describes both a background non-equilibrium fluid configurations and its perturbations, to be able to account for the backreaction of the latter on the former. Our system of equations includes the usual conservation laws for the energy-momentum tensor and for the electric current, and the equations for two new tensors that encode the information about dissipation. To make contact with kinetic theory, we write the different tensors as the moments of a non-equilibrium one-particle distribution function (1pdf) which, for illustrative purposes, we take in the form of a Grad-like ansatz. Although this choice limits the applicability of the formalism to states not far from equilibrium, it retains the main fe

preprint2015arXiv

Two-gluon and trigluon glueballs from dynamical holography QCD

We study the scalar, vector and tensor two-gluon and trigluon glueball spectra in the framework of 5-dimension dynamical holographic QCD model, where the metric structure is deformed self-consistently by the dilaton field. For comparison, the glueball spectra are also calculated in the hard-wall and soft-wall holographic QCD models. In order to distinguish glueballs with even and odd parities, we introduce the positive and negative coupling between the dilaton field and glueballs, and for higher spin glueballs, we introduce a deformed 5-dimension mass. With this set-up, there is only one free parameter from the quadratic dilaton profile in the dynamical holographic QCD model, which is fixed by the scalar glueball spectra. It is found that the two-gluon glueball spectra produced in the dynamical holographic QCD model are in good agreement with lattice data. Among six trigluon glueballs, the produced masses for $1^{\pm -}$ and $2^{--}$ are in good agreement with lattice data, and the produced masses for $0^{--}$, $0^{+-}$ and $2^{+-}$ are around 1.5 {\rm GeV} lighter than lattice results. This result might indicate that the three trigluon glueballs of $0^{--}$, $0^{+-}$ and $2^{+-}$

preprint2016arXiv

Perspective on the origin of hadron masses

The energy-momentum tensor in chiral QCD, $T_{μν}$, exhibits an anomaly, viz. $Θ_0 :=T_{μμ} \neq 0$. Measured in the proton, this anomaly yields $m_p^2$, where $m_p$ is the proton's mass; but, at the same time, when computed in the pion, the answer is $m_π^2=0$. Any attempt to understand the origin and nature of mass, and identify observable expressions thereof, must explain and unify these two apparently contradictory results, which are fundamental to the nature of our Universe. Given the importance of Poincaré-invariance in modern physics, the utility of a frame-dependent approach to this problem seems limited. That is especially true of any approach tied to a rest-frame decomposition of $T_{μν}$ because a massless particle does not possess a rest-frame. On the other hand, the dynamical chiral symmetry breaking (DCSB) paradigm, connected with a Poincaré-covariant treatment of the continuum bound-state problem, provides a straightforward, simultaneous explanation of both these identities, and also a diverse array of predictions, testable at existing and proposed facilities. From this perspective, $\langle π| Θ_0 |π\rangle =0$ owing to exact, symmetry-driven cancellations which

preprint2016arXiv

Evaporation Spectrum of Black Holes from a Local Quantum Gravity Perspective

We revisit the hypothesis of a possible line structure in the Hawking evaporation spectrum of black holes. Because of nonperturbative quantum gravity effects, this would take place arbitrarily far away from the Planck mass. We show, based on a speculative but consistent hypothesis, that this naive prediction might in fact hold in the specific context of loop quantum gravity. A small departure from the ideal case is expected for some low-spin transitions and could allow us to distinguish several quantum gravity models. We also show that the effect is not washed out by the dynamics of the process, by existence of a mass spectrum up to a given width, or by the secondary component induced by the decay of neutral pions emitted during the time-integrated evaporation.

preprint2016arXiv

Flavor violating leptonic decays of the Higgs boson

Recent data from the ATLAS and CMS detectors at the Large Hadron Collider at CERN give a hint of possible violation of flavor in the leptonic decays of the Higgs boson. In this work we analyze the flavor violating leptonic decays $H^0_1\to l_i \bar l_j$ ($i\neq j$) within the framework of an MSSM extension with a vectorlike leptonic generation. Specifically we focus on the decay mode $H^0_1\to μτ$. The analysis is done including tree and loop contributions involving exchange of $W, Z$, charge and neutral higgs and leptons and mirror leptons, charginos and neutralinos and sleptons and mirror sleptons. It is found that a substantial branching ratio of $H^0_1\to μτ$, i.e., of as much a ${\cal{O}}(1)\%$, can be achieved in this model, the size hinted by the ATLAS and CMS data. The flavor violating decays $H^0_1\to eμ, eτ$ are also analyzed and found to be consistent with the current experimental limits. An analysis of the dependence of flavor violating decays on CP phases is given. The analysis is extended to include flavor decays of the heavier Higgs bosons. A confirmation of the flavor violation in Higgs boson decays with more data that is expected from LHC at $\sqrt s=13$ TeV will b

preprint2016arXiv

Flavor structure in $SO(32)$ heterotic string theory

We study the flavor structure in $SO(32)$ heterotic string theory on six-dimensional torus with magnetic fluxes. In particular, we focus on models with the flavor symmetries $SU(3)_f$ and $Δ(27)$. In both models, we can realize the realistic quark masses and mixing angles.

preprint2016arXiv

Pathways to Naturally Small Dirac Neutrino Masses

If neutrinos are truly Dirac fermions, the smallness of their masses may still be natural if certain symmetries exist beyond those of the standard model of quarks and leptons. We perform a systematic study of how this may occur at tree level and in one loop. We also propose a scotogenic version of the left-right gauge model with naturally small Dirac neutrino masses in one loop.

preprint2016arXiv

Color-kinematics duality and Sudakov form factor at five loops for N=4 supersymmetric Yang-Mills theory

Using color-kinematics duality, we construct for the first time the full integrand of the five-loop Sudakov form factor in N=4 super-Yang-Mills theory, including non-planar contributions. This result also provides a first manifestation of the color-kinematics duality at five loops. The integrand is explicitly ultraviolet finite when D<26/5, coincident with the known finiteness bound for amplitudes. If the double-copy method could be applied to the form factor, this would indicate an interesting ultraviolet finiteness bound for N=8 supergravity at five loops. The result is also expected to provide an essential input for computing the five-loop non-planar cusp anomalous dimension.

preprint2015arXiv

Iso-spin asymmetry of quark distributions and implications for single top-quark production at the LHC

We present an improved determination of the up- and down-quark distributions in the proton using recent data on charged lepton asymmetries from $W^\pm$ gauge-boson production at the LHC and Tevatron. The analysis is performed in the framework of a global fit of parton distribution functions. The fit results are consistent with a non-zero iso-spin asymmetry of the sea, $x(\bar d - \bar u)$, at small values of Bjorken $x\sim 10^{-4}$ indicating a delayed onset of the Regge asymptotics of a vanishing $(\bar d - \bar u)$-asymmetry at small-$x$. We compare with up- and down-quark distributions available in the literature and provide accurate predictions for the production of single top-quarks at the LHC, a process which can serve as a standard candle for the light quark flavor content of the proton.

preprint2015arXiv

Next-to-next-to-leading-order QCD corrections to $χ_{c0,2}\rightarrow γγ$

We calculate the next-to-next-to-leading-order (NNLO) perturbative corrections to $P$-wave quarkonia annihilation decay to two photons, in the framework of nonrelativistic QCD (NRQCD) factorization. The order-$α_s^2$ short-distance coefficients associated with each helicity amplitude are presented in a semi-analytic form, including the "light-by-light" contributions. With substantial NNLO corrections, we find disquieting discrepancy when confronting our state-of-the-art predictions with the latest \textsf{BESIII} measurements, especially fail to account for the measured $χ_{c2}\toγγ$ width. Incorporating the effects of spin-dependent forces would even exacerbate the situation, since it lifts the degeneracy between the nonperturbative NRQCD matrix elements of $χ_{c0}$ and $χ_{c2}$ toward the wrong direction. We also present the order-$α_s^2$ predictions to $χ_{b0,2}\toγγ$, which await the future experimental test.

preprint2017arXiv

Gluon Green functions free of Quantum fluctuations

This letter reports on how the Wilson flow technique can efficaciously kill the short-distance quantum fluctuations of 2- and 3-gluon Green functions, removes the $Λ_{\rm QCD}$ scale and destroys the transition from the confining non-perturbative to the asymptotically-free perturbative sector. After the Wilson flow, the behavior of the Green functions with momenta can be described in terms of the quasi-classical instanton background. The same behavior also occurs, before the Wilson flow, at low-momenta. This last result permits applications as, for instance, the detection of instanton phenomenological properties or a cheap lattice calibration.

preprint2016arXiv

Spontaneous topological transitions of electromagnetic fields in spatially inhomogeneous CP-odd domains

Metastable CP-odd domains of the hot QCD matter are coupled to QED via the chiral anomaly. The topology of electromagnetic field in these domains is characterized by magnetic helicity. It is argued, using the Maxwell-Chern-Simons model, that spatial inhomogeneity of the domains induces spontaneous transitions of electromagnetic field between the opposite magnetic helicity states.

preprint2016arXiv

Contributions of axion-like particles to lepton dipole moments

Contributions of a spin 0 axion-like particle (ALP) to lepton dipole moments, g-2 and EDMs, are examined. Barr-Zee and light-by-light loop effects from a light pseudoscalar ALP are found to be capable of resolving the long-standing muon g-2 discrepancy at the expense of relatively large ALP-gammagamma couplings. The compatibility of such large couplings with direct experimental constraints and perturbative unitarity bounds is discussed. Future tests of such a scenario are described. For CP violating ALP couplings, the electron EDM is found to probe much smaller, theoretically more easily accommodated ALP interactions. Future planned improvement in electron EDM searches is advocated as a way to not only significantly constrain ALP parameters but also, to potentially unveil a new source of CP violation which could have far reaching ramifications.

preprint2016arXiv

Baryon number fluctuations at finite temperature and density

We investigate baryon number fluctuations for finite temperature and density in two-flavor QCD. This is done within a QCD-improved low-energy effective theory in an extension of the approach put forward in [1,2]. In the present work we aim at improving the predictive power of this approach for large temperatures and density, that is, for small collision energies. This is achieved by taking into account the full frequency dependence of the quark dispersion. This ensures the necessary Silver Blaze property of finite density QCD for the first time, which so far was only implemented approximately. Moreover, we show that Polyakov loop fluctuations have a sizeable impact at large temperatures and density. The results for the kurtosis of baryon number fluctuations are compared to previous effective theory results, lattice results and recent experimental data from STAR.

1027 works