High Energy Physics - Phenomenology Publications (50)

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High Energy Physics - Phenomenology Publications

We extract polarized parton distribution functions (PPDFs), referred to as "KTA17", together with the highly correlated strong coupling $\alpha_s$ from recent and up-to-date $g_1$ and $g_2$ polarized structure functions world data at next-to-next-to-leading order (NNLO) in perturbative Quantum Chromodynamic (pQCD). The stability and reliability of the results are ensured by including non-perturbative target mass corrections (TMCs) as well as higher twist (HT) terms which are particularly important at the large-$x$ region at low Q$^2$. Their role in extracting the PPDFs in the nucleon is studied. Read More


We calculate the spectrum of scalar and tensor glueballs on the baryonic branch of the Klebanov-Strassler field theory by making use of its dual gravity description, hence providing a rigorous example of a strongly-coupled, multi-scale system that yields a parametrically light mass for one of the composite scalar particles: the dilaton. We briefly discuss the potential of such system towards finding a satisfactory solution to both the big and little hierarchy problems of the electro-weak theory. Read More


The Sauter-Schwinger effect predicts the creation of electron-positron pairs out of the quantum vacuum by a strong and slowly varying electric field. This effect can be dynamically assisted by an additional weaker time-dependent field, which may drastically enhance the pair-creation probability. In previous studies, it has been found that the enhancement may crucially depend on the temporal shape of this weaker pulse, e. Read More


Motivated by recent results by the ATLAS and CMS collaborations on the angular distribution of the $B \to K^* \mu^+\mu^-$ decay, we perform a state-of-the-art analysis of rare $B$ meson decays based on the $b \to s \mu \mu$ transition. Using standard estimates of hadronic uncertainties, we confirm the presence of a sizable discrepancy between data and SM predictions. We do not find evidence for a $q^2$ or helicity dependence of the discrepancy. Read More


We study confinement-deconfinement phase transition in a holographic soft-wall QCD model. By solving the Einstein-Maxwell-scalar system analytically, we obtain the phase structure of the black hole backgrounds. We then impose probe open strings in such background to investigate the confinement-deconfinement phase transition from different open string configurations under various temperatures and chemical potentials. Read More


A symmetry-preserving treatment of a vector-vector contact interaction is used to study charmed heavy-light mesons. The contact interaction is a representation of nonperturbative kernels used in Dyson-Schwinger and Bethe-Salpeter equations of QCD. The Dyson-Schwinger equation is solved for the $u,\,d,\,s$ and $c$ quark propagators and the bound-state Bethe-Salpeter amplitudes respecting spacetime-translation invariance and the Ward-Green-Takahashi identities associated with global symmetries of QCD are obtained to calculate masses and electroweak decay constants of the pseudoscalar $\pi,\,K$, $D$ and $D_s$ and vector $\rho$, $K^*$, $D^*$, and $D^*_s$ mesons. Read More


We present a method to calculate, without making assumptions about the local dark matter velocity distribution, the maximal and minimal number of signal events in a direct detection experiment given a set of constraints from other direct detection experiments and/or neutrino telescopes. The method also allows to determine the velocity distribution that optimizes the signal rates. We illustrate our method with three concrete applications: i) to derive a halo-independent upper limit on the cross section from a set of null results, ii) to confront in a halo-independent way a detection claim to a set of null results and iii) to assess, in a halo-independent manner, the prospects for detection in a future experiment given a set of current null results. Read More


We study a simple one-loop induced neutrino mass model that contains both bosonic and fermionic dark matter candidates and has the capacity to explain the muon anomalous magnetic moment anomaly. We perform a comprehensive analysis by taking into account the relevant constraints of charged lepton flavor violation, electric dipole moments, and neutrino oscillation data. We examine the constraints from lepton flavor-changing $Z$ boson decays at one-loop level, particularly when the involved couplings contribute to the muon $g-2$. Read More


This is a review of the results on black hole physics in the framework of loop quantum gravity. The key feature underlying the results is the discreteness of geometric quantities at the Planck scale predicted by this approach to quantum gravity. Quantum discreteness follows directly from the canonical quantization prescription when applied to the action of general relativity that is suitable for the coupling of gravity with gauge fields and specially with Fermions. Read More


The strong and radiative decay properties of the low-lying $\Omega_c$ states are studied in a constituent quark model. We find that the newly observed $\Omega_c$ states by the LHCb Collaboration can fit in well the decay patterns. Thus, their spin-parity can be possibly assigned as the following: (i) The $\Omega_c(3000)$ and $\Omega_c(3090)$ can be assigned to be two $J^P=1/2^-$ states, $|^2P_{\lambda}\frac{1}{2}^-\rangle$ and $|^4P_{\lambda}\frac{1}{2}^-\rangle$, respectively. Read More


Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in heavy-ion collisions to search for the QCD phase transition and critical point. In this paper, we performed a systematical analysis on the various cumulants and cumulant ratios of event-by-event net-strangeness distributions in Au+Au collisions at $\sqrt{s_{NN}}$=7.7, 11. Read More


The existence of doubly heavy baryons have not been well established in experiments so far. Searching for them is one of the important purposes at the Large Hadron Collider (LHC) where plenty of heavy quarks have been generated. In this Letter we study the weak decays of doubly charmed baryons, $\Xi_{cc}^{++}$ and $\Xi_{cc}^{+}$, using the light-front quark model to calculate the transition form factors and firstly considering the rescattering mechanism for the long-distance contributions to predict the corresponding branching fractions. Read More


Recent LHCb measurements of the $J/\psi$ meson production in jets is analyzed using fragmentation jet function formalism. It is shown that disagreement with theoretical predictions for distribution over the fraction of $J/\psi$ transverse momentum $z(J/\psi)$ in the cases of prompt production can be explained if one takes into account evolution of the fragmentation function and contributions from double parton scattering mechanism. Read More


We report on the first fully differential calculation for $W^\pm Z$ production in hadron collisions up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. Leptonic decays of the $W$ and $Z$ bosons are consistently taken into account, i.e. Read More


We investigate the process $B_c^+\to B_s^0\pi^+\pi^0$ via $B\bar{K}^*$ rescattering. The kinematic conditions for triangle singularities are perfectly satisfied in the rescattering diagrams. A resonance-like structure around the $B\bar{K}$ threshold, which we denote as $X(5777)$, is predicted to be present in the invariant mass distribution of $B_s^0 \pi^+$. Read More


We investigate a model with a massless fermion and a massive scalar field with the Yukawa interaction between these two fields. The model possess a discrete symmetry. The chiral condensate is calculated in one-loop approximation in $(1+1)$-dimensional spacetime. Read More


Following our earlier finding based on RHIC data on the dominant jet production from nucleus corona region, we reconsider this effect in nucleus-nucleus collisions at LHC energy. Our hypothesis was based on experimental data, which raised the idea of a finite formation time for the produced medium. At RHIC energy and in low density corona region this time reaches about 2 fm/c. Read More


We propose a new class of inflationary models in which inflation takes place while the inflaton is climbing up a potential hill due to a gravity effect. We study their attractor behavior, and investigate its relation with known attractors. We also discuss a possible realization of this type of models with the natural inflation, and show that the inflationary predictions come well within the region consistent with the observation of the cosmic microwave background. Read More


For the investigation of back-reactions of composite mesons in the NJL model, a variational path-integral treatment is formulated which yields an effective action $\mathscr{A}_{\rm eff}[D_{\sigma},D_{\pi}; S]$, depending on the propagators $D_\sigma$, $D_\pi$ of $\sigma-$ and $\pi-$mesons and on the full quark propagator $S$. The stationarity conditions $\delta \mathscr{A}_{\rm eff}/ \delta S = 0$, $\delta \mathscr{A}_{\rm eff}/ \delta D_\sigma = 0$, $\delta \mathscr{A}_{\rm eff}/ \delta D_\pi = 0$, then lead to coupled Schwinger-Dyson (SD) equations for the quark self-energy and the meson polarization functions. These results reproduce and extend results of the so-called "$\Phi-$derivable" approach and provide a functional formulation for diagrammatic resummations of $1/N_c-$corrections in the NJL model. Read More


We present a halo-independent determination of the unmodulated signal corresponding to the DAMA modulation if interpreted as due to dark matter weakly interacting massive particles (WIMPs). First we show how a modulated signal gives information on the WIMP velocity distribution function in the Galactic rest frame, from which the unmodulated signal descends. Then we perform a mathematically-sound profile likelihood analysis in which we profile the likelihood over a continuum of nuisance parameters (namely, the WIMP velocity distribution). Read More


Experiments using nuclei to probe new physics beyond the Standard Model, such as neutrinoless $\beta\beta$ decay searches testing whether neutrinos are their own antiparticle, and direct detection experiments aiming to identify the nature of dark matter, require accurate nuclear physics input for optimizing their discovery potential and for a correct interpretation of their results. This demands a detailed knowledge of the nuclear structure relevant for these processes. For instance, neutrinoless $\beta\beta$ decay nuclear matrix elements are very sensitive to the nuclear correlations in the initial and final nuclei, and the spin-dependent nuclear structure factors of dark matter scattering depend on the subtle distribution of the nuclear spin among all nucleons. Read More


A light stop around the weak scale is a hopeful messenger of natural supersymmetry (SUSY), but it has not shown up at the current stage of LHC. Such a situation raises question on the fate of natural SUSY. Actually, a relatively lighter stop can be easily hidden in a compressed spectra such as mild mass degeneracy between stop and neutralino plus top quark. Read More


A fundamental feature of microscopic quantum theories for massless spin-$\frac{1}{2}$ fermions is the chiral anomaly. Recently there has been significant interest in the study of macroscopic manifestation of chiral anomaly in many-body systems of such fermions through induced anomalous chiral transport processes. A notable example is the Chiral Magnetic Effect (CME) where a vector current (e. Read More


Recently, the experimental results of LHCb Collaboration suggested the existence of five new excited states of $\Omega_c^0$, $\Omega_c(3000)^0$, $\Omega_c(3050)^0$, $\Omega_c(3066)^0$, $\Omega_c(3090)^0$ and $\Omega_c(3119)^0$, the quantum numbers of these new particles are not determined now. To understand the nature of the states, a dynamical calculation of 5-quark systems with quantum numbers $IJ^P=0(\frac{1}{2})^-$, $0(\frac{3}{2})^-$ and $0(\frac{5}{2})^-$ is performed in the framework of chiral quark model with the help of gaussian expansion method. The results show the $\Xi-\bar{D}$, $\Xi_c\bar{K}$ and $\Xi_c^*\bar{K}$ are possible the candidates of these new particles. Read More


Dirac and Weyl fermions appear as quasi-particle excitations in many different condensed-matter systems. They display various quantum transitions which represent unconventional universality classes related to the variants of the Gross-Neveu model. In this work we study the bosonized version of the standard Gross-Neveu model -- the Gross-Neveu-Yukawa theory -- at three-loop order, and compute critical exponents in $4-\epsilon$ dimensions for general number of fermion flavors. Read More


It is well recognized that looking for new physics at lower energy colliders is a tendency which is complementary to high energy machines such as LHC. Based on large database of BESIII, we may have a unique opportunity to do a good job. In this paper we calculate the branching ratios of semi-leptonic processes $D^+_s \to K^+ e^-e^+$, $D^+_s \to K^+ e^-\mu^+$ and leptonic processes $D^0 \to e^-e^+$, $D^0 \to e^-\mu^+$ in the frames of $U(1)'$ model, 2HDM and unparticle separately. Read More


The small quark mixing, described by the Cabibbo-Kobayashi-Maskawa (CKM) matrix in the Standard Model, may be a clue to reveal new physics around the TeV scale. We consider a simple scenario that extra particles in a hidden sector radiatively mediate the flavor violation to the quark sector around the TeV scale and effectively realize the observed CKM matrix. The lightest particle in the hidden sector, whose contribution to the CKM matrix is expected to be dominant, is a good dark matter (DM) candidate, so we focus on the contribution, and discuss the DM physics. Read More


2017Mar
Affiliations: 1Univ. of Cyprus & The Cyprus Inst., 2Temple Univ., 3Centro Fermi & Rome Tor Vergata, 4Rome Tor Vergata, 5The Cyprus Inst., 6DESY-Zeuthen, 7The Cyprus Inst., 8Bonn Univ., 9The Cyprus Inst., 10Grenoble, 11Univ. of Utah, 12Univ. of Bern

We present results on the light, strange and charm nucleon scalar and tensor charges from lattice QCD, using simulations with $N_f=2$ flavors of twisted mass Clover-improved fermions with a physical value of the pion mass. Both connected and disconnected contributions are included, enabling us to extract the isoscalar, strange and charm charges for the first time directly at the physical point. Furthermore, the renormalization is computed non-perturbatively for both isovector and isoscalar quantities. Read More


In recent years, the quasi parton distribution has been introduced for extracting the parton distribution functions from lattice QCD simulations. The quasi and standard distribution share the same perturbative collinear singularity and the renormalized quasi distribution can be factorized into the standard distribution with a perturbative matching factor. The quasi parton distribution is known to have power-law UV divergences, which do not exist in the standard distribution. Read More


In this paper, we study the $B \to K^*$ transition form factors (TFFs) within the QCD light-cone sum rules (LCSR) approach. Two correlators, i.e. Read More


We study an extension of the Inert Higgs Doublet Model (IHDM) by three copies of right handed neutrinos and heavy charged leptons such that both the inert Higgs doublet and the heavy fermions are odd under the $Z_2$ symmetry of the model. The neutrino masses are generated at one loop in the scotogenic fashion. Assuming the neutral scalar of the inert Higgs to be the dark matter candidate, we particularly look into the region of parameter space where dark matter relic abundance is primarily governed by the inert Higgs coupling with the leptons. Read More


The cosmic neutrino background is a key prediction of Big Bang cosmology which has not been observed yet. The movement of the earth through this neutrino bath creates a force on a pendulum, as if it was exposed to a cosmic wind. We revise here estimates for the resulting pendulum acceleration and compare it to the theoretical sensitivity of an experimental setup where the pendulum position is measured using current laser interferometer technology as employed in gravitational wave detectors. Read More


The factorization of amplitudes into hard, soft and collinear parts is known to be violated in situations where incoming particles are collinear to outgoing ones. This result was first derived by studying limits where non-collinear particles become collinear. We show that through an effective field theory framework with Glauber operators, these factorization-violating effects can be reproduced from an amplitude that is factorized before the splitting occurs. Read More


We compute the leading-order evolution of parton distribution functions for all the Standard Model fermions and bosons up to energy scales far above the electroweak scale, where electroweak symmetry is restored. Our results include the 52 PDFs of the unpolarized proton, evolving according to the SU(3), SU(2), U(1), mixed SU(2) x U(1) and Yukawa interactions. We illustrate the numerical effects on parton distributions at large energies, and show that this can lead to important corrections to parton luminosities at a future 100 TeV collider. Read More


We study a vectorial asymptotically free gauge theory, with gauge group $G$ and $N_f$ massless fermions in a representation $R$ of this group, that exhibits an infrared (IR) zero in its beta function, $\beta$, at the coupling $\alpha=\alpha_{IR}$ in the non-Abelian Coulomb phase. For general $G$ and $R$, we calculate the scheme-independent series expansions of (i) the anomalous dimension of the fermion bilinear, $\gamma_{\bar\psi\psi,IR}$, to $O(\Delta_f^4)$ and (ii) the derivative $\beta' = d\beta/d\alpha$, to $O(\Delta_f^5)$, both evaluated at $\alpha_{IR}$, where $\Delta_f$ is an $N_f$-dependent expansion variable. These are the highest orders to which these expansions have been calculated. Read More


2017Mar
Affiliations: 1NIKHEF, Amsterdam & Leiden U., 2NIKHEF, Amsterdam, 3NIKHEF, Amsterdam, 4Liverpool U., Dept. Math.

We have computed the self-energies and a set of three-particle vertex functions for massless QCD at the four-loop level in the MSbar renormalization scheme. The vertex functions are evaluated at points where one of the momenta vanishes. Analytical results are obtained for a generic gauge group and with the full gauge dependence, which was made possible by extensive use of the Forcer program for massless four-loop propagator integrals. Read More


Charged Higgs bosons $H^\pm$ are predicted by some non-minimal Higgs scenarios, such as models containing Higgs triplets and two-Higgs-doublet models, so that the experimental observation of these bosons would indicate physics beyond the Standard Model. In the present work, we introduce a new channel to indirect search for the charged Higgses through the hadronic decay of polarized top quarks where a top quark decays into a charged Higgs $H^+$ and a bottom-flavored hadron $B$ via the hadronization process of the produced bottom quark, $t(\uparrow)\rightarrow H^++b(\to B+jet)$. To obtain the energy spectrum of produced $B$-hadrons we present, for the first time, an analytical expression for the ${\cal O}(\alpha_s)$ corrections to the differential decay width of the process $t\rightarrow H^+b$ in the presence of a massive b-quark in the General-Mass Variable-Flavor-Number Scheme (GM-VFNS). Read More


We consider high-mass systems of two or more particles that are produced by QCD hard scattering in hadronic collisions. We examine the azimuthal correlations between the system and one of its particles. We point out that the perturbative QCD computation of such azimuthal correlations and asymmetries can lead to divergent results at fixed perturbative orders. Read More


The talk summarises work done by the authors consisting of a detailed study of the possible vacua in models with three Higgs doublets with $S_3$ symmetry and without explicit CP violation. Different vacua require special regions of the parameter space which were analysed in our work. We establish the possibility of spontaneous CP violation in this framework and we also show which complex vacua conserve CP. Read More


We search for sterile neutrinos in the holographic dark energy cosmology by using the latest observational data. To perform the analysis, we employ the current cosmological observations, including the cosmic microwave background temperature power spectrum data from Planck mission, the baryon acoustic oscillation measurements, the type Ia supernova data, the redshift space distortion measurements, the shear data of weak lensing observation, the Planck lensing measurement, and the latest direct measurement of $H_0$ as well. We show that, compared to the $\Lambda$CDM cosmology, the holographic dark energy cosmology with sterile neutrinos can relieve the tension between the Planck observation and the direct measurement of $H_0$ much better. Read More


The recent measurement by ATLAS of light-by-light scattering in LHC Pb-Pb collisions is the first direct evidence for this basic process. We find that it requires the mass scale of a nonlinear Born-Infeld extension of QED to be $\gtrsim 100$~GeV, a much stronger constraint than those derived previously. In the case of a Born-Infeld extension of the Standard Model in which the U(1)$_{\rm Y}$ hypercharge gauge symmetry is realized nonlinearly, the limit on the corresponding mass scale is $\gtrsim 90$~GeV, which in turn imposes a lower limit of $\gtrsim 11$~TeV on the magnetic monopole mass in such a U(1)$_{\rm Y}$ Born-Infeld theory. Read More


As a successful theory for heavy quarkonium, nonrelativistic QCD (NRQCD) factorization now encounters some notable difficulties in describing quarkonium production. This may be due to the inadequate treatment of soft hadrons emitted in the hadronization process, which causes bad convergence of velocity expansion in NRQCD. In this paper, starting from QCD we propose a new factorization approach, soft gluon factorization (SGF), to better deal with the effects of soft hadrons. Read More


We consider the phenomenon of "tunnelling of the 3rd kind", whereby a magnetic field may traverse a classically impenetrable barrier by pair creation of unimpeded quantum fermions. These propagate through the barrier and generate a magnetic field on the other side. We study this numerically using quantum fermions coupled to a classical Higgs-gauge system, where we set up a magnetic field outside a box shielded by two superconducting barriers. Read More


We propose a simple modification of the no-scale supergravity Wess-Zumino model of Starobinsky-like inflation to include a Polonyi term in the superpotential. The purpose of this term is to provide an explicit mechanism for supersymmetry breaking at the end of inflation. We show how successful inflation can be achieved for a gravitino mass satisfying the strict upper bound $m_{3/2}< 10^3$ TeV, with favoured values $m_{3/2}\lesssim\mathcal{O}(1)$ TeV. Read More


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, and are studied in Minkowski space, yielding a direct proof of positivity violation and confinement from first principles. Complex conjugated poles are found for the gluon propagator. Read More


We present holographic desciptions of dynamical electroweak symmetry breaking models that incorporate the top mass generation mechanism. The models allow computation of the spectrum in the presence of large anomalous dimensions due to walking and strong NJL interactions. Technicolour and QCD dynamics are described by the bottom-up Dynamic AdS/QCD model for arbitrary gauge groups and numbers of quark flavours. Read More


We derive two-loop anomalous dimensions for four-Fermi operators in supersymmetric theories using the effective Kahler potential. We introduce the general forms in generic gauge theories and apply our results to the flavor-changing operators in (minimal) supersymmetric standard models. Read More


2017Mar
Affiliations: 1ETH Zürich, 2Ecole polytechnique, CPHT

We extend the study of quark spin-orbit correlations in the nucleon to the case of transverse polarization. At the leading-twist level, this completes the spin structure of the quark kinetic energy-momentum tensor. In particular, we revisit the transversity decomposition of angular momentum proposed a decade ago by Burkardt and introduce a new transverse correlation, namely between quark transversity and orbital angular momentum. Read More


There are some controversies about the influences of ultraviolet (UV) physics on the primordial density perturbation. In this paper, we point out the quantum corrections of the UV physics can be of order $\mathcal{O}\left(1\right)$ rather than $\mathcal{O}\left( H/\Lambda_{\rm UV} \right)$ or $\mathcal{O}\left( H^{2}/\Lambda_{\rm UV}^{2}\right)$ by using the fact that there is a strong correspondence related to the UV corrections between the renormalized (inflationary) vacuum field fluctuation and the effective potential. This important aspect of quantum field theory (QFT) has been overlooked so far in this context. Read More


Using local central Yukawa-type Malfliet-Tjon interactions reproducing the low-energy parameters and phase shifs of the $nn$ system and the latest updates of the $n\Lambda$ and $\Lambda\Lambda$ Nijmegen ESC08c potentials we study the possible existence of a ${}_{\Lambda\Lambda}^{\,\,\,\,4}n$ bound state. Our results indicate that the ${}_{\Lambda\Lambda}^{\,\,\,\,4}n$ is unbound, being just above threshold. We discuss the role played by the $^1S_0$ $nn$ repulsive term of the Yukawa-type Malfliet-Tjon interaction. Read More