HEP Phenomenology·hep-ph
28 papers—21 primary·7 cross-listed·reconstructed*
With Run-II of the LHC starting its final year of data-taking, high precision theoretical predictions through Monte-Carlo event generators whose uncertainties match that of the recorded data are of highest importance. This talk summarises the progress of the field and highlight a number of recent developments.
Gilvana C. Penedo🇧🇷 · Werner K. Sauter🇧🇷
In the high energy regime, the proton structure consists of a very large number of particles called partons (quarks and gluons) that interact with each other, according to the theory of strong interactions, Quantum Chromodynamics (QCD). Through QCD, the number of partons in the proton is described by equations of parton evolution that depend on kinematic variables. These equations can be linear, the DGLAP equations, and nonlinear, the GLR-MQ equation. We have studied some analytic solutions of the equations of parton evolution. In order to generate the preliminary results, we used an ansatz for the solution of the equations of evolution of the gluon distribution, and compared with results of parametrizations of Parton Distributions Functions (PDFs). Another method proposed in the literature is the solution via Laplace transform that will be applied in the future.
Ernesto Arganda🇦🇷 · Victor Martin-Lozano🇩🇪 · Anibal D. Medina🇦🇷 · Nicolás Mileo🇦🇷
In this work we present a new search strategy for the discovery of staus at the LHC in the context of the minimal supersymmetric standard model. The search profits from the large s-channel -quark annihilation production of the heavy CP-even and CP-odd Higgs bosons (H/A) which can be attained in regions of that avoid the stringent searches via decays into stau pairs. We also focus on regions where the staus branching ratios are dominated by the decays into a tau lepton and the lightest neutralino. Thus the experimental signature consists of final states made up of a tau-lepton pair plus large missing transverse energy. We take advantage of the large stau-pair production cross sections via heavy Higgs boson decays, which are between one or two orders of magnitude larger than the usual electroweak production cross sections for staus. A set of basic cuts allow us to obtain significances of the signal over the SM backgrounds at the discovery level (5 standard deviations) in the next LHC run with a center-of-mass energy of 14 TeV and a total integrated luminosity of only 100 fb.
N.N. Achasov🇷🇺 · G.N. Shestakov🇷🇺
Anomalous isotopic symmetry breaking in the decay through a mechanism featuring anomalous Landau thresholds in the form of logarithmic triangle singularities, i.e., through the transition, has been analyzed. It has been shown that this effect can be correctly quantified only by taking into account the nonzero width. Different scales of isotopic symmetry breaking associated with the mass difference are compared.
Mikhail Danilov🇷🇺 · Sergey Demidov🇷🇺 · Dmitry Gorbunov🇷🇺
New light vector particles - hidden photons - are present in many extensions of the Standard Model of particle physics. They can be produced in nuclear reactors and registered by neutrino detectors. We obtain new limits on the models with the hidden photons from an analysis of published results of the TEXONO neutrino experiment. Accounting for oscillations between the visible and hidden photons, we find that the neutrino experiments are generally insensitive to the hidden photons lighter than \,eV.
Majid Hashemi🇮🇷 · Mostafa MahdaviKhorrami🇮🇷
In this paper, the b quark pair production events are analyzed as a source of neutral Higgs bosons of the two Higgs doublet model type I at linear colliders. The production mechanism is e+e- -> Z/gamma -> HA -> bbbb assuming a fully hadronic final state. The analysis aim is to identify both scalar and pseudo-scalar Higgs bosons in different benchmark points accommodating moderate boson masses. Due to pair production of Higgs bosons, the analysis is most suitable for a linear collider operating at sqrt(s) = 1 TeV. Results show that in selected benchmark points, signal peaks are observable in the b-jet pair invariant mass distributions at integrated luminosity of 500 fb-1.
Sushanta Tripathy🇮🇳 · Sudipan De🇮🇳 · Mohammed Younus🇮🇳 · Raghunath Sahoo🇮🇳
Xe+Xe collision at relativistic energies may provide us with a partonic system whose size is approximately in between those produced by p+p and Pb+Pb collisions. The experimental results on anisotropic flow in Xe+Xe and Pb+Pb collisions should provide us with an opportunity to study system size dependence of . In the present work, we have used AMPT transport model to calculate charged particles' for Xe+Xe collisions at =5.44 TeV. We have also tried to demonstrate the no. of constituent quark, , and scaling of the elliptic flow. We find that scaling of is not observed for the identified hadrons. The results from Xe+Xe collisions have also been compared to Pb+Pb collisions at = 5.02 TeV. We find that flow of charged particles in (50-60)\% central collisions for Xenon nuclei is almost 30\% less than particle flow developed in lead ion collisions, implying the important role the system size play in development of particle collective motion in relativistic heavy ion collisions.
Felix Karbstein🇩🇪 · Marc Wagner🇩🇪 · Michelle Weber🇩🇪
While lattice QCD allows for reliable results at small momentum transfers (large quark separations), perturbative QCD is restricted to large momentum transfers (small quark separations). The latter is determined up to a reference momentum scale , which is to be provided from outside, e.g. from experiment or lattice QCD simulations. In this article, we extract for QCD with dynamical quark flavors by matching the perturbative static quark-antiquark potential in momentum space to lattice results in the intermediate momentum regime, where both approaches are expected to be applicable. In a second step, we combine the lattice and the perturbative results to provide a complete analytic parameterization of the static quark-antiquark potential in position space up to the string breaking scale. As an exemplary phenomenological application of our all-distances potential we compute the bottomonium spectrum in the static limit.
U. Ozdem🇹🇷
The magnetic dipole moments of the spin- doubly heavy baryons are extracted in the framework of light-cone QCD sum rule. The electromagnetic properties of the doubly heavy baryons encodes important information of their internal structure. The results for the magnetic dipole moments of doubly heavy baryons acquired in this work are compared with the predictions of the other theoretical approaches.
R. Foot🇦🇺
Plasma dark matter, which arises in dissipative dark matter models, can give rise to large annual modulation signals from keV electron recoils. Previous work has argued that the DAMA annual modulation signal could have an explanation within such a scenario. However, detailed predictions are difficult due to the inherent complexities involved in modelling the halo plasma interactions with Earth-bound dark matter. Here, we consider a simple phenomenological model for the dark matter velocity function relevant for direct detection experiments, and compare the resulting electron scattering rate with the new DAMA/LIBRA phase 2 data. We also consider the constraints from other experiments, including XENON100 and DarkSide-50.
Luise Adams🇩🇪 · Ekta Chaubey🇩🇪 · Stefan Weinzierl🇩🇪
We compute systematically for the planar double box Feynman integral relevant to top pair production with a closed top loop the Laurent expansion in the dimensional regularisation parameter . This is done by transforming the system of differential equations for this integral and all its sub-topologies to a form linear in , where the -part is strictly lower triangular. This system is easily solved order by order in the dimensional regularisation parameter . This is an example of an elliptic multi-scale integral involving several elliptic sub-topologies. Our methods are applicable to similar problems.
A. Bermudez Martinez🇩🇪 · P. Connor🇩🇪 · F. Hautmann🇬🇧 · H. Jung🇩🇪 · A. Lelek🇩🇪 · V. Radescu🇨🇭 · R. Zlebcik🇩🇪
Collinear and transverse momentum dependent (TMD) parton densities are obtained from fits to precision measurements of deep inelastic scattering (DIS) cross sections at HERA. The parton densities are evolved by DGLAP evolution with next-to-leading-order (NLO) splitting functions using the parton branching method, allowing one to determine simultaneously collinear and TMD densities for all flavors over a wide range in , and , relevant for predictions at the LHC. The DIS cross section is computed from the parton densities using perturbative NLO coefficient functions. Parton densities satisfying angular ordering conditions are presented. Two sets of parton densities are obtained, differing in the renormalization scale choice for the argument in the strong coupling alpha_s. This is taken to be either the evolution scale or the transverse momentum . While both choices yield similarly good values for the fit to DIS measurements, especially the gluon density turns out to differ between the two sets. The TMD densities are used to predict the transverse momentum spectrum of Z-bosons at the LHC.
We present the first dynamical calculation of the -meson as a resonance in the Dyson-Schwinger/Bethe-Salpeter framework by including explicit two-pion exchange in addition to the t-channel one-gluon exchange of rainbow-ladder in the interaction kernel. The width is determined from the imaginary part of the resonance pole and is generated by the singularity structure of the integrand, treated by means of suitable path deformations. We find the resonant mass and width to be MeV and MeV respectively, corresponding to a coupling constant ; repulsive corrections beyond rainbow-ladder are known to bring these in alignment with experiment. Furthermore we present the dependence of these parameters on the pion mass and compare with results from lattice QCD.
We study hadronic decays within the effective field theory framework. We consider the colour-singlet and colour-octet contributions and study their properties using (p)NRQCD effective theory. We show that infrared singularities in collinear integrals of the colour-singlet amplitudes can be absorbed into the renormalisation of the colour-octet matrix elements. The heavy quark spin symmetry allows us to establish a relation between the colour-octet matrix elements and to define the spin symmetry breaking corrections which are free from infrared singularities. We apply obtained results for a phenomenological description of the branching fractions.
Jan Heisig🇩🇪 · Joern Kersten🇳🇴 · Nick Murphy🇩🇰 · Inga Strümke🇳🇴
Gaugino mediation is an attractive supersymmetry breaking scheme naturally avoiding flavor problems by suppressing the soft sfermion masses at a high-energy scale. We consider an extension of the original model which yields non-vanishing trilinear scalar couplings. This increases the viable parameter space predicting a sufficiently large Higgs mass. Assuming the gravitino to be the lightest superparticle, we consider additional constraints from direct searches at the LHC, finding allowed points with a neutralino, sneutrino or stau next-to-lightest superparticle.
D.K. Papoulias🇬🇷 · R. Sahu🇮🇳 · T.S. Kosmas🇬🇷 · V.K.B. Kota🇮🇳 · B. Nayak🇮🇳
Event detection rates for WIMP-nucleus interactions are calculated for Ga, Ge, As and I (direct dark matter detectors). The nuclear structure form factors, that are rather independent of the underlying beyond the Standard Model particle physics scenario assumed, are evaluated within the context of the deformed nuclear shell model (DSM) based on Hartree-Fock nuclear states. Along with the previously published DSM results for Ge, the neutrino-floor due to coherent elastic neutrino-nucleus scattering (CENS), an important source of background to dark matter searches, is extensively calculated. The impact of new contributions to CENS due to neutrino magnetic moments and mediators at direct dark matter detection experiments is also examined and discussed. The results show that the neutrino-floor constitutes a crucial source of background events for multi-ton scale detectors with sub-keV capabilities.
Shi-Ping He🇨🇳 · Ying-nan Mao🇨🇳 · Chen Zhang🇹🇼 · Shou-hua Zhu🇨🇳
We re-analyze the -vertex with the form , where is the 125 GeV Higgs boson and is an exotic pseudo-axion, based on the effective field theory (EFT) analysis and choose the simplest little Higgs (SLH) model as an example. For a pure gauge singlet pseudoscalar , after carefully removing all off-diagonal two-point transitions, we show that its coefficient cannot appear before level, where is the ratio between the electro-weak scale and a high scale . The same behavior arises in the simplest little Higgs (SLH) model, which is quite different from the result that has already existed for a long time.
Bithika Karmakar🇮🇳 · Aritra Bandyopadhyay🇧🇷 · Najmul Haque🇮🇳 · Munshi G Mustafa🇮🇳
Based on transversality condition of gauge boson self-energy we have systematically constructed the general structure of the gauge boson two-point functions using four linearly independent basis tensors in presence of a nontrivial background, i.e., hot magnetized material medium. The hard thermal loop approximation has been used for the heat bath to compute various form factors associated with the gauge boson's two point functions both in strong and weak field approximation. We have also analyzed the dispersion of a gauge boson (e.g., gluon) using the effective propagator both in strong and weak magnetic field approximation. The formalism is also applicable to QED. The presence of only thermal background leads to a longitudinal (plasmon) mode and a two-fold degenerate transverse mode. In presence of a hot magnetized background medium the degeneracy of the two transverse modes is lifted and one gets three quasiparticle modes. In weak field approximation one gets two transverse modes and one plasmon mode. On the other hand, in strong field approximation also one gets the three modes in Lowest Landau Level. The general structure of two-point function may be useful for computing the thermo-magnetic correction of various quantities associated with a gauge boson.
Johann Brehmer🇺🇸 · Kyle Cranmer🇺🇸 · Gilles Louppe🇧🇪 · Juan Pavez🇨🇱
We present powerful new analysis techniques to constrain effective field theories at the LHC. By leveraging the structure of particle physics processes, we extract extra information from Monte-Carlo simulations, which can be used to train neural network models that estimate the likelihood ratio. These methods scale well to processes with many observables and theory parameters, do not require any approximations of the parton shower or detector response, and can be evaluated in microseconds. We show that they allow us to put significantly stronger bounds on dimension-six operators than existing methods, demonstrating their potential to improve the precision of the LHC legacy constraints.
Tao Han🇺🇸 · Satyanarayan Mukhopadhyay🇺🇸 · Xing Wang🇺🇸
In a large class of scenarios, dark matter (DM) particles that belong to a multiplet of the standard model (SM) weak interactions are challenging to probe in direct detection experiments due to loop-suppressed cross-sections. Direct production at colliders is thus crucial to look for such DM candidates, and under current estimates, future runs of the 14-TeV LHC are projected to probe masses of around 300 GeV for DM belonging to an SU(2) doublet (Higgsino-like), and 900 GeV for SU(2) triplet (wino-like). We examine how far this mass reach can be extended at the proposed 27-TeV high-energy upgrade of the LHC (HE-LHC), and compare the results to the case for a 100-TeV hadron collider. Following a detector setup similar to that of the ATLAS tracking system for the Run-2 LHC upgrade, with a new Insertable B-Layer (IBL), a disappearing charged track analysis at the HE-LHC can probe Higgsino-like (wino-like) DM mass of up to 600 GeV (2.1 TeV) at the 95% C.L. The monojet and missing transverse momentum search, on the otherhand, has a weaker reach of 490 GeV (700 GeV) at 95% C.L. for the Higgsino-like (wino-like) states. The mass range accessible in the collider searches can be complementary to the indirect detection probes using gamma rays from dwarf-spheroidal galaxies.
Johann Brehmer🇺🇸 · Kyle Cranmer🇺🇸 · Gilles Louppe🇧🇪 · Juan Pavez🇨🇱
We develop, discuss, and compare several inference techniques to constrain theory parameters in collider experiments. By harnessing the latent-space structure of particle physics processes, we extract extra information from the simulator. This augmented data can be used to train neural networks that precisely estimate the likelihood ratio. The new methods scale well to many observables and high-dimensional parameter spaces, do not require any approximations of the parton shower and detector response, and can be evaluated in microseconds. Using weak-boson-fusion Higgs production as an example process, we compare the performance of several techniques. The best results are found for likelihood ratio estimators trained with extra information about the score, the gradient of the log likelihood function with respect to the theory parameters. The score also provides sufficient statistics that contain all the information needed for inference in the neighborhood of the Standard Model. These methods enable us to put significantly stronger bounds on effective dimension-six operators than the traditional approach based on histograms. They also outperform generic machine learning methods that do not make use of the particle physics structure, demonstrating their potential to substantially improve the new physics reach of the LHC legacy results.
Juan C. Macías🇧🇷 · Marcus Benghi Pinto🇧🇷
The \textit{optimized perturbation theory} (OPT) is implemented in the flavor symmetric Nambu--Jona-Lasinio (NJL) model to generate non-pertubative corrections to the quark pressure beyond the large- approximation. The correctness of this implementation is verified by the recovery of the already known non-perturbative results in the Hartree-Fock approximation, and by having the large- approximation as a limiting case. This formalism is then used to revisit a discussion on the discordance between the lattice data and the two flavor model prediction of the dynamical vector repulsive interactions, beyond the pseudocritical temperature. It is shown that these contradictory predictions can be corrected by considering a three quark flavor system.
Jacquelyn Noronha-Hostler🇺🇸 · Claudia Ratti🇺🇸
A long standing question in the field of heavy-ion collisions is whether charm quarks are thermalized within the Quark Gluon Plasma. In recent years, progress in lattice QCD simulations has led to reliable results for the equation of state of a system of 2+1 flavors (up, down, and strange) and 2+1+1 flavors (up, down, strange, and charm). We find that the equation of state strongly affects differential flow harmonics and a preference is seen for thermalized charm quarks at the LHC. Predictions are also made for the event-plane correlations at RHIC AuAu GeV collisions, and the scaling of differential flow observables and factorization breaking for all charged particles at LHC PbPb TeV collisions compared to LHC XeXe TeV collisions, which could be useful in answering the question: are charm quarks thermalized?
J. R. C. C. C. Correia🇵🇹 · I. S. C. R. Leite🇵🇹 · C. J. A. P. Martins🇵🇹
Domain walls form at phase transitions which break discrete symmetries. In a cosmological context they often overclose the universe (contrary to observational evidence), although one may prevent this by introducing biases or forcing anisotropic evolution of the walls. In a previous work [Correia {\it et al.}, Phys.Rev.D90, 023521 (2014)] we numerically studied the evolution of various types of biased domain wall networks in the early universe, confirming that anisotropic networks ultimately reach scaling while those with a biased potential or biased initial conditions decay. We also found that the analytic decay law obtained by Hindmarsh was in good agreement with simulations of biased potentials, but not of biased initial conditions, and suggested that the difference was related to the Gaussian approximation underlying the analytic law. Here we extend our previous work in several ways. For the cases of biased potential and biased initial conditions we study in detail the field distributions in the simulations, confirming that the validity (or not) of the Gaussian approximation is the key difference between the two cases. For anisotropic walls we carry out a more extensive set of numerical simulations and compare them to the canonical velocity-dependent one-scale model for domain walls, finding that the model accurately predicts the linear scaling regime after isotropization. Overall, our analysis provides a quantitative description of the cosmological evolution of these networks.
Shan-Liang Zhang🇨🇳 · Tan Luo🇨🇳 · Xin-Nian Wang🇨🇳 · Ben-Wei Zhang🇨🇳
The impact of jet quenching on -tagged jets in relativistic heavy-ion collisions at the Large Hadron Collider (LHC) is investigated. We employ Sharpa Monte Carlo program that combines next-to-leading order matrix elements with matched resummation of parton shower to compute the initial +jet production. The Linear Boltzmann Transport (LBT) model is then used to simulate the propagation, energy attenuation of and medium response induced by jet partons in the quark-gluon plasma. With both higher-order corrections and matched soft/collinear radiation as well as a sophisticated treatment of parton energy loss and medium response in LBT, our numerical calculations can provide the best description so far of all available observables of +jet simultaneously in both p+p and Pb+Pb collisions, in particular, the shift of the distribution in transverse momentum asymmetry , the modification of azimuthal angle correlation in and the overall suppression of average number of -tagged jets per boson at TeV as measured by the CMS experiment. We also show that higher-order corrections to +jet production play an indispensable role in understanding +jet azimuthal angle correlation at small and intermediate , and momentum imbalance at small . Jet quenching of the sub-leading jets is shown to lead to suppression of +jet correlation at small azimuthal angle difference and at small .
T. G. Blackburn🇸🇪 · D. Seipt🇬🇧 · S. S. Bulanov🇺🇸 · M. Marklund🇸🇪
The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as are found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes . We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.
We study formulations of bound state (Bethe-Salpeter) equations on arbitrary Riemannian manifolds. We obtain a hierarchy of equations for multipartice wave functions. These equations, at each number of particles, depend on certain choices of combinatorial origin, which together with the metric, define the equations completely.
Any particle dark matter (DM) scenario featuring a suppressed power spectrum of astrophysical relevance results in a delay of galaxy formation. As a consequence, such scenarios can be constrained using the global 21-cm absorption signal initiated by the UV radiation of the first stars. The Experiment to Detect the Global Epoch of Reionization Signature (EDGES) recently reported the first detection of such an absorption signal at redshift . While its amplitude might indicate the need for new physics, we solely focus on the timing of the signal to test non-cold DM models. Assuming conservative limits for the stellar-to-baryon fraction () and for the minimum cooling temperature ( Kelvin) motivated by radiation-hydrodynamic simulations, we are able to derive unprecedented constraints on a variety of non-cold DM models. For example, the mass of thermal warm DM is limited to keV, while mixed DM scenarios (featuring a cold and a hot component) are constrained to a hot DM fraction below 17 percent. The ultra-light axion DM model is limited to masses eV, a regime where its wave-like nature is pushed far below the kiloparsec scale. Finally, sterile neutrinos from resonant production can be fully disfavoured as a dominant DM candidate. The results of this paper show that the 21-cm absorption signal is a powerful discriminant of non-cold dark matter, allowing for significant improvements over to the strongest current limits. Confirming the result from EDGES is paramount in this context.
* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.