HEP Phenomenology·hep-ph
28 papers—24 primary·4 cross-listed·reconstructed*
Saturation and geometrical scaling (GS) of gluon distributions are a consequence of the non-linear evolution equations of QCD. We argue that in pp GS holds for the inelastic cross-section rather than for the multiplicity distributions. We also discuss possible fluctuations of the proton saturation scale in pA collisions at the LHC.
Giuseppe Degrassi🇮🇹 · Pier Paolo Giardino🇺🇸 · Fabio Maltoni🇧🇪 · Davide Pagani🇧🇪
We propose a method to determine the trilinear Higgs self coupling that is alternative to the direct measurement of Higgs pair production total cross sections and differential distributions. The method relies on the effects that electroweak loops featuring an anomalous trilinear coupling would imprint on single Higgs production at the LHC. We first calculate these contributions to all the phenomenologically relevant Higgs production (, VBF, , , ) and decay (, , , ) modes at the LHC and then estimate the sensitivity to the trilinear coupling via a one-parameter fit to the single Higgs measurements at the LHC 8 TeV. We find that the bounds on the self coupling are already competitive with those from Higgs pair production and will be further improved in the current and next LHC runs.
Brian Shuve🇺🇸 · Michael E. Peskin🇺🇸
We revisit the recent limits from LHCb on a Majorana neutrino N in the mass range 250 - 5000 MeV. These limits are among the best currently available, and they will be improved soon by the addition of data from Run 2 of the LHC. LHCb presented a model-independent constraint on the rate of like-sign leptonic decays, and then derived a constraint on the mixing angle V{\mu}4 based on a theoretical model for the B decay width to N and the N lifetime. The model used is unfortunately unsound. We revise the conclusions of the paper based on a decay model similar to the one used for the tau lepton and provide formulae useful for future analyses.
Aneesh Manohar🇺🇸 · Paolo Nason🇮🇹 · Gavin P. Salam🇨🇭 · Giulia Zanderighi🇨🇭
It has become apparent in recent years that it is important, notably for a range of physics studies at the Large Hadron Collider, to have accurate knowledge on the distribution of photons in the proton. We show how the photon parton distribution function (PDF) can be determined in a model-independent manner, using electron-proton () scattering data, in effect viewing the process as an electron scattering off the photon field of the proton. To this end, we consider an imaginary, beyond Standard Model process with a flavour changing photon-lepton vertex. We write its cross section in two ways, one in terms of proton structure functions, the other in terms of a photon distribution. Requiring their equivalence yields the photon distribution as an integral over proton structure functions. As a result of the good precision of data, we constrain the photon PDF at the level of 1-2% over a wide range of momentum fractions.
Alejandro de la Puente🇨🇦 · Daniel Stolarski🇨🇦
Gauge invariance dictates that a resonance produced from initial state gluons must be produced through a non-renormalizable operator or a loop process. Should such a resonance be discovered, uncovering the dynamics that give rise to its couplings to gluons will be crucial to understanding the nature of the new state. Here we study how the production of this resonance at high transverse momentum in association with one (or more) jets can be used to directly measure the scale of the operator or the mass of the particles in the loop. We use a 750 GeV diphoton resonance as an example application, and we study how the non-renormalizable operator case can be described by a slowly converging effective field theory (EFT) expansion with operators of dimension five and seven. We show that with O(100) events, one can put strong constraints on the scale of the EFT, particularly in theories with strong coupling. We also compare the EFT analysis to that of a UV completion with vector-like quarks, and outline how the mass of said quarks could be measured.
Vedran Brdar🇩🇪 · Joachim Kopp🇩🇪 · Jia Liu (Johannes Gutenberg University Mainz)🇩🇪
Many theories of dark matter (DM) predict that DM particles can be captured by stars via scattering on ordinary matter. They subsequently condense into a DM core close to the center of the star and eventually annihilate. In this work, we trace DM capture and annihilation rates throughout the life of a massive star and show that this evolution culminates in an intense annihilation burst coincident with the death of the star in a core collapse supernova. The reason is that, along with the stellar interior, also its DM core heats up and contracts, so that the DM density increases rapidly during the final stages of stellar evolution. We argue that, counterintuitively, the annihilation burst is more intense if DM annihilation is a -wave process than for -wave annihilation because in the former case, more DM particles survive until the supernova. If among the DM annihilation products are particles like dark photons that can escape the exploding star and decay to Standard Model particles later, the annihilation burst results in a flash of gamma rays accompanying the supernova. For a galactic supernova, this "dark gamma ray burst" may be observable in CTA.
Eung Jin Chun🇰🇷 · Sunghoon Jung🇺🇸 · Jong-Chul Park🇰🇷
We present a study of the Very Degenerate Higgsino Dark Matter (DM), whose mass splitting between the lightest neutral and charged components is (1) MeV, much smaller than radiative splitting of 355 MeV. The scenario is realized in the minimal supersymmetric standard model by small gaugino mixing. In contrast to the pure Higgsino DM with the radiative splitting only, various observable signatures with distinct features are induced. First of all, the very small mass splitting makes (a) sizable Sommerfeld enhancement and Ramsauer-Townsend (RT) suppression relevant to ~1 TeV Higgsino DM, and (b) Sommerfeld-Ramsauer-Townsend effect saturate at lower velocities . As a result, annihilation signals can be large enough to be observed from the galactic center and/or dwarf galaxies, while relative signal sizes can vary depending on the location of Sommerfeld peaks and RT dips. In addition, at collider experiments, stable chargino signature can be searched for to probe the model in the future. DM direct detection signal, however, depends on the Wino mass; even no detectable signal can be induced if the Wino is heavier than about 10 TeV.
Takeshi Kobayashi🇮🇹 · Fuminobu Takahashi🇯🇵
A QCD axion with a time-dependent decay constant has been known to be able to accommodate high-scale inflation without producing topological defects or too large isocurvature perturbations on CMB scales. We point out that a dynamical decay constant also has the effect of enhancing the small-scale axion isocurvature perturbations. The enhanced axion perturbations can even exceed the periodicity of the axion potential, and thus lead to the formation of axionic domain walls. Unlike the well-studied axionic walls, the walls produced from the enhanced perturbations are not bounded by cosmic strings, and thus would overclose the universe independently of the number of degenerate vacua along the axion potential.
Christoph Englert🇬🇧 · Karl Nordstrom🇬🇧 · Liam Moore🇬🇧 · Michael Russell🇬🇧
We investigate the prospects to systematically improve generic effective field theory-based searches for new physics in the top sector during LHC run 2 as well as the high luminosity phase. In particular, we assess the benefits of high momentum transfer final states on top EFT-fit as a function of systematic uncertainties in comparison with sensitivity expected from fully-resolved analyses focusing on production. We find that constraints are typically driven by fully-resolved selections, while boosted top quarks can serve to break degeneracies in the global fit. This demystifies and clarifies the importance of high momentum transfer final states for global fits to new interactions in the top sector from direct measurements.
We study the influence of the magnetic field on the photon emission from the quark-gluon plasma created in collisions. We find that even for very optimistic assumption on the magnitude of the magnetic field for noncentral collisions the effect of magnetic field is very small.
Felix Kahlhoefer🇩🇪 · Sebastian Wild🇩🇪
The interpretation of dark matter direct detection experiments is complicated by the fact that neither the astrophysical distribution of dark matter nor the properties of its particle physics interactions with nuclei are known in detail. To address both of these issues in a very general way we develop a new framework that combines the full formalism of non-relativistic effective interactions with state-of-the-art halo-independent methods. This approach makes it possible to analyse direct detection experiments for arbitrary dark matter interactions and quantify the goodness-of-fit independent of astrophysical uncertainties. We employ this method in order to demonstrate that the degeneracy between astrophysical uncertainties and particle physics unknowns is not complete. Certain models can be distinguished in a halo-independent way using a single ton-scale experiment based on liquid xenon, while other models are indistinguishable with a single experiment but can be separated using combined information from several target elements.
Christian Bierlich🇸🇪 · Gösta Gustafson🇸🇪 · Leif Lönnblad🇸🇪
We review the state-of-the-art of Glauber-inspired models for estimating the distribution of the number of participating nucleons in pA and AA collisions. We argue that there is room for improvement in these models when it comes to the treatment of diffractive excitation processes, and present a new simple Glauber-like model where these processes are better taken into account. We also suggest a new way of using the number of participating, or wounded, nucleons to extrapolate event characteristics from pp collisions, and hence get an estimate of basic hadronic final-state properties in pA collisions, which may be used to extract possible nuclear effects. The new method is inspired by the Fritiof model, but based on the full, semi-hard multiparton interaction model of Pythia 8.
A. Ozansoy🇹🇷 · V. Arı🇹🇷 · V. Çetinkaya🇹🇷
We study the potential of the next collider, namely LHeC, with two options TeV TeV, to search for excited spin-1/2 and spin-3/2 neutrinos. We calculate the single production cross section of excited spin-1/2 and spin-3/2 neutrinos according to their effective currents describing their interactions between gauge bosons and SM leptons. We choose the decay mode of excited neutrinos and decay mode of -boson for the analysis. We put some kinematical cuts for the final state detectable particles and plot the invariant mass distributions for signal and the corresponding backgrounds. In order to obtain accessible limits for excited neutrino couplings, we show the and contour plots for excited spin-1/2 and excited spin-3/2 neutrinos, respectively.
Rafal Maciula🇵🇱 · Antoni Szczurek🇵🇱
We discuss how to search for a possibe signal of the recently observed 750 GeV enhancement in the diphoton channel in the four-jet production. In the present studies we assume that the produced state is pseudoscalar. This fact, when combined with specificity of the corresponding amplitude, allows to improve the signal-to-background (S/B) ratio. We discuss in detail how to impose cuts on jets in rapidity and transverse momenta in order to find optimal S/B ratio and not to loose too much statistics. Our study suggest a measurement of two soft (low cut on ) large-rapidity jets and two hard (high cut on ) mid-rapidity jets. Azimuthal correlation between the soft external jets may be useful to further improve the situation. Several differential distributions in rapidities and transverse momenta of jets as well as dijet invariant mass are shown. The integrated cross sections corresponding to different cuts are collected in a table and number of events are presented.
In a general two Higgs doublet model (2HDM), the anomaly of muon anomalous magnetic moment (muon g-2) can be explained by flavor violating Yukawa couplings, motivated by the recent CMS excess in Higgs boson decay . We study Michel parameters for decays in the 2HDM with the lepton flavor violation, and show that they can be sensitive to the flavor structure as well as the Lorentz and chiral structures of the model. We find that the correction to the Michel parameter in is correlated to the contribution to the muon g-2, and it can be as large as in the parameter region where the flavor violating Yukawa couplings explain the muon g-2 anomaly. Therefore the precision measurement of the Michel parameter at the level of would significantly probe the interesting parameter space for the solution to the muon g-2 anomaly.
The early stages of heavy ion collisions are dominated by high density systems of gluons that carry each a small fraction of the momenta of the colliding nucleons. A distinguishing feature of such systems is the phenomenon of "saturation" which tames the expected growth of the gluon density as the energy of the collision increases. The onset of saturation occurs at a particular transverse momentum scale, the "saturation momentum", that emerges dynamically and that marks the onset of non-linear gluon interactions. At high energy, and for large nuclei, the saturation momentum is large compared to the typical hadronic scale, making high density gluons amenable to a description with weak coupling techniques. This paper reviews some of the challenges faced in the study of such dense systems of small gluons, and of the progress made in addressing them. The focus is on conceptual issues, and the presentation is both pedagogical, and critical. Examples where high gluon density could play a visible role in heavy ion collisions are briefly discussed at the end, for illustration purpose.
Suchismita Sahoo🇮🇳 · Rukmani Mohanta🇮🇳
We study the scalar leptoquark effects on the rare semileptonic decays of baryon, governed by the quark level transition . We estimate the branching ratios, forward-backward asymmetries, lepton polarization parameters and the lepton flavour non-universality effects in these decay channels. We find significant deviations from the corresponding standard model predictions in some of the observables due to leptoquark effects. We also investigate the lepton flavour violating decays , the branching ratios of which are found to be .
We present the {\tt Mathematica} package {\tt TopoID} which aims at the automation of several steps in multiloop calculations. The algorithm which lies at the very core of the package is described and illustrated with an example. The main features of {\tt TopoID} are stated and some of them are briefly demonstrated for NLO or NNLO Higgs boson production.
Shi-Ping He🇨🇳 · Shou-hua Zhu🇨🇳
Though the 125 GeV Higgs boson is consistent with the standard model (SM) prediction until now, the triple Higgs coupling can deviate from the SM value in the physics beyond the SM (BSM). In this paper, the radiative correction to the triple Higgs coupling is investigated in the minimal extension of the SM by adding a real gauge singlet scalar. In this model there are two scalars and , and both of them are mixing states of the doublet and singlet. Provided that the mixing angle is set to be zero, namely the SM limit, is the pure left-over of the doublet and its behaviour is the same as that of the SM at the tree level. However the loop corrections can alter -related couplings. In this SM limit case, the effect of the singlet may show up in the -related couplings, especially the triple coupling. Our numerical results show that the deviation is sizable. For (see the text for definition), the deviation around threshold can be more than if mass of the new scalar is light. For , the deviation can reach above in the vicinity of threshold. For , can be light. The deviation is negative in this case and can be even in the threshold enhanced region. The radiative correction for the coupling is from the counter-term, which is universal in this model and always with negative sign. is independent of the sign of and its typical size is . When combining and precision measurements together, parameter space of this model can be probed well including the sign and size of .
Mariana Frank🇨🇦 · Nima Pourtolami🇨🇦 · Manuel Toharia🇨🇦
We consider scenarios of warped extra-dimensions with all matter fields in the bulk and in which both the hierarchy and the flavor puzzles of the Standard Model are addressed. The simplest extra dimensional extension of the Standard Model Higgs sector, i.e a 5D bulk Higgs doublet, can be a natural and simple explanation to the 750 GeV excess of diphotons hinted at the LHC, with the resonance responsible for the signal being the lightest CP odd excitation coming from the Higgs sector. No new matter content is invoked, the only new ingredient being the presence of (positive) brane localized kinetic terms associated to the 5D bulk Higgs, which allow to reduce the mass of the lightest CP odd Higgs excitation to 750 GeV. Production and decay of this resonance can naturally fit the observed signal when the mass scale of the rest of extradimensional resonances is of order 1 TeV.
Tomáš Ježo🇮🇹 · Jonas M. Lindert🇨🇭 · Paolo Nason🇮🇹 · Carlo Oleari🇮🇹 · Stefano Pozzorini🇨🇭
We present a Monte Carlo generator that implements significant theoretical improvements in the simulation of top-quark pair production and decay at the LHC. Spin correlations and off-shell effects in top-decay chains are described in terms of exact matrix elements for at NLO QCD, where the leptons and belong to different families, and quarks are massive. Thus, the contributions from and single-top production as well as their quantum interference are fully included. Matrix elements are matched to the Pythia8 parton shower using a recently proposed method that allows for a consistent treatment of resonances in the POWHEG framework. These theoretical improvements are especially important for the interpretation of precision measurements of the top-quark mass, for single-top analyses in the channel, and for and backgrounds in the presence of jet vetoes or cuts that enhance off-shell effects. The new generator is based on a process-independent interface of the OpenLoops amplitude generator with the POWHEGBOX framework.
Martin Bauer🇩🇪 · Anja Butter🇩🇪 · Juan Gonzalez-Fraile🇩🇪 · Tilman Plehn🇩🇪 · Michael Rauch🇩🇪
Motivated by a di-photon anomaly observed by ATLAS and CMS we develop an SFitter analysis for a combined electroweak-Higgs sector, and a scalar portal at the LHC. The theoretical description is based on the linear effective Lagrangian for the Higgs and gauge fields, combined with an additional singlet scalar. The key feature is the extraction of reliable information on the portal structure of the combined scalar potential. For the specific di-photon anomaly we find that the new state might well form such a Higgs portal. To obtain more conclusive results we define and test the connection of the Wilson coefficients in the Higgs and heavy scalar sectors, as suggested by a portal setup.
Audrey K. Kvam🇺🇸 · David C. Latimer🇺🇸
Composite dark matter (DM) comprised of electrically charged constituents can interact with the electromagnetic field via the particle's dipole moment. This interaction results in a dispersive optical index of refraction for the DM medium. We compute this refractive index for atomic dark matter and more strongly bound systems, modeled via a harmonic oscillator potential. The dispersive nature of the index will result in a time lag between high and low energy photons simultaneously emitted from a distant astrophysical observable. This time lag, due to matter dispersion, could confound potential claims of Lorentz invariance violation (LIV) which can also result in such time lags. We compare the relative size of the two effects and determine that the dispersion due to DM is dwarfed by potential LIV effects for energies below the Planck scale.
James M. Overduin🇺🇸 · Hamna Ali🇺🇸
We use experimental limits on Lorentz violation to obtain new constraints on Kaluza-Klein-type theories in which the extra dimensions may be large but do not necessarily have units of length. The associated variation in fundamental quantities such as rest mass must occur slowly, on cosmological scales.
Jorge Segovia🇩🇪 · Craig D. Roberts🇺🇸
In Poincaré-covariant continuum treatments of the three valence-quark bound-state problem, the force behind dynamical chiral symmetry breaking also generates nonpointlike, interacting diquark correlations in the nucleon and its resonances. We detail the impact of these correlations on the electromagnetically-induced nucleon- and nucleon-Roper transitions, providing a flavour-separation of the latter and associated predictions that can be tested at modern facilities.
Yu.N. Uzikov🇷🇺 · J. Haidenbauer🇩🇪
Scattering of protons with transversal polarization on deuterons with tensor polarization provides a null-test signal for time-reversal (T) invariance violating but parity (P) conserving effects. We calculate the corresponding null-test observable at beam energies 100-1000 MeV within the spin-dependent Glauber theory considering T-violating P-conserving nucleon-nucleon interactions. The S-wave component of the deuteron wave function as well as the D-wave are taken into account and the latter is found to play an important role for the magnitude and the energy dependence of the observable in question. Specifically, with inclusion of the D wave the maximum of the obtained signal is shifted to higher beam energies, i.e. to 700-800 MeV.
Adi Armoni🇬🇧 · Edwin Ireson🇬🇧
We propose a holographic computation of the meson scattering in a curved string background, dual to a QCD-like theory. We recover the Veneziano amplitude and compute a perturbative correction due to the background curvature. The result implies a small deviation from a linear trajectory, which is a requirement of the UV regime of QCD.
Zhan-Wei Liu🇦🇺 · Waseem Kamleh🇦🇺 · Derek B. Leinweber🇦🇺 · Finn M. Stokes🇦🇺 · Anthony W. Thomas🇦🇺 · Jia-Jun Wu🇦🇺
We examine the phase shifts and inelasticities associated with the Roper resonance and connect these infinite-volume observables to the finite-volume spectrum of lattice QCD using Hamiltonian effective field theory. We explore three hypotheses for the structure of the Roper resonance. All three hypotheses are able to describe the scattering data well. In the third hypothesis the Roper resonance couples the low-lying bare basis-state component associated with the ground state nucleon with the virtual meson-baryon contributions. Here the non-trivial superpositions of the meson-baryon scattering states are complemented by bare basis-state components explaining their observation in contemporary lattice QCD calculations. The merit of this scenario lies in its ability to not only describe the observed nucleon energy levels in large-volume lattice QCD simulations but also explain why other low-lying states have been missed in today's lattice QCD results for the nucleon spectrum.
* 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.