Mon·Aug 23, 2021Monday·August 23, 2021

1. 01*

   On linear power corrections in certain collider observables

   Fabrizio Caola🇬🇧 · Silvia Ferrario Ravasio🇬🇧 · Giovanni Limatola🇮🇹 · Kirill Melnikov🇩🇪 · Paolo Nason🇮🇹

   We study linear power corrections $\mathcal{O}({\Lambda }_{\mathrm{QCD}}/Q)$ to certain collider observables. We present arguments that prove that such corrections cannot appear in observables that are inclusive with respect to QCD radiation, such as total cross sections as well as rapidity and transverse momentum distributions of color-neutral particles. Although our calculations are carried out in a simplified framework, our arguments and conclusions are applicable, with some reservations, to processes both at lepton and hadron colliders. We also show how an improved understanding of the origin of linear power corrections allows us to simplify their calculation. As an application, we compute the leading non-perturbative corrections to the $C$-parameter and the thrust in $e^{+}{e}^{-}$ annihilation in a generic three-jet configuration.

   hep-phJHEP(2022)·63 citations
2. 02*

   Direct discovery of new light states at the FCCee

   Simon Knapen🇨🇭 · Andrea Thamm🇦🇺

   Light new states are ubiquitous in many models which address fundamental outstanding questions within the Standard Model (SM). The FCCee provides an excellent opportunity to probe these new particles with masses between $1$ and $100$GeV and their electroweak couplings. Here we discuss the theory motivations for axion-like particles and heavy neutral leptons and detail the potential of direct discovery at the FCCee. We highlight that our current understanding requires light new states to be embedded within a bigger theory framework and thus the complementarity of the precision frontier at the FCCee and the high energy frontier of the FCChh program.

   hep-phEur.Phys.J.Plus(2021)·5 citations
3. 03*

   CP-violating Axions

   Luca Di Luzio🇮🇹

   While the axion was originally introduced to wash out CP violation from strong interactions, new sources of CP violation beyond QCD might manifest themselves via a tiny scalar axion-nucleon component. The latter can be experimentally probed in axion-mediated force experiments, as suggested long ago by J.E. Moody and F. Wilczek. In the present note, I review the physical origin of CP-violating axion couplings and point out the special role of the QCD axion as a low-energy portal to high-energy sources of CP violation.

   hep-phPoS(2022)·10 citations
4. 04*

   PDF4LHC21: Update on the benchmarking of the CT, MSHT and NNPDF global PDF fits

   Thomas Cridge (on behalf of the PDF4LHC21 combination group)🇬🇧

   There have been recent updates to the three global PDF fits (CT, MSHT and NNPDF), all adding large amounts of data from the LHC, and this has resulted in significant changes to the global PDFs. Given the impact that the new PDFs will have on physics comparisons at the LHC, it is crucial to perform a benchmarking among the PDFs, similar in spirit to that which was carried out for PDF4LHC15, widely used for LHC physics. In this article we detail a benchmarking comparison of three global PDF sets - CT18, MSHT20 and NNPDF3.1 - and their similarities and differences that have been observed. The end result of this study will be a new PDF4LHC21 ensemble of combined PDFs suitable for a wide range of LHC applications.

   hep-phSciPost Phys.Proc.(2022)·24 citations
5. 05*

   $D^{\ast }$ meson production in jet from combination of charm quark with light one

   Chuanhui Jiang🇨🇳 · Honglei Li🇨🇳 · Shi-Yuan Li🇨🇳 · Shufen Liu🇨🇳 · Xinyue Yin🇨🇳

   In the framework of the perturbative Quantum Chromodynamics factorization, the cross section of the heavy meson production via the combination of a heavy quark with a light one can be factorized to be the convolution of the combination matrix element, the light quark distribution function, and the hard partonic sub-cross section of the heavy quark production. The partonic distribution and the combination matrix element are functions of a scaling variable, respectively, which is the momentum fraction of the corresponding quark with respect to the heavy meson. We studied the $D^{\ast \pm }$ production in jet via combination in pp collision at the LHC. Our calculation can be summed with the fragmentation contribution, and the total result is comparable with the experimental data. The combination matrix elements can be further studied in various hadron production processes.

   hep-ph1 citation
6. 06*

   On non-factorisable contributions to $t$-channel single-top production

   Christian Brønnum-Hansen🇩🇪 · Kirill Melnikov🇩🇪 · Jérémie Quarroz🇩🇪 · Chen-Yu Wang🇩🇪

   We compute the non-factorisable contribution to the two-loop helicity amplitude for $t$-channel single-top production, the last missing piece of the two-loop virtual corrections to this process. Our calculation employs analytic reduction to master integrals and the auxiliary mass flow method for their fast numerical evaluation. We study the impact of these corrections on basic observables that are measured experimentally in the single-top production process.

   hep-phJHEP(2021)·16 citations
7. 07*

   Inelastic Axial and Vector Structure Functions for Lepton-Nucleon Scattering 2021 Update

   Arie Bodek🇺🇸 · Un Ki Yang🇰🇷 · Yang Xu🇺🇸

   We report on an update (2021) of a phenomenological model for inelastic neutrino- and electron-nucleon scattering cross sections using effective leading order parton distribution functions with a new scaling variable ${\xi }_w$. Non-perturbative effects are well described using the ${\xi }_w$ scaling variable in combination with multiplicative $K$ factors at low $Q^2$. The model describes all inelastic charged-leptron-nucleon scattering data (HERA/NMC/BCDMS/SLAC/JLab) ranging from very high $Q^2$ to very low $Q^2$ and down to the $Q^2=0$ photo-production region. The model has been developed to be used in analysis of neutrino oscillation experiments in the few GeV region. The 2021 update accounts for the difference between axial and vector structure function which brings it into much better agreement with neutrino-nucleon total cross section measurements. The model has been developed primarily for hadronic final state masses $W$ above 1.8 GeV. However with additional parameters the model also describe the $average$ neutrino cross sections in the resonance region down to $W$=1.4 GeV.

   hep-phhep-ex22 citations
8. 08*

   Gravitational Wave and CMB Probes of Axion Kination

   Raymond T. Co🇺🇸 · David Dunsky🇺🇸 · Nicolas Fernandez🇺🇸 · Akshay Ghalsasi🇺🇸 · Lawrence J. Hall🇺🇸 · Keisuke Harigaya🇺🇸 · Jessie Shelton🇺🇸

   Rotations of an axion field in field space provide a natural origin for an era of kination domination, where the energy density is dominated by the kinetic term of the axion field, preceded by an early era of matter domination. Remarkably, no entropy is produced at the end of matter domination and hence these eras of matter and kination domination may occur even after Big Bang Nucleosynthesis. We derive constraints on these eras from both the cosmic microwave background and Big Bang Nucleosynthesis. We investigate how this cosmological scenario affects the spectrum of possible primordial gravitational waves and find that the spectrum features a triangular peak. We discuss how future observations of gravitational waves can probe the viable parameter space, including regions that produce axion dark matter by the kinetic misalignment mechanism or the baryon asymmetry by axiogenesis. For QCD axion dark matter produced by the kinetic misalignment mechanism, a modification to the inflationary gravitational wave spectrum occurs above 0.01 Hz and, for high values of the energy scale of inflation, the prospects for discovery are good. We briefly comment on implications for structure formation of the universe.

   hep-phastro-ph.COJHEP(2022)·127 citations
9. 09*

   Gauge hierarchy from electroweak vacuum metastability

   Justin Khoury🇺🇸 · Thomas Steingasser🇩🇪

   We consider the possibility that the gauge hierarchy is a byproduct of the metastability of the electroweak vacuum, i.e., that whatever mechanism is responsible for the latter also sets the running Higgs mass to a value smaller than its natural value by many orders of magnitude. This perspective is motivated by the early-time framework for eternal inflation put forth recently, which favors vacua that are relatively short-lived, but applies more generally to any theoretical approach predicting that our vacuum should be metastable. We find that the metastability of the electroweak vacuum, together with the requirement that such a non-trivial vacuum exists, requires the Higgs mass to be smaller than the instability scale by around one order of magnitude. While this bound is quite weak in the Standard Model (SM), as the instability scale is $\sim 10^{11}$ GeV, simple and well-motivated extensions of the SM - concretely, the $\nu$MSM with an approximate $B-\tilde{L}$ symmetry and the minimal SU(4)/Sp(4) composite Higgs model - can significantly tighten the bound by lowering the instability scale. We find that the bound can be brought down to $\simeq 10$ TeV where our perturbative treatment of the decay rate becomes unreliable. Our results imply that, assuming the SM symmetry breaking pattern, small running Higgs masses are a universal property of theories giving rise to metastability, suggesting a common origin of the two underlying fine-tunings and providing a strong constraint on any attempt to explain metastability.

   hep-phastro-ph.COhep-thPRD(2022)·38 citations
10. 10*

    Paths to proton stability in grand unification

    Lisa L. Everett🇺🇸 · Oleg Popov🇰🇷

    We explore scenarios within grand unification in which proton decay can be suppressed and possibly eliminated due to novel embeddings of the Standard Model matter fields into irreducible representations of the grand unified group and residual symmetries. The scenarios are based on an $SU(7)$ gauge group, in which the matter fields are embedded within an anomaly-free set of fields that can be realized as a natural subgroup of the fundamental spinor representation of an $SO(14)$ gauge symmetry. Depending on the embedding, proton decay can either be forbidden at tree level and generated via one-loop diagrams, or the proton can be made stable by forcing it to decay channels that must have an even number of leptons, independently of the bosonic content of the theory. We describe the theoretical and phenomenological implications of such scenarios, including their implications for dark matter and neutrino masses.

    hep-ph3 citations
11. 11*

    Investigating top tagging with Y${}_{\text{m}}$-Splitter and N-subjettiness

    Mrinal Dasgupta🇬🇧 · Jack Helliwell🇬🇧

    We study top-tagging from an analytical QCD perspective focusing on the role of two key steps therein : a step to find three-pronged substructure and a step that places constraints on radiation. For the former we use a recently introduced modification of Y-Splitter, known as Y${}_{\text{m}}$-Splitter, and for the latter we use the well-known N-subjettiness variable. We derive resummed results for this combination of variables for both signal jets and background jets, also including pre-grooming of the jet. Our results give new insight into the performance of top tagging tools in particular with regard to the role of the distinct steps involved.

    hep-phJHEP(2021)·5 citations
12. 12*

    Resonant Spontaneous Bremsstrahlung Effect In The Scattering Of Ultrarelativistic Electrons On Nuclei In A Strong Laser Field

    S. P. Roshchupkin🇷🇺 · A.V. Dubov🇷🇺 · V. V. Dubov🇷🇺 · S. S. Starodub🇺🇦

    The process of resonant spontaneous bremsstrahlung radiation during the scattering of ultrarelativistic electrons with energies of the order $\sim 100\text{GeV}$ by the nuclei in strong laser fields with intensities up to $I\sim {10}^{24}\text{Wc}{\text{m}}^{\text{-2}}$ is theoretically studied. Under resonant conditions, an intermediate electron in the wave field enters the mass shell. As a result, the initial second-order process by the fine structure constant is effectively reduced to two first-order processes: laser-stimulated Compton effect and laser-assisted Mott process. The resonant kinematics for two reaction channels (A and B) is studied in detail. It is shown that in the resonant case there is a characteristic parameter that determines a significant number of absorbed laser photons in the laser-stimulated Compton effect. This parameter is determined by the parameters of the laser installation, the energy of the initial electrons and is proportional to the intensity of the laser wave. An analytical resonant differential cross-section with simultaneous registration of the frequency and the outgoing angle of a spontaneous gamma-quantum is obtained. It is shown that the resonant differential cross-section has the largest value in the region of average laser fields ($I\sim {10}^{18}\text{Wc}{\text{m}}^{\text{-2}}$) and can be of the order of $\sim {10}^{18}$ in units $Z^2\alpha r_e^2$. With an increase in the intensity of the laser wave, the value of the resonant differential cross-section decreases and for the intensity $I\sim {10}^{24}\text{Wc}{\text{m}}^{\text{-2}}$ is of the order of $\sim {10}^4$ in units $Z^2\alpha r_e^2$. The obtained results reveal new features of spontaneous emission of ultrarelativistic electrons on nuclei in strong laser fields and can be tested at international laser installations.

    hep-phphysics.plasm-phNew J.Phys.(2022)·15 citations
13. 13*

    Lattice simulations of the QCD chiral transition at real baryon density

    Szabolcs Borsanyi🇩🇪 · Zoltan Fodor🇩🇪 · Matteo Giordano🇭🇺 · Sandor D. Katz🇭🇺 · Daniel Nogradi🇭🇺 · Attila Pasztor🇭🇺 · Chik Him Wong🇩🇪

    State-of-the-art lattice QCD studies of hot and dense strongly interacting matter currently rely on extrapolation from zero or imaginary chemical potentials. The ill-posedness of numerical analytic continuation puts severe limitations on the reliability of such methods. Here we use the more direct sign reweighting method to perform lattice QCD simulation of the QCD chiral transition at finite real baryon density on phenomenologically relevant lattices. This method does not require analytic continuation and avoids the overlap problem associated with generic reweighting schemes, so has only statistical but no uncontrolled systematic uncertainties for a fixed lattice setup. This opens up a new window to study hot and dense strongly interacting matter from first principles. We perform simulations up to a baryochemical potential-temperature ratio of ${\mu }_B/T=2.5$ covering most of the RHIC Beam Energy Scan range in the chemical potential. We also clarify the connection of the approach to the more traditional phase reweighting method.

    ↳ hep-lathep-phnucl-thPRD(2022)·49 citations
14. 14*

    Cosmic birefringence tomography and calibration-independence with reionization signals in the CMB

    Blake D. Sherwin🇬🇧 · Toshiya Namikawa🇯🇵

    The search for cosmic polarization rotation or birefringence in the CMB is well-motivated because it can provide powerful constraints on parity-violating new physics, such as axion-like particles. In this paper we point out that since the CMB polarization is produced at two very different redshifts - it is generated at both reionization and recombination - new parity-violating physics can generically rotate the polarization signals from these different sources by different amounts. We explore two implications of this. First, measurements of CMB birefringence are challenging because the effect is degenerate with a miscalibration of CMB polarization angles; however, by taking the difference of the reionization and recombination birefringence angles (measured from different CMB angular scales), we can obtain a cosmological signal that is immune to instrumental angle miscalibration. Second, we note that the combination with other methods for probing birefringence can give tomographic information, constraining the redshift origin of any physics producing birefringence. We forecast that the difference of the reionization and recombination birefringence angles can be competitively determined to within ~0.05 degrees for future CMB satellites such as LiteBIRD. Although much further work is needed, we argue that foreground mitigation for this measurement should be less challenging than for inflationary B-mode searches on similar scales due to larger signals and lower foregrounds.

    ↳ astro-ph.COhep-phMNRAS(2023)·53 citations

* 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.