High Energy Physics - Phenomenology (hep-ph)

Abstract: In this paper, we present a new proposal on how to measure quark/gluon jet properties at the LHC. The measurement strategy takes advantage of the fact that the LHC has collected data at different energies. Measurements at two or more energies can be combined to yield distributions of any jet property separated into quark and gluon jet samples on a statistical basis, without the need for an independent event-by-event tag. We illustrate our method with a variety of different angularity observables, and discuss how to narrow down the search for the most useful observables.

Abstract: We compute the planar three-loop Quantum Chromodynamics (QCD) corrections to the helicity amplitudes involving a vector boson $V=Z,W^\pm,\gamma^*$, two quarks and a gluon. These amplitudes are relevant to vector-boson-plus-jet production at hadron colliders and other precision QCD observables. The planar corrections encompass the leading colour factors $N^3$, $N^2 N_f$, $N N_f^2$ and $N_f^3$. We provide the finite remainders of the independent helicity amplitudes in terms of multiple polylogrithms, continued to all kinematic regions and in a form which is compact and lends itself to efficient numerical evaluation.

Abstract: An updated global fit on the parameter-space of the Aligned Two-Higgs-Doublet model has been performed with the help of the open-source package \texttt{HEPfit}, assuming the Standard-Model Higgs to be the lightest scalar. No new sources of CP violation, other than the phase in the CKM matrix of the Standard Model, have been considered. A similar global fit was previously performed in Ref. \cite{Eberhardt:2020dat} with a slightly different set of parameters. Our updated fit incorporates improved analyses of the theoretical constraints required for positivity of the scalar potential and perturbative unitarity, additional flavour observables and updated data on direct searches of heavy scalars at the LHC, Higgs signal strengths and electroweak precision observables. Although not included in the main fit, the implications of the CDF measurement of the $W^\pm$ mass are also discussed.

Abstract: The ATLAS and TOTEM collaborations have measured the differential elastic cross section at centre-of mass energy $\sqrt{s}$=13 TeV and at small four-moment squared $|t|$. The data at very small $|t|$ i.e. $|t|<0.01GeV^{2}$ have been analysed in terms of so called AKM (Auberson, Kinoshita and Martin) oscillations. An indication of a possible oscillation of this type had previously been reported at $\sqrt{s}$=541 GeV using data from the UA4/2 experiment. There are no such indications in the data at 13 TeV examined here.

Abstract: The majority of Monte-Carlo (MC) simulation campaigns for future $e^+e^-$ colliders has so far been based on the leading-order (LO) matrix elements provided by Whizard 1.95, followed by parton shower and hadronization in Pythia6, using the tune of the OPAL experiment at LEP. In this contribution, we test and develop the interface between Whizard3 and Pythia8. As a first step, we simulate the $e^+e^-\to q\bar{q}$ process with LO matrix elements, and compare three tunes in Pythia8: the standard Pythia8 tune, the OPAL tune and the ALEPH tune. At stable-hadron level, predictions of charged and neutral hadron multiplicities of these tunes are compared to LEP data, since they are strongly relevant to the performance of particle flow algorithms. The events are used to perform a full detector simulation and reconstruction of the International Large Detector concept (ILD) as an example for a particle-flow-optimised detector. At reconstruction level, a comparison of the jet energy resolution in these tunes is presented. We found good agreement with previous results that were simulated by Whizard1+Pythia6. In addition, the preliminary next-to-leading order (NLO) results are also presented. This modern MC simulation chain, with matched NLO matrix elements in the future, should be introduced to ILC or other future $e^+e^-$ colliders.

Abstract: We conducted an investigation into Affleck-Dine baryogenesis within the context of D-term inflation, specifically focusing on its relationship with a recent reheating formalism. It was found that by considering a specific reheating temperature, the observed baryon asymmetry can be accounted through Affleck-Dine baryogenesis. Additionally, the majority of gravitinos are inferred to be generated from the decay of the next-to-lightest supersymmetric particle, with Q-balls potentially serving as a source of gravitinos via NSP decay. The temperature at which decay occurs depends on the charge of the Q-balls, which is determined by the fragmentation of the Affleck-Dine condensate. Remarkably, the gravitino mass required for dark matter aligns naturally with the theoretical gravitino mass.

Abstract: An overview of the phenomenology and experimental results on open heavy-flavour and quarkonium production in heavy-ion collisions at the RHIC and at the LHC energies is presented, with special emphasis on observables that carry information from the different collision stages. Perspective for future measurements and phenomenological modeling, that will shed light on the current open question in heavy-ion collisions, will be also discussed.

Abstract: Sterile neutrinos are well-motivated and simple dark matter (DM) candidates. However, sterile neutrino DM produced through oscillations by the Dodelson-Widrow mechanism is excluded by current $X$-ray observations and bounds from structure formation. One minimal extension, that preserves the attractive features of this scenario, is self-interactions among sterile neutrinos. In this work, we analyze how sterile neutrino self-interactions mediated by a scalar affect the production of keV sterile neutrinos for a wide range of mediator masses. We find four distinct regimes of production characterized by different phenomena, including partial thermalization for low and intermediate masses and resonant production for heavier mediators. We show that significant new regions of parameter space become available which provide a target for future observations.

Abstract: In this addendum we present the stand-alone C++ program MSSMEFTHiggs3L, which implements the 3-loop FlexibleEFTHiggs approach to calculate the lightest CP-even Higgs boson pole mass in the real MSSM at N$^3$LL and N$^3$LO with $x_q$ resummation, presented in JHEP 07 (2020) 197 (arXiv:2003.04639).

Abstract: Exploiting a mapping between transport theory and fluid dynamics, we show how a fluid-dynamic description of the diffusion of charm quarks in the QCD plasma is feasible. We show results for spectra of charmed hadrons obtained with a fluid-dynamic description of the quark-gluon plasma (QGP) coupled with the conservation of a heavy-quark - antiquark current. We compare our calculations with the most recent experimental data in order to provide further constraints on the transport coefficients of the QGP.

Abstract: The detection of ultra high energy gamma-rays provides an opportunity to explore the existence of ALPs at the multi-hundred TeV and PeV energy scales. We discover that we can employ analytic methods to investigate the propagation of photon-ALP beams in scenarios where the energy of photons $\omega \geq 100$ TeV. Our analytical calculations uncover the presence of two distinct modes of photon propagation resulting from the interplay between ALP-photon mixing and attenuation effects. Next, we analyze observable quantities such as the degree of polarization and survival probability in these two modes. We determine the conditions under which a significant polarization effect can be observed and identify the corresponding survival probability. Finally, we extend our analytic methods to cover the energy range of $10^{-3}$ to $10^4$ GeV and analyze the influence of ALPs on the experimental signals.

Abstract: A light Higgs boson, with mass of the order of 100 GeV, is still not excluded by the existing experimental data, provided its coupling to gauge bosons is strongly suppressed compared to a SM-like Higgs boson at the same mass. Also other couplings of such a scalar could be very different from the SM predictions leading to non-standard decay paterns. Considered in the presented study is the feasibility of direct observation of the 96 GeV Higgs boson of N2HDM model with dominant decays to tau lepton pairs.

Abstract: The increasingly high accuracy of top-quark studies at the LHC calls for a theoretical description of $t\bar t$ production and decay in terms of exact matrix elements for the full $2\to 6$ process that includes the off-shell production and the chain decays of $t\bar t$ and $tW$ intermediate states, together with their quantum interference. Corresponding NLO QCD calculations matched to parton showers are available for the case of dileptonic channels and are implemented in the bb4l Monte Carlo generator, which is based on the resonance-aware POWHEG method. In this paper, we present the first NLOPS predictions of this kind for the case of semileptonic channels. In this context, the interplay of off-shell $t\bar t+tW$ production with various other QCD and electroweak subprocesses that yield the same semileptonic final state is discussed in detail. On the technical side, we improve the resonance-aware POWHEG procedure by means of new resonance histories based on matrix elements, which enable a realistic separation of $t\bar t$ and $tW$ contributions. Moreover, we introduce a general approach which makes it possible to avoid certain spurious terms that arise from the perturbative expansion of decay widths in any off-shell higher-order calculation, and which are large enough to jeopardise physical finite-width effects. These methods are implemented in a new version of the bb4l Monte Carlo generator, which is applicable to all dileptonic and semileptonic channels, and can be extended to fully hadronic channels. The presented results include a NLOPS comparison of off-shell against on-shell $t\bar t+tW$ production and decay, where we highlight various non-trivial aspects related to NLO and parton-shower radiation in leptonic and hadronic top decays.

Abstract: Heavy and light quarks produced in high-$p_T$ partonic collisions radiate differently. Heavy quarks regenerate their color field, stripped-off in the hard reaction, much faster than the light ones and radiate a significantly smaller fraction of the initial quark energy. This peculiar feature of heavy-quark jets leads to a specific shape of the fragmentation functions observed in $e^+e^-$ annihilation. Differently from light flavors, the heavy quark fragmentation function strongly peaks at large fractional momentum $z$, i.e. the produced heavy-light mesons, $B$ or $D$, carry the main fraction of the jet momentum. This is a clear evidence of the dead-cone effect, and of a short production time of a heavy-light mesons. Contrary to propagation of a small $q\bar q$ dipole, which survives in the medium due to color transparency, a heavy-light $Q\bar q$ dipole promptly expands to a large size. Such a big dipole has no chance to remain intact in a dense medium produced in relativistic heavy ion collisions. On the other hand, a breakup of such a dipole does not affect much the production rate of $Q\bar q$ mesons, differently from the case of light $q\bar q$ meson production.

Abstract: In this work we explore the low energy effects induced from the integration of the heavy Higgs boson modes, $H$, $A$ and $H^\pm$, within the Two Higgs Doublet Model (2HDM) by assuming that the lightest Higgs boson $h$ is the one observed experimentally at $m_h \sim 125$ GeV. We work within the context of Effective Field Theories, focusing on the Higgs Effective Field Theory (HEFT), although some comparisons with the Standard Model Effective Field Theory (SMEFT) case are also discussed through this work. Our main focus is placed in the computation of the non-decoupling effects from the heavy Higgs bosons and the capture of such effects by means of the HEFT coefficients which are expressed in terms of the input parameters of the 2HDM. Our approach to solve this issue is by matching the amplitudes of the 2HDM and the HEFT for physical processes involving the light Higgs boson $h$ in the external legs, instead of the most frequently used matching procedure at the Lagrangian level. More concretely, we perform the matching at the amplitudes level for the following physical processes, including scattering and decays: $h\to WW^*\to Wf\bar{f'}$, $h\to ZZ^*\to Zf\bar{f}$, $WW \to hh$, $ZZ \to hh$, $hh \to hh$, $h \to \gamma \gamma$ and $h \to \gamma Z$. One important point of this work is that the matching is required to happen at low energies compared to the heavy Higgs boson masses, and these are heavier than the other particle masses. The proper expansion for this heavy mass limit is also defined here, which provides the results for the non-decoupling effects presented in this work. We finally discuss the implications of the resulting effective coefficients, and remark on the interesting correlations detected among them.