The photoleptonic decay B^-→γℓ^-ν is the simplest low-energy process that probes the substructure of the B meson, making it an excellent candidate to determine the parameters of B-meson light-cone distribution amplitudes from experimental data. More recently, the decay B^-→γ^∗(→ℓ^' -ℓ^' +)ℓ^-ν has received attention as an alternative probe of these parameters. Both decays are described through a common set of hadronic form factors, which, if computed within the framework of QCD factorization, give rise to the sensitivity to the B-meson light-cone distribution amplitudes. Nevertheless, in this case the form factors still receive so-called soft contributions that can only be estimated but not rigorously computed. In this work, we provide results for the QCD factorization expressions for the form factors, including terms at next-to-leading power in the b quark mass and in the photon energy. We further use these results to estimate the soft contributions within a light-cone sum rule setup. Finally, using numerical results obtained from a benchmark model of the light-cone distribution amplitudes, we show that the soft contributions are under significantly better theoretical control at a mildly spacelike photon virtuality.

We consider a model of dark matter where the mediator corresponds to a superposition of a scalar and pseudoscalar, and the scenario where, after reheating, the number densities of the dark sector particles, i.e. the dark matter and the mediators, are negligible. If the coupling of the mediators to the Standard Model is feeble, but the coupling to the dark matter is large enough, the dark sector may reach equilibrium at a temperature distinct from that of the thermal bath. The relic density is then said to be obtained via decoupled freeze out (DFO). We focus on the s-wave annihilation scenario, which particularly benefits from the DFO mechanism by evading standard CMB limits while still yielding indirect detection signals. We calculate the relic density by solving a set of four coupled Boltzmann equations for the number densities of the dark sector particles and the energy transfer from the light to dark sector. We finally perform a thorough analysis of experimental bounds on this scenario, namely from indirect detection and the CMB, as well as from BBN, and find that, while there are considerable constraints on the parameter space where the correct relic density is obtained, a viable region remains to be explored.

The current Large Hadron Collider (LHC) data show no clear indication of new physics and only incremental improvements are anticipated at the energy frontier in the near future. However, while the focus of the LHC has been on constraining TeV scale physics, new particles could still be hiding below the electroweak scale. In order to obtain sensitivity to a new light boson with couplings to SM fermions, a potentially promising decay channel, for resonances with mass ≳ O(10) GeV, would be the decay to bb̅ pairs. The measurement of such signatures is challenging due to the trigger requirements at the LHC. In this work, we explore the LHC sensitivity to a light pseudoscalar, or axion-like particle (ALP), in the bb̅ final state with an associated photon, using jet substructure techniques, in the mass range between 10 GeV and 100 GeV. We obtain projected exclusions on the ALP-fermion coupling in a region of phase space which has not so far been probed by direct searches. We further discuss the impact that lower trigger thresholds may have on the LHC reach.

The current Large Hadron Collider (LHC) data show no clear indication of new physics and only incremental improvements are anticipated at the energy frontier in the near future. However, while the focus of the LHC has been on constraining TeV scale physics, new particles could still be hiding below the electroweak scale. In order to obtain sensitivity to a new light boson with couplings to SM fermions, a potentially promising decay channel, for resonances with mass greater than or similar to O(10) GeV, would be the decay to b pairs. The measurement of such signatures is challenging due to the trigger requirements at the LHC. In this work, we explore the LHC sensitivity to a light pseudoscalar, or axionlike particle (ALP), in the bb final state with an associated photon, using jet substructure techniques, in the mass range between 10 and 100 GeV. We obtain projected exclusions on the ALP-fermion coupling in a region of phase space which has not so far been probed by direct searches. We further discuss the impact that lower trigger thresholds may have on the LHC reach. b

Recent experimental advances now severely constrain electroweak-scale WIMPs produced via thermal freeze-out, leading to a shift away from this standard paradigm. Here we consider an axion-like particle (ALP), the pseudo-Goldstone boson of an approximate U(1) global symmetry spontaneously broken at a high scale 𝑓𝑎, as a mediator between the Standard Model (SM) particles and the dark matter (DM) particles. We explore the case where the couplings are too small to allow for DM generation via freeze-out and the mediator particle and the DM constitute a hidden sector which is thermally decoupled from the SM particles. However, alternative generation mechanisms such as freeze-in and decoupled freeze-out are now appropriate. Having determined the region of parameter space where the correct relic density is obtained, we then revisit experimental constraints on ALPs from electron beam dump experiments, astrophysics and rare 𝐵 and 𝐾 decays.

We consider an axion-like particle (ALP) coupled to Standard Model (SM) fermions as a mediator between the SM and a fermionic dark matter (DM) particle. We explore the case where the ALP-SM and/or the ALP-DM couplings are too small to allow for DM generation via standard freeze-out. DM is therefore thermally decoupled from the visible sector and must be generated through either freeze-in or decoupled freeze-out (DFO). In the DFO regime, we present an improved approach to obtain the relic density by solving a set of three stiff coupled Boltzmann equations, one of which describes the energy transfer from the SM to the dark sector. Having determined the region of parameter space where the correct relic density is obtained, we revisit experimental constraints from electron beam dump experiments, rare B and K decays, exotic Higgs decays at the LHC, astrophysics, dark matter searches and cosmology. In particular, for our specific ALP scenario we (re) calculate and improve beam dump, flavour and supernova constraints. Throughout our calculation we implement state-of-the-art chiral perturbation theory results for the ALP partial decay width to hadrons. We find that while the DFO region, which predicts extremely small ALP-fermion couplings, can probably only be constrained by cosmological observables, the freeze-in region covers a wide area of parameter space that may be accessible to other more direct probes. Some of this parameter space is already excluded, but a significant part should be accessible to future collider experiments.

In the last ten years, there has been great progress in calculations of decays of B and D mesons, and baryons containing a heavy b or c quark. One propelling factor has been the measurement of several anomalies in b→ s and b→ c transitions, these are one of the only signs of physics beyond the Standard Model. The deviations included measurements of branching ratios, angular observables and lepton universality ratios. Another factor is the exclusive-inclusive discrepancy in the determination of the CKM elements V_ub and V_cb . We will first review recent calculations involving b→ s and c→ u transitions that could shed light on the neutral current anomalies. We will then summarise the progress the determination of the CKM elements, V_ub and V_cb . Finally we will discuss the current theoretical status and experimental prospects for the lepton universality ratios in b→ s and b→ c semileptonic decays.

The measured branching fractions of $B$-mesons into leptonic final states derived by the LHCb collaboration hint towards the breakdown of lepton flavour universality. In this work we take at face value the so-called $R_{D^{(*)}}$ observables that are defined as the ratios of neutral $B$-meson charged-current decays into a charged $D$-meson, a charged lepton and a neutrino final state in the tau and muon channels. A well-studied and simple solution to this charged current anomaly is to introduce a scalar leptoquark $S_1$ that couples to the second and third generation of fermions. We investigate how $S_1$ can also serve as a mediator between the Standard Model and a dark sector. We study this scenario in detail and estimate the constraints arising from collider searches for leptoquarks, collider searches for missing energy signals, direct detection experiments and the dark matter relic abundance. We stress that the production of a pair of leptoquarks that decays into different final states (i.e. the commonly called mixed channels) provides critical information for identifying the underlying dynamics, and we exemplify this by studying the $t \tau b \nu$ and the resonant $S_1$ plus missing energy channels. We find that direct detection data provides non-negligible constraints on the leptoquark coupling to the dark sector, which in turn affects the relic abundance. We also show that the correct relic abundance can not only arise via standard freeze-out, but also through conversion-driven freeze-out. We illustrate the rich phenomenology of the model with a few selected benchmark points, providing a broad stroke of the interesting connection between lepton flavour violation and dark matter.

The next generation electron-positron colliders are designed for precision studies of the Standard Model and its extensions, in particular in the Higgs sector. We consider the potential for discovery of composite Higgs models in Higgs pair production through photon collisions. This process is loop-generated, thus it provides access to all Higgs couplings and can show new physics effects in polarized and unpolarized cross-sections starting at relatively low collider energies. It is, therefore, relevant for all electron-positron colliders planned or in preparation. Sizeable deviations from the Standard Model predictions are present in a general class of composite Higgs models, as couplings of one or more Higgs bosons to fermions, or fermionic and scalar resonances, modify the destructive interference present in the Standard Model. In particular, large effects are due to the new quartic coupling of the Higgs to tops and to the presence of a light scalar resonance.

In Standard Model (SM) Higgs Boson pair production initiated by photons (γγ→ h h) is loop-generated process and thereby very sensitive to any new couplings and particles that may come in loops. The Composite Higgs Models provide an alternate mechanism to address the hierarchy problem of SM where Higgs instead of being an elementary field could be a bound state of a strongly interacting sector. These set of models apart from modifying the SM Higgs couplings could also introduce new effective couplings that can have substantial impact on the loop processes. In this work we have studied the impact of such modifications by Composite Higgs models in γγ→ h h production process.

Abstract In this paper we consider the decay D + → π + ℓ + ℓ − , addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q 2 and at high q 2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e + e − → (hadrons) and τ → (hadrons) + ν τ data as well as the branching ratios for the resonant decays D + → π + R(R → ℓ + ℓ − ), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q 2. Focusing then on the observables F H and A FB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

In this paper we consider the decay D+ -> pi (+)l(+)l(-), addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q(2) and at high q(2), adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e(+)e(-) -> (hadrons) and tau -> (hadrons) + nu (tau) data as well as the branching ratios for the resonant decays D+ -> pi R+(R -> l(+)l(-)), with R = rho, omega, and phi. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q(2). Focusing then on the observables F-H and A(FB), we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

We consider the decay B→ℓℓℓ^'ν, taking into account the leading 1/m_b and q^2 corrections calculated in the QCD factorization framework as well as the soft corrections calculated employing dispersion relations and quark-hadron duality. We extend the existing results for the radiative decay B→γℓν to the case of non-zero (but small) q^2, the invariant mass squared of the dilepton pair ℓ^+ℓ^-. This restricts us to the case ℓ≠ℓ' as otherwise the same sign ℓ and ℓ' cannot be distinguished. We further study the sensitivity of the results to the leading moment of the B-meson distribution amplitude and discuss the potential to extract this quantity at LHCb and the Belle II experiment.

In Standard Model (SM) Higgs Boson pair production initiated by photons ($\gamma \gamma \to h h$) is loop-generated process and thereby very sensitive to any new couplings and particles that may come in loops. The Composite Higgs Models provide an alternate mechanism to address the hierarchy problem of SM where Higgs instead of being an elementary field could be a bound state of a strongly interacting sector. These set of models apart from modifying the SM Higgs couplings could also introduce new effective couplings that can have substantial impact on the loop processes. In this work we have studied the impact of such modifications by Composite Higgs models in $\gamma\gamma \to h h$ production process.

We consider the decay $B\to\ell\ell\ell^{\prime}\nu$, taking into account the leading $1/m_b$ and $q^2$ corrections calculated in the QCD factorization framework as well as the soft corrections calculated employing dispersion relations and quark-hadron duality. We extend the existing results for the radiative decay $B\to\gamma\ell\nu$ to the case of non-zero (but small) $q^2$, the invariant mass squared of the dilepton pair $\ell^+\ell^-$. This restricts us to the case $\ell\neq\ell'$ as otherwise the same sign $\ell$ and $\ell'$ cannot be distinguished. We further study the sensitivity of the results to the leading moment of the $B$-meson distribution amplitude and discuss the potential to extract this quantity at LHCb and the Belle II experiment.

Two of the elements of the Cabibbo-Kobayashi-Maskawa quark mixing matrix, $|V_{ub}|$ and $|V_{cb}|$, are extracted from semileptonic B decays. The results of the B factories, analysed in the light of the most recent theoretical calculations, remain puzzling, because for both $|V_{ub}|$ and $|V_{cb}|$ the exclusive and inclusive determinations are in clear tension. Further, measurements in the $\tau$ channels at Belle, Babar, and LHCb show discrepancies with the Standard Model predictions, pointing to a possible violation of lepton flavor universality. LHCb and Belle II have the potential to resolve these issues in the next few years. This article summarizes the discussions and results obtained at the MITP workshop held on April 9--13, 2018, in Mainz, Germany, with the goal to develop a medium-term strategy of analyses and calculations aimed at solving the puzzles. Lattice and continuum theorists working together with experimentalists have discussed how to reshape the semileptonic analyses in view of the much higher luminosity expected at Belle II, searching for ways to systematically validate the theoretical predictions in both exclusive and inclusive B decays, and to exploit the rich possibilities at LHCb.

We report on the status of efforts to improve the reinterpretation of searches and measurements at the LHC in terms of models for new physics, in the context of the LHC Reinterpretation Forum. We detail current experimental offerings in direct searches for new particles, measurements, technical implementations and Open Data, and provide a set of recommendations for further improving the presentation of LHC results in order to better enable reinterpretation in the future. We also provide a brief description of existing software reinterpretation frameworks and recent global analyses of new physics that make use of the current data.

This report presents the activities of the `New Physics' working group for the `Physics at TeV Colliders' workshop (Les Houches, France, 10--28 June, 2019). These activities include studies of direct searches for new physics, approaches to exploit published data to constrain new physics, as well as the development of tools to further facilitate these investigations. Benefits of machine learning for both the search for new physics and the interpretation of these searches are also presented.

We examine the collider signatures of a WIMP dark matter scenario comprising a singlet fermion and an SU(2) n-plet fermion, with a focus on n = 3 and n = 5. The singlet and n-plet masses are of the order of the electroweak scale. The n-plet contains new charged particles which will be copiously pair-produced at the LHC. Small mixing angles and near-degenerate masses, both of which feature naturally in these models, give rise to long-lived particles and their characteristic collider signatures. In particular, the n = 5 model can be constrained by displaced lepton searches independently of the mixing angle, generically ruling out 5-plet masses below about 280 GeV. For small mixing angles, we show that there is a parameter range for which the model reproduces the observed thermal relic density but is severely constrained by disappearing track searches in both the n = 3 and the n = 5 cases. The n = 3 model is further constrained by soft di-lepton searches irrespective of whether any of the new particles are long-lived.