Search

Measurements of Ultra-High Energy Cosmic Rays (UHECR) suggest a complex composition with significant contributions from heavy nuclei at the highest energies. We systematically explore how the selection and number of primary nuclei included in the analysis impact the inferred UHECR mass composition. Introducing a distance measure in the space of $X_{\rm max}$ distribution moments, we demonstrate that limiting the analysis to a few primaries can introduce significant biases, particularly as observational data improves. We provide lists of primaries approximately equidistant in the new measure, which guaranty unbiased results at given statistical confidence. Additionally, we explore consistent inclusion of nuclei heavier than iron and up to plutonium, deriving first observational upper bounds on their contributions to UHECR with the Pierre Auger Open Data., Comment: 11 pages, 8 figures

The recent Belle II observation of $B \to K E_{\rm miss}$ challenges theoretical interpretations in terms of Standard Model neutrino final states. Instead, we consider new physics scenarios where up to two new light-invisible particles of spin 0 up to 3/2 are present in the final state. We identify viable scenarios by reconstructing the (binned) likelihoods of the relevant $B \to K^{(*)} E_{\rm miss}$ and also $B_s \to E_{\rm miss}$ experimental analyses and present preferred regions of couplings and masses. In particular, we find that the current data prefers two-body decay kinematics involving the emission of a single massive scalar or a vector particle, or alternatively, three-body decays involving pairs of massive scalars or spin 1/2 fermions. When applicable, we compare our findings with existing literature and briefly discuss some model-building implications., Comment: 16 pages, 10 figures

We consider the combined measurements of CP-averaged decay rates and direct CP asymmetries of $B^\pm\to K^\pm \ell^+ \ell^-$ and $B^\pm\to \pi^\pm \ell^+ \ell^-$ to probe (non-local) four-quark operator matrix element contributions to rare semileptonic B meson decays. We also explore how their effects could be in principle disentangled from possible local new physics effects using $U$-spin relations. To this end, we construct a ratio of CP-odd decay rate differences which are exactly predicted within the standard model in the $U$-spin limit, while the leading $U$-spin breaking effects can also be systematically calculated. Our results motivate binned measurements of the direct CP asymmetry in $B^\pm\to \pi^\pm \ell^+ \ell^-$ as well as dedicated theoretical estimates of $U$-spin breaking both in local form factors as well as in four-quark matrix elements., Comment: 7 pages, 2 figures

Recent advances in $b$, $c$, and $s$ quark tagging coupled with novel statistical analysis techniques will allow future high energy and high statistics electron-positron colliders, such as the FCC-ee, to place phenomenologically relevant bounds on flavor violating Higgs and $Z$ decays to quarks. We assess the FCC-ee reach for $Z/h\to bs, cu$ decays as a function of jet tagging performance. We also update the SM predictions for the corresponding branching ratios, as well as the indirect constraints on the flavor violating Higgs and $Z$ couplings to quarks. Using type III two Higgs doublet model as an example of beyond the standard model physics, we show that the searches for $h\to bs, cu$ decays at FCC-ee can probe new parameter space not excluded by indirect searches. We also reinterpret the FCC-ee reach for $Z\to bs , cu$ in terms of the constraints on models with vectorlike quarks., Comment: 22 pages, 15 figures

We explore CP-violating (CPV) effects of heavy New Physics in flavour-changing quark dipole transitions, within the framework of Standard Model Effective Field Theory (SMEFT). First, we establish the relevant dimension six operators and consider the Renormalisation Group (RG) evolution of the appropriate Wilson coefficients. We investigate RG-induced correlations between different flavour-violating processes and electric dipole moments (EDMs) within the Minimal Flavour Violating and $U(2)^3$ quark flavour models. At low energies, we set bounds on the Wilson coefficients of the dipole operators using CPV induced contributions to observables in non-leptonic and radiative $B$, $D$ and $K$ decays as well as the neutron and electron EDMs. This enables us to connect observable CPV effects at low energies and general NP appearing at high scales. We present bounds on the Wilson coefficients of the relevant SMEFT operators at the high scale $\Lambda = 5~{\rm TeV}$, and discuss most sensitive CPV observables for future experimental searches., Comment: 41 pages, 4 figures, 7 tables

We show that the maximum shower depth distributions of Ultra-High Energy Cosmic Rays (UHECRs), as measured by fluorescence telescopes, can be augmented by building a mapping to observables collected by surface detectors. The resulting statistical improvement of such augmented dataset depends in a universal way on the strength of the correlation exhibited by the mapping. Building upon the publicly available data on "golden hybrid" events from the Pierre Auger Observatory we project possible improvements in the inferred composition of UHECRs for a range of possible mappings with varying correlation strengths., Comment: 8 pages, 6 figures, method corrected

We apply statistical inference on the Pierre Auger Open Data to discern for the first time the full mass composition of cosmic rays at different energies. Working with longitudinal electromagnetic profiles of cosmic ray showers, in particular their peaking depths $X_{\rm max}$, we employ central moments of the $X_{\rm max}$ distributions as features to discriminate between different shower compositions. We find that already the first few moments entail the most relevant information to infer the primary cosmic ray mass spectrum. Our approach, based on an unbinned likelihood, allows us to consistently account for sources of statistical uncertainties due to finite datasets, both measured and simulated, as well as systematic effects. Finally, we provide a quantitative comparison of different high energy hadronic interaction models available in the atmospheric shower simulation codes., Comment: 28 pages + 16 page Appendix, 27 figures

We extend the use of Classification Without Labels for anomaly detection with a hypothesis test designed to exclude the background-only hypothesis. By testing for statistical independence of the two discriminating dataset regions, we are able to exclude the background-only hypothesis without relying on fixed anomaly score cuts or extrapolations of background estimates between regions. The method relies on the assumption of conditional independence of anomaly score features and dataset regions, which can be ensured using existing decorrelation techniques. As a benchmark example, we consider the LHC Olympics dataset where we show that mutual information represents a suitable test for statistical independence and our method exhibits excellent and robust performance at different signal fractions even in presence of realistic feature correlations., Comment: 10 pages, 3 figures, 1 Table. Matches published version at Physics Letters B. All code is available at https://github.com/ManuelSzewc/Null_Hypothesis_Test_for_Anomaly_Detection. Comments welcome!

We propose an extension of the existing experimental strategy for measuring branching fractions of top quark decays, targeting specifically $t\to j_q W$, where $j_q$ is a light quark jet. The improved strategy uses orthogonal $b$- and $q$-taggers, and adds a new observable, the number of light-quark-tagged jets, to the already commonly used observable, the fraction of $b$-tagged jets in an event. Careful inclusion of the additional complementary observable significantly increases the expected statistical power of the analysis, with the possibility of excluding $|V_{tb}|=1$ at $95\%$ C.L. at the HL-LHC, and accessing directly the standard model value of $|V_{td}|^2+|V_{ts}|^2$., Comment: 19 pages, 7 figures

We consider the time-dependent analysis of rare $B_d$ and $B_s$ decays mediated by $b\to s \nu \bar \nu$ transitions. The inclusion of time evolution allows us to construct novel observables with specific sensitivity to CP-odd phases in these processes. The sensitivity to CP violation of corresponding time-integrated measurements in presence of flavor-tagging is also explored. We provide precise predictions for these observables in the SM and explore their sensitivity to new CP-violating NP contributions at present and planned future $B$-physics experiments. As such, these observables provide unique probes of CP violation in $b \to s \nu \bar \nu$ transitions.

We summarize the discussions at a virtual Community Workshop on Cold Atoms in Space concerning the status of cold atom technologies, the prospective scientific and societal opportunities offered by their deployment in space, and the developments needed before cold atoms could be operated in space. The cold atom technologies discussed include atomic clocks, quantum gravimeters and accelerometers, and atom interferometers. Prospective applications include metrology, geodesy and measurement of terrestrial mass change due to, e.g., climate change, and fundamental science experiments such as tests of the equivalence principle, searches for dark matter, measurements of gravitational waves and tests of quantum mechanics. We review the current status of cold atom technologies and outline the requirements for their space qualification, including the development paths and the corresponding technical milestones, and identifying possible pathfinder missions to pave the way for missions to exploit the full potential of cold atoms in space. Finally, we present a first draft of a possible road-map for achieving these goals, that we propose for discussion by the interested cold atom, Earth Observation, fundamental physics and other prospective scientific user communities, together with ESA and national space and research funding agencies., Comment: Summary of the Community Workshop on Cold Atoms in Space and corresponding Road-map: https://indico.cern.ch/event/1064855/

Monte Carlo (MC) generators are crucial for analyzing data in particle collider experiments. However, often even a small mismatch between the MC simulations and the measurements can undermine the interpretation of the results. This is particularly important in the context of LHC searches for rare physics processes within and beyond the standard model (SM). One of the ultimate rare processes in the SM currently being explored at the LHC, $pp\to t\bar tt \bar t$ with its large multi-dimensional phase-space is an ideal testing ground to explore new ways to reduce the impact of potential MC mismodelling on experimental results. We propose a novel statistical method capable of disentangling the 4-top signal from the dominant backgrounds in the same-sign dilepton channel, while simultaneously correcting for possible MC imperfections in modelling of the most relevant discriminating observables -- the jet multiplicity distributions. A Bayesian mixture of multinomials is used to model the light-jet and $b$-jet multiplicities under the assumption of their conditional independence. The signal and background distributions generated from a deliberately mistuned MC simulator are used as model priors. The posterior distributions, as well as the signal and background fractions, are then learned from the data using Bayesian inference. We demonstrate that our method can mitigate the effects of large MC mismodellings in the context of a realistic $t\bar tt\bar t$ search, leading to corrected posterior distributions that better approximate the underlying truth-level spectra., Comment: Matches accepted version at PRD. 11 pages, 8 figures. This expanded version includes a toy model and explicit tests of the model validity for Four-Tops. Code available at https://github.com/ManuelSzewc/bayes-4tops

We investigate the consequences of deviations from the Standard Model observed in $b\to s\mu\mu$ transitions for flavour-changing neutral-current processes involving down-type quarks and neutrinos, under generic assumptions concerning the structure of New Physics. We derive the relevant Wilson coefficients within an effective field theory approach respecting the SM gauge symmetry, including right-handed currents and assuming a flavour structure based on approximate $U(2)$ symmetry, and only SM-like light neutrinos. We discuss correlations among $B \to K^{(*)} \nu \bar \nu$ and $K\to \pi \nu \bar \nu$ branching ratios in the case of linear Minimal Flavour Violation and in a more general framework, highlighting in each case the role played by various New Physics scenarios proposed to explain $b\to s\mu\mu$ deviations. This talk is based on arXiv:2005.03734., Comment: Contribution to the 2021 EW session of the 55th Rencontres de Moriond

We propose a novel method to probe the persistent hints of Lepton Flavour Universality violation observed in semileptonic $B$ decays. Relying on the specific properties of the Belle II experiment, it consists in comparing the inclusive rates of $\Upsilon(4S) \to e^\pm \mu^\mp X$, $\Upsilon(4S) \to \mu^\pm \tau_{\rm had}^\mp X$ and $\Upsilon(4S) \to e^\pm \tau_{\rm had}^\mp X$. We show that such a measurement can be directly related to the ratio $R(X)_{\tau\ell} \equiv \Gamma (b\to X \tau \nu ) / \Gamma (b \to X \ell \nu)$ ($\ell=e$ or $\mu$), once appropriate experimental cuts are applied to suppress the effects of neutral $B$ mixing and leptons emitted through charm or tau decays. Such a measurement would thus constitute an additional and potentially competitive probe of Lepton Flavour Universality in $b\to c\ell\nu$ transitions, complementary to existing exclusive measurements, accessible in the Belle II environment., Comment: 8 pages, 1 figure

We explore the interplay of New Physics (NP) effects in $(g-2)_\ell$ and $h \to \ell^+ \ell^-$ within the Standard Model Effective Field Theory (SMEFT) framework, including one-loop Renormalization Group (RG) evolution of the Wilson coefficients as well as matching to the observables below the electroweak symmetry breaking scale. We include both the leading dimension six chirality flipping operators including a Higgs and $SU(2)_L$ gauge bosons as well as four-fermion scalar and tensor operators, forming a closed operator set under the SMEFT RG equations. We compare present and future experimental sensitivity to different representative benchmark scenarios. We also consider two simple UV completions, a Two Higgs Doublet Model and a single scalar LeptoQuark extension of the SM, and show how tree level matching to SMEFT followed by the one-loop RG evolution down to the electroweak scale can reproduce with high accuracy the $(g-2)_\ell$ and $h \to \ell^+ \ell^-$ contributions obtained by the complete one- and even two-loop calculations in the full models., Comment: 24 pages, 9 figures; v2: corrected typos, added Rb result for electron anomalous moment

Unsupervised anomaly detection could be crucial in future analyses searching for rare phenomena in large datasets, as for example collected at the LHC. To this end, we introduce a physics inspired variational autoencoder (VAE) architecture which performs competitively and robustly on the LHC Olympics Machine Learning Challenge datasets. We demonstrate how embedding some physical observables directly into the VAE latent space, while at the same time keeping the classifier manifestly agnostic to them, can help to identify and characterise features in measured spectra as caused by the presence of anomalies in a dataset., Comment: Version as published

We reconsider decays of pseudoscalar mesons (P) to neutrino pairs and possibly additional photons in presence of (light) Majorana neutrinos. For this purpose we derive a model-independent general parametrization of neutrino mass matrices with physically interpretable and irreducible set of parameters. The parametrization is valid for any number of neutrinos and interpolates smoothly between the heavy Majorana and the (pseudo)Dirac neutrino limits. We apply the new parametrization to the study of $P \rightarrow \nu \nu$ and $P \rightarrow \nu \nu \gamma$ decays within the SM extended by additional singlet fermions. We update the SM predictions for the branching ratios of $B_{s,d} \rightarrow \nu \nu \gamma$ and discuss the sensitivity of the $B_{s,d} \rightarrow E_{\rm miss} (\gamma)$ decays to neutrino mass and mixing parameters., Comment: 20 pages, 6 figures, added one appendix, conclusions unchanged, version as published

We use machine learning (ML) and non-ML techniques to study optimized $CP$-odd observables, directly and maximally sensitive to the $CP$-odd $i \tilde \kappa \bar t \gamma^5 t h$ interaction at the LHC and prospective future hadron colliders using the final state with a Higgs boson and a top quark pair, $pp\to t\bar t h$, followed by semileptonic $t$ decays. We perform phase-space optimization of manifestly $CP$-odd observables ($\boldsymbol \omega$), sensitive to the sign of $\tilde \kappa$, and constructed from experimentally accessible final state momenta. We identify a simple optimized linear combination $\boldsymbol \alpha\cdot \boldsymbol\omega$ that gives similar sensitivity as the studied fully fledged ML models. Using $\boldsymbol\alpha\cdot \boldsymbol\omega$ we project the expected sensitivities to $\tilde \kappa$ at HL-LHC, HE-LHC, and FCC-hh., Comment: As published

We describe a technique to learn the underlying structure of collider events directly from the data, without having a particular theoretical model in mind. It allows to infer aspects of the theoretical model that may have given rise to this structure, and can be used to cluster or classify the events for analysis purposes. The unsupervised machine-learning technique is based on the probabilistic (Bayesian) generative model of Latent Dirichlet Allocation. We pair the model with an approximate inference algorithm called Variational Inference, which we then use to extract the latent probability distributions describing the learned underlying structure of collider events. We provide a detailed systematic study of the technique using two example scenarios to learn the latent structure of di-jet event samples made up of QCD background events and either $t\bar{t}$ or hypothetical $W' \to (\phi \to WW) W$ signal events., Comment: 38 pages, 23 figures

We investigate the consequences of deviations from the Standard Model observed in $b\to s\mu\mu$ transitions for flavour-changing neutral-current processes involving down-type quarks and neutrinos. We derive the relevant Wilson coefficients within an effective field theory approach respecting the SM gauge symmetry, including right-handed currents, a flavour structure based on approximate $U(2)$ symmetry, and assuming only SM-like light neutrinos. We discuss correlations among $B \to K^{(*)} \nu \bar \nu$ and $K\to \pi \nu \bar \nu$ branching ratios in the case of linear Minimal Flavour Violation and in a more general framework, highlighting in each case the role played by various New Physics scenarios proposed to explain $b\to s\mu\mu$ deviations., Comment: 7 pages, 2 figures

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., Comment: 58 pages, minor revision following comments from SciPost referees

We analyze the prospects of probing the $CP$-odd $i \tilde \kappa \bar t \gamma^5 t h$ interaction at the LHC and its projected upgrades, the high-luminosity and high-energy LHC, directly using associated on-shell Higgs boson and top quark or top quark pair production. To this end we first construct a $CP$-odd observable based on top quark polarization in $W b \to t h$ scattering with optimal linear sensitivity to $\tilde \kappa$. For the corresponding hadronic process $pp \to t h j$ we present a method of extracting the phase-space dependent weight function that allows to retain close to optimal sensitivity to $\tilde{\kappa}$. We project future sensitivity to the signal in $pp \to t(\to \ell \nu b )h(\to b\bar b) j$. Based on these insights we propose novel $CP$-odd observables for top quark pair production in association with the Higgs, $pp \to t \bar t h$, with semileptonically decaying tops and $h\to \bar b b$, that rely solely on measuring the momenta of leptons and $b$-jets from the decaying tops without having to distinguish the charge of the $b$-jets. Among the many possibilities we single out an observable that can potentially probe $\tilde \kappa \sim 0.5$ at the high-luminosity LHC and $\tilde \kappa \sim 0.1$ at high-energy LHC with $2\sigma$ confidence., Comment: Updated sensitivity plots due to better data samples

We apply techniques from Bayesian generative statistical modeling to uncover hidden features in jet substructure observables that discriminate between different a priori unknown underlying short distance physical processes in multi-jet events. In particular, we use a mixed membership model known as Latent Dirichlet Allocation to build a data-driven unsupervised top-quark tagger and $t\bar t$ event classifier. We compare our proposal to existing traditional and machine learning approaches to top jet tagging. Finally, employing a toy vector-scalar boson model as a benchmark, we demonstrate the potential for discovering New Physics signatures in multi-jet events in a model independent and unsupervised way., Comment: 8 pages, 3 figures; v2: matches published version. Additional clarifying comments added in sections I and II. Updated references

We propose a novel strategy to test lepton flavor universality (LFU) in top decays, applicable to top pair production at colliders. Our proposal exploits information in kinematic distributions and mostly hinges on data-driven techniques, thus having very little dependence on our theoretical understanding of top pair production. Based on simplified models accommodating recent hints of LFU violation in charged current B meson decays, we show that existing LHC measurements already provide non-trivial information on the flavor structure and the mass scale of such new physics (NP). We also project that the measurements of LFU in top decays at the high-luminosity LHC could reach a precision at the percent level or below, improving the sensitivity to LFU violating NP in the top sector by more than an order of magnitude compared to existing approaches., Comment: 31 pages, 9 figures. v2: version published in JHEP

We introduce a set of clockwork models of flavor that can naturally explain the large hierarchies of the Standard Model quark masses and mixing angles. Since the clockwork only contains chains of new vector-like fermions without any other dynamical fields, the flavor constraints allow for relatively light new physics scale. For two benchmarks with gear masses just above 1 TeV, allowed by flavor constraints, we discuss the collider searches and the possible ways of reconstructing gear spectra at the LHC. We also examine the similarities and differences with the other common solutions to the SM flavor puzzle, i.e., with the Froggatt-Nielsen models, where we identify a new {\it clockworked } version, and with the Randall-Sundrum models.

We investigate the bounds on light pseudoscalars that arise from a variety of collider searches. Special attention is thereby devoted to the mass regions $[3, 5] \, {\rm GeV}$ and $[9,11] \, {\rm GeV}$, in which a meaningful theoretical description has to include estimates of non-perturbative effects such as the mixing of the pseudoscalar with QCD bound states. A compendium of formulas that allows to deal with the relevant corrections is provided. It should prove useful for the interpretation of future LHC searches for light CP-odd spin-0 states., Comment: 17 pages, 3 figures, 2 tables; v3: new draft includes the constraints from CMS-PAS-HIG-17-024 and CMS-PAS-HIG-17-029; a similar version has been published in JHEP. also contained in arXiv:1803.10379

We propose a direct measurement of the CKM element $V_{td}$ at the LHC. Taking profit of the imbalance between $d$ and $\bar d$ quark content in the proton, we show that a non-zero $V_{td}$ induces a charge asymmetry in the $tW$ associated production. The main backgrounds to this process, $t\bar t$ production, and $tW$ associated production mediated by $V_{tb}$, give charge symmetric contributions at leading order in QCD. Therefore, using specific kinematic features of the signal, we construct a charge asymmetry in the di-lepton final state which, due also to a reduction of systematic uncertainties in the asymmetry, is potentially sensitive to $V_{td}$ suppressed effects. In particular, using signal and background simulations up to detector level, we show that this new observable could improve the current direct upper bound on $|V_{td}|$ already with existing LHC data. We also project that $|V_{td}|$ values down to $\sim 10$ times the Standard Model prediction could be probed in the high luminosity phase of the LHC., Comment: 10 pages, 6 figures

We show that new physics models without new flavor violating interactions can explain the recent anomalies in the $b\to s\ell^+\ell^-$ transitions. The $b\to s\ell^+\ell^-$ arises from a $Z'$ penguin which automatically predicts the $V-A$ structure for the quark currents in the effective operators. This framework can be realized either in a renormalizable $U(1)'$ setup or be due to new strongly interacting dynamics. The di-muon resonance searches at the LHC are becoming sensitive to this scenario since the $Z'$ is relatively light, and could well be discovered in future searches by ATLAS and CMS., Comment: 5 pages, 3 figures, correction of a mistake in eq. (16), Fig. 2 updated, conclusions unchanged

We design a search strategy for the Standard Model $t\bar t t \bar t$ production at the LHC in the same-sign dilepton and trilepton channels. We study different signal features and, given the small expected number of signal events, we scrutinize in detail all reducible and irreducible backgrounds. Our analysis shows that by imposing a set of basic jet and lepton selection criteria, the SM $pp \to t\bar t t \bar t$ process could be evidenced in the near future, within Run-II, when combining both multi-lepton search channels. We argue that this search strategy should also be used as a guideline to test New Physics coupling predominantly to top-quarks. In particular, we show that a non-resonant New Physics enhancement in the four-top final state would be detectable through this search strategy. We study two {\it top-philic} simplified models of this kind, a neutral scalar boson and a $Z^\prime$, and present current and future exclusion limits on their mass and couplings., Comment: 31 pages, 12 figures. v2: references added, minor typos corrected. Published in Nucl. Phys. B

We confront the indications of lepton flavor universality (LFU) violation observed in semi-tauonic $B$ meson decays with new physics (NP) searches using high $p_T$ tau leptons at the LHC. Using effective field theory arguments we correlate possible non-standard contributions to semi-tauonic charged currents with the $\tau^+ \tau^-$ signature at high energy hadron colliders. Several representative standard model extensions put forward to explain the anomaly are examined in detail: (i) weak triplet of color-neutral vector resonances, (ii) second Higgs doublet and (iii) scalar or (iv) vector leptoquark. We find that, in general, $\tau^+ \tau^-$ searches pose a serious challenge to NP explanations of the LFU anomaly. Recasting existing 8 TeV and 13 TeV LHC analyses, stringent limits are set on all considered simplified models. Future projections of the $\tau^+ \tau^-$ constraints as well as caveats in interpreting them within more elaborate models are also discussed., Comment: 11 pages, 6 figures

The diphoton excess around $m_S=750$ GeV observed at ATLAS and CMS can be interpreted as coming from $S=H$ and $A$, the neutral components of a second Higgs doublet. If so, then the consistency of the light Higgs decays with the Standard Model predictions provides upper bounds on the rates of $S\to VV, hZ, hh$ decays. On the other hand, if $h\to\tau\mu$ decay is established, then a lower bound on the rate of $S\to\tau\mu$ decay arises. Requiring that $\Gamma_S\lesssim45$ GeV gives both an upper and a lower bound on the rotation angle from the Higgs basis $(\Phi_v,\Phi_A)$ to the mass basis $(\Phi_h,\Phi_H)$. The charged scalar, with $m_{H^\pm}\simeq750$ GeV, is produced in association with a top quark, and can decay to $\mu^\pm\nu$, $\tau^\pm\nu$, $tb$ and $W^\pm h$, Comment: 10 pages, 6 figures

If the 750 GeV resonance in the diphoton channel is confirmed, what are the measurements necessary to infer the properties of the new particle and understand its nature? We address this question in the framework of a single new scalar particle, called digamma ($\digamma$). We describe it by an effective field theory, which allows us to obtain general and model-independent results, and to identify the most useful observables, whose relevance will remain also in model-by-model analyses. We derive full expressions for the leading-order processes and compute rates for higher-order decays, digamma production in association with jets, gauge or Higgs bosons, and digamma pair production. We illustrate how measurements of these higher-order processes can be used to extract couplings, quantum numbers, and properties of the new particle., Comment: 53 pages, 21 figures. v2: references added

We study the constraints implied by partial wave unitarity on new physics in the form of spin-zero di-boson resonances at LHC. We derive the scale where the effective description in terms of the SM supplemented by a single resonance is expected to break down depending on the resonance mass and signal cross-section. Likewise, we use unitarity arguments in order to set perturbativity bounds on renormalizable UV completions of the effective description. We finally discuss under which conditions scalar di-boson resonance signals can be accommodated within weakly-coupled models., Comment: 34 pages, 9 figures. Revised version, to appear in EPJC. v3: mistake in Appendix A.2 corrected

We show that the 750 GeV di-photon excess could be explained by the ${\mathcal Q}-$onium system of a new QCD-like theory with fermions vectorial under the SM. Beside the spin-0 di-photon singlet this scenario predicts almost degenerate colored scalars and spin-1 resonances analogous to the $J/\Psi$ in QCD. All these states are within the reach of the LHC. An apparent large width can be explained as due to production of excited states with splitting $\Delta m\sim \Gamma$., Comment: 6 pages. v2: QCD effects and splitting of SU(2) multiplets added. v3: final version to appear in PLB

The diphoton excess around 750 GeV observed by ATLAS and CMS can be interpreted as coming from a massive spin-2 excitation. We explore this possibility in the context of warped five-dimensional models with the Standard Model (SM) fields propagating in the bulk of the extra dimension. The 750 GeV resonance is identified with the first Kaluza-Klein (KK) excitation of the five-dimensional graviton that is parametrically lighter than KK resonances of SM fields. Our set-up makes it possible to realize non-universal couplings of the spin-2 resonance to matter, and thus to explain non-observation of the 750 GeV resonance in leptonic channels. Phenomenological predictions of the model depend on the localization of fields in the extra dimension. If, as required by naturalness arguments, the zero modes of the Higgs and top fields are localized near the IR brane, one expects large branching fractions to ttbar, hh, WW, and ZZ final states. Decays to a Z boson and a photon can also be observable when the KK graviton couplings to the SM gauge fields are non-universal., Comment: 9 pages; v2: discussion of radion ghost issue added, Eqs. 5 and 8 fixed, references added

We consider the diphoton excess observed by ATLAS and CMS using the most up-to-date data and estimate the preferred enhancement in the production rate between 8 TeV and 13 TeV. Within the framework of effective field theory (EFT), we then show that for both spin-0 and spin-2 Standard Model (SM) gauge-singlet resonances, two of the three processes S to ZZ, S to Z gamma, and S to WW must occur with a non-zero rate. Moreover, we demonstrate that these branching ratios are highly correlated in the EFT. Couplings of S to additional SM states may be constrained and differentiated by comparing the S production rates with and without the vector-boson fusion (VBF) cuts. We find that for a given VBF to inclusive production ratio there is maximum rate of S to gauge bosons, b b-bar, and lighter quark anti-quark pairs. Simultaneous measurements of the width and the VBF ratio may be able to point towards the existence of hidden decays., Comment: 31 pages, 8 figures; version as published

We study the phenomenology of light spin-0 particles and stress that they can be efficiently searched for at the LHCb experiment in the form of dimuon resonances. Given the large production cross sections in the forward rapidity region together with the efficient triggering and excellent mass resolution, it is argued that LHCb can provide unique sensitivity to such states. We illustrate our proposal using the recent measurement of Upsilon production by LHCb, emphasising the importance of mixing effects in the bottomonium resonance region. The implications for dimuon decays of spin-0 bottomonium states are also briefly discussed., Comment: 13 pages, 5 figures, typos corrected, version as published

Motivated by the tantalizing excesses recently reported in the di-photon invariant mass spectrum at the LHC, we scrutinize some implications of scalar di-photon resonances in high energy proton-proton collisions. In particular, indications of a large width impose several challenges for model building. We show how calculability and unitarity considerations severely limit possible perturbative realizations of such a signal and propose a simple criterion that can be adapted to any renormalizable model. Furthermore, we discuss correlations between a di-photon excess and precision observables, including the anomalous magnetic and electric dipole moments of quarks and leptons, neutral meson oscillations and radiative flavor changing neutral current mediated decays of heavy leptons and hadrons. We find that existing searches and measurements significantly constrain the possibilities for a scalar resonance decaying into final states involving Standard Model fermions. We propose future search strategies which could elucidate some remaining currently unconstrained decay channels and discuss possible correlations between the di-photon excess and several recently reported flavor anomalies, showing that the latter can be addressed in a new incarnation of a gauged $U(1)^\prime$ model, with the di-photon resonance being the physical remnant of the $U(1)^\prime$-breaking field., Comment: 34 pages, 4 figures. Minor changes, version accepted in JHEP

Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter., Comment: v2: 45 pages, 12 figures, final. Factor of 2 changed in table 1, 4th row

We discuss a class of weak-scale extensions of the Standard Model which is completely invisible to low-energy indirect probes. The typical signature of this scenario is the existence of new charged and/or colored states which are stable on the scale of high-energy particle detectors., Comment: 4 pages, 2 figures. To appear in the proceedings of the 27th Rencontres the Blois on Particle Physics and Cosmology, May 31 - June 05, 2015

We investigate the phenomenology of flavored dark matter (DM). DM stability is guaranteed by an accidental ${\mathcal Z}_3$ symmetry, a subgroup of the standard model (SM) flavor group that is not broken by the SM Yukawa interactions. We consider an explicit realization where the quark part of the SM flavor group is fully gauged. If the dominant interactions between DM and visible sector are through flavor gauge bosons, as we show for Dirac fermion flavored DM, then the DM mass is bounded between roughly $0.5$ TeV and $5$ TeV if the DM multiplet mass is split only radiatively. In general, however, no such relation exists. We demonstrate this using scalar flavored DM where the main interaction with the SM is through the Higgs portal. For both cases we derive constraints from flavor, cosmology, direct and indirect DM detection, and collider searches., Comment: 46 pages, 16 figures

We classify weak-scale extensions of the Standard Model which automatically preserve its accidental and approximate symmetry structure at the renormalizable level and which are hence invisible to low-energy indirect probes. By requiring the consistency of the effective field theory up to scales of 10^15 GeV and after applying cosmological constraints, we arrive at a finite set of possibilities that we analyze in detail. One of the most striking signatures of this framework is the presence of new charged and/or colored states which can be efficiently produced in high-energy particle colliders and which are stable on the scale of detectors., Comment: 55 pages, 13 figures

We speculate about the possible interpretations of the recently observed excess in the $h \to \tau \mu$ decay. We derive a robust lower bound on the Higgs boson coupling strength to a tau and a muon, even in presence of the most general new physics affecting other Higgs properties. Then we reevaluate complementary indirect constraints coming from low energy observables as well as from theoretical considerations. In particular, the tentative signal should lead to $\tau \to \mu \gamma$ at rates which could be observed at Belle II. In turn we show that, barring fine-tuned cancellations, the effect can only be accommodated within models with an extended scalar sector. These general conclusions are demonstrated using a number of explicit new physics models. Finally we show how, given the $h \to \tau \mu$ signal, the current and future searches for $\mu \to e \gamma$ and $\mu \to e$ nuclear conversions unambiguously constrain the allowed rates for $h \to \tau e$., Comment: 34 pages, 9 figures, expanded Section V.D with the fine-tuning solution; conclusions unchanged

We study the LHC phenomenology of flavor changing Yukawa couplings between top quark, Higgs boson, and either an up or charm quark. Such $tuh$ or $tch$ couplings arise for instance in models in which Higgs sector is extended by the existence of additional Higgs bosons or by higher dimensional operators. We emphasize the importance of anomalous single top plus Higgs production in these scenarios, in addition to the more widely studied $t \to h j$ decays. By recasting existing CMS searches in multilepton and diphoton plus lepton final states, we show that bounds on $tuh$ couplings are improved by a factor of 1.5 when single top plus Higgs production is accounted for. We also recast the CMS search for vector boson plus Higgs production into new, competitive constraints on $tuh$ and $tch$ couplings, setting the limits of $BR(t\to hu) < 0.7%$ and $BR(t\to hc) <1.2%$. We then investigate the sensitivity of future searches in multilepton channel and in fully hadronic channel. In multilepton searches, studying the lepton rapidity distributions and charge assignments can be used to discriminate between $tuh$ couplings, for which anomalous single top production is relevant, and $tch$ couplings, for which it is suppressed by the parton distribution function of the charm quark. An analysis of fully hadronic $t+h$ production and $t\to h j$ decay can be competitive with the multilepton search at 100 fb$^{-1}$ of 13 TeV data if jet substructure techniques are employed to reconstruct boosted top quarks and Higgs bosons. To show this we develop a modified version of the HEPTopTagger algorithm, optimized for tagging $t \to h j$ decays. Our sensitivity estimates on $BR(t\to hu)$ ($BR(t\to hc)$) at 100 fb$^{-1}$ of 13 TeV data for multilepton searches, vector boson plus Higgs search and fully hadronic search are $0.22%$ ($0.33%$), $0.15%$ ($0.19%$) and $0.36%$ ($0.48%$), respectively., Comment: Version published in JHEP

We study the possibility of detecting New Physics (NP) phenomena at the LHC through a new search strategy looking at the monotop (top plus missing energy) signature which is common to a variety of NP models. We focus on the leptonic top decay mode and study the discovery or exclusion reach of the 2012 LHC data for three example models. Contrary to the hadronic mode, in this case the problematic QCD multijet background can be safely neglected. We find that the key kinematic variable to suppress most of the remaining SM backgrounds is the transverse mass of the charged lepton and missing energy. In fact, one could expect that the single-top production measurements already address the monotop signature in this mode. This is however not the case because in the SM single-top production the transverse mass has an end point determined by the W mass, while the NP signals typically have an additional source of missing energy. We compare, under the same conditions, our monotop search strategy with existing single-top measurements and find a considerable improvement in the monotop signature reach., Comment: 21 pages, 6 figures

We perform an analysis of Higgs portal models of dark matter (DM), where DM is light enough to contribute to invisible Higgs decays. Using effective field theory we show that DM can be a thermal relic only if there are additional light particles present with masses below a few 100 GeV. We give three concrete examples of viable Higgs portal models of light DM: (i) the SM extended by DM scalar along with an electroweak triplet and a singlet, (ii) a Two Higgs Doublet Model of type II with additional scalar DM, (iii) SM with DM and an extra scalar singlet that is lighter than DM. In all three examples the Br(h to invisible) constraint is not too restrictive, because it is governed by different parameters than the relic abundance. Additional light particles can have implications for flavor violation and collider searches., Comment: 31 pages, 9 figures; version as published

Light vector-like quarks with non-renormalizable couplings to the Higgs are a common feature of models trying to address the electroweak (EW) hierarchy problem by treating the Higgs as a pseudo-goldstone boson of a global (approximate) symmetry. We systematically investigate the implications of the leading dimension five operators on Higgs phenomenology in presence of dynamical up- and down-type weak singlet as well as weak doublet vector-like quarks. After taking into account constraints from precision EW and flavour observables we show that contrary to the renormalizable models, significant modifications of Higgs properties are still possible and could shed light on the role of vector-like quarks in solutions to the EW hierarchy problem. We also briefly discuss implications of higher dimensional operators for direct vector-like quark searches at the LHC., Comment: 25 pages, 5 figures; version as published