Jernej F. Kamenik, Manuel Szewc
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.
Cédric Delaunay, Jernej F. Kamenik, Gilad Perez, Lisa Randall
Recently the LHCb collaboration reported evidence for direct CP violation in charm decays. The value is sufficiently large that either substantially enhanced Standard Model contributions or non-Standard Model physics is required to explain it. In the latter case only a limited number of possibilities would be consistent with other existing flavor-changing constraints. We show that warped extra dimensional models that explain the quark spectrum through flavor anarchy can naturally give rise to contributions of the size required to explain the the LHCb result. The D meson asymmetry arises through a sizable CP-violating contribution to a chromomagnetic dipole operator. This happens naturally without introducing inconsistencies with existing constraints in the up quark sector. We discuss some subtleties in the loop calculation that are similar to those in Higgs to γγ. Loop-induced dipole operators in warped scenarios and their composite analogs exhibit non-trivial dependence on the Higgs profile, with the contributions monotonically decreasing when the Higgs is pushed away from the IR brane. We show that the size of the dipole operator quickly saturates as the Higgs profile approaches the IR brane, implying small dependence on the precise details of the Higgs profile when it is quasi IR localized. We also explain why the calculation of the coefficient of the lowest dimension 5D operator is guaranteed to be finite. This is true not only in the charm sector but also with other radiative processes such as electric dipole moments, b to sγ, ε'/ε_K and μ to eγ. We furthermore discuss the interpretation of this contribution within the framework of partial compositeness in four dimensions and highlight some qualitative differences between the generic result of composite models and that obtained for dynamics that reproduces the warped scenario.
Ezequiel Alvarez, Leandro Da Rold, Mariel Estevez, Jernej F. Kamenik
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.
Ilja Dorsner, Svjetlana Fajfer, Admir Greljo, Jernej F. Kamenik, Nejc Kosnik, Ivan Nisandzic
We speculate about the possible interpretations of the recently observed excess in the $h \to τμ$ 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 $τ\to μγ$ 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 $h \to τμ$ signal, the current and future searches for $μ\to e γ$ and $μ\to e$ nuclear conversions unambiguously constrain the allowed rates for $h \to τe$.
Jernej F. Kamenik
The effective theory based on combined chiral and heavy quark symmetry, the heavy meson chiral perturbation theory, is applied to studying the role of resonances in various processes of heavy mesons within and beyond the Standard Model. Chiral corrections including both positive and negative parity heavy meson doublets are calculated to the effective strong couplings featuring in the effective theory leading order interaction Lagrangian, to the Isgur-Wise functions in semileptonic B to D decays and to the complete set of supersymmetric four-quark operators mediating heavy neutral meson mixing. Bare values of the effective strong couplings are extracted from the measured decay widths of charmed resonances. Chiral behavior of the couplings, Isgur-Wise functions and heavy meson bag parameters is studied in the leading logarithmic approximation. In semileptonic heavy to light decays we determine resonance contributions to the various form factors within an effective theory inspired model at zero recoil. We employ a form factor parameterization based on effective theory limits to extrapolate our results to the whole kinematical region in charm decays. We compare our results with experimental data and lattice calculations. Very rare nonleptonic decays of the B_c meson are studied within the Standard Model where they are mediated by box loop diagrams, and within a number of Standard Model extensions. Based on existing experimental searches for related B meson decays, limits are imposed on some of the models studied. The most promissing nonleptonic two- and three-body decay channels of the B_c meson in the search for such new physics contributions are identified.
Luca Di Luzio, Ramona Grober, Jernej F. Kamenik, Marco Nardecchia
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.
Jernej F. Kamenik, Jure Zupan
We show that the discovery channel for dark matter (DM) production at colliders can be through flavor violating interactions resulting in a novel signature of a single top and large missing transverse energy. We discuss several examples where the production of DM is dominated by flavor violating couplings: minimal flavor violating models with a large bottom Yukawa, models with horizontal symmetries, and DM in nontrivial flavor group representations. Discovery at the 7 TeV LHC with a few fb^-1 may already be possible.
Jernej F. Kamenik, Christopher Smith
The most general basis of operators parametrizing a low-scale departure from the SM particle content is constructed. The SM gauge invariance is enforced, and operators of lowest dimensions are retained separately for a new light neutral particle of spin 0, 1/2, 1, and 3/2. The basis is further decomposed into couplings to the SM Higgs/gauge fields, to pairs of quark/lepton fields, and to baryon/lepton number violating combinations of fermion fields. This basis is then used to systematically investigate the discovery potential of the rare FCNC decays of the K and B mesons with missing energy in the final state. The most sensitive decay modes in the s to d, b to d, and b to s sectors are identified and compared for each type of couplings to the new invisible state.
Ezequiel Alvarez, Darius A. Faroughy, Jernej F. Kamenik, Roberto Morales, Alejandro Szynkman
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.
Darius A. Faroughy, Jernej F. Kamenik, Manuel Szewc, Jure Zupan
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 $|V_{td}|^2+|V_{ts}|^2$.
Luca Di Luzio, Ramona Grober, Jernej F. Kamenik, Marco Nardecchia
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.
Fady Bishara, Admir Greljo, Jernej F. Kamenik, Emmanuel Stamou, Jure Zupan
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.
Blaž Bortolato, Jernej F. Kamenik, Michele Tammaro
Apr 21, 2023·astro-ph.HE·PDF 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.
Diego Aristizabal Sierra, Audrey Degee, Jernej F. Kamenik
We study the implications of the global U(1)R symmetry present in minimal lepton flavor violating implementations of the seesaw mechanism for neutrino masses. In the context of minimal type I seesaw scenarios with a slightly broken U(1)R, we show that, depending on the R-charge assignments, two classes of generic models can be identified. Models where the right-handed neutrino masses and the lepton number breaking scale are decoupled, and models where the parameters that slightly break the U(1)R induce a suppression in the light neutrino mass matrix. We show that within the first class of models, contributions of right-handed neutrinos to charged lepton flavor violating processes are severely suppressed. Within the second class of models we study the charged lepton flavor violating phenomenology in detail, focusing on mu to e gamma, mu to 3e and mu to e conversion in nuclei. We show that sizable contributions to these processes are naturally obtained for right-handed neutrino masses at the TeV scale. We then discuss the interplay with the effects of the right-handed neutrino interactions on primordial B - L asymmetries, finding that sizable right-handed neutrino contributions to charged lepton flavor violating processes are incompatible with the requirement of generating (or even preserving preexisting) B - L asymmetries consistent with the observed baryon asymmetry of the Universe.
Ilja Dorsner, Svjetlana Fajfer, Admir Greljo, Jernej F. Kamenik
We consider the impact of colored scalars that can couple directly to matter fields on the recently measured h to gamma gamma excess. Among all possible candidates only scalar states transforming as (8, 2,1/2) and (6,3,1/3) under the Standard Model gauge group can individually accommodate the excess and remain in agreement with all available data. Current experimental constraints require such colored states to have an order one coupling to the Standard Model Higgs and a mass below 300 GeV. We use the best fit values to predict the correlated effect in h to Z gamma and di-Higgs production. We furthermore discuss where and how these states appear in extensions of the Standard Model with primary focus on scenarios of matter unification. We revisit two simple SU(5) setups to show that these two full-fledged models not only accommodate a light color octet state but correlate its mass with observable partial proton decay lifetimes.
Admir Greljo, J. Julio, Jernej F. Kamenik, Christopher Smith, Jure Zupan
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.
Svjetlana Fajfer, Jernej F. Kamenik, Ivan Nisandzic, Jure Zupan
Present measurements of b->c tau nu and b->u tau nu transitions differ from the standard model predictions of lepton flavor universality by almost 4sigma. We examine new physics interpretations of this anomaly. An effective field theory analysis shows that minimal flavor violating models are not preferred as an explanation, but are also not yet excluded. Allowing for general flavor violation, right-right vector and right-left scalar quark currents are identified as viable candidates. We discuss explicit examples of two Higgs doublet models, leptoquarks as well as quark and lepton compositeness. Finally, implications for LHC searches and future measurements at the (super)B- factories are presented.
Darius A. Faroughy, Admir Greljo, Jernej F. Kamenik
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 $τ^+ τ^-$ 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, $τ^+ τ^-$ 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 $τ^+ τ^-$ constraints as well as caveats in interpreting them within more elaborate models are also discussed.
Alexander L. Kagan, Jernej F. Kamenik, Gilad Perez, Sheldon Stone
We suggest that top physics can be studied at the LHCb experiment, and that top production could be observed. Since LHCb covers a large pseudorapidity region in the forward direction, it has unique abilities to probe new physics in the top sector. Furthermore, we demonstrate that LHCb may be able to measure a t\bar t production rate asymmetry, and thus indirectly probe an anomalous forward backward t\bar t asymmetry in the forward region; a possibility suggested by the enhanced forward-backward asymmetry reported by the CDF experiment.
Jernej F. Kamenik, Michele Papucci, Andreas Weiler
We investigate the direct and indirect bounds on dipole operators involving the top quark. A careful analysis shows that the experimental upper limit on the neutron electric dipole moment strongly constrains the chromo-electric dipole of the top. We improve previous bounds by two orders of magnitude. This has significant implications for new physics models and it also means that CP violation in top pair production mediated by dipole operators will not be accessible at the LHC. The CP conserving chromo-magnetic dipole moments are constrained by recent measurements of the t\bar t spectrum by the ATLAS collaboration. We also update the indirect constraints on electric and magnetic dipole moments from radiative b -> s transitions, finding that they can be considerably larger than their colored counterparts.