arXiv subjects

Aldo Deandrea

Publications and source records attributed to Aldo Deandrea.

At least 55 records · Page 3Linked to original sources

arXiv2020

Reinterpretation of LHC Results for New Physics: Status and Recommendations after Run 2

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.

hep-ph↗

arXiv2020

A new mechanism for symmetry breaking from nilmanifolds

We present a method to obtain a scalar potential at tree level from a pure gauge theory on nilmanifolds, a class of negatively-curved compact spaces, and discuss the spontaneous symmetry breaking mechanism induced in the residual Minkowski space after compactification at low energy. We show that the scalar potential is completely determined by the gauge symmetries and the geometry of the compact manifold. In order to allow for simple analytic calculations we consider three extra space dimensions as the minimal example of a nilmanifold, therefore considering a pure Yang-Mills theory in seven dimensions.

hep-th↗

arXiv2019

Sigma-assisted natural composite Higgs

We show that the presence of a lightish scalar resonance, $σ$, that mixes with the composite Goldstone-Higgs boson can relax the typical bounds found in this class of models. This mechanism, inbred in models with a walking dynamics above the condensation scale, allows for a low compositeness scale $f \gtrsim 400$ GeV, corresponding to a misalignment angle $\sinθ\lesssim 0.6$, contrary to the common lore of a smaller angle. According to recent lattice results, the light $σ$ emerges thanks to a near-conformal phase above the condensation scale, consistent to the requirements from flavour physics. We study this effect in a general way, showing that it appears in all cosets emerging from an underlying gauge-fermion dynamics, in the presence of top partial compositeness. The scenario is testable both on the Lattice and experimentally, as it requires the presence of a second broad Higgs-like resonance, below 1 TeV, that can be revealed at the LHC in the $ZZ$ and $t\bar{t}$ channels.

hep-ph↗

arXiv2019

Composite Higgs and Dark Matter Model in SU(6)/SO(6)

We consider a realisation of composite Higgs models in the context of $SU(6)/ SO(6)$ symmetry, which features a custodial bi-triplet, two Higgs doublets and dark matter candidates. This model can arise from an underlying gauge-fermion theory. The general vacuum structure is explored using the top partial compositeness to generate a special vacuum characterised by a single angle aligned with the first Higgs doublet. We present the CP and Dark Matter $\mathbb{Z}_2$ parity in two different pNGB bases and analyse the spectra in the absence of tadpoles and tachyons. For the phenomenology, we discuss the constraints from electroweak precision tests and from a potentially light CP-odd singlet (other than the Dark Matter) in the model.

hep-ph↗

arXiv2019

Next-to-leading-order predictions for single vector-like quark production at the LHC

We propose simulation strategies for single production of third generation vector-like quarks at the LHC, implementing next-to-leading-order corrections in QCD and studying in detail their effect on cross sections and differential distributions. We also investigate the differences and the relative incertitudes induced by the use of the Four-Flavour Number Scheme ${\it versus}$ the Five-Flavour Number Scheme. As a phenomenological illustration, we concentrate on the production of vector-like quarks coupling to the third generation of the Standard Model in association with a jet and assuming standard couplings to gauge and Higgs bosons.

hep-ph↗

arXiv2019

Vacuum misalignment and pattern of scalar masses in the SU(5)/SO(5) composite Higgs model

Composite Higgs models based on SU(5)/SO(5) are characterised by the presence of custodial triplets, like the Georgi-Machacek model. We classify all the operators giving rise to the top mass and Higgs potential in presence of fermion partial compositeness, with top partners in two-index representations of SU(5). A detailed study of each operator allows us to find correlations in the couplings of Higgs and non-Higgs pseudo-Nambu-Goldstone bosons, which depend only on one, two or three independent parameters. We also analyse the Higgs potential, finding that a misalignment along the custodial invariant triplet direction is forbidden by CP conservation. Avoiding custodial breaking allows us to select a handful of feasible models, which feature universal patterns in the scalar masses related to their transformation properties under the custodial symmetry. Finally, we briefly study the LHC phenomenology of the scalars, which are always below 1 TeV even for multi-TeV condensation scales, and find promising same-sign lepton final states enriched by hard photons.

hep-ph↗

arXiv2018

LHC constraints and potential on resonant monotop production

We discuss the phenomenology associated with a resonant monotop collider signal, i.e. a signal in which a single top quark is resonantly produced in association with missing energy through an s-channel scalar exchange. We study both the bounds originating from dedicated monotop searches performed by the ATLAS and CMS experiments, and the constraints associated with other processes that could be induced by a new physics context favouring monotop production at colliders. The latter class of constraints includes, in particular, the recasting of analyses from the LHC and the TeVatron. All theoretical calculations are performed at the next-to-leading order accuracy in QCD, and we finally combine all results to establish the present limits on the parameter space and test the relevance of the monotop signal at the LHC Run 2.

hep-ph↗

arXiv2018

The LHC potential of Vector-like quark doublets

The existence of new vector-like quarks is often predicted by models of new physics beyond the Standard Model, and the development of discovery strategies at colliders is the object of an intense effort from the high-energy community. Our analysis aims at identifying the constraints on and peculiar signatures of simplified scenarios containing \textit{two} vector-like quark doublets mixing with \textit{any} of the SM quark generations. This scenario is a necessary ingredient of a broad class of theoretically motivated constructions. We focus on the two charge $2/3$ states $t_{1,2}^\prime$ that, due to their peculiar mixing patterns, feature new production and decay modes that are not searched for at the LHC: single production of the heavier state can dominate over the light one, while pair production via electroweak interactions overcomes the QCD one for masses at the TeV scale.

hep-ph↗

arXiv2017

Unification of gauge and Yukawa couplings

The unification of gauge and top Yukawa couplings is an attractive feature of gauge-Higgs unification models in extra-dimensions. This feature is usually considered difficult to obtain based on simple group theory analyses. We reconsider a minimal toy model including the renormalisation group running at one loop. Our results show that the gauge couplings unify asymptotically at high energies, and that this may result from the presence of an UV fixed point. The Yukawa coupling in our toy model is enhanced at low energies, showing that a genuine unification of gauge and Yukawa couplings may be achieved.

hep-ph↗

arXiv2017

Probing vector-like quark models with Higgs-boson pair production

We investigate Higgs-boson pair production at the LHC when the final state system arises from decays of vector-like quarks coupling to the Higgs boson and the Standard Model quarks. Our phenomenological study includes next-to-leading-order QCD corrections, which are important to guarantee accurate predictions, and focuses on a detailed analysis of a di-Higgs signal in the four $b$-jet channel. Whereas existing Run II CMS and ATLAS analyses are not specifically designed for probing non-resonant, vector-like-quark induced, di-Higgs production, we show that they nevertheless offer some potential for these modes. We then investigate the possibility of distinguishing between the various di-Higgs production mechanisms by exploiting the kinematic properties of the signal.

hep-ph↗

arXiv2016

Search for a lighter Higgs in Two Higgs Doublet Models

We consider present constraints on Two Higgs Doublet Models, both from the LHC at Run 1 and from other sources in order to explore the possibility of constraining a neutral scalar or pseudo-scalar particle lighter than the 125 GeV Higgs boson. Such a lighter particle is not yet completely excluded by present data. We show with a simplified analysis that some new constraints could be obtained at the LHC if such a search is performed by the experimental collaborations, which we therefore encourage to continue carrying out light diphoton resonance searches at $\sqrt{s}=$ 13 TeV in the context of Two Higgs Doublet Models.

hep-ph↗

arXiv2016

Vector and Axial-vector resonances in composite models of the Higgs boson

We provide a non-linear realisation of composite Higgs models in the context of the SU(4)/Sp(4) symmetry breaking pattern, where the effective Lagrangian of the spin-0 and spin-1 resonances is constructed via the CCWZ prescription using the Hidden Symmetry formalism. We investigate the EWPT constraints by accounting the effects from reduced Higgs couplings and integrating out heavy spin-1 resonances. This theory emerges from an underlying theory of gauge interactions with fermions, thus first principle lattice results predict the massive spectrum in composite Higgs models. This model can be used as a template for the phenomenology of composite Higgs models at the LHC and at future 100 TeV colliders, as well as for other application. In this work, we focus on the formalism for spin-1 resonances and their bounds from di-lepton and di-boson searches at the LHC.

hep-ph↗

arXiv2016

Towards Kaluza-Klein Dark Matter on Nilmanifolds

We present a first study of the field spectrum on a class of negatively-curved compact spaces: nilmanifolds or twisted tori. This is a case where analytical results can be obtained, allowing to check numerical methods. We focus on the Kaluza-Klein expansion of a scalar field. The results are then applied to a toy model where a natural Dark Matter candidate arises as a stable massive state of the bulk scalar.

hep-th↗

arXiv2016

The evolution of gauge couplings and the Weinberg angle in 5 dimensions for an SU(3) gauge group

We test in a simplified 5-dimensional model with SU(3) gauge symmetry, the evolution equations of the gauge couplings of a model containing bulk fields, gauge fields and one pair of fermions. In this model we assume that the fermion doublet and two singlet fields are located at fixed points of the extra-dimension compactified on an $S^{1}/Z_{2}$ orbifold. The gauge coupling evolution is derived at one-loop in 5-dimensions, for the gauge group $G = SU(3)$, and used to test the impact on lower energy observables, in particular the Weinberg angle. The gauge bosons and the Higgs field arise from the gauge bosons in 5 dimensions, as in a gauge-Higgs model. The model is used as a testing ground as it is not a complete and realistic model for the electroweak interactions.

hep-th↗

arXiv2016

Dark matter and localised fermions from spherical orbifolds?

We study a class of six-dimensional models based on positive curvature surfaces (spherical 2-orbifolds) as extra-spaces. Using the Newman-Penrose formalism, we discuss the particle spectrum in this class of models. The fermion spectrum problem, which has been addressed with flux compactifications in the past, can be avoided using localised fermions. In this framework, we find that there are four types of geometry compatible with the existence of a stable dark matter candidate and we study the simplest case in detail. Using the complementarity between collider resonance searches and relic density constraints, we show that this class of models is under tension, unless the model lies in a funnel region characterised by a resonant Higgs s-channel in the dark matter annihilation.

hep-ph↗

arXiv2015

Composite scalars at the LHC: the Higgs, the Sextet and the Octet

We present a phenomenological theory of scalar particles that transform as a sextet and an octet of QCD interactions. These particles may arise as light bound states of a fundamental dynamics giving rise to a composite Higgs boson and partial compositeness for the top. As a concrete example, we discuss an explicit UV completion based on the SU(4)/Sp(4) coset, where QCD colour is carried by additional fundamental fermions charged under the confining gauge group. Top partners, as well as potentially even lighter coloured scalars, arise as bound states of the coloured fermions. We study production and detection at LHC Run I and II of the octet and sextet, setting lower limits on masses and couplings to Standard Model particles using existing 8 TeV analyses. We finally explore prospects for the ongoing 13 TeV Run II: we focus on final states with two same sign leptons, that have the potential to discriminate the sextet.

hep-ph↗

arXiv2015

A scalar hint from the diboson excess?

In view of the recent diboson resonant excesses reported by both ATLAS and CMS Collaborations, we suggest that a new weak singlet pseudo-scalar particle, $η_W$, may decay into two weak bosons while being produced in gluon fusion at the LHC. The couplings to the gauge bosons can arise from a Wess-Zumino-Witten anomaly term and thus we study an effective model based on the anomaly term as a well motivated phenomenological model. In models where the pseudo-scalar arises as a composite state, the coefficients of the anomalous couplings can be related to the fermion components of the underlying dynamics. We provide an example to test the feasibility of the idea.

hep-ph↗

arXiv2015

Dark Matter Benchmark Models for Early LHC Run-2 Searches: Report of the ATLAS/CMS Dark Matter Forum

This document is the final report of the ATLAS-CMS Dark Matter Forum, a forum organized by the ATLAS and CMS collaborations with the participation of experts on theories of Dark Matter, to select a minimal basis set of dark matter simplified models that should support the design of the early LHC Run-2 searches. A prioritized, compact set of benchmark models is proposed, accompanied by studies of the parameter space of these models and a repository of generator implementations. This report also addresses how to apply the Effective Field Theory formalism for collider searches and present the results of such interpretations.

hep-ex↗