A
bstract
We demonstrate that the inclusion of a realistic lepton sector can relax significantly the upper bound on top partner masses in minimal composite Higgs models, induced by the lightness of ...the Higgs boson. To that extend, we present a comprehensive survey of the impact of different realizations of the fermion sectors on the Higgs potential, with a special emphasis on the role of the leptons. The non-negligible compositeness of the
τ
R
in a general class of models that address the flavor structure of the lepton sector and the smallness of the corresponding FCNCs, can have a significant effect on the potential. We find that, with the
τ
R
in the symmetric representation of SO(5), an increase in the maximally allowed mass of the lightest top partner of ≳ 1 TeV is possible for minimal quark setups like the MCHM
5,10
, without increasing the tuning. A light Higgs boson
m
H
∼ (100−200) GeV is a natural prediction of such models, which thus provide a new setup that can evade ultralight top partners without ad-hoc tuning in the Higgs mass. Moreover, we advocate a more minimal realization of the lepton sector than generally used in the literature, which still can avoid light partners due to its contributions to the Higgs mass in a different and very natural way, triggered by the seesaw mechanism. This allows to construct the most economical SO(5)
/
SO(4) composite Higgs models possible. Using both a transparent 4D approach, as well as presenting numerical results in the 5D holographic description, we demonstrate that, including leptons, minimality and naturalness do not imply light partners. Leptonic effects, not considered before, could hence be crucial for the viability of composite models.
Exceptional composite dark matter Ballesteros, Guillermo; Carmona, Adrián; Chala, Mikael
The European physical journal. C, Particles and fields,
07/2017, Volume:
77, Issue:
7
Journal Article
Peer reviewed
Open access
We study the dark matter phenomenology of non-minimal composite Higgs models with
SO
(7) broken to the exceptional group
G
2
. In addition to the Higgs, three pseudo-Nambu–Goldstone bosons arise, one ...of which is electrically neutral. A parity symmetry is enough to ensure this resonance is stable. In fact, if the breaking of the Goldstone symmetry is driven by the fermion sector, this
Z
2
symmetry is automatically unbroken in the electroweak phase. In this case, the relic density, as well as the expected indirect, direct and collider signals are then uniquely determined by the value of the compositeness scale,
f
. Current experimental bounds allow one to account for a large fraction of the dark matter of the Universe if the dark matter particle is part of an electroweak triplet. The totality of the relic abundance can be accommodated if instead this particle is a composite singlet. In both cases, the scale
f
and the dark matter mass are of the order of a few TeV.
Charming ALPs Carmona, Adrian; Scherb, Christiane; Schwaller, Pedro
The journal of high energy physics,
08/2021, Volume:
2021, Issue:
8
Journal Article
Peer reviewed
Open access
A
bstract
Axion-like particles (ALPs) are ubiquitous in models of new physics explaining some of the most pressing puzzles of the Standard Model. However, until relatively recently, little attention ...has been paid to its interplay with flavour. In this work, we study in detail the phenomenology of ALPs that exclusively interact with up-type quarks at the tree-level, which arise in some well-motivated ultra-violet completions such as QCD-like dark sectors or Froggatt-Nielsen type models of flavour. Our study is performed in the low-energy effective theory to highlight the key features of these scenarios in a model independent way. We derive all the existing constraints on these models and demonstrate how upcoming experiments at fixed-target facilities and the LHC can probe regions of the parameter space which are currently not excluded by cosmological and astrophysical bounds. We also emphasize how a future measurement of the currently unavailable meson decay
D
→
π
+ invisible could complement these upcoming searches.
A
bstract
We propose a search for long lived axion-like particles (ALPs) in exotic top decays. Flavour-violating ALPs appear as low energy effective theories for various new physics scenarios such as ...t-channel dark sectors or Froggatt-Nielsen models. In this case the top quark may decay to an ALP and an up- or charm-quark. For masses in the few GeV range, the ALP is long lived across most of the viable parameter space, suggesting a dedicated search. We propose to search for these long lived ALPs in
t
t
¯
events, using one top quark as a trigger. We focus on ALPs decaying in the hadronic calorimeter, and show that the ratio of energy deposits in the electromagnetic and hadronic calorimeters as well as track vetoes can efficiently suppress Standard Model backgrounds. Our proposed search can probe exotic top branching ratios smaller than 10
−
4
with a conservative strategy at the upcoming LHC run, and potentially below the 10
−
7
level with more advanced methods. Finally we also show that measurements of single top production probe these branching ratios in the very short and very long lifetime limit at the 10
−
3
level.
We consider the associated production of a scalar resonance with the standard model Higgs boson. We demonstrate via a realistic phenomenological analysis that couplings of such a resonance to the ...Higgs boson can be constrained in a meaningful way in future runs of the LHC, providing insights on its origin and its relation to the electroweak symmetry breaking sector. Moreover, the final state can provide a direct way to determine whether the new resonance is produced predominantly in gluon fusion or quark-antiquark annihilation. The analysis focuses on a resonance coming from a scalar field with vanishing vacuum expectation value and its decay to a photon pair. It can, however, be straightforwardly generalized to other scenarios.
A clockwork solution to the flavor puzzle Alonso, Rodrigo; Carmona, Adrian; Dillon, Barry M. ...
The journal of high energy physics,
10/2018, Volume:
2018, Issue:
10
Journal Article
Peer reviewed
Open access
A
bstract
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
clockworked
version, and with the Randall-Sundrum models.
A warped scalar portal to fermionic dark matter Carmona, Adrian; Castellano Ruiz, Javier; Neubert, Matthias
The European physical journal. C, Particles and fields,
2021/1, Volume:
81, Issue:
1
Journal Article
Peer reviewed
Open access
We argue that extensions of the SM with a warped extra dimension, together with a new
Z
2
-odd scalar singlet, provide a natural explanation not only for the hierarchy problem but also for the nature ...of fermion bulk masses and the observed dark matter relic abundance. In particular, the Kaluza-Klein excitations of the new scalar particle, which is required to naturally obtain fermion bulk masses through Yukawa-like interactions, can be the leading portal to any fermion propagating into the bulk of the extra dimension and playing the role of dark matter. Moreover, such scalar excitations will necessarily mix with the Higgs boson, leading to modifications of the Higgs couplings and branching ratios, and allowing the Higgs to mediate the coannihilation of the fermionic dark matter. We study these effects and explore the viability of fermionic dark matter in the presence of these new heavy scalar mediators both in the usual freeze-out scenario and in the case where the freeze-out happens during an early period of matter domination.
A
bstract
Extensions of the Standard Model featuring a warped extra dimension compactified on an
S
1
/ℤ
2
orbifold, in which the fermions and gauge bosons live in the bulk of the fifth dimension, ...offer one of the most compelling mechanisms for addressing both the hierarchy problem and the flavor puzzle of the Standard Model. However, the five-dimensional mass terms of bulk fermions must be odd functions on the orbifold, and as such they should be described by a field depending on the coordinate of the extra dimension. We demonstrate the feasibility of dynamically generating these fermion bulk masses with a bulk scalar field in warped extra dimensions. The bulk scalar acquires a vacuum expectation value, which is odd under the orbifold symmetry and gives rise to the fermion bulk masses through non-universal Yukawa-like interactions. Like in the conventional Randall-Sundrum setup, the localization of the different fermion zero modes along the extra dimension naturally explains the observed flavor structure and four-dimensional mass hierarchy of the SM fermions. We study the phenomenological implications of the backreaction on the metric and the modified fermion profiles due to the bulk scalar field on electroweak precision and flavor observables. Using up-to-date data, we show that the contributions to the
S
,
T
, and
ϵ
K
parameters require the mass of the first Kaluza-Klein gluon resonance to be of order 14 and 10 TeV in the minimal and the custodial model, respectively, regardless of the effect of the backreaction. Furthermore, effective flavor-changing interactions among the SM fermions induced by the bulk scalar are discussed. We also comment on the potential impact of the Higgs portal interaction of the bulk scalar on the couplings of the Higgs boson.
We present a new class of models of lepton flavor in the composite Higgs framework. Following the concept of minimality, they lead to a rich phenomenology in good agreement with the current ...experimental picture. Because of a unification of the right-handed leptons, our scenario is very predictive and can naturally lead to a violation of lepton-flavor universality in neutral current interactions. We will show that, in particular, the anomaly in R_{K}=B(B→Kμ^{+}μ^{-})/B(B→Ke^{+}e^{-}), found by LHCb, can be addressed, while other constraints from quark- and lepton-flavor physics are met. In fact, the minimal structure of the setup allows for the implementation of a very powerful flavor protection, which avoids the appearance of new sources of flavor-changing neutral currents to very good approximation. Finally, the new lepton sector provides a parametrically enhanced correction to the Higgs mass, such that the need for ultralight top partners is weakened considerably, linking the mass of the latter with the size of the neutrino masses.
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