Collider probes of axion-like particles Bauer, Martin; Neubert, Matthias; Thamm, Andrea
The journal of high energy physics,
12/2017, Volume:
2017, Issue:
12
Journal Article
Peer reviewed
Open access
A
bstract
Axion-like particles (ALPs), which are gauge-singlets under the Standard Model (SM), appear in many well-motivated extensions of the SM. Describing the interactions of ALPs with SM fields ...by means of an effective Lagrangian, we discuss ALP decays into SM particles at one-loop order, including for the first time a calculation of the
a
→
πππ
decay rates for ALP masses below a few GeV. We argue that, if the ALP couples to at least some SM particles with couplings of order (0.01 − 1) TeV
−1
, its mass must be above 1 MeV. Taking into account the possibility of a macroscopic ALP decay length, we show that large regions of so far unconstrained parameter space can be explored by searches for the exotic, on-shell Higgs and
Z
decays
h
→
Za
,
h
→
aa
and
Z
→
γa
in Run-2 of the LHC with an integrated luminosity of 300 fb
−1
. This includes the parameter space in which ALPs can explain the anomalous magnetic moment of the muon. Considering subsequent ALP decays into photons and charged leptons, we show that the LHC provides unprecedented sensitivity to the ALP-photon and ALP-lepton couplings in the mass region above a few MeV, even if the relevant ALP couplings are loop suppressed and the
a
→
γγ
and
a
→ ℓ
+
ℓ
−
branching ratios are significantly less than 1. We also discuss constraints on the ALP parameter space from electroweak precision tests.
Hunting all the hidden photons Bauer, Martin; Foldenauer, Patrick; Jaeckel, Joerg
The journal of high energy physics,
07/2018, Volume:
2018, Issue:
7
Journal Article
Peer reviewed
Open access
A
bstract
We explore constraints on gauge bosons of a weakly coupled U(1)
B
−
L
,
U
1
L
μ
−
L
e
,
U
1
L
e
−
L
τ
and
U
1
L
μ
−
L
τ
. To do so we apply the full constraining power of experimental ...bounds derived for a hidden photon of a secluded U(1)
X
and translate them to the considered gauge groups. In contrast to the secluded hidden photon that acquires universal couplings to charged Standard Model particles through kinetic mixing with the photon, for these gauge groups the couplings to the different Standard Model particles can vary widely. We take finite, computable loop-induced kinetic mixing effects into account, which provide additional sensitivity in a range of experiments. In addition, we collect and extend limits from neutrino experiments as well as astrophysical and cosmological observations and include new constraints from white dwarf cooling. We discuss the reach of future experiments in searching for these gauge bosons.
Axion-like particles at future colliders Bauer, Martin; Heiles, Mathias; Neubert, Matthias ...
The European physical journal. C, Particles and fields,
2019/1, Volume:
79, Issue:
1
Journal Article
Peer reviewed
Open access
Axion-like particles (ALPs) are pseudo Nambu–Goldstone bosons of spontaneously broken global symmetries in high-energy extensions of the Standard Model (SM). This makes them a prime target for future ...experiments aiming to discover new physics which addresses some of the open questions of the SM. While future high-precision experiments can discover ALPs with masses well below the GeV scale, heavier ALPs can be searched for at future high-energy lepton and hadron colliders. We discuss the reach of the different proposed colliders, focusing on resonant ALP production, ALP production in the decay of heavy SM resonances, and associate ALP production with photons,
Z
bosons or Higgs bosons. We consider the leading effective operators mediating interactions between the ALP and SM particles and discuss search strategies for ALPs decaying promptly as well as ALPs with delayed decays. Projections for the high-luminosity run of the LHC and its high-energy upgrade, CLIC, the future
e
+
e
-
ring-colliders CEPC and FCC-ee, the future
pp
colliders SPPC and FCC-hh, and for the MATHUSLA surface array are presented. We further discuss the constraining power of future measurements of electroweak precision parameters on the relevant ALP couplings.
Flavor probes of axion-like particles Bauer, Martin; Neubert, Matthias; Renner, Sophie ...
The journal of high energy physics,
09/2022, Volume:
2022, Issue:
9
Journal Article
Peer reviewed
Open access
A
bstract
Axions and axion-like particles (ALPs) are well-motivated low-energy relics of high-energy extensions of the Standard Model (SM). We investigate the phenomenology of an ALP with ...flavor-changing couplings, and present a comprehensive analysis of quark and lepton flavor-changing observables within a general ALP effective field theory. Observables studied include rare meson decays, flavor oscillations of neutral mesons, rare lepton decays, and dipole moments. We derive bounds on the general ALP couplings as a function of its mass, consistently taking into account the ALP lifetime and branching ratios. We further calculate quark flavor-changing effects that are unavoidably induced by running and matching between the new physics scale and the scale of the measurements. This allows us to derive bounds on benchmark ALP models in which only a single (flavorless or flavor-universal) ALP coupling to SM particles is present at the new physics scale, and in this context we highlight the complementarity and competitiveness of flavor bounds with constraints derived from collider, beam dump and astrophysical measurements. We find that searches for ALPs produced in meson decays provide some of the strongest constraints in the MeV-GeV mass range, even for the most flavorless of ALP models. Likewise, we discuss the interplay of flavor-conserving and flavor-violating couplings of the ALP to leptons, finding that constraints from lepton flavor-violating observables generally depend strongly on both. Additionally, we analyze whether an ALP can provide an explanation for various experimental anomalies including those observed in rare
B
-meson decays, measurements at the ATOMKI and KTeV experiments, and in the anomalous magnetic moments of the muon and the electron.
Leading academic institutions, governments, and funders of research across the world have spent the last few decades fretting publicly about the need for scientists and research organisations to ...engage more widely with the public and be open about their research. While a global literature asserts that public communication has changed from a virtue to a duty for scientists in many countries and disciplines, our knowledge about what research institutions are doing and what factors drive their 'going public' is very limited. Here we present the first cross-national study of N = 2,030 research institutes within universities and large scientific organisations in Brazil, Germany, Italy, Japan, the Netherlands, Portugal, the United Kingdom, and the United States of America. We find that institutes embrace communication with non-peers and do so through a variety of public events and traditional news media-less so through new media channels-and we find variation across countries and sciences, yet these are less evident than we expected. Country and disciplinary cultures contribute to the level of this communication, as do the resources that institutes make available for the effort; institutes with professionalised staff show higher activity online. Future research should examine whether a real change in the organisational culture is happening or whether this activity and resource allocation is merely a means to increase institutional visibility.
There is increasing interest in studying science communication from an institutional point of view. With much of the empirical research focusing on views of institutional actors on communication and ...their roles in the organisation, less attention has been paid to practices and dispositions of universities to communicate their research with publics. Universities have professionalised communication structures for external relations, and science communication has been absorbed in this. Yet, the evidence on what those practices represent for the university-at different levels of the organisation-is insufficient to understand the role of science communication within the university landscape. This study investigates science communication at central offices of research universities. Sampling whole populations of universities in four European countries (Germany, Italy, Portugal, and the United Kingdom; 44% response rate), we disentangle practices of communication as a centralised function. To the best of our knowledge, this is the first cross-national study on this topic based on all universities within the surveyed countries. We compare general trends in science communication of universities across countries. The evidence shows that science communication is a secondary function at central offices of universities, strongly medialised, and points to a supporting role for central structures in facilitating science communication at other levels while moving away from doing it themselves. Universities might need to consider their long-term positioning in enhancing national science culture by fostering science communication through models of dialogue and public debate.
A
bstract
We study a new class of renormalisable simplified models for dark matter searches at the LHC that are based on two Higgs doublet models with an additional pseudoscalar mediator. In contrast ...to the spin-0 simplified models employed in analyses of Run I data these models are self-consistent, unitary and bounds from Higgs physics typically pose no constraints. Predictions for various missing transverse energy (
E
T
,miss
) searches are discussed and the reach of the 13 TeV LHC is explored. It is found that the proposed models provide a rich spectrum of complementary observables that lead to non-trivial constraints. We emphasise in this context the sensitivity of the
t
t
¯
+
E
T
,
miss
, mono-
Z
and mono-Higgs channels, which yield stronger limits than mono-jet searches in large parts of the parameter space. Constraints from spin-0 resonance searches, electroweak precision measurements and flavour observables are also derived and shown to provide further important handles to constraint and to test the considered dark matter models.
A
bstract
Axions and axion-like particles (ALPs) are well-motivated low-energy relics of high-energy extensions of the Standard Model, which interact with the known particles through ...higher-dimensional operators suppressed by the mass scale Λ of the new-physics sector. Starting from the most general dimension-5 interactions, we discuss in detail the evolution of the ALP couplings from the new-physics scale to energies at and below the scale of electroweak symmetry breaking. We derive the relevant anomalous dimensions at two-loop order in gauge couplings and one-loop order in Yukawa interactions, carefully considering the treatment of a redundant operator involving an ALP coupling to the Higgs current. We account for one-loop (and partially two-loop) matching contributions at the weak scale, including in particular flavor-changing effects. The relations between different equivalent forms of the effective Lagrangian are discussed in detail. We also construct the effective chiral Lagrangian for an ALP interacting with photons and light pseudoscalar mesons, pointing out important differences with the corresponding Lagrangian for the QCD axion.
We present a consistent implementation of weak decays involving an axion or axionlike particle in the context of an effective chiral Lagrangian. We argue that previous treatments of such processes ...have used an incorrect representation of the flavor-changing quark currents in the chiral theory. As an application, we derive model-independent results for the decays K−→ π−a and π−→ e−¯ νea at leading order in the chiral expansion and for arbitrary axion couplings and mass. In particular, we find that the K−→ π−a branching ratio is almost 40 times larger than previously estimated.
Extensions of the Standard Model with an Abelian gauge group are constrained by gauge anomaly cancellation, so that only a limited number of possible charge assignments is allowed without the ...introduction of new chiral fermions. For flavor universal charges, couplings of the associated hidden photon to Standard Model fermions are flavor conserving at tree level. We show explicitly that even the flavor-specific charge assignments allowed by anomaly cancellation condition lead to flavor-conserving tree-level couplings of the hidden photon to quarks and charged leptons if the Cabibbo-Kobayashi-Maskawa or Pontecorvo-Maki-Nakagawa-Sakata matrix can be successfully reconstructed. Further, loop-induced flavor-changing couplings are strongly suppressed. As a consequence, the structure of the Majorana mass matrix is constrained and flavor-changing tree-level couplings of the hidden photon to neutrino mass eigenstates are identified as a means to distinguish the U ( 1 ) B−L gauge boson from any other anomaly-free extension of the Standard Model without new chiral fermions. We present a comprehensive analysis of constraints and projections for future searches for a U (1) B−3Li gauge boson, calculate the reach of resonance searches in B meson decays and comment on the implications for nonstandard neutrino interactions.
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