104 research outputs found
Reconciling EFT and hybrid calculations of the light MSSM Higgs-boson mass
Various methods are used in the literature for predicting the lightest
CP-even Higgs boson mass in the Minimal Supersymmetric Standard Model (MSSM).
Fixed-order diagrammatic calculations capture all effects at a given order and
yield accurate results for scales of supersymmetric (SUSY) particles that are
not separated too much from the weak scale. Effective field theory calculations
allow a resummation of large logarithmic contributions up to all orders and
therefore yield accurate results for a high SUSY scale. A hybrid approach,
where both methods have been combined, is implemented in the computer code
FeynHiggs. So far, however, at large scales sizeable differences have been
observed between FeynHiggs and other pure EFT codes. In this work, the various
approaches are analytically compared with each other in a simple scenario in
which all SUSY mass scales are chosen to be equal to each other. Three main
sources are identified that account for the major part of the observed
differences. Firstly, it is shown that the scheme conversion of the input
parameters that is commonly used for the comparison of fixed-order results is
not adequate for the comparison of results containing a series of higher-order
logarithms. Secondly, the treatment of higher-order terms arising from the
determination of the Higgs propagator pole is addressed. Thirdly, the effect of
different parametrizations in particular of the top Yukawa coupling in the
non-logarithmic terms is investigated. Taking into account all of these
effects, in the considered simple scenario very good agreement is found for
scales above 1 TeV between the results obtained using the EFT approach and the
hybrid approach of FeynHiggs.Comment: 31 pages, 5 figures, matches version published in EPJ
Two-loop matching of renormalizable operators: general considerations and applications
Low-energy effective field theories (EFT) encode information about the
physics at high energies--i.e., the high-energy theory (HET). To extract this
information the EFT and the HET have to be matched to each other. At the
one-loop level, general results for the matching of renormalizable operators
have already been obtained in the literature. In the present paper, we take a
step towards a better understanding of renormalizable operator matching at the
two-loop level: Focusing on the diagrammatic method, we discuss in detail the
various contributions to two-loop matching conditions and compare different
approaches to derive them. Moreover, we discuss which observables are best
suited for the derivation of matching conditions. As a concrete application, we
calculate the and matching conditions of the scalar four-point
couplings between the Standard Model (SM) and the Two-Higgs-Doublet Model
(THDM) as well as the THDM and the Minimal Supersymmetric Standard Model
(MSSM). We use the derived formulas to improve the prediction of the SM-like
Higgs mass in the MSSM using the THDM as EFT.Comment: 42 pages, 4 figures, 4 ancillary files; matches version published in
JHE
The forgotten channels: charged Higgs boson decays to a and a non-SM-like Higgs boson
The presence of charged Higgs bosons is a generic prediction of multiplet
extensions of the Standard Model (SM) Higgs sector. Focusing on the
Two-Higgs-Doublet-Model (2HDM), we discuss the charged Higgs boson collider
phenomenology in the theoretically and experimentally viable parameter space.
While almost all existing experimental searches at the LHC target the fermionic
decays of charged Higgs bosons, we point out that the bosonic decay channels --
especially the decay into a non-SM-like Higgs boson and a boson -- often
dominate over the fermionic channels. Moreover, we revisit two genuine BSM
effects on the properties of the discovered Higgs boson -- the charged Higgs
contribution to the diphoton rate and the Higgs decay to two light Higgs bosons
-- and their implication for the charged Higgs boson phenomenology. As main
result of the present paper, we propose five two-dimensional benchmark
scenarios with distinct phenomenological features in order to facilitate the
design of dedicated LHC searches for charged Higgs bosons decaying into a
boson and a light, non-SM-like Higgs boson.Comment: 57 pages, 26 figures, data tables for cross sections and benchmark
scenarios included as ancillary files, updated text to match journal versio
External-leg corrections as an origin of large logarithms
Obtaining precise theoretical predictions for both production and decay
processes of heavy new particles is of great importance to constrain the
allowed parameter spaces of Beyond-the-Standard-Model (BSM) theories, and to
properly assess the sensitivity for discoveries and for discriminating between
different possible BSM scenarios. In this context, it is well known that large
logarithmic corrections can appear in the presence of widely separated mass
scales. We point out the existence of a new type of possible large,
Sudakov-like, logarithms in external-leg corrections of heavy scalars. To the
difference of usual Sudakov logarithms, these can furthermore potentially be
enhanced by large trilinear couplings. Such large logarithms are associated
with infrared singularities and we review several techniques to address these
at one loop. In addition to this discussion, we also present the derivation of
the two-loop corrections containing this type of large logarithms, pointing out
in this context the importance of adopting an on-shell renormalisation scheme.
Finally, we illustrate our calculations and examine the possible magnitude of
these corrections for a simple scalar toy model as well as for decay processes
involving heavy stop quarks in the Minimal Supersymmetric Standard Model and a
heavy Higgs boson in the Next-to-Two-Higgs-Doublet Model.Comment: 8 pages, 2 figures. Contribution to the proceedings of the conference
"Loops and Legs in Quantum Field Theory - LL2022," 25-30 April, 2022, Ettal,
German
Experimental probes and theoretical concepts for BSM trilinear couplings: a case study for scalar top quarks
After the possible discovery of new particles, it will be crucial to
determine the properties, and in particular the couplings, of the new states.
Here, we focus on scalar trilinear couplings, employing as an example the case
of the trilinear coupling of scalar top quarks (stops) to the Higgs boson in
the Minimal Supersymmetric Standard Model (MSSM). We discuss possible
strategies for experimentally determining the stop trilinear coupling
parameter, which controls the stop--stop--Higgs interaction, and we demonstrate
the impact of different prescriptions for the renormalisation of this
parameter. We find that the best prospects for determining the stop trilinear
coupling arise from its quantum effects entering the model prediction for the
mass of the SM-like Higgs boson in comparison to the measured value, pointing
out that the prediction for the Higgs-boson mass has a high sensitivity to the
stop trilinear coupling even for heavy masses of the non-standard particles.
Regarding the renormalisation of the stop trilinear coupling, we identify a
renormalisation scheme that is preferred given the present level of accuracy,
and we clarify the origin of potentially large logarithms that cannot be
resummed with standard renormalisation group methods.Comment: 6 pages, 2 figures. Contribution to the proceedings of the European
Physical Society Conference on High Energy Physics (EPS-HEP2023), 21-25
August 2023, Hamburg, German
New constraints on extended scalar sectors from the trilinear Higgs coupling
The trilinear Higgs coupling is a crucial tool to probe the
structure of the Higgs potential and to search for possible effects of physics
beyond the Standard Model (SM). Focusing on the Two-Higgs-Doublet Model as a
concrete example, we identify parameter regions in which is
significantly enhanced with respect to its SM prediction. Taking into account
all relevant corrections up to the two-loop level, we show that current
experimental bounds on already rule out significant parts of
the otherwise unconstrained parameter space. We illustrate the interpretation
of the current results and future measurement prospects on for
a benchmark scenario. Recent results from direct searches for BSM scalars in
the channel and their implications will also be discussed in this
context.Comment: 6 pages, 2 figures. Contribution to the proceedings of the European
Physical Society Conference on High Energy Physics (EPS-HEP2023), 21-25
August 2023, Hamburg, German
Topportunities at the LHC: Rare Top Decays with Light Singlets
The discovery of the top quark, the most massive elementary particle yet
known, has given us a distinct window into investigating the physics of the
Standard Model and Beyond. With a plethora of top quarks to be produced in the
High Luminosity era of the LHC, the exploration of its rare decays holds great
promise in revealing potential new physics phenomena. We consider
higher-dimensional operators contributing to top decays in the SMEFT and its
extension by a light singlet species of spin 0, 1/2, or 1, and exhibit that the
HL-LHC may observe many exotic top decays in a variety of channels. Light
singlets which primarily talk to the SM through such a top interaction may also
lead to distinctive long-lived particle signals. Searching for such long-lived
particles in top-quark decays has the additional advantage that the SM decay of
the other top quark in the same event provides a natural trigger.Comment: 26 pages, 9 figures, 1 tabl
Classifying the CP properties of the ggH coupling in H+2j production
The Higgs-gluon interaction is crucial for LHC phenomenology. To improve the
constraints on the CP structure of this coupling, we investigate Higgs
production with two jets using machine learning. In particular, we exploit the
CP sensitivity of the so far neglected phase space region that differs from the
typical vector boson fusion-like kinematics. Our results suggest that
significant improvements in current experimental limits are possible. We also
discuss the most relevant observables and how CP violation in the Higgs-gluon
interaction can be disentangled from CP violation in the interaction between
the Higgs boson and massive vector bosons. Assuming the absence of CP-violating
Higgs interactions with coloured beyond-the-Standard-Model states, our
projected limits on a CP-violating top-Yukawa coupling are stronger than more
direct probes like top-associated Higgs production and limits from a global
fit.Comment: 41 pages, 18 figure
Precise predictions for the trilinear Higgs self-coupling in the Standard Model and beyond
Deviations in the trilinear self-coupling of the Higgs boson at 125 GeV from
the Standard Model (SM) prediction are a sensitive test of physics Beyond the
SM (BSM). The LHC experiments searching for the simultaneous production of two
Higgs bosons start to become sensitive to such deviations. Therefore, precise
predictions for the trilinear Higgs self-coupling in different BSM models are
required in order to be able to test them against current and future bounds. We
present the new framework , which is a
library that can be utilized to obtain predictions for trilinear scalar
couplings up to the one-loop level in any renormalisable theory. The program
makes use of the format as input and is able to automatically
apply a wide variety of renormalisation schemes involving minimal and
non-minimal subtraction conditions. External-leg corrections are also computed
automatically, and finite external momenta can be optionally taken into
account. The library comes with convenient command-line as
well as user interfaces. We perform cross-checks using
consistency conditions such as UV-finiteness and decoupling, and also by
comparing against results know in the literature. As example applications, we
obtain results for the trilinear self-coupling of the SM-like Higgs boson in
various concrete BSM models, study the effect of external momenta as well as of
different renormalisation schemes.Comment: 6 pages, The European Physical Society Conference on High Energy
Physics (EPS-HEP2023
Testing Exotic Scalars with HiggsBounds
The program HiggsBounds is a well-established tool for testing
Beyond-the-Standard Model (BSM) theories with an extended Higgs sector against
experimental limits from collider searches at LEP, Tevatron and LHC. Thus far,
it could be applied to any neutral or charged Higgs bosons originating from the
modified Higgs sector. Implicitly, these particles were assumed to exhibit a
somewhat hierarchical Yukawa structure as present in the Standard Model, where
in particular the couplings to first generation fermions could be neglected. In
this work, we extend the HiggsBounds functionalities to go beyond these
restrictions, thus making the code applicable to any neutral or charged BSM
scalars. Moreover, we develop a new approach to implement experimental searches
whose kinematic acceptance depends significantly on the values of the involved
couplings. We achieve this by recasting the searches to general scalar models.
Using this approach we incorporate relevant current experimental limits from
LHC searches for exotic scalars, and present the implications of these limits
for a dark matter scalar mediator model, a flipped Two-Higgs-Doublet Model and
a supersymmetric model with R-parity violation.Comment: 28 pages, 7 figures, the FeynRules implementation of the generic
scalar model is included as an ancillary file; v2: matches version published
in EPJ
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