25 research outputs found
Phenomenology of the Higgs sectors of the uvSSM and the N2HDM
Tesis Doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Ciencias, Departamento de Física Teórica. Fecha de Lectura: 05-09-201
2HDM interpretations of the CMS diphoton excess at 95 GeV
In both Run 1 and Run 2 of the LHC, the CMS collaboration has observed an
excess of events in the searches for low-mass Higgs bosons in the diphoton
final state at a mass of about 95 GeV. After a recent update of the
experimental analysis, in which the full Run 2 data collected at 13 TeV has
been included and an improved experimental calibration has been applied, the
local significance of the excess amounts to . The presence of this
diphoton excess is especially interesting in view of a further excess observed
by CMS in ditau final states at a comparable mass and similar local
significance. Moreover, an excess of events with about local
significance and consistent with a mass of 95 GeV was observed in LEP searches
for a Higgs boson decaying to pairs of bottom quarks. We interpret the CMS
diphoton excess in combination with the ditau excess in terms of a pseudoscalar
resonance in the CP-conserving two-Higgs-doublet model (2HDM). Furthermore, we
discuss the possibility that, if CP-violation is taken into account, a CP-mixed
scalar state can in addition describe the LEP result, thus accommodating all
three excesses simultaneously. We find that the region of parameter space where
both the CMS diphoton and ditau excesses can be fitted is in tension with
current constraints from the flavour sector, potentially calling for other
new-physics contributions to flavour-physics observables, most notably transitions. We also comment on the compatibility with the recent
ATLAS di-photon searches.Comment: 37 pages, 13 figure
Direct detection of pseudo-Nambu-Goldstone dark matter in a two Higgs doublet plus singlet extension of the SM
We calculate the leading radiative corrections to the dark-matter-nucleon
scattering in the pseudo-Nambu-Goldstone dark matter model augmented with a
second Higgs doublet (S2HDM). In this model, the cross sections for the
scattering of the dark-matter on nuclei vanishes at tree-level in the limit of
zero momentum-transfer due to a U(1) symmetry. However, this symmetry is softly
broken in order to give a mass to the dark-matter particle. As a consequence,
non-vanishing scattering cross sections arise at the loop level. We find that
the current cross-section limits from dark-matter direct-detection experiments
can hardly constrain the parameter space of the S2HDM. However, the
loop-corrected predictions for the scattering cross sections can be well within
the reach of future direct-detection experiments. As a consequence, future
phenomenological analyses of the S2HDM should take into account cross-section
predictions beyond tree-level and the experimental constraints from dark-matter
direct-detection experiments.Comment: 27 pages, 9 figure
Complementarity of Resonant Scalar, Vector-Like Quark and Superpartner Searches in Elucidating New Phenomena
The elucidation of the nature of new phenomena requires a multi-pronged
approach to understand the essential physics that underlies it. As an example,
we study the simplified model containing a new scalar singlet accompanied by
vector-like quarks, as motivated by the recent diphoton excess at the LHC. To
be specific, we investigate three models with -doublet, vector-like
quarks with Yukawa couplings to a new scalar singlet and which also couple
off-diagonally to corresponding Standard Model fermions of the first or third
generation through the usual Higgs boson. We demonstrate that three classes of
searches can play important and complementary roles in constraining this model.
In particular, we find that missing energy searches designed for superparticle
production, supply superior sensitivity for vector-like quarks than the
dedicated new quark searches themselves.Comment: References added; small bug found in model and analysis
implementation, numerical results slightly modified, conclusions unchange
Fate of electroweak symmetry in the early Universe: Non-restoration and trapped vacua in the N2HDM
Extensions of the Higgs sector of the Standard Model allow for a rich
cosmological history around the electroweak scale. We show that besides the
possibility of strong first-order phase transitions, which have been thoroughly
studied in the literature, also other important phenomena can occur, like the
non-restoration of the electroweak symmetry or the existence of vacua in which
the Universe becomes trapped, preventing a transition to the electroweak
minimum. Focusing on the next-to-minimal two-Higgs-doublet model (N2HDM) of
type II and taking into account the existing theoretical and experimental
constraints, we identify the scenarios of electroweak symmetry non-restoration,
vacuum trapping and first-order phase transition in the thermal history of the
Universe. We analyze these phenomena and in particular their relation to each
other, and discuss their connection to the predicted phenomenology of the N2HDM
at the LHC. Our analysis demonstrates that the presence of a global electroweak
minimum of the scalar potential at zero temperature does not guarantee that the
corresponding N2HDM parameter space will be physically viable: the existence of
a critical temperature at which the electroweak phase becomes the deepest
minimum is not sufficient for a transition to take place, necessitating an
analysis of the tunnelling probability to the electroweak minimum for a
reliable prediction of the thermal history of the Universe.Comment: 44 pages, 10 figures. Final version published in JCA
The trap in the early Universe: impact on the interplay between gravitational waves and LHC physics in the 2HDM
We analyze the thermal history of the 2HDM and determine the parameter
regions featuring a first-order electroweak phase transition (FOEWPT) and also
much less studied phenomena like high-temperature electroweak (EW) symmetry
non-restoration and the possibility of vacuum trapping (i.e. the Universe
remains trapped in an EW-symmetric vacuum throughout the cosmological
evolution, despite at the EW breaking vacuum is deeper). We show that the
presence of vacuum trapping impedes a first-order EW phase transition in 2HDM
parameter-space regions previously considered suitable for the realization of
electroweak baryogenesis. Focusing then on the regions that do feature such a
first-order transition, we show that the 2HDM parameter space that would yield
a stochastic gravitational wave signal potentially detectable by the future
LISA observatory is very contrived, and will be well probed by direct searches
of 2HDM Higgs bosons at the HL-LHC, and (possibly) also via measurements of the
self-coupling of the Higgs boson at 125 GeV. This has an important impact on
the interplay between LISA and the LHC regarding the exploration of first-order
phase transition scenarios in the 2HDM: the absence of new physics indications
at the HL-LHC would severely limit the prospects of a detection by LISA.
Finally, we demonstrate that as a consequence of the predicted enhancement of
the self-coupling of the Higgs boson at 125 GeV the ILC would be able to probe
the majority of the 2HDM parameter space yielding a FOEWPT through measurements
of the self-coupling, with a large improvement in precision with respect to the
HL-LHC.Comment: 41 pages, 13 figure