65 research outputs found
Interference Effects in the Decays of Spin-Zero Resonances into and
We consider interference effects in the production via gluon fusion in LHC
collisions at 13 TeV and decays into and final
states of one or two putative new resonant states , assumed here to be
scalar and/or pseudo scalar particles. Although our approach is general, we use
for our numerical analysis the example of the putative GeV state for
which a slight excess was observed in the initial LHC TeV data. We revisit
previous calculations of the interferences between the heavy-fermion
loop-induced signal and the continuum QCD background, which can alter the production rate as well as
modify the line-shape and apparent mass. We find a modest enhancement by % under favorable circumstances, for a large width. The effect of
interference on the apparent scalar-pseudoscalar mass difference in a
two-Higgs-doublet model is found to be also modest. An exploratory study
indicates that similar effects are to be expected in the channel. In this and other models with a large total width, the
dominant decays are expected to be into final states. We
therefore also study the effects of interference of the signal with the continuum QCD background and show that in
the presence of standard fermions only in the loops, it is
destructive causing a dip in the mass distribution. Including
additional vector-like quarks leads to a different picture as peaks followed by
dips can then occur. We use the absence of such effects in ATLAS and CMS data
to constrain models of the production and decays of the state(s).Comment: 31 pages, v2 contains additional comment
Prospects for Higgs physics at energies up to 100 TeV
We summarise the prospects for Higgs boson physics at future proton-proton
colliders with centre of mass (c.m.) energies up to 100 TeV. We first provide
the production cross sections for the Higgs boson of the Standard Model from 13
TeV to 100 TeV, in the main production mechanisms and in subleading but
important ones such as double Higgs production, triple production and
associated production with two gauge bosons or with a single top quark. We then
discuss the production of Higgs particles in beyond the Standard Model
scenarios, starting with the one in the continuum of a pair of scalar,
fermionic and vector dark matter particles in Higgs-portal models in various
channels with virtual Higgs exchange. The cross sections for the production of
the heavier CP-even and CP-odd neutral Higgs states and the charged Higgs
states in two-Higgs doublet models, with a specific study of the case of the
Minimal Supersymmetric Standard Model, are then given. The sensitivity of a 100
TeV proton machine to probe the new Higgs states is discussed and compared to
that of the LHC with a c.m. energy of 14 TeV and at high luminosity.Comment: 61 pages, 16 figures, 6 tables; review article. v2: numbers and
figures updated, aknowledgments modified, references added and typos
corrected. Matches the published versio
Future Collider Signatures of the Possible 750 GeV State
If the recent indications of a possible state with mass GeV
decaying into two photons reported by ATLAS and CMS in LHC collisions at 13 TeV
were to become confirmed, the prospects for future collider physics at the LHC
and beyond would be affected radically, as we explore in this paper. Even
minimal scenarios for the resonance and its decays
require additional particles with masses . We consider
here two benchmark scenarios that exemplify the range of possibilities: one in
which is a singlet scalar or pseudoscalar boson whose production and
decays are due to loops of coloured and charged fermions, and
another benchmark scenario in which is a superposition of (nearly)
degenerate CP-even and CP-odd Higgs bosons in a (possibly supersymmetric)
two-Higgs doublet model also with additional fermions to account for the
decay rate. We explore the implications of these benchmark
scenarios for the production of and its new partners at colliders in
future runs of the LHC and beyond, at higher-energy colliders and at and colliders, with emphasis on the bosonic partners
expected in the doublet scenario and the fermionic partners expected in both
scenarios.Comment: 52 pages, 24 figures, v2 corrects two plots and some typos, and
contains a new section on production in electron-positron collisions as well
as additional reference
Thermal and non-thermal production of dark matter via Z'-portal(s)
We study the genesis of dark matter in the primordial Universe for
representative classes of Z'-portals models. For weak-scale Z' mediators we
compute the range of values of the kinetic mixing allowed by WMAP/PLANCK
experiments corresponding to a FIMP regime. We show that very small values of
the kinetic coupling (1.e-12 < delta < 1.e-11) are sufficient to produce the
right amount of dark matter. We also analyse the case of very massive gauge
mediators, whose mass is larger than the reheating temperature, "T_RH", with a
weak-scale coupling to ordinary matter. Relic abundance constraints then impose
a direct correlation between T_RH and the effective scale "Lambda" of the
interactions: Lambda ~ 1.e3--1.e5 * T_RH. Finally we describe in some detail
the process of dark thermalisation and study its consequences on the
computation of the relic abundance.Comment: version accepted for publication in JCA
Searching for the QCD Axion with Gravitational Microlensing
The phase transition responsible for axion dark matter production can create
large amplitude isocurvature perturbations which collapse into dense objects
known as axion miniclusters. We use microlensing data from the EROS survey, and
from recent observations with the Subaru Hyper Suprime Cam to place constraints
on the minicluster scenario. We compute the microlensing event rate for
miniclusters treating them as spatially extended objects with an extended mass
function. Using the published bounds on the number of microlensing events we
bound the fraction of DM collapsed into miniclusters, . For an
axion with temperature dependent mass consistent with the QCD axion we find
, which represents the first
observational constraint on the minicluster fraction. We forecast that a
high-efficiency observation of ten nights with Subaru would be sufficient to
constrain over the entire QCD axion mass range. We
make various approximations to derive these constraints and dedicated analyses
by the observing teams of EROS and Subaru are necessary to confirm our results.
If accurate theoretical predictions for can be made in future then
microlensing can be used to exclude, or discover, the QCD axion. Further
details of our computations are presented in a companion paper.Comment: 5 pages, 4 figures, v2 contains an improved description of our
modeling of miniclusters and lensing with revised limits, matches version
accepted in PR
Extending the Universal One-Loop Effective Action: Heavy-Light Coefficients
The Universal One-Loop Effective Action (UOLEA) is a general expression for
the effective action obtained by evaluating in a model-independent way the
one-loop expansion of a functional path integral. It can be used to match UV
theories to their low-energy EFTs more efficiently by avoiding redundant steps
in the application of functional methods, simplifying the process of obtaining
Wilson coefficients of operators up to dimension six. In addition to loops
involving only heavy fields, matching may require the inclusion of loops
containing both heavy and light particles. Here we use the recently-developed
covariant diagram technique to extend the UOLEA to include heavy-light terms
which retain the same universal structure as the previously-derived heavy-only
terms. As an example of its application, we integrate out a heavy singlet
scalar with a linear coupling to a light doublet Higgs. The extension presented
here is a first step towards completing the UOLEA to incorporate all possible
structures encountered in a covariant derivative expansion of the one-loop path
integral.Comment: 20 pages, 1 figure, 5 tables, 1 Mathematica Noteboo
Trace Anomaly of Weyl Fermions via the Path Integral
We compute the trace, diffeomorphism and Lorentz anomalies of a free Weyl
fermion in a gravitational background field by path integral methods. This is
achieved by regularising the variation of the determinant of the Weyl operator
building on earlier work by Leutwyler. The trace anomaly is found to be one
half of the one of a Dirac fermion. Most importantly we establish that the
potential parity-odd curvature term , corresponding to the
Pontryagin density, vanishes. This is to the contrary of some recent findings
in the literature which gave rise to a controversy. We verify, that the
regularisation does not lead to (spurious) anomalies in the Lorentz and
diffeomorphism symmetries. We argue that no parity-odd terms appear in the
trace anomaly in any even dimension, provided parity is not broken explicitly.Comment: 22 page
Into the multi-TeV scale with a Higgs golden ratio
AbstractWith the upgrade of the LHC, the couplings of the observed Higgs particle to fermions and gauge bosons will be measured with a much higher experimental accuracy than current measurements, but will still be limited by an order 10% theoretical uncertainty. In this paper, we re-emphasize the fact that the ratio of Higgs signal rates into two photons and four leptons, Dγγ=σ(pp→H→γγ)/σ(pp→H→ZZ⁎→4ℓ±) can be made free of these ambiguities. Its measurement would be limited only by the statistical and systematic errors, which can in principle be reduced to the percent level at a high-luminosity LHC. This decay ratio would then provide a powerful probe of new physics effects in addition to high precision electroweak observables or the muon g−2. As an example, we show that the Higgs couplings to top quarks and vector bosons can be constrained at the percent level and that new Higgs or supersymmetric particles that contribute to the Hγγ loop can be probed up to masses in the multi-TeV range and possibly larger than those accessible directly
Axion-like ALPs
The Effective Field Theory (EFT) Lagrangian for a generic axion-like particle
(ALP) has many free parameters, and leaves quite some freedom for the expected
phenomenology. In this work, we set up more constrained EFTs by enforcing true
axion-like properties for the ALP. Indeed, though the Peccei-Quinn symmetry of
the QCD axion is anomalous, it is so in specific ways, and this shows up as
consistency conditions between the gauge boson and fermion couplings. We
propose to enforce such conditions, as inspired from the DFSZ and KSVZ
scenarios, on the generic ALP EFTs. These truly axion-like ALP EFTs are then
particularly well-suited as benchmark scenarios, to be used in the search for
ALPs both at colliders and at low-energy experiments.Comment: 22 pages, 7 figure
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