41 research outputs found
QCD axion and topological susceptibility in chiral effective Lagrangian models at finite temperature
In this work we compute the axion mass and, from this (exploiting a
well-known relation), we also derive an expression for the QCD topological
susceptibility in the finite-temperature case, both below and above the chiral
phase transition at , making use of a chiral effective Lagrangian model
which includes the axion, the scalar and pseudoscalar mesons and implements the
axial anomaly of the fundamental theory. We also provide a numerical
estimate of the topological susceptibility at (in the physical case of
three light quark flavors) and discuss the question of the temperature and
quark-mass dependence of the topological susceptibility in the high-temperature
regime.Comment: 26 pages, revised version, published in Phys. Rev.
Minimal Dark Matter bound states at future colliders
The hypothesis that Dark Matter is one electroweak multiplet leads to
predictive candidates with multi-TeV masses that can form electroweak bound
states. Bound states with the same quantum numbers as electroweak vectors are
found to be especially interesting, as they can be produced resonantly with
large cross sections at lepton colliders. Such bound states exist e.g. if DM is
an automatically stable fermionic weak 5-plet with mass 14 TeV such
that the DM abundance is reproduced thermally. In this model, a muon collider
could resolve three such bound states. Production rates are so large that
details of DM spectroscopy can be probed with larger statistics: we compute the
characteristic pattern of single and multiple lines.Comment: v2, to appear on JHE
Asymmetric accidental composite dark matter
The goal of this work is to find the simplest UV completion of Accidental Composite Dark Matter Models (ACDM) that can dynamically generate an asymmetry for the DM candidate, the lightest dark baryon (DCb), and simultaneously annihilate the symmetric component. In this framework the DCb is a bound state of a confining SU(N)(DC) gauge group, and can interact weakly with the visible sector. The constituents of the DCb can possess non-trivial charges under the Standard Model gauge group. The generation of asymmetry for such candidate is a two-flavor variation of the out-of-equilibrium decay of a heavy scalar, with mass M-phi greater than or similar to 10(10) GeV. Below the scale of the scalars, the models recover accidental stability, or long-livedness, of the DM candidate. The symmetric component is annihilated by residual confined interactions provided that the mass of the DCb m(DCb) less than or similar to 75 TeV. We implement the mechanism of asymmetry generation, or a variation of it, in all the original ACDM models, managing to generate the correct asymmetry for DCb of masses in this range. For some of the models found, the stability of the DM candidate is not spoiled even considering generic GUT completions or asymmetry generation mechanisms in the visible sector
Stellar limits on scalars from electron-nucleus bremsstrahlung
We revisit stellar energy-loss bounds on the Yukawa couplings
of baryophilic and leptophilic scalars . The white-dwarf luminosity
function yields and , based on bremsstrahlung from and
collisions with electrons. In models with a Higgs portal, this
also implies a bound on the scalar-Higgs mixing angle . Our new bounds apply for and are
among the most restrictive ones, whereas for
long-range force measurements dominate. Besides a detailed calculation of the
bremsstrahlung rate for degenerate and semi-relativistic electrons, we prove
with a simple argument that non-relativistic bremsstrahlung by the heavy
partner is suppressed relative to that by the light one by their squared-mass
ratio. This large reduction was overlooked in previous much stronger bounds on
. In an Appendix, we provide fitting formulas (few percent
precision) for the bremsstrahlung emission of baryophilic and leptophilic
scalars as well as axions for white-dwarf conditions, i.e., degenerate,
semi-relativistic electrons and ion-ion correlations in the ``liquid'' phase.Comment: 22 pages + appendices, 7 figure
Unveiling dark forces with the Large Scale Structure of the Universe
Cosmology offers opportunities to test Dark Matter independently of its
interactions with the Standard Model. We study the imprints of long-range
forces acting solely in the dark sector on the distribution of galaxies, the
so-called Large Scale Structure (LSS). We derive the strongest constraint on
such forces from a combination of Planck and BOSS data. Along the way we
consistently develop, for the first time, the Effective Field Theory of LSS in
the presence of new dynamics in the dark sector. We forecast that future
surveys will improve the current bound by an order of magnitude.Comment: 5+18 pages, 4 figure
Closing the window on WIMP Dark Matter
We study scenarios where Dark Matter is a weakly interacting particle (WIMP) embedded in an ElectroWeak multiplet. In particular, we consider real SU(2) representations with zero hypercharge, that automatically avoid direct detection constraints from tree-level Z-exchange. We compute for the first time all the calculable thermal masses for scalar and fermionic WIMPs, including Sommerfeld enhancement and bound states formation at leading order in gauge boson exchange and emission. WIMP masses of few hundred TeV are shown to be compatible both with s-wave unitarity of the annihilation cross-section, and perturbativity. We also provide theory uncertainties on the masses for all multiplets, which are shown to be significant for large SU(2) multiplets. We then outline a strategy to probe these scenarios at future experiments. Electroweak 3-plets and 5-plets have masses up to about 16 TeV and can efficiently be probed at a high energy muon collider. We study various experimental signatures, such as single and double gauge boson emission with missing energy, and disappearing tracks, and determine the collider energy and luminosity required to probe the thermal Dark Matter masses. Larger multiplets are out of reach of any realistic future collider, but can be tested in future γ-ray telescopes and possibly in large-exposure liquid Xenon experiments
The last complex WIMPs standing
We continue the study of weakly interacting massive particles (WIMP) started
in [arXiv:2107.09688], focusing on a single complex electroweak -plet with
non-zero hypercharge added to the Standard Model. The minimal splitting between
the Dark Matter and its electroweak neutral partner required to circumvent
direct detection constraints allows only multiplets with hypercharge smaller or
equal to 1. We compute for the first time all the calculable WIMP masses up to
the largest multiplet allowed by perturbative unitarity. For the minimal
allowed splitting, most of these multiplets can be fully probed at future
large-exposure direct detection experiments, with the notable exception of the
doublet with hypercharge 1/2. We show how a future muon collider can fully
explore the parameter space of the complex doublet combining missing mass,
displaced track and long-lived track searches. In the same spirit, we study how
a future muon collider can probe the parameter space of complex WIMPs in
regions where the direct detection cross section drops below the neutrino
floor. Finally, we comment on how precision observables can provide additional
constraints on complex WIMPs.Comment: 15 pages + appendices, 6 + 6 figures, 1 + 3 table
Towards a muon collider
A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work
Towards a Muon Collider
A muon collider would enable the big jump ahead in energy reach that is
needed for a fruitful exploration of fundamental interactions. The challenges
of producing muon collisions at high luminosity and 10 TeV centre of mass
energy are being investigated by the recently-formed International Muon
Collider Collaboration. This Review summarises the status and the recent
advances on muon colliders design, physics and detector studies. The aim is to
provide a global perspective of the field and to outline directions for future
work.Comment: 118 pages, 103 figure