453 research outputs found
An Indirect Model-Dependent Probe of the Higgs Self-Coupling
The Higgs associated production cross section at an collider is
indirectly sensitive to the Higgs self-coupling, , at next-to-leading
order (NLO). Utilizing this, a new indirect method is proposed for constraining
deviations in the self-coupling below the di-Higgs production threshold in
certain models. Although this indirect constraint is model-dependent, making it
valid only under specific assumptions, meaningful indirect constraints on the
self-coupling may be realized. Specific realistic scenarios where the indirect
constraint applies are discussed and in particular it is shown that in the
well-motivated class of two Higgs-doublet models there exist regions of
parameter space in which the NLO effects from a modified self-coupling dominate
over the LO modifications, demonstrating a concrete scenario in which large
modifications of the Higgs self-coupling may be indirectly constrained using
the proposed method. Other models, such as strongly coupled scenarios, are also
discussed. The indirect method would give valuable constraints on deviations in
the Higgs self-coupling, and would be complementary to the direct measurements
possible with di-Higgs production at other colliders, providing precious
additional information in the effort to unravel the properties of the Higgs
boson.Comment: 8 pages, 4 figures. Eq.10 Typo corrected and rearranged to neater
form. Note added with additional references. Plots and numerical results
unchange
Capture of Inelastic Dark Matter in White Dwarves
We consider the capture of inelastic dark matter in white dwarves by
inelastic spin-independent scattering on nuclei. We show that if the dark
matter annihilates to standard-model particles then, under the assumption of
primordial globular cluster formation, the observation of cold white dwarves in
the globular cluster M4 appears inconsistent with explanations of the observed
DAMA/LIBRA annual modulation signal based on spin-independent inelastic dark
matter scattering. Alternatively if the inelastic dark matter scenario were to
be confirmed and it was found to annihilate to standard-model particles then
this would imply a much lower dark matter density in the core of M4 than would
be expected if it were to have formed in a dark matter halo. Finally we argue
that cold white dwarves constitute a unique dark matter probe, complementary to
other direct and indirect detection searches.Comment: 8 pages, 5 figures. Typos corrected. References and discussion added.
Figures updated. Main conclusions unchanged. v3 Journal versio
Neutrino Masses from Neutral Top Partners
We present theories of `Natural Neutrinos' in which neutral fermionic top
partner fields are simultaneously the right-handed neutrinos (RHN), linking
seemingly disparate aspects of the Standard Model structure: a) The RHN top
partners are responsible for the observed small neutrino masses, b) They help
ameliorate the tuning in the weak scale and address the little hierarchy
problem, and c) The factor of arising from in the top-loop Higgs mass
corrections is countered by a factor from the number of vector-like
generations of RHN. The RHN top partners may arise in
pseudo-Nambu-Goldstone-Boson (pNGB) Higgs models such as the Twin Higgs, as
well as more general Composite, Little, and Orbifold Higgs scenarios, and three
simple example models are presented. This framework firmly predicts a TeV-scale
seesaw, as the RHN masses are bounded to be below the TeV scale by naturalness.
The generation of light neutrino masses relies on a collective breaking of
lepton number, allowing for comparatively large neutrino Yukawa couplings and a
rich associated phenomenology. The structure of the neutrino mass mechanism
realizes in certain limits the Inverse or Linear classes of seesaw. Natural
Neutrino models are testable at a variety of current and future experiments,
particularly in tests of lepton universality, searches for lepton flavor
violation, and precision electroweak and Higgs coupling measurements possible
at high energy and hadron colliders.Comment: 18 pages, 5 figures; v2: references added, additional discussion of
proton deca
Modified Higgs Sectors and NLO Associated Production
Many beyond the Standard Model (BSM) scenarios involve Higgs couplings to
additional electroweak fields. It is well established that these new fields may
modify Higgs gamma-gamma and gamma-Z decays at one-loop. However, one
unexplored aspect of such scenarios is that by electroweak symmetry one should
also expect modifications to the Higgs Z-Z coupling at one-loop and, more
generally, modifications to Higgs production and decay channels beyond
tree-level. In this paper we investigate the full BSM modified electroweak
corrections to associated Higgs production at both the LHC and a future lepton
collider in two simple SM extensions. From both inclusive and differential NLO
associated production cross sections we find BSM-NLO corrections can be as
large as O(>10%) when compared to the SM expectation, consistent with other
precision electroweak measurements, even in scenarios where modifications to
the Higgs diphoton rate are not significant. At the LHC such corrections are
comparable to the involved QCD uncertainties. At a lepton collider the Higgs
associated production cross section can be measured to high accuracy (O(1%)
independent of uncertainties in total width and other couplings), and such a
deviation could be easily observed even if the new states remain beyond
kinematic reach. This should be compared to the expected accuracy for a
model-independent determination of the Higgs diphoton coupling at a lepton
collider, which is O(15%). This work demonstrates that precision measurements
of the Higgs associated production cross section constitute a powerful probe of
modified Higgs sectors and will be valuable for indirectly exploring BSM
scenarios.Comment: 22 pages, 8 figure
A Clockwork Theory
The clockwork is a mechanism for generating light particles with
exponentially suppressed interactions in theories which contain no small
parameters at the fundamental level. We develop a general description of the
clockwork mechanism valid for scalars, fermions, gauge bosons, and gravitons.
This mechanism can be implemented with a discrete set of new fields or, in its
continuum version, through an extra spatial dimension. In both cases the
clockwork emerges as a useful tool for model-building applications. Notably,
the continuum clockwork offers a solution to the Higgs naturalness problem,
which turns out to be the same as in linear dilaton duals of Little String
Theory. We also elucidate the similarities and differences of the continuum
clockwork with large extra dimensions and warped spaces. All clockwork models,
in the discrete and continuum, exhibit novel phenomenology with a distinctive
spectrum of closely spaced resonances.Comment: Body of text 26 page
Dark Nuclei I: Cosmology and Indirect Detection
In a companion paper (to be presented), lattice field theory methods are used
to show that in two-color, two-flavor QCD there are stable nuclear states in
the spectrum. As a commonly studied theory of composite dark matter, this
motivates the consideration of possible nuclear physics in this and other
composite dark sectors. In this work, early Universe cosmology and indirect
detection signatures are explored for both symmetric and asymmetric dark
matter, highlighting the unique features that arise from considerations of dark
nuclei and associated dark nuclear processes. The present day dark matter
abundance may be composed of dark nucleons and/or dark nuclei, where the latter
are generated through it dark nucleosynthesis. For symmetric dark matter,
indirect detection signatures are possible from annihilation, dark
nucleosynthesis, and dark nuclear capture and we present a novel explanation of
the galactic center gamma ray excess based on the latter. For asymmetric dark
matter, dark nucleosynthesis may alter the capture of dark matter in stars,
allowing for captured particles to be processed into nuclei and ejected from
the star through dark nucleosynthesis in the core. Notably, dark
nucleosynthesis realizes a novel mechanism for indirect detection signals of
asymmetric dark matter from regions such as the galactic center, without having
to rely on a symmetric dark matter component.Comment: 31 pages, 9 figure
The New Flavor of Higgsed Gauge Mediation
Recent LHC bounds on squark masses combined with naturalness and flavor
considerations motivate non-trivial sfermion mass spectra in the supersymmetric
Standard Model. These can arise if supersymmetry breaking is communicated to
the visible sector via new extended gauge symmetries. Such extended symmetries
must be spontaneously broken, or confined, complicating the calculation of soft
masses. We develop a new formalism for calculating perturbative gauge-mediated
two-loop soft masses for gauge groups with arbitrary patterns of spontaneous
symmetry breaking, simplifying the framework of "Higgsed gauge mediation." The
resulting expressions can be applied to Abelian and non-Abelian gauge groups,
opening new avenues for supersymmetric model building. We present a number of
examples using our method, ranging from grand unified threshold corrections in
standard gauge mediation to soft masses in gauge extensions of the Higgs sector
that can raise the Higgs mass through non-decoupling D-terms. We also outline a
new mediation mechanism called "flavor mediation", where supersymmetry breaking
is communicated via a gauged subgroup of Standard Model flavor symmetries.
Flavor mediation can automatically generate suppressed masses for
third-generation squarks and implies a nearly exact U(2) symmetry in the first
two generations, yielding a "natural SUSY" spectrum without imposing ad hoc
global symmetries or giving preferential treatment to particular generations.Comment: 13 pages, 3 figures; v2: typos corrected, references adde
Multiple Gamma Lines from Semi-Annihilation
Hints in the Fermi data for a 130 GeV gamma line from the galactic center
have ignited interest in potential gamma line signatures of dark matter.
Explanations of this line based on dark matter annihilation face a parametric
tension since they often rely on large enhancements of loop-suppressed cross
sections. In this paper, we pursue an alternative possibility that dark matter
gamma lines could arise from "semi-annihilation" among multiple dark sector
states. The semi-annihilation reaction with a single final state photon is
typically enhanced relative to ordinary annihilation into photon pairs.
Semi-annihilation allows for a wide range of dark matter masses compared to the
fixed mass value required by annihilation, opening the possibility to explain
potential dark matter signatures at higher energies. The most striking
prediction of semi-annihilation is the presence of multiple gamma lines, with
as many as order N^3 lines possible for N dark sector states, allowing for dark
sector spectroscopy. A smoking gun signature arises in the simplest case of
degenerate dark matter, where a strong semi-annihilation line at 130 GeV would
be accompanied by a weaker annihilation line at 173 GeV. As a proof of
principle, we construct two explicit models of dark matter semi-annihilation,
one based on non-Abelian vector dark matter and the other based on retrofitting
Rayleigh dark matter.Comment: 15 pages of text, 8 figures. v2: refs adde
Hunting for Dark Particles with Gravitational Waves
The LIGO observation of gravitational waves from a binary black hole merger
has begun a new era in fundamental physics. If new dark sector particles, be
they bosons or fermions, can coalesce into exotic compact objects (ECOs) of
astronomical size, then the first evidence for such objects, and their
underlying microphysical description, may arise in gravitational wave
observations. In this work we study how the macroscopic properties of ECOs are
related to their microscopic properties, such as dark particle mass and
couplings. We then demonstrate the smoking gun exotic signatures that would
provide observational evidence for ECOs, and hence new particles, in
terrestrial gravitational wave observatories. Finally, we discuss how
gravitational waves can test a core concept in general relativity: Hawking's
area theorem.Comment: 44 pages, 14 figures. Revised version to appear in JCA
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