32 research outputs found
Dark matter and Higgs boson physics
A vector-like colorless fermion doublet and a singlet added to the Standard
Model allow a consistent interpretation of dark matter in terms of the lightest
neutral particle, as they may help in obtaining successful gauge coupling
unification. We analyze in detail the mass range of the lightest neutral
particle below the W mass, i.e. in a range of the parameters where the physics
of the Standard Model Higgs boson may be substantially affected either directly
or indirectly.Comment: 17 pages, 7 figures. v3: published version (small corrections
Thermal Axions: What’s next?
Scattering and decay processes of thermal bath particles in the early universe can dump relativistic axions in the primordial plasma. If produced with a significant abundance, their presence can leave observable signatures in cosmological observables probing both the early and the late universe. We focus on the QCD axion and present recent and significant improvements for the calculation of the axion production rate across the different energy scales during the expansion of the universe. We apply these rates to predict the abundance of produced axions and to derive the latest cosmological bounds on the axion mass and couplings
Constraints on the excitations in the Strongly Coupled Standard Model
The Strongly Coupled Standard Model predicts a rich spectrum of excited
states at the Fermi scale. We study the first radial excitations of the vector
bosons. The inclusion of these new states affects the low energy phenomenology
of the model. We put constraints on the effective couplings by performing a
global fit with the electroweak observables, and we find that the excitations
have to be rather decoupled from the low-energy states.Comment: 23 pages, 6 figures, uses RevTeX
Supergravity Computations without Gravity Complications
The conformal compensator formalism is a convenient and versatile
representation of supergravity (SUGRA) obtained by gauge fixing conformal
SUGRA. Unfortunately, practical calculations often require cumbersome
manipulations of component field terms involving the full gravity multiplet. In
this paper, we derive an alternative gauge fixing for conformal SUGRA which
decouples these gravity complications from SUGRA computations. This yields a
simplified tree-level action for the matter fields in SUGRA which can be
expressed compactly in terms of superfields and a modified conformal
compensator. Phenomenologically relevant quantities such as the scalar
potential and fermion mass matrix are then straightforwardly obtained by
expanding the action in superspace.Comment: 10 pages; v2: references update
Transverse Momentum Broadening and the Jet Quenching Parameter, Redux
We use Soft Collinear Effective Theory (SCET) to analyze the transverse
momentum broadening, or diffusion in transverse momentum space, of an energetic
parton propagating through quark-gluon plasma. Since we neglect the radiation
of gluons from the energetic parton, we can only discuss momentum broadening,
not parton energy loss. The interaction responsible for momentum broadening in
the absence of radiation is that between the energetic (collinear) parton and
the Glauber modes of the gluon fields in the medium. We derive the effective
Lagrangian for this interaction, and we show that the probability for picking
up transverse momentum k_\perp is given by the Fourier transform of the
expectation value of two transversely separated light-like path-ordered Wilson
lines. This yields a field theoretical definition of the jet quenching
parameter \hat q, and shows that this can be interpreted as a diffusion
constant. We close by revisiting the calculation of \hat q for the strongly
coupled plasma of N=4 SYM theory, showing that previous calculations need some
modifications that make them more straightforward and do not change the result.Comment: 18 pages, 7 figures; v2, minor revisions, references added; v3,
version to appear in Phys. Rev. D: Feynman rules corrected, improved
explanations of the gauge invariance of our calculation and of how the
scaling of SCET operators differs from that in other contexts in the
literature; no changes to any result
The Spectrum of Goldstini and Modulini
When supersymmetry is broken in multiple sectors via independent dynamics,
the theory furnishes a corresponding multiplicity of "goldstini" degrees of
freedom which may play a substantial role in collider phenomenology and
cosmology. In this paper, we explore the tree-level mass spectrum of goldstini
arising from a general admixture of F-term, D-term, and almost no-scale
supersymmetry breaking, employing non-linear superfields and a novel gauge
fixing for supergravity discussed in a companion paper. In theories of F-term
and D-term breaking, goldstini acquire a mass which is precisely twice the
gravitino mass, while the inclusion of no-scale breaking renders one of these
modes, the modulino, massless. We argue that the vanishing modulino mass can be
explained in terms of an accidental and spontaneously broken "global"
supersymmetry.Comment: 10 pages, 2 figures; v2: typo corrected, references updated; v3:
version to appear in JHE
The Two Faces of Anomaly Mediation
Anomaly mediation is a ubiquitous source of supersymmetry (SUSY) breaking
which appears in almost every theory of supergravity. In this paper, we show
that anomaly mediation really consists of two physically distinct phenomena,
which we dub "gravitino mediation" and "Kahler mediation". Gravitino mediation
arises from minimally uplifting SUSY anti-de Sitter (AdS) space to Minkowski
space, generating soft masses proportional to the gravitino mass. Kahler
mediation arises when visible sector fields have linear couplings to SUSY
breaking in the Kahler potential, generating soft masses proportional to beta
function coefficients. In the literature, these two phenomena are lumped
together under the name "anomaly mediation", but here we demonstrate that they
can be physically disentangled by measuring associated couplings to the
goldstino. In particular, we use the example of gaugino soft masses to show
that gravitino mediation generates soft masses without corresponding goldstino
couplings. This result naively violates the goldstino equivalence theorem but
is in fact necessary for supercurrent conservation in AdS space. Since
gravitino mediation persists even when the visible sector is sequestered from
SUSY breaking, we can use the absence of goldstino couplings as an unambiguous
definition of sequestering.Comment: 21 pages, 1 table; v2, references added, extended discussion in
introduction and appendix; v3, JHEP versio