11,171 research outputs found
Commutative Quantum Operator Algebras
A key notion bridging the gap between {\it quantum operator algebras}
\cite{LZ10} and {\it vertex operator algebras} \cite{Bor}\cite{FLM} is the
definition of the commutativity of a pair of quantum operators (see section 2
below). This is not commutativity in any ordinary sense, but it is clearly the
correct generalization to the quantum context. The main purpose of the current
paper is to begin laying the foundations for a complete mathematical theory of
{\it commutative quantum operator algebras.} We give proofs of most of the
relevant results announced in \cite{LZ10}, and we carry out some calculations
with sufficient detail to enable the interested reader to become proficient
with the algebra of commuting quantum operators.Comment: 22 pages, Late
The 125 GeV Higgs and Electroweak Phase Transition Model Classes
Recently, the ATLAS and CMS detectors have discovered a bosonic particle
which, to a reasonable degree of statistical uncertainty, fits the profile of
the Standard Model Higgs. One obvious implication is that models which predict
a significant departure from Standard Model phenomenology, such as large exotic
(e.g., invisible) Higgs decay or mixing with a hidden sector scalar, are
already ruled out. This observation threatens the viability of electroweak
baryogenesis, which favors, for example, a lighter Higgs and a Higgs coupled to
or mixed with light scalars. To assess the broad impact of these constraints,
we propose a scheme for classifying models of the electroweak phase transition
and impose constraints on a class-by-class basis. We find that models, such as
the MSSM, which rely on thermal loop effects are severely constrained by the
measurement of a 125 GeV Higgs. Models which rely on tree-level effects from a
light singlet are also restricted by invisible decay and mixing constraints.
Moreover, we find that the parametric region favored by electroweak
baryogenesis often coincides with an enhanced symmetry point with a distinctive
phenomenological character. In particular, enhancements arising through an
approximate continuous symmetry are phenomenologically disfavored, in contrast
with enhancements from discrete symmetries. We also comment on the excess of
diphoton events observed by ATLAS and CMS. We note that although Higgs portal
models can accommodate both enhanced diphoton decay and a strongly first order
electroweak phase transition, the former favors a negative Higgs portal
coupling whereas the latter favors a positive one, and therefore these two
constraints are at tension with one another.Comment: 35 pages, 7 figure
Baryogenesis at a Lepton-Number-Breaking Phase Transition
We study a scenario in which the baryon asymmetry of the universe arises from
a cosmological phase transition where lepton-number is spontaneously broken. If
the phase transition is first order, a lepton-number asymmetry can arise at the
bubble wall, through dynamics similar to electroweak baryogenesis, but
involving right-handed neutrinos. In addition to the usual neutrinoless double
beta decay in nuclear experiments, the model may be probed through a variety of
"baryogenesis by-products," which include a stochastic background of
gravitational waves created by the colliding bubbles. Depending on the model,
other aspects may include a network of topological defects that produce their
own gravitational waves, additional contribution to dark radiation, and a light
pseudo-Goldstone boson (majoron) as dark matter candidate.Comment: 21 pages + 10 appendices & references, 3 figure
Strongly First Order Phase Transitions Near an Enhanced Discrete Symmetry Point
We propose a group theoretic condition which may be applied to extensions of
the Standard Model in order to locate regions of parameter space in which the
electroweak phase transition is strongly first order, such that electroweak
baryogenesis may be a viable mechanism for generating the baryon asymmetry of
the universe. Specifically, we demonstrate that the viable corners of parameter
space may be identified by their proximity to an enhanced discrete symmetry
point. At this point, the global symmetry group of the theory is extended by a
discrete group under which the scalar sector is non-trivially charged, and the
discrete symmetry is spontaneously broken such that the discrete symmetry
relates degenerate electroweak preserving and breaking vacua. This idea is used
to investigate several specific models of the electroweak symmetry breaking
sector. The phase transitions identified through this method suggest
implications for other relics such as dark matter and gravitational waves.Comment: 17 pages, 4 figure
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