139 research outputs found
Transplanckian Censorship and Global Cosmic Strings
Large field excursions are required in a number of axion models of inflation.
These models also possess global cosmic strings, around which the axion follows
a path mirroring the inflationary trajectory. Cosmic strings are thus an
interesting theoretical laboratory for the study of transplanckian field
excursions. We describe connections between various effective field theory
models of axion monodromy and study the classical spacetimes around their
supercritical cosmic strings. For small decay constants and large
winding numbers , the EFT is under control and the string cores
undergo topological inflation, which may be either of exponential or power-law
type. We show that the exterior spacetime is nonsingular and equivalent to a
decompactifying cigar geometry, with the radion rolling in a potential
generated by axion flux. Signals are able to circumnavigate infinite straight
strings in finite but exponentially long time, . For
finite loops of supercritical string in asymptotically flat space, we argue
that if topological inflation occurs, then topological censorship implies
transplanckian censorship, or that external observers are forbidden from
threading the loop and observing the full excursion of the axion.Comment: v2: refs added, fig 6 extended. published in JHEP. 28 pages, 7
figure
Exotic Higgs boson decays and the electroweak phase transition
Light new physics weakly coupled to the Higgs can induce a strong first-order electroweak phase transition (EWPT). Here, we argue that scenarios in which the EWPT is driven first-order by a light scalar with mass between ∼10 GeV−mh/2 and small mixing with the Higgs will be conclusively probed by the high-luminosity LHC and future Higgs factories. Our arguments are based on analytic and numerical studies of the finite-temperature effective potential and provide a well-motivated target for exotic Higgs decay searches at the LHC and future lepton colliders
Supersymmetric Electroweak Baryogenesis Via Resonant Sfermion Sources
We calculate the baryon asymmetry produced at the electroweak phase
transition by quasi-degenerate third generation sfermions in the minimal
supersymmetric extension of the Standard Model. We evaluate constraints from
Higgs searches, from collider searches for supersymmetric particles, and from
null searches for the permanent electric dipole moment (EDM) of the electron,
of the neutron and of atoms. We find that resonant sfermion sources can in
principle provide a large enough baryon asymmetry in various corners of the
sfermion parameter space, and we focus, in particular, on the case of large
, where third-generation down-type (s)fermions become relevant. We
show that in the case of stop and sbottom sources, the viable parameter space
is ruled out by constraints from the non-observation of the Mercury EDM. We
introduce a new class of CP violating sources, quasi-degenerate staus, that
escapes current EDM constraints while providing large enough net chiral
currents to achieve successful "slepton-mediated" electroweak baryogenesis.Comment: 35 pages, 9 figures; v2: several revisions, but conclusions
unchanged. Matches version published in PR
Accidental Supersymmetric Dark Matter and Baryogenesis
We show that "accidental" supersymmetry is a beyond-the-Standard Model
framework that naturally accommodates a thermal relic dark matter candidate and
successful electroweak baryogenesis, including the needed strongly first-order
character of the electroweak phase transition. We study the phenomenology of
this setup from the standpoint of both dark matter and baryogenesis. For
energies around the electroweak phase transition temperature, the low-energy
effective theory is similar to the MSSM with light super-partners of the
third-generation quarks and of the Higgs and gauge bosons. We calculate the
dark matter relic abundance and the baryon asymmetry across the accidental
supersymmetry parameter space, including resonant and non-resonant CP-violating
sources. We find that there are regions of parameter space producing both the
observed value of the baryon asymmetry and a dark matter candidate with the
correct relic density and conforming to present-day constraints from dark
matter searches. This scenario makes sharp predictions for the particle
spectrum, predicting a lightest neutralino mass between 200 and 500 GeV, with
all charginos and neutralinos within less than a factor 2 of the lightest
neutralino mass and the heavy Higgs sector within 20-25% of that mass, making
it an interesting target for collider searches. In addition, we demonstrate
that successful accidental supersymmetric dark matter and baryogenesis will be
conclusively tested with improvements smaller than one order of magnitude to
the current performance of electron electric dipole moment searches and of
direct dark matter searches, as well as with IceCube plus Deep Core neutrino
telescope data.Comment: 36 pages, 10 figure
Nonperturbative analysis of the gravitational waves from a first-order electroweak phase transition
We present the first end-to-end nonperturbative analysis of the gravitational wave power spectrum from a thermal first-order electroweak phase transition (EWPT), using the framework of dimensionally reduced effective field theory and preexisting nonperturbative simulation results. We are able to show that a first-order EWPT in any beyond the Standard Model (BSM) scenario that can be described by a Standard Model-like effective theory at long distances will produce gravitational wave signatures too weak to be observed at existing and planned detectors. This implies that colliders are likely to provide the best chance of exploring the phase structure of such theories, while transitions strong enough to be detected at gravitational wave experiments require either previously neglected higher-dimension operators or light BSM fields to be included in the dimensionally reduced effective theory and therefore necessitate dedicated nonperturbative studies. As a concrete application, we analyze the real singlet-extended Standard Model and identify regions of parameter space with single-step first-order transitions, comparing our findings to those obtained using a fully perturbative method. We discuss the prospects for exploring the electroweak phase diagram in this model at collider and gravitational wave experiments in light of our nonperturbative results.Peer reviewe
Probing the Electroweak Phase Transition with Exotic Higgs Decays
An essential goal of the Higgs physics program at the LHC and beyond is to explore the nature of the Higgs potential and shed light on the mechanism of electroweak symmetry breaking. An important class of models alter the thermal history of electroweak symmetry breaking from the predictions of the Standard Model (SM). This paper reviews the existence of a region of parameter space where a strong first-order electroweak phase transition is compatible with exotic decays of the SM-like Higgs boson. A dedicated search for exotic Higgs decays can actively explore this framework at the Large Hadron Collider (LHC), while future exotic Higgs decay searches at the high-luminosity LHC and future Higgs factories will be vital to conclusively probe the scenario
Detecting gravitational waves from cosmological phase transitions with LISA: an update
We investigate the potential for observing gravitational waves from cosmological phase transitions with LISA in light of recent theoretical and experimental developments. Our analysis is based on current state-of-the-art simulations of sound waves in the cosmic fluid after the phase transition completes. We discuss the various sources of gravitational radiation, the underlying parameters describing the phase transition and a variety of viable particle physics models in this context, clarifying common misconceptions that appear in the literature and identifying open questions requiring future study. We also present a web-based tool, PTPlot, that allows users to obtain up-to-date detection prospects for a given set of phase transition parameters at LISA.acceptedVersio
Horizontal Transfer of Symbiosis Genes within and Between Rhizobial Genera : Occurrence and Importance
Rhizobial symbiosis genes are often carried on symbiotic islands or plasmids that can be transferred (horizontal transfer) between different bacterial species. Symbiosis genes involved in horizontal transfer have different phylogenies with respect to the core genome of their ‘host’. Here, the literature on legume–rhizobium symbioses in field soils was reviewed, and cases of phylogenetic incongruence between rhizobium core and symbiosis genes were collated. The occurrence and importance of horizontal transfer of rhizobial symbiosis genes within and between bacterial genera were assessed. Horizontal transfer of symbiosis genes between rhizobial strains is of common occurrence, is widespread geographically, is not restricted to specific rhizobial genera, and occurs within and between rhizobial genera. The transfer of symbiosis genes to bacteria adapted to local soil conditions can allow these bacteria to become rhizobial symbionts of previously incompatible legumes growing in these soils. This, in turn, will have consequences for the growth, life history, and biogeography of the legume species involved, which provides a critical ecological link connecting the horizontal transfer of symbiosis genes between rhizobial bacteria in the soil to the above-ground floral biodiversity and vegetation community structure
Nanohertz Frequency Determination for the Gravity Probe B HF SQUID Signal
In this paper, we present a method to measure the frequency and the frequency
change rate of a digital signal. This method consists of three consecutive
algorithms: frequency interpolation, phase differencing, and a third algorithm
specifically designed and tested by the authors. The succession of these three
algorithms allowed a 5 parts in 10^10 resolution in frequency determination.
The algorithm developed by the authors can be applied to a sampled scalar
signal such that a model linking the harmonics of its main frequency to the
underlying physical phenomenon is available. This method was developed in the
framework of the Gravity Probe B (GP-B) mission. It was applied to the High
Frequency (HF) component of GP-B's Superconducting QUantum Interference Device
(SQUID) signal, whose main frequency fz is close to the spin frequency of the
gyroscopes used in the experiment. A 30 nHz resolution in signal frequency and
a 0.1 pHz/sec resolution in its decay rate were achieved out of a succession of
1.86 second-long stretches of signal sampled at 2200 Hz. This paper describes
the underlying theory of the frequency measurement method as well as its
application to GP-B's HF science signal.Comment: The following article has been submitted to Review of Scientific
Instruments. After it is published, it will be found at (http://rsi.aip.org/
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