248 research outputs found
Caustic Structures and Detectability of Circumbinary Planets in Microlensing
Recent discoveries of circumbinary planets in Kepler data show that there is
a viable channel of planet formation around binary main sequence stars.
Motivated by these discoveries, we have investigated the caustic structures and
detectability of circumbinary planets in microlensing events. We have produced
a suite of animations of caustics as a function of the projected separation and
angle of the binary host to efficiently explore caustic structures over the
entire circumbinary parameter space. Aided by these animations, we have derived
a semi-empirical analytic expression for the location of planetary caustics,
which are displaced in circumbinary lenses relative to those of planets with a
single host. We have used this expression to show that the dominant source of
caustic motion will be due to the planet's orbital motion and not that of the
binary star. Finally, we estimate the fraction of circumbinary microlensing
events that are recognizable as such to be significant (5-50 percent) for
binary projected separations in the range 0.1-0.5 in units of Einstein radii.Comment: 15 pages, 1 table, 18 figures. Accepted for publication in Ap
Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars
Radial velocity (RV) detection of planets is hampered by astrophysical processes on the surfaces of stars that induce a stochastic signal, or "jitter," which can drown out or even mimic planetary signals. Here, we empirically and carefully measure the RV jitter of more than 600 stars from the California Planet Search sample on a star by star basis. As part of this process, we explore the activity–RV correlation of stellar cycles and include appendices listing every ostensibly companion-induced signal we removed and every activity cycle we noted. We then use precise stellar properties from Brewer et al. to separate the sample into bins of stellar mass and examine trends with activity and with evolutionary state. We find that RV jitter tracks stellar evolution and that in general, stars evolve through different stages of RV jitter: the jitter in younger stars is driven by magnetic activity, while the jitter in older stars is convectively driven and dominated by granulation and oscillations. We identify the "jitter minimum"—where activity-driven and convectively driven jitter have similar amplitudes—for stars between 0.7 and 1.7 M⊙ and find that more-massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. Finally, we comment on how these results can inform future RV efforts, from prioritization of follow-up targets from transit surveys like TESS to target selection of future RV surveys
What is the Discrete Gauge Symmetry of the MSSM?
We systematically study the extension of the Supersymmetric Standard Model
(SSM) by an anomaly-free discrete gauge symmetry Z_N. We extend the work of
Ibanez and Ross with N=2,3 to arbitrary values of N. As new fundamental
symmetries, we find four Z_6, nine Z_9 and nine Z_18. We then place three
phenomenological demands upon the low-energy effective SSM: (i) the presence of
the mu-term in the superpotential, (ii) baryon-number conservation upto
dimension-five operators, and (iii) the presence of the see-saw neutrino mass
term LHLH. We are then left with only two anomaly-free discrete gauge
symmetries: baryon-triality, B_3, and a new Z_6, which we call proton-hexality,
P_6. Unlike B_3, P_6 prohibits the dimension-four lepton-number violating
operators. This we propose as the discrete gauge symmetry of the Minimal SSM,
instead of R-parity.Comment: Typo in item 2 below Eq.(6.9) corrected (wrong factor of "3"); 27
pages, 5 table
What is the discrete gauge symmetry of the R-parity violating MSSM?
The lack of experimental evidence for supersymmetry motivates R-parity
violating realizations of the MSSM. Dropping R-parity, alternative symmetries
have to be imposed in order to stabilize the proton. We determine the possible
discrete R and non-R symmetries, which allow for renormalizable R-parity
violating terms in the superpotential and which, at the effective level, are
consistent with the constraints from nucleon decay. Assuming a gauge origin, we
require the symmetry to be discrete gauge anomaly-free, allowing also for
cancellation via the Green Schwarz mechanism. Furthermore, we demand lepton
number violating neutrino mass terms either at the renormalizable or
non-renormalizable level. In order to solve the mu problem, the discrete Z_N or
Z_N^R symmetries have to forbid any bilinear superpotential operator at tree
level. In the case of renormalizable baryon number violation the smallest
possible symmetry satisfying all conditions is a unique hexality Z_6^R. In the
case of renormalizable lepton number violation the smallest symmetries are two
hexalities, one Z_6 and one Z_6^R.Comment: 25 pages, version to appear in PR
Proton Hexality from an Anomalous Flavor U(1) and Neutrino Masses - Linking to the String Scale
We devise minimalistic gauged U(1)_X Froggatt-Nielsen models which at
low-energy give rise to the recently suggested discrete gauge Z_6 symmetry,
proton hexality, thus stabilizing the proton. Assuming three generations of
right-handed neutrinos, with the proper choice of X-charges, we obtain viable
neutrino masses. Furthermore, we find scenarios such that no X-charged hidden
sector superfields are needed, which from a bottom-up perspective allows the
calculation of g_string, g_X and G_SM's Kac-Moody levels. The only mass scale
apart from M_grav is m_soft.Comment: 32 pages, 8 tables, references updated, matches published versio
Astrophysical Insights into Radial Velocity Jitter from an Analysis of 600 Planet-search Stars
Radial velocity (RV) detection of planets is hampered by astrophysical processes on the surfaces of stars that induce a stochastic signal, or "jitter," which can drown out or even mimic planetary signals. Here, we empirically and carefully measure the RV jitter of more than 600 stars from the California Planet Search sample on a star by star basis. As part of this process, we explore the activity–RV correlation of stellar cycles and include appendices listing every ostensibly companion-induced signal we removed and every activity cycle we noted. We then use precise stellar properties from Brewer et al. to separate the sample into bins of stellar mass and examine trends with activity and with evolutionary state. We find that RV jitter tracks stellar evolution and that in general, stars evolve through different stages of RV jitter: the jitter in younger stars is driven by magnetic activity, while the jitter in older stars is convectively driven and dominated by granulation and oscillations. We identify the "jitter minimum"—where activity-driven and convectively driven jitter have similar amplitudes—for stars between 0.7 and 1.7 M⊙ and find that more-massive stars reach this jitter minimum later in their lifetime, in the subgiant or even giant phases. Finally, we comment on how these results can inform future RV efforts, from prioritization of follow-up targets from transit surveys like TESS to target selection of future RV surveys
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