83 research outputs found
Resurgent Supersymmetry and String Theory
We study a realization of accidental supersymmetry in type IIB string theory
as a proof-of-principle of the mechanism and as a prototype of the strong
sector present in resurgent supersymmetry, a warped UV-completion of natural
supersymmetry. We first introduce the mechanism of accidental supersymmetry as
a way of producing a supersymmetric spectrum in the IR of a quasi-conformal
field theory, and then go on to discuss the utility of the mechanism in the
specific BSM model of resurgent supersymmetry. The realization of accidental
SUSY that we study is IIB string theory on an orbifold of the
Klebanov-Strassler solution.Comment: 15 pages plus appendix, 4 figure
New Light Species and the CMB
We consider the effects of new light species on the Cosmic Microwave
Background. In the massless limit, these effects can be parameterized in terms
of a single number, the relativistic degrees of freedom. We perform a thorough
survey of natural, minimal models containing new light species and numerically
calculate the precise contribution of each of these models to this number in
the framework of effective field theory. After reviewing the relevant details
of early universe thermodynamics, we provide a map between the parameters of
any particular theory and the predicted effective number of degrees of freedom.
We then use this map to interpret the recent results from the Cosmic Microwave
Background survey done by the Planck satellite. Using this data, we present new
constraints on the parameter space of several models containing new light
species. Future measurements of the Cosmic Microwave Background can be used
with this map to further constrain the parameter space of all such models.Comment: 38 pages plus appendices and references; 10 figures and 1 table;
references added, discussion of anapole moments added; supernovae cooling
bounds added, discussion of models condense
Partially massless higher-spin theory II: one-loop effective actions
We continue our study of a generalization of the D-dimensional linearized
Vasiliev higher-spin equations to include a tower of partially massless (PM)
fields. We compute one-loop effective actions by evaluating zeta functions for
both the "minimal" and "non-minimal" parity-even versions of the theory.
Specifically, we compute the log-divergent part of the effective action in
odd-dimensional Euclidean AdS spaces for D=7 through 19 (dual to the a-type
conformal anomaly of the dual boundary theory), and the finite part of the
effective action in even-dimensional Euclidean AdS spaces for D=4 through 8
(dual to the free energy on a sphere of the dual boundary theory). We pay
special attention to the case D=4, where module mixings occur in the dual field
theory and subtlety arises in the one-loop computation. The results provide
evidence that the theory is UV complete and one-loop exact, and we conjecture
and provide evidence for a map between the inverse Newton's constant of the
partially massless higher-spin theory and the number of colors in the dual CFT.Comment: 36 pages. v2 clarifications, corrections and refs, version appearing
in JHE
The Interplay Between Natural and Accidental Supersymmetry
In this thesis, we will explore the subject of the little hierarchy problem which plagues solutions to the big hierarchy problem of the Standard Model of particle physics.
In the first half of this thesis, we study the theoretical framework for a supersymmetric resolution of the little hierarchy problem, known as natural supersymmetry, and argue that regions of the parameter space of this model have been missed by search strategies employed at the large hadron collider, but could be searched for with new search strategies.
In the second half of this thesis, we explore the possibility of embedding natural supersymmetry in models of warped extra dimensions in order to UV-complete them by utilizing a mechanism known as accidental supersymmetry. We study the mechanism of accidental supersymmetry in the Randall-Sundrum framework by focusing
on a toy model, and argue that accidental supersymmetry is capable solving the little hierarchy problem in that toy model. Finally, as models in the Randall-Sundrum framework themselves require UV completions, we demonstrate that it is possible to
realize the mechanism of accidental supersymmetry within the UV-complete framework of type IIB superstring theory
Identifying boosted new physics with non-isolated leptons
We demonstrate the utility of leptons which fail standard isolation criteria
in searches for new physics at the LHC. Such leptons can arise in any event
containing a highly boosted particle which decays to both leptons and quarks.
We begin by considering multiple extensions to the Standard Model which
primarily lead to events with non-isolated leptons and are therefore missed by
current search strategies. We emphasize the failure of standard isolation
variables to adequately discriminate between signal and SM background for any
value of the isolation cuts. We then introduce a new approach which makes use
of jet substructure techniques to distinguish a broad range of signals from QCD
events. We proceed with a simulated, proof-of-principle search for R-parity
violating supersymmetry to demonstrate both the experimental reach possible
with the use of non-isolated leptons and the utility of new substructure
variables over existing techniquesComment: 15 pages plus references, 11 figures; references adde
SUSY Stops at a Bump
We discuss collider signatures of the "natural supersymmetry" scenario with
baryon-number violating R-parity violation. We argue that this is one of the
few remaining viable incarnations of weak scale supersymmetry consistent with
full electroweak naturalness. We show that this intriguing and challenging
scenario contains distinctive LHC signals, resonances of hard jets in
conjunction with relatively soft leptons and missing energy, which are easily
overlooked by existing LHC searches. We propose novel strategies for
distinguishing these signals above background, and estimate their potential
reach at the 8 TeV LHC. We show that other multi-lepton signals of this
scenario can be seen by currently existing searches with increased statistics,
but these opportunities are more spectrum-dependent.Comment: 23 pages, 7 figures, 3 tables. V2: spectrum discussion corrected,
most of the changes are in Sec. 2. Benchmarks, analysis and conclusions
unchanged. References adde
Photoactivation of the BLUF protein PixD Probed by the Site-Specific Incorporation of Fluorotyrosine Residues
The flavin chromophore in blue light using FAD (BLUF) photoreceptors is surrounded by a hydrogen bond network that senses and responds to changes in the electronic structure of the flavin on the ultrafast time scale. The hydrogen bond network includes a strictly conserved Tyr residue, and previously we explored the role of this residue, Y21, in the photoactivation mechanism of the BLUF protein AppA by the introduction of fluorotyrosine (F-Tyr) analogs that modulated the pKa and reduction potential of Y21 by 3.5 pH units and 200 mV, respectively. Although little impact on the forward (dark to light adapted form) photoreaction was observed, the change in Y21 pKa led to a 4,000-fold increase in the rate of dark state recovery. In the present work we have extended these studies to the BLUF protein PixD, where, in contrast to AppA, modulation in the Tyr (Y8) pKa has a profound impact on the forward photoreaction. In particular, a decrease in Y8 pKa by 2 or more pH units prevents formation of a stable light state, consistent with a photoactivation mechanism that involves proton transfer or proton coupled electron transfer from Y8 to the electronically excited FAD. Conversely, the effect of pKa on the rate of dark recovery is markedly reduced in PixD. These observations highlight very significant differences between the photocycles of PixD and AppA, despite their sharing highly conserved FAD binding architectures
SUSY, the Third Generation and the LHC
We develop a bottom-up approach to studying SUSY with light stops and
sbottoms, but with other squarks and sleptons heavy and beyond reach of the
LHC. We discuss the range of squark, gaugino and Higgsino masses for which the
electroweak scale is radiatively stable over the "little hierarchy" below ~ 10
TeV. We review and expand on indirect constraints on this scenario, in
particular from flavor and CP tests. We emphasize that in this context,
R-parity violation is very well motivated. The phenomenological differences
between Majorana and Dirac gauginos are also discussed. Finally, we focus on
the light subsystem of stops, sbottom and neutralino with R-parity, in order to
probe the current collider bounds. We find that 1/fb LHC bounds are mild and
large parts of the motivated parameter space remain open, while the 10/fb data
can be much more decisive.Comment: 42 pages, 8 figures, 1 table. V2: minor corrections, references adde
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