arXiv subjects

Yael Shadmi

Publications and source records attributed to Yael Shadmi.

At least 37 records · Page 2Linked to original sources

arXiv2012

Kinematic Edges with Flavor Splitting and Mixing

The kinematic edges of invariant mass distributions provide an important tool for the possible measurements of superpartner masses in supersymmetric models with a neutralino LSP. We examine the effect of lepton flavor dependence on the kinematic endpoints of the di-lepton invariant mass distribution, with the leptons being electrons and muons. In the presence of slepton mass splitting and mixing, each of these distributions exhibits multiple edges, which are likely to be close. Furthermore, flavor subtraction, which is usually employed to eliminate backgrounds, dilutes the signal. We propose to extract the endpoints from the flavor-added distribution, which is insensitive to the slepton mixing. We also discuss the extraction of the slepton flavor parameters in such scenarios. To demonstrate our results, we use an example with a small slepton mass splitting of 3 GeV leading to a 6 GeV edge splitting, at both small mixing and large mixing.

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arXiv2012

Flavor and LHC Searches for New Physics

Uncovering the physics of electroweak symmetry breaking (EWSB) is the raison-d'etre of the LHC. Flavor questions, it would seem, are of minor relevance for this quest, apart from their role in constraining the possible structure of EWSB physics. In this short review article, we outline, using flavor-dependent sleptons as an example, how flavor can affect both searches for supersymmetry, and future measurements aimed at understanding the nature of any new discoveries. If the production cross-sections for supersymmetry are relatively low, as indicated by the fact that it has not revealed itself yet in standard searches, the usual assumptions about the superpartner spectra need re-thinking. Furthermore, one must consider more intricate searches, such as lepton-based searches, which could be susceptible to flavor effects. We start by reviewing the flavor structure of existing frameworks for mediating supersymmetry breaking, emphasizing flavor-dependent models proposed recently. We use the kinematic endpoints of invariant mass distributions to demonstrate how flavor dependence can impact both searches for supersymmetry and the Inverse Problem. We also discuss methods for measuring small-mass splittings and mixings at the LHC, both in models with a neutralino LSP and in models with a charged slepton (N)LSP.

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arXiv2011

When a Muon Is Not a Muon--- Detecting Fast Long-Lived Charged Particles from Cascade Decays Using a Mass Scan

If produced at the LHC, long-lived charged particles (LLCPs) would leave tracks in the muon detector. Time-of-Flight based methods for detecting these particles become less efficient if the LLCPs are fast, which would typically be the case if they are produced in the decays of some mother particle which is either heavy or very boosted. Thus for example, in supersymmetric models with long-lived sleptons, the long-lived sleptons produced in neutralino decays are often fast, with beta above 0.95 even at a 7 TeV LHC. We propose to use the (mis-measured) invariant mass distribution of "muon"-lepton pairs, where the "muon" could be a slepton LLCP, to detect it. This distribution peaks somewhat below the neutralino mass. The peak can be further enhanced by evaluating the distribution for different values of candidate "muon" masses. We simulate two GMSB-like models to show that this procedure can be used to detect the long-lived sleptons and measure both their mass and the neutralino mass.

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arXiv2011

Singlet Assisted Supersymmetry Breaking

We describe a simple recipe for obtaining local supersymmetry-breaking vacua in s-confining theories coupled to gauge singlets. This recipe gives rise to effective O'Raifeartaigh models in the IR, with calculable supersymmetry-breaking minima near the origin, and can be applied to both vector-like and chiral theories. Since the properties of the vacuum are largely determined by superpotential terms that are non-renormalizable in the UV, it is calculable even when all dimensionless couplings are taken to be of order one. By construction, the models preserve a large subgroup of the original global symmetry. While we only study here s-confining theories, we expect our tools to be useful for inducing dynamical supersymmetry breaking in many gauge theories.

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arXiv2011

Metastable Rank-Condition Supersymmetry Breaking in a Chiral Example

We discuss generalizations of Intriligator-Seiberg-Shih (ISS) vacua to chiral models. We study one example, of an s-confining theory, in detail. In the IR, this example reduces to two ISS-like sectors, and exhibits a supersymmetry-breaking vacuum with all pseudo-moduli stabilized at the origin, and with the R-symmetry unbroken. The IR theory is interesting from the point of view of R-symmetry breaking. This theory is an O'Raifeartaigh model with all charges zero or two, but the presence of a second R-charged pseudo-modulus with superpotential couplings to the messengers in principle allows for R-symmetry breaking.

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arXiv2011

WIMPless Dark Matter from Non-Abelian Hidden Sectors with Anomaly-Mediated Supersymmetry Breaking

In anomaly-mediated supersymmetry breaking (AMSB) models, superpartner masses are proportional to couplings squared. Their hidden sectors therefore naturally contain WIMPless dark matter, particles whose thermal relic abundance is guaranteed to be of the correct size, even though they are not weakly-interacting massive particles (WIMPs). We study viable dark matter candidates in WIMPless AMSB models with non-Abelian hidden sectors and highlight unusual possibilities that emerge in even the simplest models. In one example with a pure SU(N) hidden sector, stable hidden gluinos freeze out with the correct relic density, but have an extremely low, but natural, confinement scale, providing a framework for self-interacting dark matter. In another simple scenario, hidden gluinos freeze out and decay to visible Winos with the correct relic density, and hidden glueballs may either be stable, providing a natural framework for mixed cold-hot dark matter, or may decay, yielding astrophysical signals. Last, we present a model with light hidden pions that may be tested with improved constraints on the number of non-relativistic degrees of freedom. All of these scenarios are defined by a small number of parameters, are consistent with gauge coupling unification, preserve the beautiful connection between the weak scale and the observed dark matter relic density, and are natural, with relatively light visible superpartners. We conclude with comments on interesting future directions.

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arXiv2009

Measuring Slepton Masses and Mixings at the LHC

Flavor physics may help us understand theories beyond the standard model. In the context of supersymmetry, if we can measure the masses and mixings of sleptons and squarks, we may learn something about supersymmetry and supersymmetry breaking. Here we consider a hybrid gauge-gravity supersymmetric model in which the observed masses and mixings of the standard model leptons are explained by a U(1) x U(1) flavor symmetry. In the supersymmetric sector, the charged sleptons have reasonably large flavor mixings, and the lightest is metastable. As a result, supersymmetric events are characterized not by missing energy, but by heavy metastable charged particles. Many supersymmetric events are therefore fully reconstructible, and we can reconstruct most of the charged sleptons by working up the long supersymmetric decay chains. We obtain promising results for both masses and mixings, and conclude that, given a favorable model, precise measurements at the LHC may help shed light not only on new physics, but also on the standard model flavor parameters.

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arXiv2009

Three-Body Decays of Sleptons with General Flavor Violation and Left-Right Mixing

We determine the widths of three-body decays of sleptons, $\tilde{l}^- \to \tilde{l}^{\pm} l^- l^{\mp}, \tilde{l}^- ν\barν, \tilde{l}^- q \bar{q}$, in the presence of arbitrary slepton flavor violation and left-right mixing. These decays are important in scenarios in which the lightest supersymmetric particle is the gravitino, a generic possibility in models with gauge- and gravity-mediated supersymmetry breaking. Three-body decays have been discussed previously assuming flavor conservation and left-right mixing in only the stau sector. Flavor violation and general left-right mixing open up many new decay channels, which provide new avenues for precision mass measurements and may play an essential role in solving the standard model flavor problem. We present results for toy models with two-generation mixing, and discuss the implementation of these results in SPICE, a program that simplifies collider event simulations of flavor-violating supersymmetric models.

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arXiv2009

The Shifted Peak: Resolving Nearly Degenerate Particles at the LHC

We propose a method for determining the mass difference between two particles, \slep_1 and \slep_2, that are nearly degenerate, with Δ{m}, defined as m_2-m_1, being much less than m_1. This method applies when (a) the \slep_1 momentum can be measured, (b) \slep_2 can only decay to \slep_1, and (c) \slep_1 and \slep_2 can be produced in the decays of a common mother particle. For small Δ{m}, \slep_2 cannot be reconstructed directly, because its decay products are too soft to be detected. Despite this, we show that the existence of \slep_2 can be established by observing the shift in the mother particle invariant-mass peak, when reconstructed from decays to \slep_2. We show that measuring this shift would allow us to extract Δ{m}. As an example, we study supersymmetric gauge-gravity hybrid models in which \slep_1 is a meta-stable charged slepton next-to-lightest supersymmetric particle and \slep_2 is the next-to-lightest slepton with Δ{m} of about 5 GeV.

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arXiv2007

The Standard Model and Supersymmetric Flavor Puzzles at the Large Hadron Collider

Can the Large Hadron Collider explain the masses and mixings of the known fermions? A promising possibility is that these masses and mixings are determined by flavor symmetries that also govern new particles that will appear at the LHC. We consider well-motivated examples in supersymmetry with both gravity- and gauge-mediation. Contrary to spreading belief, new physics need not be minimally flavor violating. We build non-minimally flavor violating models that successfully explain all known lepton masses and mixings, but span a wide range in their predictions for slepton flavor violation. In natural and favorable cases, these models have metastable sleptons and are characterized by fully reconstructible events. We outline many flavor measurements that are then possible and describe their prospects for resolving both the standard model and new physics flavor puzzles at the Large Hadron Collider.

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arXiv2007

Comments on the Meta-Stable Vacuum in N_f=N_c SQCD and Direct Mediation

We revisit N_f=N_c SQCD and its non-supersymmetric minima conjectured by Intriligator, Seiberg and Shih (ISS). We argue that the existence of such minima depends on the signs of three non-calculable parameters and that no evidence can be inferred by deforming the theory. We demonstrate this by studying a deformation of the theory which involves additional gauge singlets. In this case, the conjectured minimum is destabilized. We comment on the consequences of such singlets in models of direct mediation and in particular in the Pentagon model.

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arXiv2007

Lorentz Violation and Superpartner Masses

We consider Lorentz violation in supersymmetric extensions of the standard model. We perform a spurion analysis to show that, in the simplest natural constructions, the resulting supersymmetry-breaking masses are tiny. In the process, we argue that one of the strongest bounds on Lorentz violation in the photon Lagrangian, which comes from the absence of birefringence from distant astrophysical sources, does not apply when Lorentz violation is parametrized by a single vector.

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arXiv2006

Supersymmetry breaking and the radion in AdS_4 brane-worlds

We compute the one-loop correction to the radion potential in the Randall-Sundrum model with detuned brane tensions, with supersymmetry broken by boundary conditions. We concentrate on the small-warping limit, where the one-loop correction is significant. With pure supergravity, the correction is negative, but with bulk hypermultiplets, the correction can be positive, so that the 4d curvature can be lowered, with the radion stable. We use both the KK theory, and the 4d radion effective theory for this study.

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arXiv2006

The radion potential and supersymmetry breaking in detuned RS

We study radiative corrections to the radion potential in the supersymmetric ``detuned RS model'', with supersymmetry broken by boundary conditions. Classically, the radion is stabilized in this model, and the 4d theory is AdS_4. With a few bulk hypermultiplets, the one-loop correction to the cosmological constant is positive. For small warping, this correction can (almost) cancel the classical result. The loop expansion is still reliable in this limit. The graviphoton zero-mode, which controls supersymmetry breaking, is a modulus of the classical theory, but is stabilized at one-loop. Both unbroken supersymmetry and maximal supersymmetry breaking are stable ground-states of the quantum theory.

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arXiv2006

Supersymmetry breaking

These lectures provide a simple introduction to supersymmetry breaking. After presenting the basics of the subject and illustrating them in tree-level examples, we discuss dynamical supersymmetry breaking, emphasizing the role of holomorphy and symmetries in restricting dynamically-generated superpotentials. We then turn to mechanisms for generating the MSSM supersymmetry-breaking terms, including ``gravity mediation'', gauge mediation, and anomaly mediation. We clarify some confusions regarding the decoupling of heavy fields in general and D-terms in particular in models of anomaly-mediation.

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arXiv2006

Supersymmetry Breaking and Moduli Stabilization in AdS

We study the one loop effective potential for the radion superfield in the supersymmetric Randall-Sundrum scenario with detuned brane tensions. At the classical level the distance between the branes is stabilized while the VEV of the fifth component of the graviphoton is a flat direction which breaks supersymmetry. At the quantum level a potential is generated. This leads to a toy model of a supersymmetric compactification with all the moduli stabilized perturbatively.

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arXiv2006

The flavor of product-group GUTs

The doublet-triplet splitting problem can be simply solved in product-group GUT models, using a global symmetry that distinguishes the doublets from the triplets. Apart from giving the required mass hierarchy, this ``triplet symmetry'' can also forbid some of the triplet couplings to matter. We point out that, since this symmetry is typically generation-dependent, it gives rise to non-trivial flavor structure. Furthermore, because flavor symmetries cannot be exact, the triplet-matter couplings are not forbidden then but only suppressed. We construct models in which the triplet symmetry gives acceptable proton decay rate and fermion masses. In some of the models, the prediction m_b ~ m_τis retained, while the similar relation for the first generation is corrected. Finally, all this can be accomplished with triplets somewhat below the GUT scale, supplying the right correction for the standard model gauge couplings to unify precisely.

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arXiv2004

Gauge Theories in $AdS_5$ and Fine-Lattice Deconstruction

The logarithmic energy dependence of gauge couplings in AdS_5 emerges almost automatically when the theory is deconstructed on a coarse lattice. Here we study the theory away from the coarse-lattice limit. While we cannot analytically calculate individual KK masses for a fine lattice, we can calculate the product of all non-zero masses. This allows us to write down the gauge coupling at low energies for any lattice-spacing and curvature. As expected, the leading log behaviour is corrected by power-law contributions, suppressed by the curvature. We then turn to intermediate energies, and discuss the gauge coupling and the gauge boson profile in perturbation theory around the coarse-lattice limit.

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