arXiv subjects

Yuri Shirman

Publications and source records attributed to Yuri Shirman.

At least 19 recordsLinked to original sources

arXiv2025

The Potency of Nilpotence

The dynamics of $\mathcal{N}=1$ SUSY gauge theories with matter in adjoint and fundamental representations and the superpotentials given by Arnold's ADE singularities has been extensively studied in the literature. It was also conjectured that supersymmetric models with $W_{A_k}$, $W_{D_{k+2}}$ and $W_{E_7}$ superpotentials possess a dual description. In this paper we revisit the analysis of the moduli space of $A_k$ and $D_{k+2}$ models by considering the duality along nilpotent directions on the moduli space. While our analysis provides additional evidence for the duality conjecture in $W_{A_k}$ models, we show that the duality conjecture fails for the $W_{D_{k+2}}$ models.

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arXiv2023

Chirality Changing RG Flows: Dynamics and Models

Chirality plays an important role in understanding the dynamics of quantum field theories. In this paper, we study the dynamics of models where renormalization group flows change the chiral structure of the theory. We introduce model building tools and construct models with a variety of chirality flows: from the appearance of new massless composite matter, to the development of mass gaps to completely general changes in the chiral matter content. The stability of chirally symmetric vacua is sensitive to the interplay between non-perturbative dynamics and deformations necessary to generate chirality flows. In particular, we show that chirality flows can be easily induced by deformations of s-confining models. On the other hand, in the absence of true s-confinement, the required deformations destabilize chirally symmetric ground states.

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arXiv2021

Generation flow in field theory and strings

Nontrivial strong dynamics often leads to the appearance of chiral composites. In phenomenological applications, these can either play the role of Standard Model particles or lift chiral exotics by partnering with them in mass terms. As a consequence, the RG flow may change the effective number of chiral generations, a phenomenon we call generation flow. We provide explicit constructions of globally consistent string models exhibiting generation flow. Since such constructions were misclassified in the traditional model searches, our results imply that more care than usually appreciated has to be taken when scanning string compactifications for realistic models.

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arXiv2021

Monopoles Entangle Fermions

We resolve the decades old mystery of what happens when a positron scatters off a minimal GUT monopole in an s-wave, first discussed by Callan in 1983. Using the language of on-shell amplitudes and pairwise helicity we show that the final state contains two up quarks and a down quark entangled with angular momentum stored in the gauge fields, which is the only particle final state that satisfies angular momentum and gauge charge conservation. The cross section for this process is as large as in the original Rubakov-Callan effect, only suppressed by the QCD scale. The final state we find cannot be seen in Callan's truncated 2D theory, since our entanglement requires more than 2 dimensions.

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arXiv2021

Multi-particle Representations of the Poincaré Group

In this work we extend the definition of asymptotic multi-particle states of the $S$-matrix, beyond the direct products of one-particle states. We identify new quantum numbers which we call pairwise helicities, or $q_{ij}$, associated with asymptotically separated pairs of particles. These signal the appearance of a new source of angular momentum, beyond the orbital and spin contributions. The essence of our construction is to first treat all single particles as well as all particle pairs independently, ultimately projecting onto the physical states. The resulting representations reproduce the usual direct product states for vanishing $q_{ij}$, while for vanishing spins they reproduce Zwanziger's electric-magnetic multi-particle states. Pairwise helicity then appears as a label for the extra little group phase for our quantum states, in addition to their standard little group transformation. Our newly defined multi-particle states are the correct asymptotic states for the scattering of electric and magnetic charges, with pairwise helicity identified as $q_{ij}=e_i g_j-e_j g_i$.

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arXiv2020

Scattering Amplitudes for Monopoles: Pairwise Little Group and Pairwise Helicity

On-shell methods are particularly suited for exploring the scattering of electrically and magnetically charged objects, for which there is no local and Lorentz invariant Lagrangian description. In this paper we show how to construct a Lorentz-invariant S-matrix for the scattering of electrically and magnetically charged particles, without ever having to refer to a Dirac string. A key ingredient is a revision of our fundamental understanding of multi-particle representations of the Poincaré group. Surprisingly, the asymptotic states for electric-magnetic scattering transform with an additional little group phase, associated with pairs of electrically and magnetically charged particles. The corresponding "pairwise helicity" is identified with the quantized "cross product" of charges, $e_1 g_2 - e_2 g_1$, for every charge-monopole pair, and represents the extra angular momentum stored in the asymptotic electromagnetic field. We define a new kind of pairwise spinor-helicity variable, which serves as an additional building block for electric-magnetic scattering amplitudes. We then construct the most general 3-point S-matrix elements, as well as the full partial wave decomposition for the $2\to 2$ fermion-monopole S-matrix. In particular, we derive the famous helicity flip in the lowest partial wave as a simple consequence of a generalized spin-helicity selection rule, as well as the full angular dependence for the higher partial waves. Our construction provides a significant new achievement for the on-shell program, succeeding where the Lagrangian description has so far failed.

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arXiv2020

UV Sensitivity of the Axion Mass from Instantons in Partially Broken Gauge Groups

We examine the contribution of small instantons to the axion mass in various UV completions of QCD. We show that the reason behind the potential dominance of such contributions is the non-trivial embedding of QCD into the UV theory. The effects from instantons in the partially broken gauge group appear as "fractional instanton" corrections in the effective theory. These will exhibit unusual dependences on the various scales in the problem whenever the index of embedding is non-trivial. We present a full one-instanton calculation of the axion mass in the simplest product group models, carefully keeping track of numerical prefactors. Rather than using a 't Hooft operator approximation we directly evaluate the contributions to the vacuum bubble, automatically capturing the effects of closing up external fermion lines with Higgs loops. This approach is manifestly finite and removes the uncertainty associated with introducing a cutoff scale for the Higgs loops. We verify that the small instantons may dominate over the QCD contribution for very high breaking scales and at least three group factors.

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arXiv2020

The Axion Mass from 5D Small Instantons

We calculate a new contribution to the axion mass that arises from gluons propagating in a 5th dimension at high energies. By uplifting the 4D instanton solution to five dimensions, the positive frequency modes of the Kaluza-Klein states generate a power-law term in the effective action that inversely grows with the instanton size. This causes 5D small instantons to enhance the axion mass in a way that does not spoil the axion solution to the strong CP problem. Moreover this enhancement can be much larger than the usual QCD contribution from large instantons, although it requires the 5D gauge theory to be near the non-perturbative limit. Thus our result suggests that the mass range of axions (or axion-like particles), which is important for ongoing experimental searches, can depend sensitively on the UV modification of QCD.

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arXiv2019

Deformations of the moduli space and superpotential flows in 3D SUSY QCD

We study the moduli space of three-dimensional $\mathcal{N}=2$ SQCD with $SU(N)$ gauge group and $F<N$ massless flavors. In the case of an $SU(2)$ theory with a single massless flavor, we explicitly calculate the quantum constraint $YM=1$ and generalize the calculation to models with arbitrary $N$ and $F=N-1$ flavors. In theories with $F<N-1$ flavors, we find that analogous constraints exist in locally defined coordinate charts of the moduli space. The existence of such constraints allows us to show that the Coulomb branch superpotential generated by single monopole effects is equivalent to the superpotential generated by multi-monopole contributions on the mixed Higgs-Coulomb branch. As a check for our result, we implement the local constraints as Lagrange multiplier terms in the superpotential and verify that deformations of a theory by a large holomorphic mass term for the matter fields results in a flow of the superpotential from the $F$-flavor model to the superpotential of an $(F-1)$-flavor model.

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arXiv2018

Twisted Sisters: KK Monopoles and their Zero Modes

We find the conditions for the existence of fermionic zero modes of the fundamental representation in the background of a Kaluza-Klein (KK) monopole. We show that while there is no zero mode without a real mass, a normalizable zero mode appears once the real mass is sufficiently large. This provides an elegant explanation for the known decoupling of KK monopole effects in supersymmetric theories when a large real mass term is added. We also present an application where the correct counting of KK zero modes plays an essential role in understanding the non-perturbative effects determining the low-energy dynamics.

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arXiv2017

Pre-ADS Superpotential from Confined Monopoles

According to the standard lore only single monopoles contribute to the superpotential on the Coulomb branch of 3D ${\mathcal N}=2$ SUSY gauge theories. However we argue that multi-monopole configurations can also generate superpotential terms in the presence of squark VEVs on the mixed Higgs-Coulomb branch. The new ingredient is the confinement of monopoles via Nielsen-Olesen flux tubes. Such confined multi-monopoles will yield a pre-ADS superpotential which depends both on the local Coulomb moduli and matter superfields but has no fractional powers. Once the lifted moduli are integrated out the familiar ADS superpotential is obtained. Our results demonstrate the important role multi-monopoles can play in generating non-perturbative effects and also sheds light on the still somewhat mysterious dynamical origin of the general 4D ADS superpotential.

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arXiv2017

Asymmetric Dark Matter and Baryogenesis from $SU(2)_{\ell}$

We propose a theory in which the Standard Model gauge symmetry is extended by a new $SU(2)_\ell$ group acting nontrivially on the lepton sector which is spontaneously broken at the TeV scale. Under this $SU(2)_\ell$ the ordinary leptons form doublets along with new lepton partner fields. This construction naturally contains a dark matter candidate, the partner of the right-handed neutrino, stabilized by a residual global $U(1)_χ$ symmetry. We show that one can explain baryogenesis through an asymmetric dark matter scenario, in which generation of related asymmetries in the dark matter and baryon sectors is driven by the $SU(2)_\ell$ instantons during a first order phase transition in the early universe.

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arXiv2014

Dynamics of 3D SUSY Gauge Theories with Antisymmetric Matter

We investigate the IR dynamics of N=2 SUSY gauge theories in 3D with antisymmetric matter. The presence of the antisymmetric fields leads to further splitting of the Coulomb branch. Counting zero modes in the instanton background suggests that more than a single direction along the Coulomb branch may remain unlifted. We examine the case of SU(4) with one or two antisymmetric fields and various flavors in detail. Using the results for the corresponding 4D theories, we find the IR dynamics of the 3D cases via compactification and a real mass deformation. We find that for the s-confining case with two antisymmetric fields, a second unlifted Coulomb branch direction indeed appears in the low-energy dynamics. We present several non-trivial consistency checks to establish the validity of these results. We also comment on the expected structure of general s-confining theories in 3D, which might involve several unlifted Coulomb branch directions.

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arXiv2014

The $m_D-b_M$ Problem of Dirac Gauginos and its Solutions

We examine the effective low-energy theory of the adjoint sector of Dirac gaugino models and its UV completions, and identify the main source of tuning. A holomorphic scalar adjoint mass square (the "$b_M$ term") is generated at the same order (1-loop) as the Dirac gaugino mass (the "$m_D$ term"), leading to the problematic relation $b_M\sim16π^2 m_D^2$, somewhat analogous to the $μ-B_μ$ problem of gauge mediation. We identify the leading operators of the low-energy effective theory contributing to the adjoint sector, and evaluate them in various UV completions, confirming the existence of this problem. We suggest a solution by introducing messenger mixing and tuning the relevant parameters. We also present a novel dynamical model for Dirac gauginos based on a strongly coupled SUSY QCD theory, where the additional adjoint $M$ is identified with a confined meson, the U(1) with a baryon-number like symmetry, and the messengers with the confined baryons. We find a SUSY breaking vacuum with a non-vanishing D-term, which after tuning the messenger mixing angles gives rise to a realistic gaugino and squark sector.

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arXiv2013

Flavored Gauge Mediation, A Heavy Higgs, and Supersymmetric Alignment

We show that the messenger-matter couplings of Flavored Gauge Mediation Models can generate substantial stop mixing, leading to Higgs masses around 126 GeV with colored superpartners below 2 TeV and even a TeV. These results are largely independent of the messenger scale. We study the spectra of a few examples with a single messenger pair coupling dominantly to the top, for different messenger scales. Flavor constraints in these models are obeyed by virtue of supersymmetric alignment: the same flavor symmetry that explains fermion masses dictates the structure of the matter-messenger couplings, and this structure is inherited by the soft terms. We also present the leading 1-loop and 2-loop contributions to the soft terms for general coupling matrices in generation space.

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arXiv2012

Supersymmetry Breaking Triggered by Monopoles

We investigate N = 1 supersymmetric gauge theories where monopole condensation triggers supersymmetry breaking in a metastable vacuum. The low-energy effective theory is an O'Raifeartaigh-like model of the kind investigated recently by Shih where the R-symmetry can be spontaneously broken. We examine several implementations with varying degrees of phenomenological interest.

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arXiv2011

A Seiberg Dual for the MSSM: Partially Composite W and Z

We examine the possibility that the SU(2) gauge group of the standard model appears as the dual "magnetic" gauge group of a supersymmetric gauge theory, thus the W and Z (and through mixing, the photon) are composite (or partially composite) gauge bosons. Fully composite gauge bosons are expected to interact strongly at the duality scale, and a large running is needed to match the electroweak gauge couplings. Alternatively one can mix the composite "magnetic" gauge bosons with some elementary ones to obtain realistic models. In the simplest and most compelling example the Higgs and top are composite, the W and Z partially composite and the light fermions elementary. The effective theory is an NMSSM-type model where the singlet is a component of the composite meson. There is no little hierarchy problem and the Higgs mass can be as large as 400 GeV. This "fat Higgs"-like model can be considered as an explicit 4D implementation of RS-type models with gauge fields in the bulk.

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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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