Scalar singlets under the Standard Model gauge group appear naturally in many well-motivated New Physics scenarios, such as the composite Higgs models. Unlike the Higgs boson in the Standard Model, they can induce large flavour-changing neutral currents (FCNCs) in the top sector. We investigate systematically the effects of a light scalar singlet $\textit{S}$ with top-quark FCNC couplings, by including the low-energy constraints from the $\textit{B}$ → $\textit{μ}$ decay, the muon anomalous magnetic moment ($\textit{g}$ − 2) and the neutron Electric Dipole Moment (EDM). We also perform a detailed Monte-Carlo simulation of the channel $\textit{pp}$ → $\textit{tS}$ + $\textit{j}$ with $\textit{S}$ → $\textit{μ}$ and $\textit{S}$ → $$ b\overline{b} $$ , and investigate the LHC sensitivity to the $\textit{tcS}$ couplings. It is found that the scalar singlet $\textit{S}$ can induce scalar-type contributions to the $\textit{B}$ $\textit{→ μ}$ decay, which do not suffer from the helicity suppression and contain a large CKM factor $$ {V}_{cs}^{\ast }{V}_{tb} $$ . As a result, constraints on the $\textit{tcS}$ couplings from the measured branching ratio $$ \mathcal{B} $$ ($\textit{B}$ → $\textit{μ}$ ) are quite stringent, being even stronger than the expected LHC sensitivity in some parameter spaces. Besides the CP-conserving $\textit{tcS}$ couplings, we have also considered the case of CP-violating $\textit{tcS}$ couplings, with $$ {y}_{R,L}^{ct}=\left|{y}_{R,L}^{ct}\right|{e}^{i{\theta}_{R,L}} $$ . It is found that the CP observables $$ {\mathcal{A}}_{\Delta {\varGamma}_s}^{\mu \mu} $$ and $$ {\mathcal{S}}_{\mu \mu} $$ of the $\textit{B}$ $\textit{→ μ}$ decay are sensitive to the phase $\textit{θ}$ , while the neutron EDM can provide bounds on the phase difference $\textit{θ}$ − $\textit{θ}$ . Therefore, they are complementary to each other in probing the CP phases of the $\textit{tcS}$ couplings.

China

Biao-Feng Hou

Xin-Qiang Li

Ya-Dong Yang

Xing-Bo Yuan

Ming-Wang Zhang

Phenomenological anatomy of top-quark FCNCs induced by a light scalar singlet

Helicity selection rules can suppress the leading contributions from dimension-6 operators in the Standard Model effective field theory (SMEFT), reducing sensitivity to potential new physics. This paper explores how the interference contributions from the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>τ</mi></math> lepton’s anomalous dipole moment is restored in different observables, in particular comparing the sensitivity to SMEFT operators of quantum information observable and more traditional spin correlations. We compute the sensitivity of various observables—including entanglement measures, Bell inequality violations, and quantum uncertainties—to new physics effects using Monte Carlo simulations. Spin correlation observables are found to outperform both the integrated cross section and quantum information observables in sensitivity to both <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math>-conserving and -violating effects, improving the sensitivity to the scale of new physics by up to a factor of 3. Our results suggest that quantum information observables are suboptimal probes for resurrecting the interference, and more in general to disentangle the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>C</mi><mi>P</mi></math> properties of new physics.

Germany

Prisco Lo Chiatto

Interference resurrection of the <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi>τ</mi></mrow></math> dipole through quantum tomography

The structure of center vortices is studied in SU(4) Yang-Mills theory for the first time to illuminate the interplay between elementary (center charge <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>±</mo><mn>1</mn></math>) and doubly charged vortices. Unlike in SU(3), where charge <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mo>+</mo><mn>2</mn></math> vortices are simply elementary vortices with reversed orientations in spacetime, these possibilities are physically distinct in SU(4). Visualizations of the vortex structure in three-dimensional slices reveal the various ways in which doubly charged objects manifest, as the convergence and matching of elementary vortices or as isolated doubly charged loops. An algorithm is described to classify every doubly charged chain as one of these three types. A collection of vortex statistics is considered to quantify the vortex structure. Many of these pertain to the novel doubly charged objects, including their relative proportions and chain lengths, which are analyzed to highlight the differences between each chain type. Three different lattice spacings are employed to investigate the approach to the continuum limit. Vortex matching chains are found to be shorter on average but also more prevalent than vortex convergences, ascribed to their interpretation as extended center monopoles. In addition, the lengths of both vortex convergences and vortex matchings are observed to follow an exponential distribution, allowing the introduction of a constant probability for a doubly charged chain to split into two elementary vortices as it propagates. Combined, these findings provide a characterization of the vortices that comprise center-vortex structures in SU(4) Yang-Mills theory.

Australia

Jackson A. Mickley

Derek B. Leinweber

Brazil

Luis E. Oxman

Structure of center-vortex matter in SU(4) Yang-Mills theory

We present a study of the transverse size of parton showers and their diminishing interaction with the medium in the high virtuality stage of jet evolution. We consider the process of a hard quark produced in deep inelastic scattering off a large nucleus. Single gluon radiation from this quark, in the absence of scattering, is rederived using wave packets. This allows for a derivation of the quantum uncertainty size of the hard quark, at the point of splitting. This uncertainty size is then incorporated within a Monte Carlo shower routine yielding transverse shower sizes noticeably larger than the classical antenna size of the shower. No clear relation is found between the full uncertainty size of the shower and the virtuality of the originating parton. The single gluon emission from the hard quark is then reanalyzed for the case of single rescattering off the remainder of the nucleus. A relation is derived between the jet transport coefficient <math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent="true"><mi>q</mi><mo>̂</mo></mover></math> and the gluon Transverse momentum-dependent parton distribution function (gTMDPDF). Solving this relation, for a simple case, clearly demonstrates the weakening of <math xmlns="http://www.w3.org/1998/Math/MathML"><mover accent="true"><mi>q</mi><mo>̂</mo></mover></math> with the virtuality of the hard splitting parton.

United States

Canada

Amit Kumar

Abhijit Majumder

Chathuranga Sirimanna

Japan

Yasuki Tachibana

Modified coherence and the transverse extent of jets

Collisional flavor instabilities, driven by differing neutrino and antineutrino reaction rates, are expected to occur in dense astrophysical environments like supernovae and neutron star mergers, but have yet to be incorporated in large-scale simulations. We derive analytical expressions for the asymptotic state resulting from a homogeneous and isotropic instability, and apply these predictions to two representative conditions from a neutron star merger simulation. We emphasize the importance of using a collision term that allows for both damping of flavor coherence and relaxation back to the classical steady state. When this classical configuration is collisional unstable, the resulting asymptotic state reflects a compromise between classical relaxation and flavor conversion, defining a “quantum” equilibrium with nonzero coherence. This analysis highlights the possibility of a tradeoff between classical and quantum effects, an important feature with regard to the inclusion of flavor oscillation physics into global simulations.

Julien Froustey

Predicting the outcome of collisional neutrino flavor conversion

Minimally doubled fermions realize one pair of Dirac fermions on the lattice. Similarities to staggered fermions exist, namely, spin and taste degrees of freedom become intertwined, and a peculiar nonsinglet chiral symmetry and ultralocality are maintained. However, charge conjugation, some space-time reflection symmetries and isotropy are broken by the cutoff. We address the most simple variant, Karsten-Wilczek (KW) fermions, in its parallel and in its perpendicular version. We derive the correct spin-taste representation from first principles. The spin-taste representation on the quark level permits construction of local or extended hadron interpolating operators for any spin-taste combination, albeit with contamination by parity partners and taste-symmetry breaking. We classify all interpolating operators for mesons and diquarks, and give examples for baryons. We also discuss the appropriate discretizations for taste-singlet or taste-isovector mass or chemical potential terms. We explain the counterterms in the spin-taste framework, and derive generic constraints on the parametric form and cutoff effects from the KW determinant and hadronic correlation functions. We derive how and why nonperturbative tuning schemes for the counterterms work, and obtain analytic, assumption-free, nonperturbative predictions for taste-symmetry breaking and other hadronic properties from first principles. In particular, we identify the origin and nature of two different types of taste-symmetry breaking cutoff effects. The few available numerical results for KW fermions validate these predictions.

Johannes Heinrich Weber

Spin-taste representation of minimally doubled fermions from first principles: Karsten-Wilczek fermions

Without invoking any cumulant determination at the input level, we present here the first calculations of direct estimates of the Lee-Yang zeros of the QCD partition function in (<math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mn>2</mn><mo>+</mo><mn>1</mn></mrow></math>)-flavor QCD. These zeros are obtained in the complex isospin chemical potential <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> plane using the unbiased exponential resummation formalism on <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>N</mi><mi>τ</mi></msub><mo>=</mo><mn>8</mn></math> lattices and with physical quark masses. For different temperatures, we illustrate the stability of the zeros closest to the origin from which we subsequently procure the radius of convergence estimates. From the temperature-dependence study of the real and imaginary parts of these zeros, we try estimating one of the possible critical points forming the second-order pion condensate critical line in the isospin phase diagram. Further, we compare these resummed estimates with the corresponding Mercer-Roberts estimates of the subsequent Taylor series expansions of the first three partition function cumulants. We also outline comparisons between resummed and Taylor series results of these cumulants for real and imaginary values of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> and highlight the behavior of different expansion orders within and beyond the obtained resummed estimates of the radius of convergence. We also reestablish that this resummed radius of convergence can efficiently capture the onset of the overlap problem for finite real <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><msub><mi>μ</mi><mi>I</mi></msub></math> simulations.

Sabarnya Mitra

Estimates of Lee-Yang zeros and a possible critical point on the pion condensate boundary in the QCD isospin phase diagram using an unbiased exponential resummation on the lattice

Perhaps the most basic question we can ask about cosmological correlations is how their strength changes as we smoothly vary kinematic parameters. The answer is encoded in differential equations that govern this evolution in kinematic space. In this Letter, we introduce a new perspective on these differential equations. We show that, in the simplified setting of conformally coupled scalars in power-law Friedmann-Robertson-Walker spacetimes, the equations for arbitrary tree-level processes can be obtained from a small number of simple combinatorial rules. While this “kinematic flow” is defined purely in terms of boundary data, it reflects the physics of bulk time evolution. The unexpected regularity of the equations suggests the existence of an autonomously defined mathematical structure from which cosmological correlations and the time evolution of the associated spacetime emerge.

Nima Arkani-Hamed

Taiwan

Netherlands

Daniel Baumann

Aaron Hillman

Austin Joyce

Hayden Lee

Italy

Guilherme L. Pimentel

Kinematic Flow and the Emergence of Time

Non-renormalisable versions of <math altimg='si1.svg'><mi>S</mi><mi>O</mi><mo stretchy='false'>(</mo><mn>10</mn><mo stretchy='false'>)</mo></math> based on irreducible representations with lesser degrees of freedom, are free of running into the catastrophe of non-perturbativity of standard model gauge couplings in contrast to the renormalisable versions having tensors with many degrees of freedom. <math altimg='si2.svg'><msub><mrow><mn>16</mn></mrow><mrow><mi>H</mi></mrow></msub></math> is the smallest representation, participates in Yukawa Lagrangian at the non-renormalisable level, contributing to the charged and neutral fermion masses, and has six distinct scalars with different <math altimg='si3.svg'><mi>B</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></math> charges. We computed the leptoquark and diquark couplings of different pairs of scalars stemming from all possible decomposition of the term resulting from the coupling of <math altimg='si2.svg'><msub><mrow><mn>16</mn></mrow><mrow><mi>H</mi></mrow></msub></math> with the <bold>16</bold> dimensional fermion multiplet of <math altimg='si1.svg'><mi>S</mi><mi>O</mi><mo stretchy='false'>(</mo><mn>10</mn><mo stretchy='false'>)</mo></math>, i.e. <math altimg='si4.svg'><mfrac><mrow><mn mathvariant='bold'>16</mn><mspace width='0.2em' /><mn mathvariant='bold'>16</mn><mspace width='0.2em' /><msub><mrow><mn>16</mn></mrow><mrow><mi>H</mi></mrow></msub><mspace width='0.2em' /><msub><mrow><mn>16</mn></mrow><mrow><mi>H</mi></mrow></msub></mrow><mrow><mi mathvariant='normal'>&#923;</mi></mrow></mfrac></math>. Computing the tree and loop level contribution of different pairs to the effective dimension six, <math altimg='si3.svg'><mi>B</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></math> conserving operators, it turns out only three pairs, viz <math altimg='si5.svg'><mi>&#963;</mi><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>(</mo><mn>1</mn><mo>,</mo><mn>1</mn><mo>,</mo><mn>0</mn><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>T</mi><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>(</mo><mn>3</mn><mo>,</mo><mn>1</mn><mo>,</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>3</mn></mrow></mfrac><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>)</mo></math>, and <math altimg='si6.svg'><mi>H</mi><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>(</mo><mn>1</mn><mo>,</mo><mn>2</mn><mo>,</mo><mo linebreak='badbreak' linebreakstyle='after'>&#8722;</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>2</mn></mrow></mfrac><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>)</mo><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi mathvariant='normal'>&#916;</mi><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>(</mo><mn>3</mn><mo>,</mo><mn>2</mn><mo>,</mo><mfrac><mrow><mn>1</mn></mrow><mrow><mn>6</mn></mrow></mfrac><mo stretchy='true' maxsize='2.4ex' minsize='2.4ex'>)</mo></math>, and <math altimg='si7.svg'><mi>H</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>T</mi></math> can induce proton decay at tree level. Assuming that the Yukawa couplings of the <math altimg='si2.svg'><msub><mrow><mn>16</mn></mrow><mrow><mi>H</mi></mrow></msub></math> are comparable to those of the <math altimg='si8.svg'><msub><mrow><mover accent='true'><mrow><mn>126</mn></mrow><mo>&#8254;</mo></mover></mrow><mrow><mi>H</mi></mrow></msub></math> of a realistic <math altimg='si1.svg'><mi>S</mi><mi>O</mi><mo stretchy='false'>(</mo><mn>10</mn><mo stretchy='false'>)</mo></math> model and setting the cutoff scale to the Planck scale typically constrains the <math altimg='si3.svg'><mi>B</mi><mo linebreak='goodbreak' linebreakstyle='after'>&#8722;</mo><mi>L</mi></math> breaking scale to be <math altimg='si9.svg'><mn>4</mn><mo>&#8764;</mo><mn>5</mn></math> orders of magnitude less than the cutoff scale (&#923;). Moreover, analysing the branching pattern of the leading two-body decay modes of the proton, we observed a preference for the proton to decay into second-generation mesons due to the hierarchical nature of Yukawa couplings. In a realistic <math altimg='si1.svg'><mi>S</mi><mi>O</mi><mo stretchy='false'>(</mo><mn>10</mn><mo stretchy='false'>)</mo></math> scenario, we find that <math altimg='si10.svg'><msub><mrow><mi>M</mi></mrow><mrow><mi>T</mi></mrow></msub><mo linebreak='goodbreak' linebreakstyle='after'>&gt;</mo><msup><mrow><mn>10</mn></mrow><mrow><mn>8</mn></mrow></msup></math> TeV, while <math altimg='si11.svg'><msub><mrow><mi>M</mi></mrow><mrow><mi mathvariant='normal'>&#916;</mi></mrow></msub></math> could be as light as a few TeV <italic>s</italic>.

India

Saurabh K. Shukla

Constraining scalars of 16 <inf><italic>H</italic></inf> through proton decays in non-renormalisable <italic>SO</italic>(10) models

We compute next-to-leading power corrections in the zero-jettiness variable for the production of colorless final states at hadron colliders at next-to-leading order in QCD. To assess if the process-independence of leading power contributions can be extended, we attempt to construct generic expansions of phase spaces and matrix elements squared through next-to-leading power in the zero-jettiness. We highlight challenges associated with the collinear limit, where universality no longer holds at the subleading power, making the result process-dependent. We show that quantities that need to be calculated in the collinear limit can be obtained using Berends-Giele currents, enabling computation of power corrections to high-multiplicity final states. As a concrete example, we apply our method to compute power corrections in the zero-jettiness for lepton pair as well as multi-photon production in $$ q\overline{q} $$ collisions.

Prem Agarwal

Kirill Melnikov

Ivan Pedron

Philip Pfohl

Power corrections to the production of a color-singlet final state in hadron collisions in the $\textit{N}$-jettiness slicing scheme at NLO QCD