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1. What is the geometry of effective field theories?

   https://doi.org/10.1103/PhysRevD.111.085012  

   Cohen, Timothy; Lu, Xiaochuan; Zhang, Zhengkang (April 2025, Physical Review D)

   We elaborate on a recently proposed geometric framework for scalar effective field theories. Starting from the action, a metric can be identified that enables the construction of geometric quantities on the associated functional manifold. These objects transform covariantly under general field redefinitions that relate different operator bases, including those involving derivatives. We present a novel geometric formula for the amplitudes of the theory, where the vertices in Feynman diagrams are replaced by their geometrized counterparts. This makes the on-shell covariance of amplitudes manifest, providing the link between functional geometry and effective field theories. Published by the American Physical Society2025 

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2. Field-theory action for the constructive standard model

   https://doi.org/10.1103/PhysRevD.110.105008  

   Christensen, Neil (November 2024, Physical Review D)

   We introduce a field-theory framework in which fields transform under the little group, rather than the Lorentz group, specific to each particle type. By utilizing these fields, along with spinor products and the $x$ factor, we construct a field-theory action that naturally reproduces the vertices of the constructive standard model (CSM). This approach eliminates unphysical components, significantly reduces the degrees of freedom compared to traditional field theory, and offers deeper insights into the power of constructive amplitudes. Our action is momentum-conserving, Lorentz-invariant, Hermitian, and nonlocal. We also discuss this as a framework for developing new constructive field theories, discussing their essential properties and potential applicability in renormalization theory and nonperturbative calculations. Published by the American Physical Society2024 

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3. Experimental Realization of Discrete Time Quasicrystals

   https://doi.org/10.1103/physrevx.15.011055  

   He, Guanghui; Ye, Bingtian; Gong, Ruotian; Yao, Changyu; Liu, Zhongyuan; Murch, Kater W; Yao, Norman Y; Zu, Chong (March 2025, Physical Review X)

   Floquet (periodically driven) systems can give rise to unique nonequilibrium phases of matter without equilibrium analogs. The most prominent example is the realization of discrete time crystals. An intriguing question emerges: What other novel phases can manifest when the constraint of time periodicity is relaxed? In this study, we explore quantum systems subjected to a quasiperiodic drive. Leveraging a strongly interacting spin ensemble in diamond, we identify the emergence of long-lived discrete time quasicrystals. Unlike conventional time crystals, time quasicrystals exhibit robust subharmonic responses at multiple incommensurate frequencies. Furthermore, we show that the multifrequency nature of the quasiperiodic drive allows for the formation of diverse patterns associated with different discrete time quasicrystalline phases. Our findings demonstrate the existence of nonequilibrium phases in quasi-Floquet settings, significantly broadening the catalog of novel phenomena in driven many-body quantum systems. Published by the American Physical Society2025 

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4. Do \({\mit \Lambda }_{\mathrm {CC}}\) and \(G\) Run?

   https://doi.org/10.5506/APhysPolB.55.12-A1  

   Donoghue, JF (December 2024, Acta Physica Polonica B)

   No AbstractPublished by the Jagiellonian University2024authors 

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5. Cyclic Products of Higher-Genus Szegö Kernels, Modular Tensors, and Polylogarithms

   https://doi.org/10.1103/PhysRevLett.133.021602  

   D’Hoker, Eric; Hidding, Martijn; Schlotterer, Oliver (July 2024, Physical Review Letters)

   A wealth of information on multiloop string amplitudes is encoded in fermionic two-point functions known as Szegö kernels. Here we show that cyclic products of any number of Szegö kernels on a Riemann surface of arbitrary genus may be decomposed into linear combinations of modular tensors on moduli space that carry all the dependence on the spin structure $\delta$. The $\delta$-independent coefficients in these combinations carry all the dependence on the marked points and are composed of the integration kernels of higher-genus polylogarithms. We determine the antiholomorphic moduli derivatives of the $\delta$-dependent modular tensors. Published by the American Physical Society2024 

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