arXiv subjects

A. Stern

Publications and source records attributed to A. Stern.

At least 19 recordsLinked to original sources

arXiv2026

Symmetry Nonrestoration in the Pati-Salam Model

We demonstrate that symmetry need not be restored in the Pati-Salam model, so that $SU(2)_L\otimes SU(2)_R\otimes SU(4)_c$ remains broken to the Standard Model group at temperatures above the Pati-Salam symmetry breaking scale. Including the leading finite-temperature corrections, suitable quartic couplings prevent a restoration transition, thereby avoiding the thermal production of 't Hooft-Polyakov monopoles after inflation, even if the reheating temperature is very high. This removes monopole-based constraints on the Pati-Salam symmetry breaking scale.

hep-ph↗

arXiv2025

Gauging the Schwarzian Action

In this work, we promote the global $SL(2,\mathbb{R})$ symmetry of the Schwarzian derivative to a local gauge symmetry. To achieve this, we develop a procedure that potentially can be generalized beyond the $SL(2,\mathbb{R})$ case: We first construct a composite field from the fundamental field and its derivative such that it transforms linearly under the group action. Then we write down its gauge-covariant extension and apply standard gauging techniques. Applying this to the fractional linear representation of $SL(2,\mathbb{R})$, we obtain the gauge-invariant analogue of the Schwarzian derivative as a bilinear invariant of covariant derivatives of the composite field. The framework enables a simple construction of N\"other charges associated with the original global symmetry. The gauge-invariant Schwarzian action introduces $SL(2,\mathbb{R})$ gauge potentials, allowing for locally invariant couplings to additional fields, such as fermions. While these potentials can be gauged away on topologically trivial domains, non-trivial topologies (e.g., $S^1$) lead to distinct topological sectors. We mention that in the context of two-dimensional gravity, these sectors could correspond to previously discussed defects in the bulk theory.

math-ph↗

arXiv2024

Embedding Space Approach to JT Gravity

We present a coordinate-free background space construction of Euclidean Jackiw-Teitelboim gravity. It is written as a gauge theory that utilizes the Killing vectors and conformal Killing vectors of a hyperboloid embedded in a three dimensional background. A novel feature of the gauge theory is that vanishing field strength does not necessarily imply that the gauge potentials are pure gauges, not even locally. As is usual, metric tensors are dynamically generated from the classical solutions of the theory, which here do not rely on coordinate charts on the two-dimensional surface. We find a special class of solutions whereby the derived metric tensor on the surface is the induced metric from the background space. The gauge theory construction given here has a natural generalization to a non-commutative space, which does not require the use of coordinates, symbols or a star product.

hep-th↗

arXiv2022

Noncommutative $AdS_2$ I: Exact solutions

We study the exact solutions of both, massless and massive, scalar field theory on the noncommutative $AdS_2$. We also discuss some important limits in order to compare with known results.

hep-th↗

arXiv2022

Noncommutative $AdS_2$ II: The Correspondence Principle

Using the exact solutions to the field equation for a massive scalar field on noncommutative $AdS_2$, we apply the $AdS/CFT$ correspondence principle to obtain an exact result for the associated two-point function on the conformal boundary. The answer satisfies conformal invariance and has the correct commutative limit and massless limit.

hep-th↗

arXiv2022

In-vacuum microwave resonator for a compact cold atom frequency standard

A physics package for a compact cold atomic clock is hereby presented. The uniqueness of this package is its small dimensions that enable, for the first time, implementation of a primary cold atomic clock in a standard package of 3U height (=133mm). These dimensions are made possible by using an in-vacuum Microwave (MW) Loop Gap Resonator (LGR) whose length and diameter can be reduced from those of a typical resonator. Following our presentation of the design, we analyze the homogeneity of the MW field amplitude and phase. We find that the expected clock instability due to non-uniformity of the MW field is $\sim1.5\cdot10^{-14}$/day. Adding other clock errors, we estimate the total uncertainty of a cold atomic clock of this design will be around $\sim2\cdot10^{-14}$/day which results in a time drift of a few nanoseconds/day. Such a clock can serve as a primary-grade frequency reference, and may replace the cesium beam atomic clock and the GPS-disciplined rubidium atomic clocks.

physics.atom-ph↗

arXiv2022

Dark Energy from the Fifth Dimension

After extending the Regge-Teitelboim formulation of gravity to include the case where the background embedding space is not flat, we examine the dynamics of the four-dimensional $k=0$ Robertson-Walker (RW) manifold embedded in various five-dimensional backgrounds. We find that when the background is five-dimensional de Sitter space, the RW manifold undergoes a transition from a de-accelerating phase to an accelerating phase. This occurs before the inclusion of matter, radiation or cosmological constant sources, and thus does not require a balance of different components. We obtain a reasonable two-parameter fit of this model to the Hubble parameter data.

gr-qc↗

arXiv2022

Cosmic acceleration in Regge-Teitelboim gravity

The Regge-Teitelboim formulation of gravity, which utilizes dynamical embeddings in a background space, effectively introduces source terms in the standard Einstein equations that are not attributable to the energy-momentum tensor. We show that for a simple class of embeddings of the Robertson-Walker metric, these source terms naturally generate cosmic acceleration.

gr-qc↗

arXiv2021

Exact solutions for scalars and spinors on quantized (Euclidean) $AdS_2$ and the correspondence principle

We obtain the exact solutions to the field equations for massless scalar and massless spinor fields on quantized two-dimensional anti-de Sitter space. We then apply the AdS/CFT correspondence principle to get exact answers for the two point correlation functions of the associated operators on the boundary. The results support the conclusion that conformal symmetry on the boundary is not spoiled by quantization of the bulk. Moreover, quantization of the bulk has no effect on the spinor two-point correlation function, while it induces an overall re-scaling in the scalar two-point correlation function.

hep-th↗

arXiv2020

Asymptotic commutativity of quantized spaces: the case of $\mathbb{CP}^{p,q}$

We present a procedure for quantizing complex projective spaces $\mathbb{CP}^{p,q}$, $q\ge 1$, as well as construct relevant star products on these spaces. The quantization is made unique with the demand that it preserves the full isometry algebra of the metric. Although the isometry algebra, namely $su(p+1,q)$, is preserved by the quantization, the Killing vectors generating these isometries pick up quantum corrections. The quantization procedure is an extension of one applied recently to Euclidean $AdS_2$, where it was found that all quantum corrections to the Killing vectors vanish in the asymptotic limit, in addition to the result that the star product trivializes to pointwise product in the limit. In other words, the space is asymptotically anti-de Sitter making it a possible candidate for the $AdS/CFT$ correspondence principle. In this article, we find indications that the results for quantized Euclidean $AdS_2$ can be extended to quantized $\mathbb{CP}^{p,q}$, i.e., noncommutativity is restricted to a limited neighborhood of some origin, and these quantum spaces approach $\mathbb{CP}^{p,q}$ in the asymptotic limit.

hep-th↗

arXiv2019

Lagrangian formulation for electric charge in a magnetic monopole distribution

We give a Lagrangian description of an electric charge in a field sourced by a continuous magnetic monopole distribution. The description is made possible thanks to a doubling of the configuration space. The Legendre transform of the nonrelativistic Lagrangian agrees with the Hamiltonian description given recently by Kupriyanov and Szabo. The covariant relativistic version of the Lagrangian is shown to introduce a new gauge symmetry, in addition to standard reparametrizations. The generalization of the system to open strings coupled to a magnetic monopole distribution is also given, as well as the generalization to particles in a non-Abelian gauge field which does not satisfy Bianchi identities in some region of the space-time.

hep-th↗

arXiv2018

Signature change in matrix model solutions

Various classical solutions to lower dimensional IKKT-like Lorentzian matrix models are examined in their commutative limit. Poisson manifolds emerge in this limit, and their associated induced and effective metrics are computed. Signature change is found to be a common feature of these manifolds when quadratic and cubic terms are included in the bosonic action. In fact, a single manifold may exhibit multiple signature changes. Regions with Lorentzian signature may serve as toy models for cosmological space-times, complete with cosmological singularities, occurring at the signature change. The singularities are resolved away from the commutative limit. Toy models of open and closed cosmological space-times are given in two and four dimensions. The four dimensional cosmologies are constructed from non-commutative complex projective spaces, and they are found to display a rapid expansion near the initial singularity.

hep-th↗

arXiv2018

The nitrogen cycles on Pluto over seasonal and astronomical timescales

Pluto's landscape is shaped by the cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia (SP) ice sheet displays a large diversity of terrains, with bright and dark plains, pits, topographic depressions and evidences of recent and past glacial flows. Outside SP, New Horizons also revealed numerous N2 ice deposits, in Tombaugh Regio and at mid-northern latitudes. These observations suggest a complex history involving volatile and glacial processes on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model able to simulate the N2 cycle over millions of years (Myrs), taking into account the changes of obliquity and orbital parameters as experienced by Pluto. Results show that over one obliquity cycle, the latitudes of SP between 25{\deg}S-30{\deg}N are dominated by N2 condensation, while the latitudes between 30-50{\deg}N are dominated by N2 sublimation. We find that a net amount of 1 km of ice has sublimed at the northern edge of SP during the last 2 Myrs. By comparing these results with the observed geology of SP, we can relate the formation of the pits and the brightness of the ice to the ice flux occurring at the annual timescale, while the glacial flows at its eastern edge and the erosion of the water ice mountains all around the ice sheet are related to the astronomical timescale. We also perform simulations with a glacial flow scheme which shows that SP is currently at its minimum extent. We also explore the stability of N2 ice outside SP. Results show that it is not stable at the poles but rather in the equatorial regions, in particular in depressions, where thick deposits may persist over tens of Myrs, before being trapped in SP. Finally, another key result is that the minimum and maximum surface pressures obtained over the simulated Myrs remain in the range of mm-Pa and Pa, respectively.

astro-ph.EP↗

arXiv2017

Further studies of isolated photon production with a jet in deep inelastic scattering at HERA

Isolated photons with high transverse energy have been studied in deep inelastic $ep$ scattering with the ZEUS detector at HERA, using an integrated luminosity of $326\,$ pb$^{-1}$ in the range of exchanged-photon virtuality $10 - 350$ GeV$^2$. Outgoing isolated photons with transverse energy $4<E_T^\gamma< 15$ GeV and pseudorapidity $-0.7 <\eta^\gamma< 0.9$ were measured with accompanying jets having transverse energy and pseudorapidity $2.5 <E_T^{jet}<35$ GeV and $-1.5<\eta^{jet}< 1.8$, respectively. Differential cross sections are presented for the following variables: the fraction of the incoming photon energy and momentum that is transferred to the outgoing photon and the leading jet; the fraction of the incoming proton energy transferred to the photon and leading jet; the differences in azimuthal angle and pseudorapidity between the outgoing photon and the leading jet and between the outgoing photon and the scattered electron. Comparisons are made with theoretical predictions: a leading-logarithm Monte Carlo simulation, a next-to-leading-order QCD prediction, and a prediction using the $k_T$-factorisation approach.

hep-ex↗

arXiv2017

Interstellar Pickup Ion Observations to 38 AU

We provide the first direct observations of interstellar H+ and He+ pickup ions in the solar wind from 22 AU to 38 AU. We use the Vasyliunas and Siscoe model functional form to quantify the pickup ion distributions, and while the fit parameters generally lie outside their physically expected ranges, this form allows fits that quantify variations in the pickup H+ properties with distance. By ~20 AU, the pickup ions already provide the dominant internal pressure in the solar wind. We determine the radial trends and extrapolate them to the termination shock at ~90 AU, where the pickup H+ to core solar wind density reaches ~0.14. The pickup H+ temperature and thermal pressure increase from 22-38 AU, indicating additional heating of the pickup ions. This produces very large extrapolated ratios of pickup H+ to solar wind temperature and pressure and an extrapolated ratio of the pickup ion pressure to the solar wind dynamic pressure at the termination shock of ~0.16. Such a large ratio has profound implications for moderating the termination shock and the overall outer heliospheric interaction. We also identify suprathermal tails in the H+ spectra and complex features in the He+ spectra, likely indicating variations in the pickup ion history and processing. Finally, we discover enhancements in both H+ and He+ populations just below their cutoff energies, which may be associated with enhanced local pickup. This study serves to document the release and as the citable reference of these pickup ion data for broad community use and analysis.

physics.space-ph↗

arXiv2017

Non-commutative $AdS_2/CFT_1$ duality: the case of massless scalar fields

We show how to construct correlators for the $CFT_1$ which is dual to non-commutative $AdS_2$ ($ncAdS_2$). We do it explicitly for the example of the massless scalar field on Euclidean $ncAdS_2$. $ncAdS_2$ is the quantization of $AdS_2$ that preserves all the isometries. It is described in terms of the unitary irreducible representations, more specifically discrete series representations, of $so(2,1)$. We write down symmetric differential representations for the discrete series, and then map them to functions on the Moyal-Weyl plane. The Moyal-Weyl plane has a large distance limit which can be identified with the boundary of $ncAdS_2$. Killing vectors can be constructed on $ncAdS_2$ which reduce to the $AdS_2$ Killing vectors near the boundary. We therefore conclude that $ncAdS_2$ is asymptotically $AdS_2$, and so the $AdS/CFT$ correspondence should apply. For the example of the massless scalar field on Euclidean $ncAdS_2$, the on-shell action, and resulting two-point function for the boundary theory, are computed to leading order in the noncommutativity parameter. The results agree with those of the commutative scalar field theory, up to a field redefinition.

hep-th↗

arXiv2017

Growing Hair on the extremal $BTZ$ black hole

We show that the nonlinear $\sigma-$model in an asymptotically $AdS_3$ space-time admits a novel local symmetry. The field action is assumed to be quartic in the nonlinear $\sigma-$model fields and minimally coupled to gravity. The local symmetry transformation simultaneously twists the nonlinear $\sigma-$model fields and changes the space-time metric, and it can be used to map an extremal $BTZ$ black hole to infinitely many hairy black hole solutions.

gr-qc↗

arXiv2017

Gauge Theories and Fibre Bundles - Applications to Particle Dynamics

The underlying mathematical structures of gauge theories are known to be geometrical in nature and the local and global features of this geometry have been studied for a long time in mathematics under the name of fibre bundles. It is now understood that the global properties of gauge theories can have a profound influence on physics. For example, instantons and monopoles are both consequences of properties of geometry in the large, and the former can lead to, e.g., CP-violation, while the latter can lead to such remarkable results as the creation of fermions out of bosons. Some familiarity with global differential geometry and fibre bundles seems therefore very desirable to a physicist who works with gauge theories. One of the purposes of the present work is to introduce the physicist to these disciplines using simple examples.

quant-ph↗