In physics, there are two great pillars of thought that don’t quite fit together. The Standard Model of particle physics describes all known fundamental particles and three forces: electromagnetism, the strong nuclear force, and the weak nuclear force. Meanwhile, Einstein’s general relativity describes gravity and the fabric of spacetime.
在物理学中，有两个很棒的思想支柱并不完全融合在一起。粒子物理学的标准模型描述了所有已知的基本颗粒和三种力：电磁，强核力和弱核力量。同时，爱因斯坦的一般相对论描述了重力和时空的结构。
However, these frameworks are fundamentally incompatible in many ways, says Jonathan Heckman, a theoretical physicist at the University of Pennsylvania. The Standard Model treats forces as dynamic fields of particles, while general relativity treats gravity as the smooth geometry of spacetime, so gravity “doesn’t fit into physics’ Standard Model,” he explains.
但是，这些框架在许多方面从根本上是不兼容的，宾夕法尼亚大学的理论物理学家乔纳森·赫克曼说。他解释说，标准模型将力视为颗粒的动态场，而常规相对论将重力视为时空的平滑几何形状，因此重力“不适合物理学的标准模型”。
In a recent paper, Heckman; Rebecca Hicks, a Ph.D. student at Penn’s School of Arts & Sciences; and their collaborators turn that critique on its head. Instead of asking what string theory predicts, the authors ask what it definitively cannot create. Their answer points to a single exotic particle that could show up at the Large Hadron Collider (LHC). If that particle appears, the entire string-theory edifice would be, in Heckman’s words, “in enormous trouble.”
在最近的一篇论文中，赫克曼；丽贝卡·希克斯（Rebecca Hicks），博士学位宾夕法尼亚大学艺术与科学学院的学生；他们的合作者将这种批评置于其头上。作者没有问弦理论预测什么，而是询问其明确无法创建的内容。他们的答案指向可能出现在大型强子对撞机（LHC）上的单个外来粒子。如果出现该粒子，用赫克曼（Heckman）的话来说，整个弦主理论的建筑物将“遇到巨大的麻烦”。
Penn Today caught up with Heckman and Hicks to learn more about string theory and why falsifying it is important.
今天，宾夕法尼亚州与赫克曼（Heckman）和希克斯（Hicks）赶上了有关弦理论的更多信息，以及为什么伪造它很重要。
String theory: the good, the bad, the energy-hungry
弦理论：好，坏，渴望能量
For decades, physicists have sought a unified theory that can reconcile quantum mechanics,and, by extension, the behavior of subatomic particles, with gravity—which is described as a dynamic force in general relativity but is not fully understood within quantum contexts, Heckman says.
数十年来，物理学家一直在寻求一种可以调和量子力学的统一理论，并扩大了带有重力的亚原子颗粒的行为，这被描述为一般相对论中的动态力，但在量子环境中尚未完全理解。
A good contender for marrying gravity and quantum phenomena is string theory, which posits that all particles, including a hypothetical one representing gravity, are tiny vibrating strings and which promises a single framework encompassing all forces and matter.
嫁给重力和量子现象的一个良好竞争者是弦理论，它认为所有粒子，包括代表重力的假设的颗粒，都是微小的振动字符串，并且有望有一个包含所有力和物质的单个框架。
“But one of the drawbacks of string theory is that it operates in high-dimensional math and a vast ‘landscape’ of possible universes, making it fiendishly difficult to test experimentally,” Heckman says, pointing to how string theory necessitates more than the familiar four dimensions— x, y, z, and time—to be mathematically consistent.
赫克曼说：“但是弦理论的缺点之一是它以高维数学和可能的宇宙的巨大'景观'运行，这使得它难以在实验上进行测试，”赫克曼指出，弦理论比熟悉的四个维度（x，y，y，y，z和时间）要多于数学。
“Most versions of string theory require a total of 10 or 11 spacetime dimensions, with the extra dimensions being sort of ‘curled up’ or folding in on one another to extremely small scales,” Hicks says.
希克斯说：“弦乐理论的大多数版本总共需要10或11个时空维度，额外的尺寸是'curl缩起来的，或者彼此折叠到极小的尺度上。”
To make matters even trickier, string theory’s distinctive behaviors only clearly reveal themselves at enormous energies, “those far beyond what we typically encounter or even generate in current colliders,” Heckman says.
为了使事情变得更加棘手，弦理论的独特行为只能清楚地表明自己是巨大的能量，“那些远远超出了我们通常在当前的墙面中遇到甚至产生的东西，”赫克曼说。
Hicks likens it to zooming in on a distant object: at everyday, lower energies, strings look like regular point-like particles, just as a faraway rope might appear to be a single line. “But when you crank the energy way up, you start seeing the interactions as they truly are—strings vibrating and colliding,” she explains. “At lower energies, the details get lost, and we just see the familiar particles again. It’s like how from far away, you can’t make out the individual fibers in the rope. You just see a single, smooth line.”
希克斯将其比作放大遥远的物体：在每天的，较低的能量，字符串看起来像常规点状的粒子，就像遥远的绳索似乎是一条线一样。她解释说：“但是，当您将能量提升时，您就开始看到它们的真实互动 - 线条振动和碰撞。”“在较低的能量下，细节丢失了，我们再次看到熟悉的颗粒。这就像从远处，您无法弄清绳索中的单个纤维。您只会看到一条平滑的线条。”
That’s why physicists hunting for signatures of string theory must push their colliders—like the LHC—to ever-higher energies, hoping to catch glimpses of fundamental strings rather than just their lower-energy disguises as ordinary particles.
这就是为什么要追求弦理论签名的物理学家必须将其相撞者（例如LHC）推向更高的能量，希望能瞥见基本的弦乐，而不仅仅是像普通粒子一样偏低的伪装。
Why serve string theory a particle it likely won’t be able to return?
为什么服务弦理论它可能无法返回的粒子？
Testing a theory often means searching for predictions that confirm its validity. But a more powerful test, Heckman says, is finding exactly where a theory fails. If scientists discover that something a theory forbids actually exists, the theory is fundamentally incomplete or flawed.
测试理论通常意味着搜索确认其有效性的预测。但是，赫克曼说，一个更强大的测试正是在理论失败的地方准确地找到了。如果科学家发现某种理论实际上存在某种东西，那么该理论从根本上是不完整或有缺陷的。
Because string theory’s predictions are vast and varied, the researchers instead asked if there’s a simple particle scenario that string theory just can’t accommodate.
由于弦理论的预测是巨大而多样的，因此研究人员询问是否有一个简单的粒子场景，字符串理论无法适应。
They zeroed in on how string theory deals with particle “families,” groups of related particles bound together by the rules of the weak nuclear force, responsible for radioactive decay. Typically, particle families are small packages, like the electron and its neutrino sibling, that form a tidy two-member package called a doublet. String theory handles these modest particle families fairly well, without issue.
他们对弦理论如何处理粒子“家族”，这些相关粒子的群体由弱核力量的规则结合在一起，负责放射性衰减。通常，粒子家族是小包装，例如电子及其中微子兄弟姐妹，形成了一个整洁的两人包装，称为Doublet。弦理论可以很好地处理这些谦虚的粒子家族，没有问题。
However, Heckman and Hicks identified a family that is conspicuously absent from any known string-based calculation: a five-member particle package, or a 5-plet. Heckman likens this to trying to order a Whopper meal from McDonald’s, “no matter how creatively you search the menu, it never materializes.”
但是，Heckman和Hicks确定了一个从任何已知的基于字符串的计算中明显不存在的家庭：一个五成员的粒子封装或5件。赫克曼（Heckman）将其比作试图从麦当劳（McDonald's）订购一顿饭菜的，“无论您在菜单上有多创造性地搜索菜单，它都无法实现。”
“We scoured every toolbox we have, and this five-member package just never shows up,” Heckman says.
赫克曼说：“我们搜寻了我们拥有的每个工具箱，而这个五成员的软件包永远不会出现。”
But what exactly is this elusive 5-plet?
但是，这个难以捉摸的5件究竟是什么？
Hicks explains it as an expanded version of the doublet, “the 5-plet is its supersized cousin, packing five related particles together.”
希克斯（Hicks）将其解释为Doublet的扩展版本：“ 5件是其超级堂兄，将五个相关的粒子包装在一起。”
Physicists encapsulate this particle family in a concise mathematical formula known as the Lagrangian, essentially the particle-physics cookbook. The particle itself is called a Majorana fermion, meaning it acts as its own antiparticle, akin to a coin that has heads on both sides.
物理学家将这个粒子家族封装在称为拉格朗日的简洁数学公式中，本质上是粒子物理食谱。粒子本身称为Majorana fermion，这意味着它是其自身的反粒子，类似于在两侧都有头的硬币。
Identifying such a particle would directly contradict what current string theory models predict is possible, making the detection of this specific particle family at the LHC a high-stakes test, one that could potentially snap string theory.
识别这种粒子将直接与当前弦理论模型预测的可能性相矛盾，这使得在LHC中对该特定粒子家族的检测是高风险测试，该测试可能可能会捕捉弦乐理论。
Why a 5-plet hasn’t been spotted and the vanishing-Track clue
为什么还没有发现5件事和消失的线索
Hicks cites two major hurdles for spotting these 5-plet structures: “production and subtlety.”
希克斯（Hicks）引用了两个主要障碍，以发现这些5件结构：“生产和微妙”。
In a collider, energy can literally turn into mass; Einstein’s E = mc² says that enough kinetic oomph (E) can be converted into the heft (m) of brand-new particles, so the heavier the quarry the rarer the creation event.
在撞机中，能量实际上可以变成质量。爱因斯坦的E =MC²表示，可以将足够的动力学（E）转换为全新颗粒的重量（m），因此采石场越重，创造事件越稀有。
“The LHC has to slam protons together hard enough to conjure these hefty particles out of pure energy,” Hicks explains, citing Einstein’s E = mc², which directly links energy (E) to mass (m). “As the masses of these particles climb toward a trillion electron volts, the chance of creating them drops dramatically.”
希克斯解释说：“ LHC必须用力将质子猛烈猛烈地扎在一起，以使这些巨大的颗粒从纯净的能量中凝结。”以爱因斯坦的e =mc²，它将能量（e）与质量（M）直接联系起来。“随着这些颗粒的质量朝着万亿电子伏特爬升，创建它们的机会会大大降低。”
View large image CMS (Compact Muon Solenoid) event display of a 2012 proton-proton collision, its golden sprays tracing the tell-tale Higgs-to-two-photon decay. The same precision tracking that captured this landmark Standard Model moment now fuels the hunt for disappearing “ghost” tracks, the subtle clues that could challenge string theory’s grip on the universe. (Image: Courtesy of CERN)
查看大型图像CMS（紧凑型MUON电磁阀）事件显示2012年质子 - 普罗顿碰撞，其金色喷雾剂追踪了Tell-Tale Higgs-to-two-Photon Decay。现在，捕获了这个具有里程碑意义的标准模型时刻的同样的精确跟踪，为消失的“幽灵”跟踪捕捉了狩猎，这可能会挑战弦理论对宇宙的掌握的微妙线索。（图片：由CERN提供）
Even if produced, detection is challenging. The charged particles in the 5-plet decay very quickly into nearly invisible products. “The heavier states decay into a soft pion and an invisible neutral particle, zero (X 0 ),” Hicks says. “The pion is so low-energy it’s basically invisible, and X 0 passes straight through. The result is a track that vanishes mid-detector, like footprints in snow suddenly stopping.”
即使产生，检测也充满挑战。5件衰减中的带电颗粒几乎不可见的产品。希克斯说：“较重的状态腐烂到软亲锋和无形的中性粒子，零（x 0）。”“锥子是如此低的能量，基本上是看不见的，X 0直通。结果是一条消失的曲目，就像雪中的足迹突然停止一样。”
Those signature tracks get picked up by LHC’s ATLAS (short for A Toroidal LHC ApparatuS) and CMS (Compact Muon Solenoid), house-sized “digital cameras” wrapped around the collision center. They sit at opposite collision points and operate independently, giving the physics community two sets of eyes on every big discovery. Penn physicists like Hicks are part of the ATLAS Collaboration, helping perform the searches that look for quirky signals like disappearing tracks.
这些签名轨道被LHC的Atlas（用于旋风LHC设备的简短）和CMS（紧凑型MUON电磁阀）所吸引，房屋大小的“数码相机”包裹在碰撞中心。他们坐在相反的碰撞点并独立运作，为物理社区提供了每一个大发现的两组眼睛。像希克斯（Hicks）这样的宾夕法尼亚大学物理学家是Atlas合作的一部分，有助于执行寻找古怪信号（例如消失的曲目）的搜索。
What the LHC has already ruled out
LHC已经排除了什么
Using existing ATLAS data from collider runs, the team searched specifically for 5-plet signals.
使用Collider运行的现有ATLAS数据，该团队专门搜索5件信号。
“We reinterpreted searches originally designed for ‘charginos’—hypothetical charged particles predicted by supersymmetry—and looked for 5-plet signatures,” Hicks says of the team’s search through the repurposed ATLAS disappearing-track data. “We found no evidence yet, which means any 5-plet particle must weigh at least 650–700 GeV, five times heavier than the Higgs boson.”
希克斯在谈到团队搜索的搜索中，通过重新利用的Atlas消失轨道数据进行搜索时说：“我们重新解释了最初为'Charginos'设计的搜索，该搜索是由超对称性预测的，这是由超对称性预测的。”“我们还没有发现任何证据，这意味着任何5件粒子必须重至少650-700 GEV，比希格斯玻色子重五倍。”
For context, Heckman says, “this early result is already a strong statement; it means lighter 5-plets don’t exist. But heavier ones are still very much on the table."
在上下文中，赫克曼说：“这一早期结果已经是一个强烈的陈述；这意味着不存在更轻的5件陈述。但是较重的陈述仍然很大。”
Future searches with upgraded LHC experiments promise even sharper tests.
通过升级的LHC实验进行的未来搜索有望更清晰的测试。
“We're not rooting for string theory to fail,” Hicks says. “We're stress-testing it, applying more pressure to see if it holds up."
希克斯说：“我们并不是要使字符串理论失败。”“我们正在对此进行压力测试，以施加更大的压力，以查看它是否坚持。”
“If string theory survives, fantastic," Heckman says."If it snaps, we'll learn something profound about nature.”
赫克曼说：“如果弦理论得以生存，那就很棒。”“如果抢购，我们将学到有关自然的深刻知识。”
ATLAS’s wheel-like end-cap reveals the maze of sensors primed to catch proton smash-ups at the LHC. Researchers comb through billions of events in search of fleeting “ghost” tracks that might expose cracks in string theory. (Image: Courtesy of CERN)
阿特拉斯（Atlas）的轮子端盖，揭示了传感器的迷宫，启动了在LHC上捕获质子粉碎的迷宫。研究人员梳理数十亿个事件，以寻找短暂的“幽灵”轨道，这些曲目可能会揭示弦理论中的裂缝。（图片：由CERN提供）
Jonathan Heckman is a professor at the School of Arts & Sciences’ Department of Physics and Astronomy, with a secondary appointment in the Department of Mathematics.
乔纳森·赫克曼（Jonathan Heckman）是艺术与科学学院物理与天文学系的教授，并在数学系进行了次要任命。
Rebecca Hicks is a Ph.D. student in the Department of Physics and Astronomy at Penn Arts & Sciences.
丽贝卡·希克斯（Rebecca Hicks）是博士学位。宾夕法尼亚州艺术与科学物理与天文学系的学生。
Other authors include Matthew Baumgart and Panagiotis Christeas of Arizona State University.
其他作者包括亚利桑那州立大学的Matthew Baumgart和Panagiotis Christeas。
This work received support from the Department of Energy (awards DE-SC0019470 and DE-SC0013528), the U.S.-Israel Binational Science Foundation (Grant No. 2022100), and the National Science Foundation.
这项工作得到了能源部（DE-SC0019470奖和DE-SC0013528），美国 - 以色列双原则科学基金会（授予2022100）和国家科学基金会的支持。
