A search is presented for massive long-lived particles in events featuring at least one displaced vertex and at least one displaced muon, using proton–proton collision data collected by the ATLAS detector at the Large Hadron Collider from 2022 to 2024 at a centre-of-mass energy of 13.6 TeV. The data sample corresponds to an integrated luminosity of 164 fb <math altimg='si22.svg'><msup><mrow /><mrow><mo>&#8722;</mo><mn>1</mn></mrow></msup></math>. The analysis targets scenarios in which long-lived particles decay inside the ATLAS inner detector, resulting in a topology of at least one massive, displaced vertex (DV) with multiple associated tracks, and at least one muon with a large transverse impact parameter relative to the primary interaction point. The muon is not required to be associated with the DV. Two signal regions are defined by the transverse distance of the reconstructed DV from the interaction point. Background contributions are estimated by using fully data-driven techniques. No significant excess above the expected background is observed. Upper limits at 95% confidence level are set on the visible cross-section and on the production cross-sections of several benchmark models of <italic>R</italic>-parity-violating supersymmetry.

France

G. Aad

Norway

E. Aakvaag

United States

B. Abbott

United Arab Emirates

S. Abdelhameed

Germany

K. Abeling

N.J. Abicht

S.H. Abidi

M. Aboelela

Morocco

A. Aboulhorma

Israel

H. Abramowicz

Italy

B.S. Acharya

A. Ackermann

C. Adam Bourdarios

Poland

L. Adamczyk

S.V. Addepalli

United Kingdom

M.J. Addison

J. Adelman

Türkiye

A. Adiguzel

T. Adye

A.A. Affolder

Y. Afik

Spain

M.N. Agaras

A. Aggarwal

Romania

C. Agheorghiesei

A. Ahmad

F. Ahmadov

S. Ahuja

China

X. Ai

G. Aielli

A. Aikot

M. Ait Tamlihat

Sweden

T.P.A. Åkesson

Japan

D. Akiyama

N.N. Akolkar

S. Aktas

G.L. Alberghi

Canada

J. Albert

Switzerland

U. Alberti

P. Albicocco

S. Alderweireldt

Z.L. Alegria

M. Aleksa

I.N. Aleksandrov

C. Alexa

Greece

T. Alexopoulos

F. Alfonsi

M. Algren

M. Alhroob

Czechia

B. Ali

H.M.J. Ali

S. Ali

S.W. Alibocus

South Africa

M. Aliev

G. Alimonti

C. Allaire

B.M.M. Allbrooke

D.R. Allen

J.S. Allen

J.F. Allen

Australia

C.S. Alley

E.R. Almazan

A. Aloisio

Argentina

F. Alonso

C. Alpigiani

A. Alvarez Fernandez

M. Alves Cardoso

M.G. Alviggi

M. Aly

Brazil

Y. Amaral Coutinho

A. Ambler

C. Amelung

M. Amerl

T. Amezza

B. Amini

K. Amirie

A. Amirkhanov

D. Amperiadou

S. An

C. Anastopoulos

T. Andeen

J.K. Anders

A.C. Anderson

A. Andreazza

S. Angelidakis

A. Angerami

A.V. Anisenkov

A. Annovi

C. Antel

E. Antipov

M. Antonelli

F. Anulli

M. Aoki

T. Aoki

M.A. Aparo

L. Aperio Bella

M. Apicella

C. Appelt

A. Apyan

M. Arampatzi

Search for massive, long-lived particles in events with displaced vertices and displaced muons in <italic>pp</italic> collisions at <math altimg='si21.svg'><mrow><msqrt><mi>s</mi></msqrt><mo linebreak='goodbreak'>=</mo><mn>13.6</mn></mrow></math> TeV with the ATLAS experiment

A measurement of the associated production of a top-quark pair with the Higgs boson ( $$ t\overline{t}H $$ ) in multilepton final states is presented. The analysis is based on a data sample of proton-proton collisions at $$ \sqrt{s}=13 $$ TeV recorded with the ATLAS detector at the CERN Large Hadron Collider and corresponding to an integrated luminosity of 140 fb . Six final states defined by the number and flavour of reconstructed charged leptons are combined in a simultaneous likelihood fit to extract the $$ t\overline{t}H $$ signal and constrain the most relevant backgrounds. The measured $$ t\overline{t}H $$ cross-section normalised to Standard Model (SM) prediction is $$ {\sigma}_{t\overline{t}H}/{\sigma}^{\mathrm{SM}}=0.{63}_{-0.19}^{+0.20} $$ . This result corresponds to an observed (expected) significance of 3.3$\textit{σ}$ (5.3$\textit{σ}$). Additionally, two other fits are used to measure the $$ t\overline{t}H $$ cross-section differentially in bins of the Higgs boson transverse momentum in the simplified template cross-section framework, and to extract the associated production cross-section of a single top-quark with the Higgs boson ($\textit{tH}$) together with the $$ t\overline{t}H $$ one. The $\textit{CP}$ structure of the top quark-Higgs boson Yukawa coupling is probed through an analysis of $$ t\overline{t}H $$ and $\textit{tH}$ events. The results are compatible with the SM hypothesis, and values of the mixing angle between $\textit{CP}$-even and $\textit{CP}$-odd top-Higgs Yukawa couplings of |$\textit{α}$| $\textit{>}$ 62 are excluded at 68% confidence level.

N. Abicht

S. Abidi

B. Acharya

S. Addepalli

M. Addison

A. Affolder

M. Agaras

Azerbaijan

B. Aitbenchikh

T. Åkesson

N. Akolkar

G. Alberghi

G. Albouy

Z. Alegria

I. Aleksandrov

Saudi Arabia

H. Ali

S. Alibocus

W. Alkakhi

B. Allbrooke

D. Allen

J. Allen

Z. Alsolami

M. Alviggi

C. Ames

Portugal

S. Amor Dos Santos

J. Anders

A. Anderson

A. Anisenkov

M. Aparo

Measurement of the Higgs boson production in association with top quarks in multilepton final states in $\textit{pp}$ collisions at $$ \sqrt{s}=13 $$ TeV with the ATLAS detector

We introduce two novel numerical approaches for computing Feynman integrals based on their complete monotonicity (CM) and Stieltjes properties. The first method uses that scalar Feynman integrals are CM, meaning that all their derivatives have a fixed sign, in the Euclidean kinematic region. This imposes strong constraints on the function space. Simultaneously, these integrals obey systems of linear differential equations with respect to kinematic parameters. By imposing that the solutions to these differential equations satisfy complete monotonicity across the Euclidean region, we develop an efficient and highly constraining numerical bootstrap method. We provide a proof of principle of the power of our approach by applying it to a class of multi-loop Feynman integrals with internal masses. The second method is based on a refinement of CM. We prove that Feynman integrals, within a certain range of parameters, such as dimension and propagator exponents, are not only CM but in fact Stieltjes functions. The latter can be described efficiently by Padé approximants that are known to converge in the cut complex plane. This means that these representations are valid also in analytically continued kinematics, such as physical scattering regions. These insights allow us to obtain rational approximations to Feynman integrals from minimal information, such as a Taylor expansion about a soft limit. We demonstrate the effectiveness of this method by applying it to a 20-loop banana-type Feynman integral. Finally, we comment on a number of extensions of these novel avenues for computing Feynman integrals.

Sara Ditsch

Johannes Henn

Prashanth Raman

Approximating Feynman integrals using complete monotonicity and Stieltjes properties

We present a systematic method for computing cosmological amplitudes, including $\textit{in-in}$ correlators and wavefunction coefficients. Specialising to cases with conformally-coupled external scalars and massive scalar exchanges, we introduce a decomposition into massive family trees, which capture the nested time structure common to these observables. We then evaluate these building blocks using the $\textit{Method of Brackets}$ (MoB), a multivariate extension of $\textit{Ramanujan’s master theorem}$ that operates directly on the integrand, translating integrals into discrete summations via a compact set of algebraic rules. This yields infinite series representations valid across the full space of external momenta and internal energies. We also develop Feynman-like diagrammatic rules that map interaction graphs to summand structures, enabling efficient and scalable computation. The resulting expressions make time evolution manifest, smoothly interpolate to the conformal limit, and are well-suited for both numerical evaluation and analytic analysis of massive field effects in cosmology.

Qinglin Yang

Mastering cosmological amplitudes using generalized Ramanujan’s theorem

The Nature of Dark Matter (DM), that constitutes approximately 25% of the energy density in the Universe, is still eluding us. An intriguing possibility is that DM does indeed interacts with SM particles only gravitationally (the only mean by which we have detected it so far), albeit in an extra-dimensional scenario yet it has not been possible to detect it by some non-gravitational means. In a three-brane Randall-Sundrum setup, with DM located on a Deep Infra-Red GeV-TeV brane, and the SM on an Infra-Red TeV-PeV one, it was shown to be possible to recover the observed DM relic abundance and somewhat relax the hierarchy problem, whilst avoiding LHC stringent bounds on DM and KK graviton masses that constrain severely similar two-brane setups. The phenomenological results, however, have been obtained under the assumption that the bulk curvatures on the left ($\textit{k}$ ) and the right ($\textit{k}$ ) of the intermediate IR-brane are identical, $\textit{k}$ → $\textit{k}$ . Since the brane tension $\textit{σ}$ of the intermediate brane is proportional to $\textit{k}$ – $\textit{k}$ and, therefore, vanishes, it is clear that this limit (for which the IR-brane becomes $\textit{evanescent}$) is unphysical. We could say that this is $\textit{no brane}$: if the brane tension of a brane vanishes, there is no brane in the bulk (pun intended). In this paper, therefore, we study in detail the theoretical framework needed to explore this interesting phenomenological possibility, $\textit{out of the evanescent brane limit}$. We show that most of the formulæ used in the $\textit{evanescent limit}$ are still valid for $$ \mathcal{O}(1) $$ differences between $\textit{k}$ and $\textit{k}$ (thus, introducing no new unjustified hierarchy in the bulk). Once the relevant couplings of radions and KK gravitons are computed, we study the (enlarged) parameter space of the model looking for the region in which the relic DM abundance is recovered.

Andrea Donini

Miguel Folgado

Alejandro Muñoz-Ovalle

Dark matter in a three-brane Randall-Sundrum scenario out of the evanescent limit

<p>We investigate quantum corrections to the Randall-Sundrum (RS) model in the near-extremal black brane background with quantum corrections in the near horizon. The near-horizon geometry is described by Jackiw-Teitelboim gravity, and the quantum fluctuations are governed by the Schwarzian action. We introduce the Schwarzian modes into the RS metric, derive the quantum-corrected equation for the Kaluza-Klein (KK) modes via the Schwinger-Dyson equation, calculate the correction to the KK mass spectrum, and discuss the impact of quantum corrections on the Goldberger-Wise mechanism. Our work introduces both quantum corrections and temperature into the RS model, providing insights into cosmology and phase transitions within it.</p>

Ying-Jian Chen

Jun Nian

Quantum corrections to Randall-Sundrum model from JT gravity

We introduce a tree-level chemical potential mechanism for spin-1 particles within cosmological collider physics, allowing them to be detected in primordial non-Gaussianities for masses above the inflationary Hubble scale. We apply this mechanism to orbifold grand unification and the massive unification partners of the standard model gauge bosons. Our mechanism requires at least a pair of massive vector fields which are singlets of the standard model, a condition which is satisfied in the classic “trinification” scenario. Assuming that the gauge hierarchy problem is solved by supersymmetry, gauge coupling running points to unification partners at ~ 10 GeV. We show that, within high-scale inflation, chemical potential enhancement can lead to observably strong signals for trinification partners in future cosmological surveys.

Arushi Bodas

Edward Broadberry

Raman Sundrum

Grand unification at the cosmological collider with chemical potential

Scenarios seeking to address the issue of electroweak symmetry breaking often have heavy colored gauge bosons coupling preferentially to the top quark. Considering the bulk Randall-Sundrum as a typical example, we consider the prospects of the first Kaluza-Klein mode (<math><msup><mi>G</mi><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></msup></math>) of the gluon being produced at the LHC in association with a <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover></math> pair. The enhanced coupling not only dictates that the dominant decay mode would be to a <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover></math> pair, but also to a very large <math><msup><mi>G</mi><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></msup></math> width, necessitating the use of a renormalized <math><msup><mi>G</mi><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></msup></math> propagator. This, along with the presence of large backgrounds (specially <math><mi>t</mi><mover><mi>t</mi><mo>¯</mo></mover><mi>j</mi><mi>j</mi></math>), renders a conventional cut-based analysis ineffective, yielding only marginal significances of only around <math><mrow><mn>2</mn><mi>σ</mi></mrow></math>. The use of machine learning (ML) techniques alleviates this problem to a great extent. In particular, the use of artificial neural networks helps us identify the most discriminating observables, thereby allowing a significance in excess of <math><mrow><mn>4</mn><mi>σ</mi></mrow></math> for <math><msup><mi>G</mi><mrow><mo>(</mo><mn>1</mn><mo>)</mo></mrow></msup></math> masses of <math><mo>∼</mo><mn>4</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>.

India

Boosted four-top production at the LHC: A window to Randall-Sundrum or extended color symmetry

We present a framework to compute amplitudes for the gravitational analog of the Raman process, a quasielastic scattering of waves off compact objects, in worldline effective field theory. As an example, we calculate third post-Minkowskian order [<math><mi>O</mi><mo>(</mo><msup><mi>G</mi><mn>3</mn></msup><mo>)</mo></math>], or two-loop, phase shifts for the scattering of a massless scalar field including all tidal effects and dissipation. Our calculation unveils two sources of the classical renormalization-group flow of dynamical Love numbers: a universal running independent of the nature of the compact object, and a running self-induced by tides. Restricting to the black hole case, we find that our effective field theory phase shifts agree exactly with those from general relativity, provided that the relevant static Love numbers are set to zero. In addition, we carry out a complete matching of the leading scalar dynamical Love number required to renormalize a universal short scale divergence in the <math><mi>S</mi></math> wave. Our results pave the way for systematic calculations of gravitational Raman scattering at higher post-Minkowskian orders.

Gravitational Raman Scattering in Effective Field Theory: A Scalar Tidal Matching at <math><mi>O</mi><mo>(</mo><msup><mi>G</mi><mn>3</mn></msup><mo>)</mo></math>

The little Randall-Sundrum (little RS) model receives significantly stronger constraints from the flavor observables in comparison to the Randall-Sundrum (RS) model. In this paper, we analyze the effect of the electroweak sector in little RS on flavor-changing decays of charged leptons. We compare the predictions of the model with the current limits on the flavor-violating branching ratios of <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>e</mi><mi>e</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>e</mi><mi>e</mi><mi>e</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>μ</mi><mi>μ</mi><mi>μ</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>μ</mi><mi>e</mi><mi>e</mi></math>, <math><mi>τ</mi><mo>→</mo><mi>e</mi><mi>μ</mi><mi>μ</mi></math>, <math><mi>μ</mi><mo>→</mo><mi>e</mi><mi>γ</mi></math>, and <math><mi>μ</mi><mi>T</mi><mi>i</mi><mo>→</mo><mi>e</mi><mi>T</mi><mi>i</mi></math>, and we show that the dominant constraint arises from the <math><mi>μ</mi><mi>T</mi><mi>i</mi><mo>→</mo><mi>e</mi><mi>T</mi><mi>i</mi></math> process which strongly limits the KK-1 gauge boson mass (<math><msub><mi>M</mi><mrow><mi>K</mi><mi>K</mi></mrow></msub></math>) to be <math><mrow><mo>≳</mo><mn>30.7</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math>. We then derive and show that generalizing the electroweak gauge sector to include the brane localized kinetic term relaxes this constraint to <math><mo>≳</mo><mn>12</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></math>. Toward the conclusion, we comment on the possibility that the large flavor-violating currents can be mitigated by relaxing the assumption regarding the unnatural thinness and rigidity of the UV brane and discuss the possibility of suppression of these currents in the presence of fat fluctuating branes.

Flavor-violating charged lepton decays in the little Randall-Sundrum model