Greg Landsberg - Brown University

Greg Landsberg
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Greg Landsberg
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Brown University
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United States

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High Energy Physics - Phenomenology (29)
 
High Energy Physics - Experiment (24)
 
High Energy Physics - Theory (4)
 
General Relativity and Quantum Cosmology (1)
 
High Energy Astrophysical Phenomena (1)
 
Cosmology and Nongalactic Astrophysics (1)

Publications Authored By Greg Landsberg

Weakly-coupled TeV-scale particles may mediate the interactions between normal matter and dark matter. If so, the LHC would produce dark matter through these mediators, leading to the familiar "mono-X" search signatures, but the mediators would also produce signals without missing momentum via the same vertices involved in their production. This document from the LHC Dark Matter Working Group suggests how to compare searches for these two types of signals in case of vector and axial-vector mediators, based on a workshop that took place on September 19/20, 2016 and subsequent discussions. Read More

This White Paper is an input to the ongoing discussion about the extension and refinement of simplified Dark Matter (DM) models. Based on two concrete examples, we show how existing simplified DM models (SDMM) can be extended to provide a more accurate and comprehensive framework to interpret and characterise collider searches. In the first example we extend the canonical SDMM with a scalar mediator to include mixing with the Higgs boson. Read More

Fermionic dark matter interacting with the Standard Model sector through a pseudoscalar portal could evade the direct detection constraints while preserving a WIMP miracle. We study the LHC constraints on the pseudoscalar production in simplified models with the pseudoscalar either dominantly coupled to b quarks or tau leptons and explore their implications for the GeV excesses in gamma ray observations. We also investigate models with new vector-like fermions that could realize the simplified models of pseudoscalar portal dark matter. Read More

2015Jun
Authors: Jalal Abdallah, Henrique Araujo, Alexandre Arbey, Adi Ashkenazi, Alexander Belyaev, Joshua Berger, Celine Boehm, Antonio Boveia, Amelia Brennan, Jim Brooke, Oliver Buchmueller, Matthew Buckley, Giorgio Busoni, Lorenzo Calibbi, Sushil Chauhan, Nadir Daci, Gavin Davies, Isabelle De Bruyn, Paul De Jong, Albert De Roeck, Kees de Vries, Daniele Del Re, Andrea De Simone, Andrea Di Simone, Caterina Doglioni, Matthew Dolan, Herbi K. Dreiner, John Ellis, Sarah Eno, Erez Etzion, Malcolm Fairbairn, Brian Feldstein, Henning Flaecher, Eric Feng, Patrick Fox, Marie-Hélène Genest, Loukas Gouskos, Johanna Gramling, Ulrich Haisch, Roni Harnik, Anthony Hibbs, Siewyan Hoh, Walter Hopkins, Valerio Ippolito, Thomas Jacques, Felix Kahlhoefer, Valentin V. Khoze, Russell Kirk, Andreas Korn, Khristian Kotov, Shuichi Kunori, Greg Landsberg, Sebastian Liem, Tongyan Lin, Steven Lowette, Robyn Lucas, Luca Malgeri, Sarah Malik, Christopher McCabe, Alaettin Serhan Mete, Enrico Morgante, Stephen Mrenna, Yu Nakahama, Dave Newbold, Karl Nordstrom, Priscilla Pani, Michele Papucci, Sophio Pataraia, Bjoern Penning, Deborah Pinna, Giacomo Polesello, Davide Racco, Emanuele Re, Antonio Walter Riotto, Thomas Rizzo, David Salek, Subir Sarkar, Steven Schramm, Patrick Skubic, Oren Slone, Juri Smirnov, Yotam Soreq, Timothy Sumner, Tim M. P. Tait, Marc Thomas, Ian Tomalin, Christopher Tunnell, Alessandro Vichi, Tomer Volansky, Neal Weiner, Stephen M. West, Monika Wielers, Steven Worm, Itay Yavin, Bryan Zaldivar, Ning Zhou, Kathryn Zurek

This document outlines a set of simplified models for dark matter and its interactions with Standard Model particles. It is intended to summarize the main characteristics that these simplified models have when applied to dark matter searches at the LHC, and to provide a number of useful expressions for reference. The list of models includes both s-channel and t-channel scenarios. Read More

In the past few years, the interest to collider searches for direct dark matter (DM) production has been growing exponentially. A variety of "Mono-X" signatures have been considered, where X stands for a probe particle recoiling against DM particles, which allows for the event to be triggerable. So far, the analysis of these signatures has been largely carried out in the framework of effective field theory (EFT), which allows for a comparison of the collider searches with searches in direct detection experiments. Read More

The success of the first three years of operations of the LHC at center-of-mass energies of 7 and 8 TeV radically changed the landscape of searches for new physics beyond the standard model and our very way of thinking about its possible origin and its hiding place. Among the paradigms of new physics that have been probed quite extensively at the LHC, are various models that predict the existence of extra spatial dimensions. In this review, the current status of searches for extra dimensions with the CMS detector is presented, along with prospects for future searches at the full energy of the LHC, expected to be reached in the next few years. Read More

In this White Paper we present and discuss a concrete proposal for the consistent interpretation of Dark Matter searches at colliders and in direct detection experiments. Based on a specific implementation of simplified models of vector and axial-vector mediator exchanges, this proposal demonstrates how the two search strategies can be compared on an equal footing. Read More

In these proceedings I cover the latest results on the production and decay of the recently discovered Higgs boson. While the spin and properties of the new boson, such as its mass and couplings to bosons and fermions, are covered in a separate report, I focus on individual results in the main channels we use to study the properties of the new boson and to search for its possible cousins, with the focus on the latest results from the LHC and the Tevatron collaborations. Read More

In this overview talk, I give highlights of the first three years of the LHC operations at high energy, spanning heavy-ion physics, standard model measurements, and searches for new particles, which culminated in the discovery of the Higgs boson by the ATLAS and CMS experiments in 2012. I'll discuss what we found about the properties of the new particle in 10 months since the discovery and then talk about the future LHC program and preparations to the 2015 run at the center-of-mass energy of ~13 TeV. These proceedings are meant to be a snapshot of the LHC results as of May 2013 - the time of the conference. Read More

Physics in curved spacetime describes a multitude of phenomena, ranging from astrophysics to high energy physics. The last few years have witnessed further progress on several fronts, including the accurate numerical evolution of the gravitational field equations, which now allows highly nonlinear phenomena to be tamed. Numerical relativity simulations, originally developed to understand strong field astrophysical processes, could prove extremely useful to understand high-energy physics processes like trans-Planckian scattering and gauge-gravity dualities. Read More

Alignment of the main energy fluxes along a straight line in a target plane has been observed in families of cosmic ray particles detected in the Pamir mountains. The fraction of events with alignment is statistically significant for families with superhigh energies and large numbers of hadrons. This can be interpreted as evidence for coplanar hard-scattering of secondary hadrons produced in the early stages of the atmospheric cascade development. Read More

There are theoretical reasons to think that space-time is lower dimensional at very short distances. If this is the case, quantum black holes produced at the LHC or in cosmic rays scattering live in lower dimensions. We discuss production cross section and signatures for the corresponding quantum black holes at the LHC within several different models of low-dimensional space-time. Read More

We propose that the effective dimensionality of the space we live in depends on the length scale we are probing. As the length scale increases, new dimensions open up. At short scales the space is lower dimensional; at the intermediate scales the space is three-dimensional; and at large scales, the space is effectively higher dimensional. Read More

Searches for extra spatial dimensions remain among the most popular new directions in our quest for physics beyond the Standard Model. High-energy collider experiments of the current decade should be able to find an ultimate answer to the question of their existence in a variety of models. We review these models and recent results from the Tevatron on searches for large, inverse-TeV-size, and Randall-Sundrum extra spatial dimensions. Read More

Search for non-Standard-Model Higgs bosons is one of the major goals of the ongoing Fermilab Tevatron run. Large data sets accumulated by the CDF and D0 experiments break new grounds in sensitivity. We review recent Tevatron results on searches for Higgs bosons in Minimal Supersymmetric Model in the multi b-jet and tau-tau final states, as well as a search for fermiophobic Higgs in the multiphoton final state. Read More

One of the most dramatic consequences of low-scale (~1 TeV) quantum gravity in models with large or warped extra dimension(s) is copious production of mini black holes at future colliders and in ultra-high-energy cosmic ray collisions. Hawking radiation of these black holes is expected to be constrained mainly to our three-dimensional world and results in rich phenomenology. In this topical review we discuss the current status of astrophysical observations of black holes and selected aspects of mini black hole phenomenology, such as production at colliders and in cosmic rays, black hole decay properties, Hawking radiation as a sensitive probe of the dimensionality of extra space, as well as an exciting possibility of finding new physics in the decays of black holes. Read More

Searches for extra spatial dimensions remain among the most popular new directions in our quest for physics beyond the Standard Model. High-energy collider experiments of the current decade should be able to find an ultimate answer to the question of their existence in a variety of models. Until the start of the LHC in a few years, the Tevatron will remain the key player in this quest. Read More

One of the most dramatic consequences of low-scale (~1 TeV) quantum gravity would be copious production of mini black holes at future accelerators and in ultra-high-energy cosmic ray interactions. Hawking radiation of these black holes is constrained mainly to our (3+1)-dimensional world and results in their rapid evaporation. We review selected topics in the mini-black-hole phenomenology, such as production rates at colliders and in cosmic rays, Hawking radiation as a sensitive probe of the dimensionality of extra space, as well as an exciting possibility of finding new physics in the decays of black holes. Read More

As was suggested about a year ago, one of the most dramatic consequences of low-scale (~1 TeV) quantum gravity is copious production of mini black holes at future accelerators and in ultra-high-energy cosmic ray collisions. Hawking radiation of these black holes is constrained mainly to our (3+1)-dimensional world and results in rich phenomenology. With the original idea having been cited over a hundred times since its appearence, we review the current status of astrophysical observations of black holes and selected topics in the mini black hole phenomenology, such as production rates at colliders and in cosmic rays, Hawking radiation as a sensitive probe of the dimensionality of extra space, as well as an exciting possibility of finding new physics in the decays of black holes. Read More

2002May

One of the most dramatic consequences of low-scale (~1 TeV) quantum gravity is copious production of mini black holes at future accelerators and in ultra-high-energy cosmic ray interactions. Hawking radiation of these black holes is constrained mainly to our (3+1)-dimensional world and results in rich phenomenology. We discuss tests of Wien's law of Hawking radiation, which is a sensitive probe of the dimensionality of extra space, as well as an exciting possibility of finding new physics in the decays of black holes. Read More

If the scale of quantum gravity is near a TeV, the LHC will be producing one black hole (BH) about every second, thus qualifying as a BH factory. With the Hawking temperature of a few hundred GeV, these rapidly evaporating BHs may produce new, undiscovered particles with masses ~100 GeV. The probability of producing a heavy particle in the decay depends on its mass only weakly, in contrast with the exponentially suppressed direct production. Read More

In theories with the standard model gauge bosons propagating in inverse-TeV-size extra dimensions, their Kaluza-Klein states interact with the rest of the SM particles confined to the 3-brane. We look for possible signals for this interaction in the present high-energy collider data, and estimate the sensitivity offered by the next generation of collider experiments. Based on the present data from the LEP 2, Tevatron, and HERA experiments, we set a lower limit on the extra dimension compactification scale Mc > 6. Read More

If the scale of quantum gravity is near a TeV, the LHC will be producing one black hole (BH) about every second. The BH decays into prompt, hard photons and charged leptons is a clean signature with low background. The absence of significant missing energy allows the reconstruction of the mass of the decaying BH. Read More

One of the most stimulating recent ideas in particle physics involves a possibility that our universe has additional compactified spatial dimensions, perhaps as large as 1 mm. In this review, we discuss the results of recent experimental searches for such large extra dimensions, as well as new developments in this field. Read More

One of the most stimulating recent ideas in particle physics involves a possibility that our universe has additional compactified spatial dimensions, perhaps as large as 1 mm. In this mini-review, we discuss the results of recent experimental searches for such large extra dimensions. Read More

The prospects for discovering and studying signals of low-scale supersymmetry breaking models at the Tevatron Run II and beyond are explored. These models include gauge-mediated supersymmetry breaking as the most compelling and concrete realization, but more generally are distinguished by the presence of a nearly massless Goldstino as the lightest supersymmetric particle. The next-lightest supersymmetric particle(s) (NLSP) decays to its partner and the Goldstino. Read More

In extended Higgs models, the Higgs boson may decay into a pair of light CP-odd scalars, with distinctive collider signatures. We study the ensuing Higgs signals at the upgraded Tevatron, considering the subsequent decays of the scalars into pairs of gluons or photons. For CP-odd scalars lighter than a few GeV, the Higgs boson manifests itself as a diphoton resonance and can be discovered up to masses of a few hundred GeV. Read More

We evaluate the prospects for detecting a non-standard light Higgs boson with a significant branching ratio to two photons, in Run II of the Fermilab Tevatron. We derive the reach for several channels: $2\gamma$ inclusive, $2\gamma+1$ jet and $2\gamma+2$ jets. We present the expected Run II limits on the branching ratio of $h\to\gamma\gamma$ as a function of the Higgs mass, for the case of ``bosonic'', as well as ``topcolor'' Higgs bosons. Read More

We present recent results on searches for non-SUSY new physics at the CDF and D0 Collaborations in the 1992-1996 Fermilab Tevatron run. While no compelling evidence for existence of new physics was found, the Tevatron data have excluded a significant region of the theoretically allowed phase space for a variety of non-SUSY extensions of the Standard Model. Tight limits on the existence of the following new phenomena are set: leptoquarks of all three generations, quark-lepton compositeness, 4-th generation quarks, fermiophobic Higgs, technicolor, etc. Read More

In the model of Arkani-Hamed, Dimopoulos, and Dvali where gravity is allowed to propagate in the extra dimensions of very large size, virtual graviton exchange between the standard model particles can give rise to signatures that can be tested in collider experiments. We study these effects in dilepton and diphoton production at hadron colliders. Specifically, we examine the double differential cross-section in the invariant mass and scattering angle, which is found to be useful in separating the gravity effects from the standard model. Read More

We discuss possibilities of detecting neutral and charged long-lived particles with the upgraded D0 detector in Run II of the Fermilab Tevatron accelerator, using photon pointing, dE/dx, and time-of-flight techniques. Such particles appear in many SM extensions, e.g. Read More