Gunion in ArXiv: A 4th generation is ruled out if the SM Higgs has mass below 200 GeV

John F. Gunion (University of California, Davis) claims in “Ruling out a 4th generation using limits on hadron collider Higgs signals,” ArXiv, 19 May 2011, that the Tevatron and LHC data have essentially eliminated the possibility of a 4th generation of elementary particles if the Higgs is SM-like and has mass below 200 GeV/c². He also claims that the absence of enhanced Higgs signals in current data sets in the and WW/ZZ final states can strongly constrain (almost eliminate) the possibility of a 4th generation in two-Higgs-doublet models of type II (like in the MSSM). The only escape would be if the Higgs boson has non-standard decays that deplete BR(h→WW) and BR(h→γγ).

Posted in LHC at CERN, News, Particle Physics, Physics, Science | | 1 Comment

Moczek in Nature: “The origins of novelty in evolutionary biology”

Clockwise from top left: Cladonota benitezi; Umbelligerus peruviensis; Nassunia binotata; and a nymph of a Cymbomorpha species.

“Treehoppers are insects that would resemble miniature cicadas were it not for the presence of the helmet. This structure appears to reside on top of the animal’s thorax, and extends dorsally, and in remarkably varied ways, to mimic thorns, animal droppings or aggressive ants. Entomologists joke that some treehoppers use their helmets to send signals to their home planet, so other-worldly is their appearance. Helmets are generally thought to aid in camouflage by disrupting the animal’s shape and outline, or by mimicking thorns, animal droppings or aggressive ants and wasps. Understanding the origin of helmets and other complex traits is among the most enduring puzzles in evolutionary biology. On the one hand, evolution operates within a framework of descent with modification — everything new must come from something old. On the other hand, structures such as the eye, the wing and the turtle’s shell stand out because they lack obvious correspondence to the old. A new paper in Nature by Prud’homme et al. provide evidence that treehoppers have overcome such suppression to produce their helmets. This addresses the puzzle by connecting a complex and highly diverse trait — the helmet of membracid treehoppers — to its origins in both development and evolution.” See Armin P. Moczek, “Evolutionary biology: The origins of novelty,” Nature 473: 34–35, 05 May 2011, which refers to Benjamin Prud’homme et al., “Body plan innovation in treehoppers through the evolution of an extra wing-like appendage,” Nature 473: 83–86, 05 May 2011.

“Helmets have been interpreted as an extension of the pronotum, the dorsal portion of the first segment of the three-segmented thorax shared by all insects. We have long known from fossil evidence that insects arrived at this organization following a period of progressive loss of wings or wing-like appendages from all abdominal segments, as well as from the first thoracic segment. Fossils of an extinct species (Stenodyctya lobata) show that expression of the wing-development program in the first thoracic segment (arrow) was common in early insects. In extant winged insects, wings are borne only on the second and third thoracic segments, with wing development on the first segment being suppressed.

Enter the treehopper Publilia modesta and its helmet. Through careful analysis of this structure’s anatomy, placement and attachment to the thorax, Prud’homme et al. discovered that the helmet may not be a mere extension of the pronotum. Instead, it is attached bilaterally to the thorax by paired articulations reminiscent of joints, much like regular wings. Moreover, when they examined its early developmental stages, the authors found that the helmet forms from paired buds — again, much like wings. The expanding buds subsequently fuse along the midline, creating the continuous helmet. Study of the expression of one gene, nubbin, normally specific to insect wing development, and two genes specific to appendage formation in general, provided additional evidence that helmet development may rely on developmental mechanisms involved in the formation of wings.

Combined, these observations suggested that treehoppers evolved a way to develop a wing-like structure using a developmental program shared by traditional wings, but in a place in which wing development is typically inhibited in modern winged insects. Prud’homme and colleagues’ investigation of Scr revealed that the gene is still expressed in the prothorax of treehoppers and is able to repress wing formation when transformed into Scr-deficient fruit flies. This implies that wing development in the first thoracic segment of treehoppers was not made possible simply by the loss of the inhibitory ability of Scr, but through some unknown mechanisms operating downstream.

The study by Prud’homme et al. is noteworthy for several reasons. First, it illustrates how, to this day, careful developmental observations can set the stage for startling discoveries. Generations of entomologists have studied treehopper diversity, but research into development has a way of revealing evolution hidden from the study of adults. Second, as with so many studies, it raises as many questions as it answers. Although the morphological observations provide strong evidence that the helmet is a modified wing, the developmental genetic data are modest and correlational: expression patterns can suggest, but not prove, function. And the mechanisms that permit wing-like development in the presence of Scr repression remain to be discovered. Nevertheless, these findings provide a valuable starting point for framing future enquiries into the origin and diversification of the treehoppers’ ‘third pair of wings’.

Finally, and most importantly, the work illustrates how novelty can arise from ancestral developmental potential — how developmental abilities can be lost or silenced over millions of years, only to be redeployed to contribute to the evolution of a complex and beautiful appendage.”

Baez & Huerta in Scientific American: “The Strangest Numbers in String Theory”

“Octonions were largely neglected since their discovery in 1843, but in the past few decades they have assumed a curious importance in string theory. And indeed, if string theory is a correct representation of the universe, they may explain why the universe has the number of dimensions it does.” John C. Baez & and John Huerta, “The Strangest Numbers in String Theory,” Scientific American, May 2011.

“The set of all real numbers forms a line, so we say that the collection of real numbers is one-dimensional. We could also turn this idea on its head: the line is one-dimensional because specifying a point on it requires one real number. The set of all complex numbers of the form a+b i, where i²=–1, and a and b are ordinary real numbers, describe points on the plane and their basic operations —addition, subtraction, multiplication and division— describe geometric manipulations in the plane. Almost everything we can do with real numbers can also be done with complex numbers.

On October 16, 1843, William Rowan Hamilton was walking with his wife along the Royal Canal to a meeting of the Royal Irish Academy in Dublin when he had a sudden revelation: quaternions a + b i + c j + d k, with i²=j²=k²=–1. Quaternions provide an efficient way to represent threedimensional rotations. Hamilton’s college friend, John Graves, discovered on December 26 a new eight-dimensional number system that he called the octaves and that are now called octonions. In 1845 the young genius Arthur Cayley rediscovered the octonions. For this reason, the octonions are also sometimes known as Cayley numbers.”

In the generalization of numbers as tuples, division is the hard part: a number system where we can divide is called a division algebra. Not until 1958 did three mathematicians prove an amazing fact that had been suspected for decades: any division algebra must have dimension one (which is just the real numbers), two (the complex numbers), four (the quaternions) or eight (the octonions).

Hamilton didn’t like the octonions because they break some cherished laws of arithmetic. Real an complex numbers are commutatitve, but quaternions are noncommutative. The octonions are much stranger. Not only are they noncommutative, they also break another familiar law of arithmetic: the associative law (xy)z = x(yz). What the octonions would be good for? They are closely related to the geometry of seven and eight dimensions, and we can describe rotations in those dimensions using the multiplication of octonions.

In the 1970s and 1980 s theoretical physicists developed a strikingly beautiful idea called supersymmetry, a symmetry between matter and the forces of nature. Every matter particle (such as an electron) has a partner particle that carries a force, and vice versa. Supersymmetry also encompasses the idea that the laws of physics would remain unchanged if we exchanged all the matter and force particles. Even though physicists have not yet found any concrete experimental evidence in  support of supersymmetry, the theory is so seductively beautiful and has led to so much enchanting mathematics that many physicists hope and expect that it is real.

In the standard three-dimensional version of quantum mechanics that physicists use every day, spinors describes the wave motion of matter particles and vectors describes that of force particles. Particle interactions require the combination of spinors and vectors by a simulacrum of multiplication. As an alternative, imagine a strange universe with no time, only space. If this universe has dimension one, two, four or eight, both matter and force particles would be waves described by a single type of vectorial object (vectors and spinors coincide), just real numbers, complex numbers, quaternions or octonions, respectively. Supersymmetry emerges  naturally, providing a unified description of matter and forces.

In string theory, every object corresponds to a little string with one dimension in space and another one in time, hence two dimensions have to be added to every point in sapce. Instead of supersymmetry in dimension one, two, four or eight, we get supersymmetry in dimension three, four, six or 10. Coincidentally string theorists have for years been saying that only 10-dimensional versions of the theory are self-consistent: anomalies appear in anything other than 10 dimensions, breaking down string theory. But 10-dimensional string theory is, as we have just seen, the version of the theory that uses octonions. So if string theory is right, the octonions are not a useless curiosity, on the contrary, they provide the deep reason why the universe must have 10 dimensions: in 10 dimensions, matter and force  particles are embodied in the same type of numbers—the octonions.

Recently physicists have started to go beyond strings to consider membranes. In string theory we had to add two dimensions to our standard collection of one, two, four and eight, now we must add three. Supersymmetric membranes naturally emerge in dimensions four, five, seven and 11. Researchers tell us that M-theory (the “M” typically stands for “membrane”) requires 11 dimensions—implying that it should naturally make use of octonions.

Neither string theory nor M-theory have as of yet made no experimentally testable predictions. They are beautiful dreams—but so far only dreams. The universe we live in does not look 10- or 11-dimensional, and we have not seen any symmetry between matter and force particles. Only time will tell if the strange octonions are of fundamental importance in understanding the world we see around us or merely a piece of beautiful mathematics.”

More information about these especulations in Peter Woit, “This Week’s Hype,” Not Even Wrong, April 28th, 2011, where the expository article about octonions by John Baez that appeared in the AMS Bulletin (copy here, a web-site here) is recommended. In the comments, Thomas Larsson recalls that “octonions is the last division algebra, but if you relax your axioms a little the Cayley-Dickson construction gives an infinite tower of increasingly uninteresting algebras: n=1, Reals; n=2, Complex numbers; n=4, Quaternions, not commutative; n=8, Octonions, not associative; n=16: Sedenions, not alternative but power associative, n=32: 32-ions?; …

See also Philip Gibbs, “Octonions in String Theory,” viXra log, April 29, 2011, and Lubos Motl, “John Baez, octonions, and string theory,” The Reference Frame, April 29, 2011.

Posted in Mathematics, Physics, Science, String Theory | | 4 Comments

Boucher in Nature Climate Change: Contrails can evolve into cirrus clouds causing more climate warming today than all the carbon dioxide emitted by aircrafts

“Contrails formed by aircraft can evolve into cirrus clouds indistinguishable from those formed naturally. These ‘spreading contrails’ may be causing more climate warming today than all the carbon dioxide emitted by aircraft since the start of aviation.Aviation is at present responsible for about 3% of all fossil fuel carbon dioxide emissions, but an estimated 2–14% of anthropogenic climate forcing. Furthermore, its contribution to climate forcing could triple by 2050, according to some scenarios. As such, mitigating the impact of aviation on climate has become a subject of considerable public and political interest. The debate is complicated, however, by the fact that aviation’s climate impact results from a number of different factors, as well as by the large uncertainty in the effect that some of these factors have on climate. Writing in Nature Climate Change, Burkhardt and Kärcher present a global modelling study that quantifies the climate effect of ‘spreading contrails’ — the least well quantified of all the aviation-related climate-forcing agents.” Olivier Boucher, “Atmospheric science: Seeing through contrails,” Nature Climate Change 1: 24–25, 29 March 2011, reviewing the paper by Ulrike Burkhardt & Bernd Kärcher, “Global radiative forcing from contrail cirrus,” Nature Climate Change 1: 54–58, 29 March 2011.

“Condensation trails (contrails) in the wake of an aircraft are formed by the mixing of hot, moist air coming out of the engine with cold ambient air. When the atmosphere is supersaturated with respect to ice, the line-shaped contrails can spread to form cirrus cloud, which has a warming effect on climate. Its relevance to the climate system remains unknown. Burkhardt and Kärcher used a model that simulates this spreading process to assess the warming effects of contrails and the cirrus clouds that form from them. Their results indicate that so-called spreading contrails cause an order of magnitude more climate warming than the line-shaped contrails alone, and are the largest single climate-forcing agent associated with aviation. However, contrail spreading is not the only mechanism that could explain this increase. It has also been suggested that aircraft-emitted aerosols could serve as ice nuclei and facilitate the formation of cirrus cloud. To understand the impact of aviation on climate, it is necessary to quantify the importance of these two mechanisms. This, however, is not a straightforward task.

These findings are important if the calculations of Burkhardt and Kärcher are correct. They provide a basis to develop mitigation strategies to reduce the impact of aviation on climate. For instance, it has been suggested that flight routes or flight altitudes could be planned and altered in real time to avoid parts of the atmosphere that are supersaturated with respect to ice, but such a strategy is likely to lead to an increase in fuel consumption. Moreover, the results by Burkhardt and Kärcher might also justify the development of a novel engine concept that seeks to condense a fraction of the water vapour in aircraft emissions in a cooling unit before it leaves the engine. Reducing the content of water vapour in the engine exhaust would make contrail formation less likely.

The work of Burkhardt and Kärcher offers some exciting pointers as to how the impacts of aviation on the climate system might be reduced, but the uncertainties remain large. Given the urgency of the issue, it is important that research on the climate impacts of contrails and on how contrails could be mitigated through technological advances or operational changes in the aviation industry are pursued in parallel.”

Posted in Climate Change | | 3 Comments

A single photon can be in as many as four places at the same time

Vladan Vuletic, “Quantum physics: Entangled quartet,” News & Views, Nature 468: 384–385, 18 November 2010, summarizes the paper K. S. Choi, A. Goban, S. B. Papp, S. J. van Enk & H. J. Kimble, “Entanglement of spin waves among four quantum memories,” Nature 468: 412-416, 18 November 2010.

“Single photons can be stored in atomic gases. Choi et al. investigate what happens to interference when light is stored simultaneously in as many as four spatially distinct atomic clouds. The authors demonstrate quantum correlations (entanglement) in this composite matter–light system, and study how entanglement ultimately fades away to leave only classical correlations.

Choi et al. have measured quantum entanglement in a composite matter–light system by combining results from particle-type and wave-type measurements. In the particle-type set-up, a photon stored in one box can reach only one detector (D1, D2, D3 or D4). In the wave-type measurement, the photon is placed simultaneously in all four boxes and the light emerging from the boxes is combined through an arrangement of partially reflecting and totally reflecting mirrors such that light from any box can reach any detector.

In a classical world, something is either a particle or a wave, so a physical system will exhibit correlations either in the particle-type or wave-type detection set-up — but not in both. However, in the quantum world that we live in, it is possible to place, for example, a single photon simultaneously in all boxes such that correlations are observed in both detection set-ups. And this is exactly what Choi et al. have done in their experiment.

The authors measured correlations between the different boxes, either in the particle-type detection set-up or in the wave-type set-up. From the combination of these measurements, they extracted the degree of entanglement of the light shared between the four boxes. Using a method previously developed for a single photon travelling simultaneously along four possible paths, they identified quantitative criteria, involving combinations of particle-type and wave-type detection results, that allowed them to distinguish among entanglement between all four boxes, or three, or just two of them. In the presence of noise and other imperfections, they observed a gradual transition from four-party entanglement to no entanglement.”

Posted in Optics, Physics, Quantum Mechanics, Science, Uncategorized | | 7 Comments

The future of the LHC at CERN

The Higgs agenda at CERN pass from Higgs discovery at the LHC (measure its mass and its width), to precision physics in the Higgs sector at the SLHC (measure cross sections x BR, ratios of couplings to particle, measure CP and spin, measure Higgs self-couplings, measure Higgs dynamics & dynamics of EWSB). “Based on the experience gained diagnosing and repairing the LHC in 2008 and 2009 the following decisions have been taken in 2010 and formalized in the Medium Term Plan 2011-2016: (1) LHC will operate until ~2030 and experiments expect to accumulate ~3000 fb-1; (2) during its last decade of operation, the LHC shall aim at a useful average luminosity of 5×1034 Hz/cm²; and (3) the High Luminosity upgrade of the LHC itself shall be implemented a few years before 2020. Two projects have been created on January 1, 2011 for studying and implementing the High Luminosity Upgrade of the LHC: (1) “HL-LHC” for the LHC itself, in order to obtain a peak luminosity of five times the design luminosity of the LHC (i.e. 5×1034 Hz/cm²); and (2) “LHC Injectors Upgrade” (LIU) for the injectors (LINAC4, the PS booster, the PS, the SPS, as well as the heavy ion chain).” Christophe Grojean, “Physics perspectives with the High Luminosity LHC,” http://indico.cern.ch/conferenceOtherViews.py?view=standard&confId=116438, Saclay, 07 February 2011.

Haber on “Present status and future prospects for a Higgs boson discovery”

“The electroweak symmetry breaking dynamics of the Minimal Standard Model (MSM) employs a self-interacting complex doublet of scalar fields, which consists of four real degrees of freedom.  Three of this four degrees of freedom has been already observed in the experiments as the longitudinal components of the massive (electroweak) gauge bosons (the $W^\pm$ and $Z$ bosons). The fourth remaining scalar degree of freedom is predicted by the standard Higgs mechanism to remain in the physical spectrum as a CP-even neutral Higgs boson. Precision electroweak data favors a Higgs mass below 200 GeV/c², in which case the scalar self-interactions are weak.” In such a case, “the Standard Model is very likely embedded in a supersymmetric theory in order to stabilize the large gap between the electroweak and the Planck scales in a natural way. The minimal supersymmetric extension of the Standard Model (MSSM) employs two complex Higgs doublets, resulting in five physical scalar degrees of freedom.  In a large range of the MSSM parameter space, the properties of the lightest scalar of the MSSM are nearly indistinguishable from those of the SM Higgs boson.” Howard E. Haber (Santa Cruz Institute for Particle Physcs, University of California), “Present status and future prospects for a Higgs boson discovery at the Tevatron and LHC,” ArXiv, 4 Nov 2010.

Let us recall from John C. Baez, “Hypercharge and Weak Isospin,” May 12, 2003, that “in the Standard Model, the weak and electromagnetic forces are two aspects of the “electroweak force” described by the symmetry group SU(2)×U(1). The familiar concept of  “electric charge” Q is less fundamental than the concepts of “weak isospin” T (with 3 components transforming under SU(2) symmetry) and “hypercharge” Y (only 1 component transforming under U(1) symmetry), in fact,  $Q=T_3+Y/2$.”

Returning to Haber, “for an arbitrary Higgs sector” a consistent perturbation theory “requires that $(2T+1)^2-3Y^2=1$The simplest solutions are Higgs singlets $(T,Y)=(0,0)$ and hypercharge-one complex Higgs doublets $(T,Y)=(1/2,1)$.” In the first case,the (Minimal) “Standard Model Higgs Boson has a mass given by: $M_{H,SM}^2=v^2\,\lambda/2$, where $\lambda$ is the Higgs self-coupling parameter, whose value is unknown at present, hence the Standard Model Higgs mass is not predicted, and $v=2\,M_W/g=$ 246 GeV.” The Next to Minimal, Standard Model Higgs corresponds to a “two-Higgs-doublet model (2HDM) consisting of two hypercharge-one scalar doublets.” In this later case, “of the eight initial degrees of freedom, three correspond to the Goldstone bosons and five are physical: a charged Higgs pair, $H^\pm$ and three neutral scalars. If CP is conserved,” as in the Minimal SM Higgs, “the Higgs spectrum contains two CP-even scalars, $h^0$ and $H^0$, and a CP-odd scalar $A^0$.” Hence, appart from a CP-even Higgs boson, there are “a CP-odd Higgs boson” (in order to restore CP conservation in the Higgs sector), “and two charged Higgs bosons.” Obviously “more exotic Higgs sectors” are possible “allowing for doubly-charged Higgs bosons, etc.”

“The Higgs sector of the Minimal Supersymmetric extension of the Standard Model (MSSM) is a 2HDM, where the neutral components of the Higgs fields acquire vacuum expectation values (vevs) $v_u$ and $v_d$, with $v^2\equiv v_d^2+v_u^2={4 M_W^2/ g^2}=$ 246 GeV². The ratio of the two vevs is an important parameter of the model, $\tan\beta\equiv v_u/v_d$. The five physical Higgs particles consist of a charged Higgs pair $H^\pm$, one CP-odd scalar $A^0$, and two CP-even scalars $h^0$ and $H^0$.” The maximum allowed mass for $h^0$ depends on the mass of the superpartner of the top quark; assuming that the top-squark mass is no heavier than about 2 TeV, results in a mass smaller than 130 GeV; this upper bound is reached when $\tan\beta\gg 1$, in the so-called maximal mixing scenario.” Note also that “in many models with extended Higgs sectors, a parameter regime exists in which one Higgs boson is light (of order $M_Z$) and all other Higgs scalars are very heavy $(\gg M_Z$). The effective low-energy Higgs theory is precisely that of the SM Higgs boson.  This is called the decoupling limit.”

“The Tevatron will continue to take data through the end of 2011. In addition to an increased integrated luminosity, there is still room for some improvements in the Higgs search analysis. Although it is possible that evidence for the Higgs boson may emerge from future Tevatron running, the discovery of the Higgs boson and the identification of its properties are expected to take place at the LHC.  Once the Higgs boson is discovered, a program of Higgs physics at the LHC must address the following important questions: How many Higgs states are there? Assuming one Higgs-like state is discovered, is it a Higgs boson? Is it the SM Higgs boson? The measurement of Higgs boson properties will be critical in order to answer the last two questions: mass, width, CP-quantum numbers (is the Higgs sector CP-violating?); branching ratios and Higgs couplings; reconstructing the Higgs potential (Higgs self-couplings).”

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